Snack Foods Processing

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Author: Edmund W. Lusas | Lloyd W. Rooney

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Table of Contents

Preface Acknowledgment List of Contributors

Section I: The Snack Foods Setting 1. OVERVIEW EDMUND W. LUSAS

1. 2. 3. 4. 5.

Introduction and Industry Scope Past Innovations Nutrition Total Quality Management of Technology References

2. THE SNACK INDUSTRY: HISTORY, DOMESTIC AND GLOBAL STATUS JAMES A. McCARTHY

1. 2. 3. 4. 5. 6.

Introduction History The Domestic Snack Food Market The Global Market The Snack Food Association References

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Section II: INGREDIENTS AND GENERAL EQUIPMENT 3. Food Quality of Corn L. W. ROONEY and E. L. SUHENDRO

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Introduction Types of Corn Corn Grades, Standards and Speciﬁcations Corn Kernel Structure and Composition Aﬂatoxins and Fumonisin Genetically Modiﬁed Organisms (GMOS) Food Corn Quality Attributes Properties of Corn for Alkaline Cooking Handling Food Corn Industrial Dry Corn Milling Dry Masa from Dry-Milled Corn Fractions Sorghum Utilization in Snack Foods Acknowledgments References

4. ALKALINE-COOKED CORN PRODUCTS CASSANDRA M. McDONOUGH, MARTA H. GOMEZ, LLOYD W. ROONEY and SERGIO O. SERNA-SALDIVAR

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Introduction Traditional Corn Products Ingredients Preparing and Using Fresh Masa Baked and Reduced-Fat Products Preparing and Using Dry Masa Flours Physicochemical Changes in Alkaline–Cooked Products Quality of Alkaline-Cooked Products Shelf Life of Corn Products Acknowledgments References

5. STARCHES FOR SNACK FOODS DAVID P. HUANG and LLOYD W. ROONEY

1. 2. 3. 4.

Introduction Starch Granules Deﬁnitions Changes in Starch

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5. 6. 7. 8. 9.

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Starch Ingredients for Savory Snack Foods Selection of Starches Conclusions Acknowledgments References

6. OILS AND INDUSTRIAL FRYING DON E. BANKS and EDMUND W. LUSAS

1. 2. 3. 4. 5. 6. 7. 8. 9.

Introduction World Oil Supply Oil Chemistry Oil Extraction and Reﬁning Oil Processing The Frying Process Selection of Frying Oils Frying Oil Management References

7. HOT AIR DRYERS ROBERT SUNDERLAND

1. 2. 3. 4. 5. 6.

Introduction Fundamentals of Drying Psychometric Charts Sizing a Drying System Selecting a Dryer Reference

Section III: Snack Foods Preparation and Dedicated Equipment 8. POTATOES AND POTATO CHIPS WILBUR A. GOULD

1. 2. 3. 4.

Potato Production Potato Analysis and Composition Potato Chip Manufacture Suggested Reading

9. USE OF DRIED POTATOES IN SNACK FOODS VELDON M. HIX

1. Introduction 2. History of Fabricated Potato Snacks 3. Dried Potato Ingredients for Fabricated Potato Snacks

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4. Other Potato Snack Ingredients 5. Future of Fabricated Potato Snacks 6. References 10. TORTILLA CHIP PROCESSING SURENDRA P. MEHTA

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Introduction Processing Steps Corn Cooking and Soaking Washing and Draining Grinding Equipment Reconstitution of Dry Masa Flour Masa Feeding/Pumping/Presheeting Sheeting/Cutting Baking Conditioning/Equilibration Frying Process Flowchart Raw Materials

11. SNACK FOODS FROM FORMERS AND HIGH-SHEAR EXTRUDERS OCTAVIAN BURTEA

1. 2. 3. 4. 5. 6.

Introduction History of Corn Snacks Processing Equipment Corn Chip Processing Extruded Bake-Type Snacks Extruded Fry-Type Snacks References

12. SNACK FOODS FROM COOKING EXTRUDERS GORDON HUBER

1. 2. 3. 4. 5. 6. 7.

Introduction Formula Hardware Software (Conditions) Extruded Products New Developments: Future of Snack Foods Extrusion References

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13. PERFECT PRETZEL PRODUCTION E. TERRY GROFF

1. 2. 3. 4. 5. 6.

The Pretzel: A Snack Food with 800 Years of History Types of Pretzels Formulation Processing Problems in Pretzel Manufacture References

14. POPCORN PRODUCTS CHARLES CRETORS

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Introduction Raw Popcorn Selection and Preparation Popping Methods Home Preparation of Popcorn and Equipment Commercial Processes for Fresh Popcorn Industrial Processes for Packaged Popcorn Commercial and Industrial Flavorings and Applicators Popcorn Packaging Relative Nutrition Marketing of Popcorn References

15. SNACK FOODS OF ANIMAL ORIGIN PETER J. BECHTEL

1. 2. 3. 4. 5. 6. 7. 8. 9.

Introduction Jerky Products Shelf-Stable Sausage Stick Snacks Other Dried Meat Products Pork Rind Products and Expanded Products Pickled Snack Foods Dairy- and Egg-Based Snack Foods Dried and Marinated Fish and Shellﬁsh Snacks References

16. RICE-BASED SNACK FOODS SHIN LU and TSE-CHIN LIN

1. Introduction 2. Rice Milling

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3. Milling Effects 4. Snack Foods 5. References 17. JAPANESE SNACK FOODS SEIICHI NAGAO

1. 2. 3. 4. 5. 6. 7. 8. 9.

Introduction Japanese Baked Confections Fried Japanese Confections Molded or Pressed Japanese Confections Coated Japanese Confections Western Confections Noodles Western Snack Foods References

18. SNACK FOODS OF INDIA SUMATI R. MUDAMBI and M.V. RAJAGOPAL

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Introduction Roasted Cereal Snack Foods Roasted Legume Snack Foods Dehydrated Snack Foods (Served After Frying) Fried Cereal Snack Foods Fried Legume Snack Foods Fried Grain and Legume Snack Foods Fried Fruit and Tuber Snack Foods Nutritional Value of Indian Snack Foods References

Section IV: Operations After Shaping and Drying 19. SNACK FOOD SEASONINGS JON SEIGHMAN

1. 2. 3. 4. 5.

Introduction Ingredients Seasoning Formulation Seasoning of Major Snack Foods Suggested Reading

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20. SNACK SEASONINGS APPLICATION DOUGLAS E. HANIFY

1. 2. 3. 4.

Introduction Coating Arenas Types of Seasoning Applications Conclusion

21. SENSORY EVALUATION IN SNACK FOODS DEVELOPMENT AND PRODUCTION DENISE JACOBY and CLAY KING

1. 2. 3. 4. 5. 6. 7.

Introduction Overview of Flavor Analytical Methods Sensory Methods Sensory Aspects of Processing Sensory Evaluation During Product Life Cycle References

22. PRODUCT PROTECTION AND PACKAGING MATERIALS TOM DUNN

1. 2. 3. 4. 5. 6.

Quality Properties of Snack Foods Assessment of Packaging Requirements Packaging Materials Functionality Properties of Snack Food Packaging Materials Current Issues in Snack Foods Packaging References

23. SNACK FOODS FILLING AND PACKAGING CURT KUHR

1. 2. 3. 4. 5. 6. 7.

Introduction Package Styles Automated Bag and Pouch Packaging Cartoning Case Packing Improving Efﬁciency and Future Considerations Suggested Reading

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24. EVALUATION METHODS AND QUALITY CONTROL FOR SNACKS RALPH D. WANISKA

1. 2. 3. 4. 5. 6.

Introduction Quality Programs Evaluation Methods Statistics in Quality Control Summary References

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Preface

T

snack foods industry is a remarkable sector of the food industry. For many years, annual snack sales in the United States have compounded at several times the rate of population increase, thus indicating a vigorous and growing industry. It has evolved as part of the trend toward increased ﬂexibility and mobility in daily living patterns as national afﬂuence increased. Most of the “snacks” we know today have been developed or signiﬁcantly modiﬁed in the United States. Yet, room still exists domestically for new snack ideas and processes. Moreover, U.S.-style snacks are being accepted in newly prosperous countries, where opportunities for additional development are plentiful. This book is for people who want a technically based practical review of how snack foods are made. Individual motivations to learn differ and may include: a new job with a snack foods producer, transfer of a talented manager in a large corporation to the snacks division, or promotion of a worker from the production line to responsibilities with a broader scope. A technical sales specialist for a machinery, ingredients, packaging materials or services supplier may be assigned to call on snack producers. Some entrepreneurs may want to assess the technical requirements for making snacks, or selling supplies or services to snack processors. Also, researchers and quality control/assurance personnel need an overview of the interrelated technologies for identifying sources of product quality problems. Savory snacks are emphasized in this book—salted, shelf-stable ﬁnger foods, including: potato and corn chips, alkali-cooked corn tortilla chips, pretzels, popcorn, extruder-puffed and dried/fried products, half-products, and animalproduct snacks. Readers are also introduced to snacks of China, Japan and India. HE

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Authors of the 24 chapters have extensive experience in their specialties, and range from pioneers to younger members of the industry. Their names, or their employers, already are familiar. Several consultants enrich the book by their experiences in snacks processing and snack-related technologies. Many have inﬂuenced development of various sectors of the industry. This book follows the Practical Short Course philosophy honed by 18 years of teaching technical processing of various products to domestic and international industry supervisors at Texas A&M University. Nearly 5,000 people have been trained through this program, many of whom have grown in responsibility and stature in their companies and the industry. We initially asked representatives of the major equipment and ingredient companies to teach what they would like prospective buyers to know about their type of equipment or ingredient when working with them—in a sense, to give the students a vocabulary and bring them to the “street smart” level of knowledge without disclosing proprietary secrets. As in the short courses, chapter authors use their company’s products as illustrations, but the vast majority are representative of multiple sources. Few secrets exist in equipment or supplies when discussing principles, although individual suppliers have their own techniques for gaining optimum performance from their product. The strength of suppliers as authors is that they typically see and solve many problems that would surface only occasionally, if at all, at any one location. Also, some have run commercial snack production lines for prolonged periods in addition to startups. Several bookshelves would be required to hold all that is known about savory snack foods but will never be published because of their proprietary nature and obligations of suppliers to keep their customers’ secrets. But, once the basic principles are understood, problems can be solved in several ways, some of which are described in this book. Chapters are arranged in a chronological need-to-know basis. The status of the industry is reviewed, followed by important properties of major ingredients, including starch, potatoes, dry potatoes, dent corn; popcorn, oils and seasonings; succeeded by manufacturing equipment, including cookers, grinders, formers, fryers, seasoning applicators, packaging materials, and weigher-ﬁller-sealers. Additionally, sections are included on sensory evaluation, and quality control— in speciﬁc chapters and throughout the book. Readers will notice that some overlap occurs between chapters, and authors differ in recommended processing conditions and equipment. This merely documents that snacks are made many different, successful ways in the real world. The book dwells slightly on the histories of various snack foods industry companies, primarily to show that multibillion-dollar industries have been built starting with simple ideas and simple ingredients (potatoes, corn and rice). It may inspire individuals around the globe to focus on new ways of utilizing local crops and resources. Many U.S.-origin corn-based snack foods are gaining popularity throughout the world. Would-be overseas processors need help in developing reliable sources of good-quality raw materials.

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This book has two objectives: —To provide new entrants with an introduction to the snack foods industry and its terminology, so they can conﬁdently reach out for more information in communicating with suppliers and associates. —To explain the technical interrelationships between the many materials and processes used in making the ﬁnished snack food, so managers, on-line supervisors and quality control/assurance personnel will better understand where to start in solving problems that arise. The reader will beneﬁt the most by: (1) reading through the book ﬁrst for scope and interrelations; (2) returning for detailed reading of those sections that relate to the speciﬁc concern at hand; and (3) keeping the book on a nearby shelf as a reference of ingredients speciﬁcations and process operating conditions. EDMUND W. LUSAS LLOYD W. ROONEY

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Acknowledgment

T

book is dedicated to the chapter authors, without whose input it could not have materialized. Individuals who make their living in the snack foods industry were invited to summarize the important principles and critical requirements of their specialties. However, they also are among the busiest of people and the modern business day leaves no time for such writing. Editors can help but little, since ideas must come from those who solve problems ﬁrst-hand. Each chapter is a gift of experience to later entrants to the industry, often written after regular work hours, in the evenings, while traveling, and sometimes during vacations—personal time that can never be replaced. We thank all for their generosity in participating. We also thank C. McDonough for her help with the graphics in this book. HIS

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List of Contributors

Mr. Don E. Banks Consultant, Edible Oil Technology 8155 San Leandro Street Dallas, TX 75218 E-mail: dbanks@ﬂash.net

Mr. Charles Cretors President C. Cretors & Company 3243 N. California Ave. Chicago, IL 60618 E-mail: [email protected]

Dr. Peter Bechtel Professor of Seafood Technology School of Fisheries and Ocean Sciences (SFOST) University of Alaska P.O. Box 99775-7220 Fairbanks, AK 99775 E-mail: [email protected]

Mr. Tom Dunn Printpack, Inc. 4335 Wendell Dr. Atlanta, GA 30336-1622 E-mail: [email protected]

Dr. Octavian Burtea Vice President, Sales Snack Foods Group Maddox Metal Works, Inc. 4031 Bronze Way Dallas, TX 75237 E-mail: oburtea@maddoxmetal works.com

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Dr. Marta H. Gomez Research Scientist, Nabisco Foods 21-11 Route 208 Fair Lawn, NJ, 07410 Dr. Wilbur A. Gould Consultant 1733 South East 43rd Street Cape Coral, FL 33904 E-mail: [email protected]

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Mr. E. Terry Groff President Reading Bakery Systems 380 Old West Penn Avenue Robesonia, PA 19565 E-mail: [email protected] Web: www.rpmcorp.com

Dr. Clay King Professor Texas Woman’s University Department Nutrition and Food Sciences Denton, TX 76204-2134 E-mail: f [email protected]

Mr. Douglas E. Hanify, P.E. Director of Sales Spray Dynamics Ltd. 108 Bolte Lane St. Clair, MO 63077 E-mail: [email protected]

Mr. Curt Kuhr Director of Marketing Services The Woodman Company Division of Kliklok Corporation 5224 Snapﬁnger Woods Drive Decatur, GA 30035 E-mail: [email protected]

Dr. Veldon Hix Director of Research Miles Willard Technologies P.O. Box 1747 Idaho Falls, ID 83403 E-mail: [email protected] Dr. David P. Huang Business Manager National Starch Company, Inc. 10 Finderne Avenue Bridgewater, NJ 08807 E-mail: david/[email protected] Mr. Gordon Huber Director, New Concept Development Wenger Manufacturing Company 714 Main Street Sabetha, KS 66534-0130 E-mail: [email protected] Ms. Denise Jacoby Frito-Lay, Inc. 7701 Legacy Drive Plano, TX 75024 E-mail: [email protected]

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Dr. Tse-Chin Lin Chief, Division of Food Processing Council of Agriculture Department of Food Science National Chung-Hsing University #250 Kwua Kwang Road Taichung, 404 Taiwan Dr. Shin Lu Professor and Head Department of Food Science National Chung-Hsing University #250 Kwuo Kwang Road Taichung, 404 Taiwan E-mail: [email protected] Dr. Edmund W. Lusas Consultant, Ed Lusas, P.S.I. 3604 Old Oaks Drive Bryan, TX 77802-4743 E-mail: [email protected] Mr. James A. McCarthy President and CEO The Snack Food Association 1711 King Street, Suite One Alexandria, VA 22314-2720 E-mail: [email protected]

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Ms. Cassandra M. McDonough Research Scientist Cereal Quality Laboratory Soil and Crop Sciences Department Texas A&M University College Station, TX 77843-2474 E-mail: [email protected] Mr. Surendra P. (Paul) Mehta Processing Systems Division Heat and Control, Inc. 24325 E. Sunnycrest Ct. Diamond Bar, CA 91765 E-mail: [email protected] Dr. Sumati R. Mudambi Food Industry Consultants RL-1, G. Block MDIC, Chinchwad Pune 411019, India E-mail: [email protected] Dr. Seiichi Nagao Wheat Flour Institute Flour Millers Association 13-6, Kabuto-CHO, Nihonbashi Chuo-Ku, Tokyo 103-0026, JAPAN Dr. Mudambi V. Rajagopal Food Industry Consultants RL-1, G. Block MDIC, Chinchwad Pune 411019, India E-mail: [email protected] Dr. Lloyd W. Rooney Faculty Fellow and Professor, Food Science and Technology Cereal Quality Laboratory Soil and Crop Sciences Department

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Texas A&M University College Station, TX 77843-2474 E-mail: [email protected] Mr. Jon Seighman Manager, Seasoning Development Givaudan-Roure Flavors 1199 Edison Drive Cincinnati, OH 45216 E-mail: [email protected] Dr. Sergio O. Serna-Saldivar Head of Food Science and Technology Departamento de Tecnologia de Alimentos Monterrey, NL, Mexico Dr. E. L. Suhendro, Research Associate Food Science and Technology Cereal Quality Laboratory Texas A&M University College Station, Texas 77843-24 E-mail: [email protected] Mr. Robert Sunderland Wenger Manufacturing Company 714 Main Street Sabetha, KS 66534-0130 E-mail: [email protected] Dr. Ralph Waniska Professor, Food Science and Technology Cereal Quality Laboratory Soil and Crop Sciences Department Texas A&M University College Station, TX 77843-2474 E-mail:[email protected]

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SECTION I

THE SNACK FOODS SETTING

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CHAPTER 1

Overview

EDMUND W. LUSAS

1. INTRODUCTION AND INDUSTRY SCOPE

1.1. CHAPTER OBJECTIVE

T

HE

objectives of this chapter are to:

r Introduce the reader to the scope of the snack foods industry, including its

development and current sales.

r Expand on processing principles and quality interlinks. r Review Total Quality Management of industry technology.

1.2. WHAT IS A SNACK FOOD? Several of the chapter authors deﬁne snack foods as “foods eaten between regular meals.” Webster’s New Ninth Collegiate Dictionary [1] deﬁnes the noun “snack” (ﬁrst recorded use, 1757) as “a light meal, food eaten between regular meals, food suitable for snacking;” and the verb “snack” (1807) as “to eat a snack.” Thus, a cold leftover from last evening’s home or restaurant meal, an afternoon bowl of breakfast cereal, a cup of soup reconstituted from a dry mix package, or cookies and milk for children returning from school in midafternoon, are properly called “snacks.” But, what if there are no, or only a few, “regular meals?” It has been estimated that less than 20% of U.S. families eat breakfast. Moreover, scheduling of “regular” meals is erratic when both parents (or a single parent) and children

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leave home at different times for work and school, when lunches are primarily eaten away from home, and when structured athletic and social activities for the children occupy weekday evenings and sometimes weekends as well. Eating in the company of others, including families gathered for a meal, workers eating box lunches together, and communal mid-morning and midafternoon coffee breaks, also have eroded. Increasingly, food is purchased at drive-up windows and consumed alone in vehicles, and many ofﬁce workers take coffee, and sometimes microwave popped corn, to their desks. A growing part of the population, no longer eats “meals,” preferring instead to “graze” as the day progresses. Clearly, the times are changing. The desires for freedom of mobility (expressed by long-distance moving for new employment, and long auto vacations) and freedom of personal action (keeping hours and eating when one wants) are reﬂected in the foods we eat. With a domestic population of about 280 million, there is no new style of living, but rather many simultaneously evolving diverse styles. Snacks are the convenience and fun foods of people on the go, and older opinions about their propriety don’t apply anymore. The terms “snacks,” “snack foods,” and “savory snacks” mean the same throughout this book. The latter term has been used frequently with various meanings, including “salty” and “seasoned.” Webster’s dictionary [1] further expands the deﬁnition of “savory” to include “pleasing to the taste” and “a dish of stimulating ﬂavor” (1661). Besides being tasty, modern savory snack foods are: r safe, and free of hazardous chemicals, other toxic substances, and r r r r r

pathogenic microorganisms as deﬁned by federal laws and enforced by various agencies typically prepared commercially in large quantities by continuous processes seasoned, usually with salt, and often with additional ﬂavorings shelf-stable, requiring no refrigeration for preservation packaged ready-to-eat, typically divided into bite-size pieces, easily handled with the ﬁngers, and may have an oily or dry appearance depending on customer expectations for the speciﬁc product sold to the customer in fresh condition, often achieved by: —employing packaging materials to exclude moisture, oxygen, and often light, to protect product crispiness, slow natural oil oxidation, and further remove an oxidation catalyst, respectively —sometimes using an inert package atmosphere (nitrogen) and/or approved anti-oxidant systems for additional oil protection —code dating packages and removing them from store shelves if not sold in time

1.3. INDUSTRY SIZE AND CURRENT TRENDS Snack Food and Wholesale Bakery includes an annual State of the Industry Report in its June issues [2]. Domestic sales of various snack groups and allied

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products through public outlets in 1999 are shown in Table 1.1. Savory snacksales amounted to $19.375 billion and 6.166 billion lb in 1999, with increases of 6.2% and 4.4%, respectively, over the previous year [2]. Numbers in Table 1.1 do not include the substantial sales of tortilla, tostada and potato chips to restaurants and mass feeding programs, or sales of popped corn at movie theatres and public events. Reliable sales information is not available for the global snack foods industry, but has been estimated at twice or more that of domestic sales, depending on deﬁnitions of “snack foods” in respective countries. Terms from the report, in Table 1.1, do not always coincide with those used in this book. Tortilla chips and tostada chips include the large and small forms (Chapter 10). Corn chips are products made from masa (alkali-cooked and ground corn), formed, and direct-fried or sheeted and then partially dried and fried (Chapter 11). Cheese snacks mainly consist of extruder-puffed degermed dry corn meals that are dried or fried before coating with cheese slurry (Chapters 11, 12, /19, and 20). Potato chips, made from fresh potatoes (Chapter 8), was theleading savory snack in dollars and volume in 1999. Snacks made from dried potatoes (Chapter 9) are included in the “other snacks” category. However, corn products in total (including tortilla chips/tostada chips, corn snacks and cheese snacks) outsold potato chips in value and volume even without considering the various popcorn products. Table 1.1 also shows that average per capita consumption of snacks, for an estimated 1999 U.S. population of 280 million, ranged between $17.11 for potato chips to $0.29 for unpopped popcorn [2]. Major changes in this dynamic industry are included in each year’s State of the Industry Report [2]. Frito-Lay, Inc., alone, introduced 13 products in 1999. As usual, some manufacturers were acquired by others, some went bankrupt and their facilities and equipment were redistributed, and new snack food companies appeared. Noted successes in 1999 included: r A 13.8% increase in corn snack sales, partially resulting from a major

manufacturer introducing a scoop-shaped chip well suited for use with dips and a new line of three-dimensional chips made from ﬁnely ground dry masa. r A 13.7% increase in snack nuts sales and a 13.1% increase in pumpkin and sunﬂower seeds—although the latter group is still at a relatively low dollar volume. r Phenomenal sales increases of 28.5% for (jerky-like) dried meat snacks and 18.4% for fried pork rinds. Meat snacks have been available for many years. Their sales increase resulted at least partially from a leading meat snack producer joining forces with a large snack foods manufacturer to take advantage of the latter’s national distribution capabilities. Publications (Dr. Atkins and the Zone diet), favoring high-protein/low-carbohydrate foods, also are credited for increased interest in fried pork rinds—popular with African Americans and Hispanics, but mainly regional products in the past.

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TABLE 1.1.

Estimated Sales of Salted Snacks and Related Products through Retail Outlets in 1999. (With permission from State of the Industry Report. Snack Food & Wholesale Bakery, 89(6):SI-3–SI-74. 2000. Estimated average U.S. per capita usage added.) Product Bakery food sales Bread aislea Cookies and crackers Baked sweet goods Refrigerated and frozen baked goods Snack bars Toaster pastries All bakery sales

1999 Volume (lb Millions)

1999 Sales ($ Millions)

% Change from Last Year

Av. per Capita Use ($U.S.)

3,108.2 −−

11,242.5 10,284.0 3,679.6

+2.9 +5.4 +4.6

−− −− −−

−− 269.1 300.2 −−

3,048.6 1,636.7 637.7 30,528.7

+2.3 +13.9 +8.1 +4.5

−− −− −− −−

1,538.5

4,688.1

+2.2

17.11

1,431.7 272.4 605.4 483.6 424.7 131.6 91.9

3,748.5 847.5 1,220.2 1,693.8 1,156.8 492.9 80.8

+5.0 +13.8 −2.2 +13.7 +1.8 +6.1 −5.1

13.68 3.09 4.45 6.18 4.22 1.80 0.29

−−

Salted food sales Potato chipsb Tortilla chips/ tostada chips Corn snacks Pretzels Snack nuts Microwave popcorn RTE popcorn Unpopped popcorn Cheese snacks (extruded snacks) Pumpkin/ sunflower seeds Meat snacks Pork rinds Variety pack Othersc All salted snacks

310.5

919.6

+13.4

3.36

45.8 96.2 66.5 82.7 584.2 6,165.7

113.3 1,321.0 420.2 337.1 2,334.9 19,374.5

+13.1 +28.5 +18.4 −1.6 +1.2 +6.2

0.41 4.82 1.53 1.23 8.52 70.71

Speciality food sales Pizzad Hot snackse Dips and salsa Rice/corn cakes Dried processed fruitf Frozen noveltyg Other specialityh All speciality snacks

−− −− −− −− −− −− −− −−

2,471.8 564.6 1,422.7 160.2 811.7 1,744.9 2,749.5 9,925.4

+9.8 +10.9 +84.7 −10.4 +5.4 +4.1 +5.6 +5.2

−− −− −− −− −− −− −− −−

Confectionery sales Chocolate candies Non-chocolate candies Gum All confectionary sales Total industry:

−− −− −− −− −−

16,910.0 9,180.0 2,650.0 28,740.0 88,568.6

NA NA NA NA NA

−− −− −− −− −−

a

Includes bread, rolls, buns, bagels, tortillas and related shelf-stable food items. From fresh potatoes. Includes potato crisps, party mixes, pumpkin/sunflower seeds, corn nuts and other miscellaneous snacks. d Includes frozen pizza and refrigerated pizza/pizza kits. e Includes refrigerated appetizers/snack rolls/frozen appetizers, snack rolls, onion rings, breaded vegetables. f Includes raisins, fruit snacks, other dried fruits. g Includes frozen pudding/mousse, frozen fruit juice and ice cream novelty products. h Includes squeezable cheese, yogurt, refrigerated puddings/gelatins/parfaits, cheese spreads/balls, flavored spreads. NA = not applicable. b c

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Notable sales losses in 1999 included: r A second full year of sales decline of snacks fried in non-caloric oils

(olestra), and continuing sales decreases of low-fat/no-fat snacks. The latter typically are made by drying in high-velocity air impingement dryers rather than deep fat frying. Low-fat snacks then are sprayed with minimal oil to adhere (“tack on”) salt and ﬂavorings, and no-fat products are sprayed with water-soluble ﬂavorings dissolved in starch or gum solutions, followed by additional drying or heating (Chapter 5). The major criticism of the three types of products has been “lack of taste.” Criticisms of products fried in non-caloric fat oil also have included “high price” and “digestive tract disturbances.” r A third year of 10% annual decreases in puffed rice and popcorn cakes. Originally, potato chips were popular in the U.S. Northeast; corn, tostada and tortilla chips in the Southwest; and pretzels in the Mid-Atlantic states and other areas with concentrations of German descendents. Modern transportation has exposed alkali-processed corn products and pretzels to the public throughout the nation. A distinct increase in pretzel consumption occurred in the early 1990s as the public became concerned about the high fat content of nuts. New fat labeling laws led to reduced portions of peanuts served by the airlines. Then, pressure by activist groups concerned about peanut allergies led to further replacement of peanuts by single-serving packages of pretzels. Now that public emphasis is on “taste,” sales of nuts is increasing, although peanut allergies are still of concern to airlines. Pretzel manufacturers are working to regain their former market share, which has slipped in recent years, including a 2.2% decrease in 1999. Individual snacks typically have life cycles in the market, with some being introduced and others retired throughout the year. Total snack food sales during the 1990–1999 decade increased by an average of 4.7% annually in dollars, and 3.1% in volume. Total volume decreased during only one year (2.7% in 1995), although sales showed a slight gain [2]. The savory snacks industry is not guaranteed to be recession proof, but the products are popular in the diet, and sales are not as adversely affected during economically trying times as are sales of other goods. There is no room for complacency in the industry. For example, snacks do not have to be salty. Shelf-stable “sweet snacks,” previously introduced by traditional breakfast cereal manufacturers, experienced a 13.9% gain in snack bar sales and an 8.1% gain in toaster pastries sales (in $1.634 and $0.636 billion product lines, respectively) in 1999 (Table 1.1). Replacements of traditional snacks could come from a wide variety of food manufacturers. Many processors are hesitant to formally deﬁne “snacks”—they want to be among those who innovate or recognize eating trends, and join in the manufacture of future foods, whatever the form.

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Data from the State of the Industry Report [2] have been recompiled on the basis of purchase outlets in Table 1.2. Supermarkets, grocery stores, mass merchandisers and warehouse clubs were arbitrarily grouped as “planned shopping outlets” on the assumption that grocery supplies are purchased at such stores by shoppers more likely to plan meals and prepare shopping lists. Neighborhood and gasoline station convenience stores, vending machines and drugstores— probably more likely to cater to impulse shoppers—were grouped as “nonplanned shopping outlets.” Because characteristics of “other outlets” in the report could not be determined, they were included in the second group. Table 1.2 shows that essentially 65–70% of savory snacks are purchased in “planned shopping outlets.” It may be argued that convenience stores, vending machines and large drugstores are limited in some parts of the country and that impulse buying can occur anywhere. But it is believed the table shows that the majority of shoppers have already planned for home use of snack foods when they purchase their groceries. This should affect some long-time rooted opinions about savory snacks as impulse purchase products and their accepted role in the U.S. diet. Two exceptions exist—approximately 45% of meat snacks and 17% of snack nuts were sold through convenience stores in 1999. This may indicate usage by motorists on long trips. The purchase of 86.7% of microwave popcorn through “planned shopping outlets,” with less than 2% through convenience stores, also is a surprise as one might expect impulse to be a greater factor in purchasing this product [2].

2. PAST INNOVATIONS The U.S. snack industry has a fascinating history [3]. Attention is called to Chapters 2, 10, 11, 13, 14, and 23 where more details are provided. r A Native American chef at a prestigious New York state spa in 1853,

irritated because a customer returned fried potatoes that were “too thick,” sliced the next batch paper-thin and fried it until brittle. The customer, a man of inﬂuence, liked the crispy product and told his friends about it. Other restaurants picked up the idea. By 1895, potato chips were being made commercially. r In 1926, a woman potato chip manufacturer in California sent sheets of waxed paper home with women employees to iron into bags in the evenings. The bags, ﬁlled with potato chips, were readily accepted by the trade. Within several years, preprinted formed bags became available. This was followed by in-plant bag makers, and eventually by machines that form, ﬁll and seal bags from laminated roll stock.

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SM

GS

MM

WC

PSO

CS

V

DS

O

NPS

Potato chips Tortilla chips Corn chips Cheese snacks Microwave popcorn Pretzels Snack nuts Meat snacks Other snacks

44.8 41.0 48.2 42.0 43.1 41.1 41.5 9.2 45.9

10.8 12.8 10.5 12.6 3.2 14.4 13.0 8.2 8.7

7.8 6.8 9.7 6.8 26.1 5.8 11.8 17.1 10.5

3.7 4.3 2.8 6.1 14.3 7.9 5.3 5.9 4.9

67.1 64.9 71.2 67.5 86.7 69.2 71.6 40.4 70.0

13.0 14.8 12.1 14.8 1.7 15.2 17.3 45.3 13.8

5.0 5.6 4.3 4.4 3.9 4.2 1.7 1.2 4.8

2.7 1.9 2.3 2.5 1.9 3.2 4.9 3.3 4.4

12.2 12.8 10.1 10.8 5.8 8.2 4.5 9.8 7.0

32.9 35.1 28.8 32.5 13.3 30.8 28.4 59.6 30.0

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“Non Planned Shopping Outlets” CS: Convenience Stores V: Vending DS: Drug Stores O: Other NPSO: Total Non-Planned Shopping

12:43

“Planned Shopping Outlets” SM: Supermarkets GS: Grocery Stores MM: Mass Merchandisers WC: Warehouse Clubs PSC: Total Planned Shopping

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Percent of Snack Foods Purchased through Various Public Outlets in 1999. (Compiled from: State of the Industry Report. Snack Food & Wholesale Bakery, 89(6):SI-3–SI-74. 2000.

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r In 1885, a young man left Decatur, Illinois, to become a street vendor in

Chicago, which was still rebuilding from the Great Fire of 1871. By the time of the 1893 Columbian Exposition, he had developed and patented a gasoline-fueled corn popper and peanut roaster. The fourth generation of his family is still in the popcorn machinery and product manufacturing businesses. r In 1932, a young man in San Antonio, Texas, who had tried his hand at other businesses, borrowed $100 from his mother to purchase a recipe, some limited hand-processing equipment, and a short list of retail accounts for a “corn chip.” Initially, the product was made in the kitchen and sold from a Model T Ford. The enterprise grew to become part of the country’s largest snack foods processor. These and other Horatio Alger-type entrepreneurs and their associates are part of the snack foods industry’s history [3]. Not much is recorded about the “also rans,” but they left their impact and contributions as well. The industry pioneers had several characteristics in common: r Logically, the time for their ideas was never right. After all, how many

people in San Antonio (and later in Dallas) would be expected to buy “snacks” in the midst of the Great Depression? But fortunately, the corn chip product tasted good, was affordable, and brought happiness to people and their children during the hard times. r The enterprises had low-tech starts—inexpensive ingredients (potatoes, corn, wax paper) and simple equipment and processes. As cash ﬂow increased, better salesmen were hired to sell more product, followed by engineers/machinists to design and build new equipment to expand production capacity, and eventually scientists to develop products that were better than those of other competitors. r All of these were “pull” type enterprises. Expanding markets “pulled” the need for more agricultural products and technologies and were a more effective motivation for agriculture than “push” type projects to ﬁnd uses for surplus crops. The snack industry has stimulated domestic technology and the economy, as well as gained from it. Increased need for potatoes, alkali-cooked corn, popcorn, frying oil and packaging has meant: (1) better and more uniform ingredients and materials, (2) methods to handle the ingredients and materials with reduced damage; and (3) potential markets to warrant inputs from other people and companies with a variety of skills. Breeders, seedsmen, contract growers, storage technologies for potatoes, techniques for cleaning, storing and conditioning corn, and improved facilities for producing frying oils became needed, as well as improved processing and packaging machinery and packaging materials.

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The companies that developed equipment, materials, and skills for the snack industry soon found multiple uses for them. Many expanded to service other industries and, in turn, reduced the economic uncertainty of supplying only one industry in case of a business cycle downturn. At times cooperation with other companies proved beneﬁcial. For example, when designing a thermostatcontrolled electric popper pan for movie theatre machines in 1936, Cretors & Company, a major manufacturer of popcorn processing machinery, working with the Wiegand Company, pioneered the ﬂat, ring-style ChromoloxTM heating element. This later was used in most commercial poppers and in many electric ranges [3]. Simply being a signiﬁcant customer also ensured a say in improvements of items such as packaging materials, carton ﬁlling, sealing, and palletizing equipment, semiautomated warehouses, in-store wire-frame display racks and delivery vans. Snack foods have been the incubator for other industries and applications. Many persons were ﬁrst introduced to salsas in Mexican food restaurants, where the common practice is to serve large tortilla chips and dips while customers wait for their food order. Acceptance of salsas as dips, cooking ingredients and condiments has grown rapidly, and domestic sales of salsas outpaced those of ketchup in the last half of the 1990s. The practice of dipping potato- and corn-based chips as appetizers, at parties and in the home, has given rise to two additional types of products: (1) Dips, a $1.423 billion business in 1999, which grew by 84.7% over the previous year [2]; and (2) sturdier snack products that don’t break when dipped. It is estimated that one third of all chips are eaten away from home, with refrigerated dips the most common accompaniment. Dips have included Mexican sauces and marinades, shelf-stable dips, and refrigerated dips. Cheese, salsa, refried beans, guacamole, and others have been popular, and single-service dips for snacks were introduced in the last several years. Scoopshaped corn chips, more sturdy for dipping, were introduced by the Frito-Lay Company in 1999. Stronger smooth and rufﬂed potato chips had been introduced in earlier years. BuglesTM , a cornucopia-shaped extruded corn product developed by the General Mills Company in the 1960s, is sold in the United States as a breakfast cereal, and is a popular snack product in England, sometimes served with dips. In some countries, where puffed corn-based snack foods are made by high-shear extruders followed by coating with a cheese and oil emulsion, similar colored corn bases are shaped using different dies and are then coated with syrups for sale as cocoa- or fruit-ﬂavored ready-to-eat (RTE) breakfast cereals. Snacks are used as cooking ingredients and meal accompaniments. The National Potato Chip Institute, predecessor to the Snack Foods Association, hired a home economics director in 1946 to demonstrate new uses for potato chips and develop recipes. Cooking with snacks continued to grow as corn products became available. Casseroles including corn chips, tortilla soup and other dishes are common in the U.S. Southwest, in home and in restaurant cooking.

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Many restaurants serve hamburgers on plates dressed with a slice of pickle and a handful or bag of potato or corn chips, and single-service snack packages are put in lunch pails and school lunch boxes. There is still room for new food ideas and improved processes in the United States. But the development of snack foods industries in other countries, based on local crops (like cassava and sorghum) and adjusted to local tastes, has hardly been explored. Development of reliable infrastructures to supply good-quality ingredients is one of the ﬁrst challenges.

3. NUTRITION

3.1. BACKGROUND In the late 1970s and early 1980s, manufacturers of snack foods and ready-toeat breakfast cereals and, to a lesser degree, fast food chains serving hamburgers and french-fried potatoes came under criticism for selling “junk” and “emptycalorie” foods. In some cases, it appeared that otherwise professional comments by nutritionists and dieticians were fanned by the news media into vicious attacks on these industries. This era was unfortunate for the nation, and mainly led to only lawyers talking to lawyers. Such scars take a long time to heal. McDonaldsTM and others sponsored full-page advertisements featuring data supporting the nutritional value of fast service foods. Interestingly, several years later, the U.S. Navy found, by weighing post-meal tray scrapings, that enlisted men aboard ships were not consuming enough “traditional” meals for adequate nutrition. As a result, fast food vendors were invited to help establish trial hamburger, salad and snack bars to serve familiar foods to young recruits on a large warship during a long voyage. The gains in food intake and improved morale were so impressive that the practice spread to other ships and to garrison feeding in other services. During the same period, ready-to-eat breakfast cereal manufacturers conducted considerable research on the relationships between presweetened cereals and the development of dental caries in children. Snack manufacturers offered products with different salt levels for individuals concerned about hypertension. Sodium chloride-potassium chloride mixtures were tried as seasonings, but negative effects on ﬂavor were experienced and concerns arose about excessive potassium intake. Now, approximately 20 years later, the complex carbohydrates of cereals (starch) are considered desirable. Processes that convert starch into nondigestible forms (resistant starch, RS) (Chapter 5), which acts beneﬁcially as dietary ﬁber, have been identiﬁed. Options for developing RS through processing and its direct addition as a food ingredient are being explored. Advances in heart disease therapy have led to medicines such as diuretics for improved

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control of salt balance. Fluoridation of municipal water supplies has helped reduce the incidence of dental caries. Nutritionists now favor Mediterranean-type diets, where the oil is high in monounsaturated fatty (oleic) acid content, instead of the earlier recommendations for polyunsaturated fatty acids. The role of natural antioxidants (typically preservatives of polyunsaturated fats) in the diet is being explored. Saturated fats (stearic acid in beef tallow and palmitic acid in palm and other tropical oils) repeatedly have been shown to have no negative effect on atherosclerosis as previously claimed, although they do raise serum cholesterol levels. Obesity still continues to increase in afﬂuent sectors in poor as well as wealthy countries. However, other factors like genetics, early childhood development, physical activity, and stress factors are being considered in addition to diet [4]. The snack food industry continually searches for products and processes that increasingly please consumers and addresses nutritional concerns, sometimes, only to ﬁnd limited demand or acceptance in the marketplace. Such was the case for snacks with reduced salt content, use of non-caloric frying oils and low-fat/no-fat snacks. People are coming to realize that increased snacks consumption is the result, rather than the cause, of our fast-changing society, and therefore cannot be blamed for all its problems. The following applaudable comment, by a qualiﬁed nutritionist, also appeared in the 1980s: Nutritionists are concerned that people eat the right amounts and combinations of foods to promote good health. Individuals should learn, however, not to feel guilty when they have a snack of a favorite food. The bottom line to the role of snacking in the American diet is that individuals need to learn how to eat in a rational way. With the exception of special medical restrictions, all foods can contribute to a healthful diet, provided individuals eat a variety of foods, and eat them in the right proportions. [5]

The public often sees depictions of the USDA food guide pyramid—in the press, printed on packages of foods and elsewhere—but each year votes for more snack foods at the checkout register. Books on nutrition repeat that 60–70% of American children eat snack foods, which contribute 12–17% of the RDA energy intake of teenagers [6]. Snack foods are here to stay, but can be modiﬁed as warranted by the needs of good health and public acceptance. Snacks need to be recognized as part of the nation’s food resources and be included in constructive plans to improve diet and health.

3.2. NUTRITIONAL LABELING There are no secrets anymore about what food products contain, except for certain ﬂavorings. Nutritional labeling, while expensive to implement and maintain, provides such information for consumers who may need and use it,

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and has done much to level the playing ﬁeld regarding composition claims and counterclaims. Although limited in market demand, snacks with reduced salt and fats contents are available. By various regulations and conventions, labeling on a typical snack food package includes: r Product name r Net weight of product contents (in ounces and grams) r Name and address of the manufacturer (If the product is a private label, or

store label, the distributor’s name and address may be used.)

r A list of ingredients, using legal names, and arranged in order of

diminishing preponderance

r Typically, some comments about the product, offers of prizes, or other

promotions to encourage shoppers to purchase the product

r A bar code to automatically enter the price in the store’s cash register, to

provide information on sales and to enable automated reordering of replacement inventory r A code that identiﬁes the plant in which the snack was made and would enable the manufacturer to recall product made at the same time and/or from the same lots of ingredients if found necessary. The code also alerts the company’s or distributor’s route men of when to remove unsold product from store shelves. Some states require that the expiration date also be readable to customers. r A Nutritional Facts panel, presented in a format speciﬁcally prescribed by the U.S. Food and Drug Administration. The snack industry has generally standardized nutrient statements on the basis of a one-ounce serving. However, statements for single-portion packages may be based on the net weight of package contents. When Nutritional Facts are presented on a one-ounce basis, they include: —Serving size —Number of pieces in one serving —Servings per container —Calories per serving —Calories from fat —Content and percent of daily (recommended) value, provided by the product for speciﬁed nutrients. These are based on a 2,000-calorie daily diet for adults, and include total fat, saturated fat, cholesterol, sodium, total carbohydrate, dietary ﬁber, sugars, protein, Vitamin A, Vitamin C, calcium, and iron. —The maximum Percent Daily Value standards also are listed for 2,000and 2,500-calorie diets for total fat, saturated fat, cholesterol and sodium, as well as recommended levels for carbohydrate and dietary ﬁber intakes.

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4. TOTAL QUALITY MANAGEMENT OF TECHNOLOGY

4.1. BACKGROUND Frederick Taylor, through his time and motion studies in the 1890–1915 era to increase productivity in assembly operations, is recognized as a founder of management science in the United States. From then until the 1950s and 1960s, the emphasis was on maximizing productivity of workers. While motivation and productivity of individuals still are important, starting in the 1970s, domestic emphasis shifted to committing ﬁrms to satisfying their customers—in other words, to making products that buyers want, rather than what companies or production departments may have preferred in earlier times. The magic word is “quality,” which in this chapter means reproducibility or consistency. Total Quality Management (TQM) is a commitment by the entire organization to make customer wants the highest priority (while ensuring a proﬁtable operation by efﬁcient use of resources). For the most part, “quality” options occur in buyer’s markets, i.e., where there is no scarcity of goods or suppliers, and the customers are qualiﬁed by having money for purchases. In buyer’s markets, purchasers are value optimizers and select products that provide the most satisfaction for the cost. In such cases, buying decisions are seldom made on price alone. Value may also include: product appearance; taste; crispiness; color; shelf life; package appearance including graphics, ease of opening and temporary reclosure features; ease of using the product; beliefs about product safety and wholesomeness; persuasion by prior advertising; lot-to-lot consistency; and other factors. For industrial buyers, ability of the supplier to repeatedly ﬁll orders, reliable and timely delivery, technical support, if needed, and defects not to exceed acceptable levels also are important. Since many suppliers can produce almost similar products, small differences may be the deciding factor for industrial buyers and consumers.

4.2. THE NEW QUALITY AGE How did we get to today’s quality control and TQM practices? The United States learned a costly lesson after World War I. The German economy had been shattered during the war. Preparation demands by neighboring countries and a general world economic recession led to severe postwar poverty where the people were ready to grasp at any hope, including the promises of a dictator. Determined that similar scenarios would not happen after World War II, the United States intentionally undertook rebuilding the economies of its former enemies. However, many people had low regard for prewar Japanese consumer goods, and their quality image had to be improved if an export economy was to be developed. Two capable quality control statisticians, William Edwards Deming

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and Joseph M. Juran, were sent to help Japan in the late 1940s and early 1950s. Deming had been with the U.S. National Bureau of Standards, involved in improving compatibility of parts for armaments and other assembled products made by many U.S. manufacturers. Juran had a long history of teaching quality control to industry and numerous publications. In Japan, Deming became known for establishing Statistical Quality Control programs, and Juran for implementing Quality Circles. The two men signiﬁcantly changed the world’s appreciation of statistical quality control and the manner in which business is done today. Deming established 14 Points for Management [7]. These are paraphrased in a different fashion, but focus on: r Creating a corporate atmosphere, where improvement of product and services is the main commitment.

r Getting all levels of employees trained in statistical quality control and

r r

r r

involved in improving quality—including breaking down hierarchical and departmental barriers as needed, and periodic retraining as new methods develop. Eliminating employee fear of suggesting changes by guaranteeing retraining if jobs are obsoleted by process improvements, and encouraging pride of workmanship. Getting top management visibly sincere and involved in quality improvement, including: (1) eliminating slogans and banners emphasizing quality if such practices are not followed; and (2) searching for problems, including asking employees. (Previous studies had shown that 85% of quality problems occur because of conditions that only management can change.) Changing emphasis in quality control from mass inspection and sorting out defects to improving processes so fewer defects occur—in other words, making the product correctly the ﬁrst time. Changing from buying supplies on price alone, reducing the number of suppliers and helping the remaining ones do a better job so they can prosper and reinvest in modernizing their businesses.

Juran’s Quality Circles, originally intended to focus on process and product improvement, soon realized that their techniques also were applicable to other company operations, including internal communications and management systems. Together, Deming’s and Juran’s principles, and those of their associates and followers, led to the evolution of concepts like “Just-in-Time delivery,” “selfcertiﬁcation,” ISO-9000, and the development of methods to determine what really is important to customers. After World War II, world manufacturers generally returned to previous systems of quality control—except for the Japanese, who were committed to

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improving the quality image of their products. However, domestic products had changed and were more complex than those made before the war. During the postwar era, the author experienced the common practice of returning new automobiles to dealers several times to correct defects that hadn’t been found before when they left the manufacturer. Also, several calls for home appliance repairs were typical before machines worked correctly. The automobile industry, admittedly, started including “planned obsolescence” in its models, thinking customers had no say in the matter. As Japanese products appeared on the U.S. market with far fewer defects, the contrast ﬁrst was ascribed to differences in commitment of Japanese labor. As Japanese-owned assembly plants in the United States began to make equally defect-free products using American labor and domestic markets were being lost, U.S. companies started sending observers to Japan and hiring Japanese consultants to help reorganize their own quality control programs.

4.3. CONTROL, CRITICAL PATHS AND POINTS The traditional functions of planning, organizing, stafﬁng, directing and controlling have been honed to maximize efﬁcient use of resources in modern management. Even though projects and types of work differ, the basic components of controlling are similar and include: r An objective, best stated in numerical terms as an acceptable range if

possible.

r A monitor to watch the process or system. r A signal to alert the system that the process has or is heading out of the

acceptable range.

r An empowered corrector to return the process to the acceptable range. r An archiving (data recording) system often is additionally added to

document that the process/system operated in a desirable fashion at a speciﬁc time. Universality of these principles is shown in the following examples. r Temperature control. The objective may be to operate a deep fat fryer at

398–402◦ F. Recording thermometers are the typical monitors, and also archive the temperature in case checking consistency of the process is desired later. When the temperature of the frying oil drops below the acceptable range, a horn may sound or a red light ﬂash to alert the operator. In simple installations, the operator may be empowered to further open a steam valve to increase the frying oil temperature. But automatic temperature controllers are relatively inexpensive and typically respond faster than operators. The common practice is to delegate such repetitive

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actions to a robot (controller which continuously adjusts and records the temperature), thus freeing the operator to focus on other parts of the process. r Product quality control. The objective may be to produce a snack containing 0.7–0.8% salt. The monitor is the quality control technician who periodically conducts salt determinations. Results of assays typically are kept in a laboratory notebook, which archives product identities, dates and time. Optionally, a computerized data acquisition system may collect and store the information until printouts are needed. If salt content of the product falls below the acceptable range, an empowered operator on the production ﬂoor typically would be alerted by the quality control laboratory to adjust the setting on the applicator. r Production throughput. Each line or plant is expected to process a speciﬁed number of product units per shift (objective). Typically, the previous day’s performance is reviewed (monitored) in a report (archive) prepared for the respective production supervisor. If a deviation out of the normal range (alert) is detected, the (empowered) supervisor is expected to ﬁnd and correct the problem. r Proﬁtability. Companies typically prepare annual plans that project their expected proﬁt (objective) based on the most realistic estimates of the various departments. Progress toward the proﬁt objective is monitored monthly (sometimes weekly or more often) by the accounting system and reported (archived) to appropriate executives. If progress toward the annual proﬁt objective falls behind, the (empowered) Chief Operating Ofﬁcer (COO) is expected to ﬁnd out why and take corrective action. If progress exceeds expectations, effective COOs also determine why and seek opportunities to further improve the results. Modern management techniques increasingly focus on “critical” or “indispensable” [1] factors. An early application was the successful planning and supervision in establishing the Polaris weapon system in the late 1950s using the PERT/CPM (Project Evaluation and Review Technique/Critical Path Method). Large projects consist of many subprojects, each requiring specialists, which often cannot be started before other subprojects are completed and, in turn, must be completed to enable the start of yet later subprojects. In a computer-assisted CPM method, relationships of the ﬁrst and last possible start and ﬁnish dates of thousands of subprojects in a program can be established relative to each other, and a “critical path” identiﬁed. The critical path is the shortest sequence of events that must occur before a project can be completed. The slack times available between the ﬁrst possible undertaking and the last ﬁnish date of subprojects not on the critical path also are calculated. Completion time of the entire project can only be shortened by accelerating the subprojects on the critical path.

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Introduction of the CPM forced examination of systems to determine what was “critical” and planning in greater detail than normally had been done previously. The advantages of using CPM were so signiﬁcant that the technique became a common tool for one-time projects like constructing buildings. Later improvements included PERT/COST techniques which also consider costs in planning and control. While PERT/CPM is less applicable to repetitive operating systems, its lessons have been useful. For example, a processing operation really does not need raw materials or supplies until the time of use, thus encouraging the carrying of smaller supply inventories and ordering of Just-In-Time deliveries. “Critical” also can mean “decisive” [1]. Examples include: (1) a label may be satisfactory for a product currently, but, after a critical date, can become illegal for the same product. (2) Snack foods may be crunchy at up to a 2% critical moisture content, but become soggy at higher levels. (3) Many types of bacteria in dry ingredients pose little hazard to health but may cause spoilage or food poisoning if the moisture content is raised above critical levels where they can grow. The properties of many materials and products change signiﬁcantly beyond certain critical conditions. An example is loss of snack protection against moisture and oxygen because of incomplete end or side seals of the package. Many companies have thoroughly reviewed their management procedures as well as product processes, and have installed critical control point checks to ensure that various operations are proceeding as expected. The sites of the checks are the points beyond which a continuously processed product should not be allowed to proceed because further expense is not warranted. An example is diverting burnt snacks after the fryer and before additional costs of seasoning and packaging are incurred. Implementation of HACCP (Hazard Analysis and Critical Control Points) programs became required by law for U.S. processors of high-moisture foods in the mid-1990s, and has since spread to essentially all food products. The program was originally motivated by the need to reduce food-borne disease in poultry and red meat products, and eventually was broadened to include general sanitation in all food processing. Under the program, processors are required to review their operations relative to risks that might develop to human health, make equipment and operation changes if necessary [9], and identify critical points where in-process products are checked and held back from further processing if previously self-established criteria are not met.

4.4. ESTABLISHING QUALITY OBJECTIVES Quality programs typically start with a corporate quality statement and evolve with need.

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Snack foods research generally is of three types: r Maintenance of existing products by ﬁnding new sources of suitable

ingredients if older materials become unavailable or too expensive; incorporation of newer processes that may be necessitated by other products also made on the same equipment; ways to save energy in processing; and typically minor changes as needed to support new and improved marketing claims. Product maintenance work usually can be supported by sensory panels described in Chapter 21, since the decisions are of the “difference-no difference” type. r Product line extensions to create new ﬂavors and shapes, often with the objective of gaining increased grocery store shelf facings for the entire line, but usually employing the same equipment, processes and ingredients with minor changes. This type of development uses consumer input, sometimes before prototypes are made and always to verify product acceptance before production is begun. r Development of new products that may differ signiﬁcantly from current lines in composition, appearance, processing, and marketing concept. Special efforts are made to involve consumers, often before the ﬁrst prototype is made in the research laboratory. Focus groups consisting of a spectrum of snack users are organized, often by independent consumer research agencies, to discuss shortfalls of currently available snacks in general, and to probe the likely acceptance of new types of products and ﬂavors. When formulation, processing, consumer acceptance and marketing research are completed, a detailed deﬁnition of the product is sent to the respective operating department, in the forms of (1) ingredient purchasing speciﬁcations; (2) manufacturing manual; (3) quality control manual, deﬁning tests to be performed on the product, target values and acceptable ranges; and (4) distribution instructions about expected product shelf life (number of days the product can be offered for sale). Unfortunately, sensory characteristics (ﬂavor, texture and color) are not easily deﬁned by numbers, but the best effort possible is made to record chemical analyses, create a “living memory” in the form of descriptive proﬁles and trained expert panels and make and preserve samples for later comparisons. After the manufacturing startup problems have been resolved, and the process is running smoothly (in control), it typically generates products whose characteristics resemble a Normal Distribution Curve, as shown in Figure 24.2(A) (Chapter 24). It is essential that the product made in the plant closely match the consumer and management objectives, as determined by consumer testing, and selected by product development and marketing personnel who authorized its commercial production. If the goal is not met, then the full beneﬁts of the product development program has been in vain. As shown in Figure 1.1 (Loss Function Curve) [8], losses occur to the company by not meeting the product speciﬁcations (designer’s target). Depending

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Figure 1.1 Loss Function Curve. (From: Robertson, G. H., 1990. Quality Through Statistical Thinking: Improving Process Control and Capability. American Supplier Institute, Livonia, Michigan [8]. With Permission.)

on severity, deviations to the left of the target are expensive. The product may require expensive sorting, rework or discarding, and result in dissatisfaction and loss of customers. Deviations to the right of the target are also expensive, often in the form of lost opportunity of producing additional units that could have been sold. Also, if a product appreciably better than average (intended designer’s mean) is sent as a sample to a potential customer for evaluation, the buyer is likely to be disappointed when shipments are received since they won’t consistently meet the raised expectations.

4.5. QUALITY CONTROL (QC) AND QUALITY ASSURANCE (QA) Quality Control is the mechanism intended to achieve management’s intended characteristics of the company’s products and services. However, guidelines and directives may not always become implemented as intended. Someone needs to certify that the mechanisms actually are in place and working, hence, Quality Assurance. Business, governmental and military organizations have long used auditors (reviewers) to certify existence of assets and prescribed records and to verify that operations are conducted as intended. Today’s QC and QA programs are merely extensions of long-established management practices, but they have acquired new names and forms tailored to the food industry.

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The roles of these two functions, responsible for ensuring product quality, and their reporting relations to senior management, vary with the size of the company. They often are two separate entities in medium- and large-size companies. r Quality Control works at the plant level to ensure that a consistent product is

made on a daily basis, although ingredients may vary. The resident QC manager often typically reports to the plant manager and is empowered/expected to make process adjustments as required to produce the intended products. However, he/she is not authorized to change the products themselves. QC personnel often are assigned additional responsibilities since they have the best technical training among resident employees. r Quality Assurance works company-wide to ensure that products reaching customers are as intended, that other functions affecting product characteristics (including purchasing, production, quality control) also are operating as intended, and that the technical requirements of various regulators are met—in a sense keeping the company out of trouble. While objectives for the Quality Control group are set internally in the company, often the QA group also is expected to identify the expected technical requirements of regulators for various product lines, and recommend and help implement corporate-approved programs before the company is found in violation or ﬁned. Examples of corporate-wide QA programs include preparing the company to meet new product labeling requirements, Good Manufacturing Practices and Hazard Analysis and Critical Control Programs as implementation deadlines draw near, and later ensuring that the added programs are being followed. Like the QC staff in its environment, QA personnel often are called on for technical matters at the corporate level because of their knowledge. The QA supervisor typically reports to a separate corporate ofﬁcer, with policy-setting powers, to insulate against pressures that might be put on the program by other operating departments. Other Quality Assurance functions may include: —Having samples of products picked up throughout the country by private services for periodic examination of their condition in supermarkets. —Being the ofﬁcial repository of ingredients purchasing, product production, and quality control manuals for the company—often to ensure they are on record. —Being aware of the extent and nature of consumer complaints regarding speciﬁc products and recommending corrective reviews as appropriate. —Auditing the operating groups (purchasing, production, quality control, and distribution) to ensure procedural manuals are kept current and followed. —Participating in approving self-certiﬁed suppliers.

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—Ensuring that a product recall program exists, in case of need. —Recruiting consultants or private inspection services to audit various operating functions for a third-party evaluation of their performance. —Advising senior management on what proposed technical legislation may mean to company operations to assist a company response and testimony at legislative hearings. —Identifying and assessing potential problems for which a company may want to prepare a technical readiness.

4.6. SELF-CERTIFICATION OF SUPPLIERS In earlier years, large amounts of capital were tied up in raw materials inventories, and warehouse costs were substantial. Development of bulk handling systems, larger trucks and interstate highways, and improved scheduling of freight trains, made deliveries more reliable and encouraged reduction of demurrage charges (resulting from holding ingredients in tank and box cars longer than needed for unloading). Just-In-Time (JIT) systems were developed in the hard goods industries to produce parts and ship them in a short time frame to arrive as needed at the ﬁnal assembly plants. However, except for perishables, JIT had limited use in food processing operations because of the practice of locally verifying compositions of ingredients before use—using tests that could require several days for completion. Thus, supplier certiﬁcation programs (later called “Self-Certiﬁcation”) were developed to enable JIT delivery of food ingredients and minimize capital invested in construction of holding tanks, silos and ingredient warehouses at processing facilities. In Self-Certiﬁcation, the seller’s analysis is used instead of waiting for the manufacturer’s assays. Authorization to purchase from Self-Certiﬁed suppliers is not given lightly, and typically is preceded by visits by the buyer to inspect production facilities and assess the capabilities and integrity of the supplier’s Quality Control program and personnel. In effect, buyers have pushed quality control and warehousing responsibilities back to suppliers, who can only accept them as an expense of doing business.

4.7. PRODUCT RELIABILITY IN DOMESTIC AND GLOBAL TRADE The trading of commodities and processed foods on an international basis, or between unacquainted buyers and sellers, requires a common “vocabulary” regarding product characteristics. Three signiﬁcant changes have occurred in the last quarter century. r Improved analytical methods. Improved chromatographic separation and

spectroscopy techniques and electronic microcircuitry have given chemists

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new, highly sensitive, affordable instruments capable of quantifying product components and characteristics that were unrecognized in the 1960s. The methods have been standardized under the oversight of various governmental agencies and professional societies and often are incorporated in purchase speciﬁcations. Chemical components and microorganisms, recognized as hazardous to public health, are excluded from food and feed supplies by laws of various countries, and are monitored by regulatory agencies—the extent dependent on their relative hazards. Typically, the ofﬁcial analytical methods used for snack foods and their ingredients in the United States have been issued by the American Association of Cereal Chemists (AACC), American Oil Chemists’ Society (AOCS), or the Association of Ofﬁcial Analytical Chemists (AOAC). Increasing use is made of rapid methods that, although not ofﬁcial, are helpful in process control because of reduced assay time. The Snack Foods Association has listed some methods speciﬁcally applicable to snack foods in its quality control manuals. r Analytical laboratory assessment and certiﬁcation procedures. Today’s business requires that analytical laboratories make correct assays of samples and that assays of the same sample by two or more laboratories be identical. Professional analytical laboratories (company-owned on-site or private off-site) are expected to have QA programs in place that continuously audit their own performances. This includes periodic checking of equipment calibration and sensors and inclusion of previously analyzed “standards” in daily runs to ensure that tests perform as expected. Professional societies, like AACC and AOCS, also administer sample check programs, which distribute samples to participating laboratories worldwide and statistically analyze and publish the results. Commercial laboratories that perform well in AOCS programs may qualify as Certiﬁed Chemists and act as referees in case of disputes on trading contracts. r International quality management standards. Establishment of the ISO 9000 program originated with the development of the Common Market in Europe, as a means of certifying that sellers have quality control systems in place that meet recognized procedural standards. The program is to be applauded for its objectives and accomplishments to date. Suppliers from various countries have found that obtaining respective ISO certiﬁcation is essentially required to trade in the Common Market, and also a beneﬁt even when trading in areas other than the European Community. Some domestic companies believe that advertising their ISO 9000 certiﬁcation is an additional stamp of “good quality.” However, it should be remembered that ISO 9000 certiﬁcation is merely conﬁrmation that a recognized quality control program is in place, not a guarantee of analytical values. It still is well to include speciﬁc requirements in purchase speciﬁcations and

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contracts, as well as a Referee Chemist and methods to be used for resolving analytical disagreements between seller and buyer.

4.8. RECALL PROGRAMS AND INGREDIENTS/PRODUCTS TRACKING With consolidation of suppliers and enlarged processing facilities, modern mistakes involve more products and cover greater areas. Processors are well advised to identify sources of ingredient lots as received, keep track of them in the system, and keep records of products made and where they went. Even if no mistakes occurred during processing, snack manufacturers may still be required to retrieve all product made from purchased ingredients that may have been contaminated or mislabeled. Some European countries are implementing Certiﬁcates of Origin, which are required to accompany food and feed ingredients and must be updated as lots are traded. Minimizing the cost of recalls requires knowing exactly where suspect ingredients and products went. If a food manufacturer cannot reliably identify the suspect product batches, regulatory agencies may require recall of all products in the distribution system, on store shelves, and publicize requests for buyers to return products in their home—obviously an expensive and embarrassing situation. Readiness in case of recalls (Chapter 24) is wise, but hopefully will never be needed. Providing (preferably refrigerated) storage space for samples of ingredients received and products shipped, until the processor is reasonably certain the products no longer are in stores or kitchens, also is advisable.

4.9. ACQUISITION AND LAYOUT OF PRODUCTION FACILITIES Total Quality Management objectives can be met more easily if buildings, work areas and equipment are properly designed. Construction standards speciﬁcally for snack food production facilities do not exist currently, but many facility construction engineers refer to Engineering for Food Safety and Sanitation, by Imholte and Imholte-Tauscher [9] for guidelines. This guide can be obtained from the publisher, or the American Institute of Baking (AIB), Manhattan, Kansas. Bakeries are reasonably similar to snack food plants. The AIB has also developed an extensive collection of applicable literature and special training courses, and offers various plant inspection services. If the product includes red meat or poultry, and is sold in interstate commerce, the manufacturing plant comes under the jurisdiction of the U.S. Department of Agriculture’s Food Safety Inspection Service (FSIS). This agency provides (processor-paid) resident inspectors and is very speciﬁc about manufacturing facility construction and sanitation requirements. Information about

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FSIS and its authority and requirements can be found in the Code of Federal Regulations (CFR), Title 9. The Imholte and Imholte-Tauscher book [9] is a good review for meeting current Good Manufacturing Practice (GMP) and expected near-term additions. Regulations regarding GMP for non-meat/poultry products are described in the U.S. Food and Drug Administration (FDA) food section in CFR, Title 21. This agency also leads the Hazard Analysis and Critical Control Point (HACCP) program and ﬁsheries products inspection. New plants are expected to be GMP and HACCP capable, and signiﬁcant expenditures may be needed to bring old facilities to a level where they can be used. Factors to consider include: r Ability to daily wash wet processing areas [using clean-in-place (CIP) r r r r r r r

techniques where feasible], suitably sloped and drained ﬂoors and acceptable means for wash water disposal. Pumpable grease/oil traps to separate spilled oil and that which comes from wash water. Ability to provide clean (often ﬁltered) air in the product processing and packaging areas. Hoods and exhaust systems to remove steam from cookers and vapors from fryers. Minimum horizontal edges on walls, overhead conduits, wireways, plumbing, and light ﬁxtures to collect dust. Adequate locker rooms, toilets and wash areas for personal sanitation. Occupational Safety and Health Act (OSHA) compliance regarding employees. Compliance with national, and respective local and state, Environmental Protection Agency (EPA) requirements.

It would be well to determine why an existing facility is for sale before negotiating for purchase. In many localities, upgrading older plants to meet current EPA requirements has become prohibitive in cost. Hidden problems, such as contamination of the soil and ground water from leaking fuel tanks or other sources, by the current or earlier owners, also may exist. For new facilities, soil characteristics, drainage, ﬂood susceptibility, availability of a processing water supply and waste disposal need to be considered in selecting a site. Past neighbor relations and zoning limitations should be included. (The aroma of frying corn chips may be pleasant to the new owner, but not to neighbors, and might require a washing system for discharged air in some localities.) The selected equipment should be easy to clean, equipped with Clean-InPlace (CIP) systems if feasible, and non-corroding. It the company is successful, the production facilities are likely to grow in increments, with enlargements of capacity made as needed. It would be wise to anticipate this during building construction and laying out of processing lines, leaving many branches available for future elongation.

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4.10. STAYING CURRENT WITH THE INDUSTRY The speed of today’s technical evolution is exceeded only by the proliferation of regulations. Although the principles summarized in this volume are basic, details about their implementation and labeling change rapidly. The snack foods technologist can easily establish a constant incoming ﬂow of news about the industry by requesting subscriptions to trade magazines such as Snack Foods and Wholesale Bakery, Food Processing, Prepared Foods, Powder/Bulk Solids, Powder and Bulk Engineering, and Food Testing & Analysis, which are free to qualiﬁed individuals. Many of these magazines also print useful Annual Buyer’s Guides, which list suppliers of equipment, ingredients and services. Memberships in technical societies typically include subscriptions, for example: Cereal Foods World (which periodically includes updates on snack foods, ingredients and extrusion technology), published by the American Association of Cereal Chemists; INFORM, published by the American Oil Chemist’s Society; Food Technology, published by the Institute of Food Technologists; and Quality Progress, published by the American Society for Quality. Annual trade shows that exhibit applicable equipment and suppliers include: SNAXPO, sponsored by the Snack Food Association; the IFT Exposition, held during the annual meeting of the Institute of Food Technologists; the exposition accompanying the American Oil Chemists’ meeting; and tabletop displays during the annual meeting of the American Association of Cereal Chemists. Various universities and institutes, and trade associations like the Snack Food Association, offer training courses in specialized topics. When questions exist about where to start gathering information and solving problems, the internet should be one of the ﬁrst choices. Its development has created a valuable self-refreshing information system, unimagined in earlier times. Most of the information is free for the ﬁnding. Snack food technologists are encouraged to surf the net, assess and select sites containing useful information, and bookmark them for future reference. Some sites also offer news updating services in their specialties.

5. REFERENCES 1. Unidentiﬁed, 1985. Webster’s Ninth New Collegiate Dictionary. Merriam-Webster, Inc., Springﬁeld, Massachusetts. 2. Unidentiﬁed, 2000. State of the industry report. Snack Food & Wholesale Bakery, 89(6):SI-3– SI-74. 3. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, 1711 King St, Suite One, Alexandria, VA 22314. 4. Krwczyk, T., 2000. The spreading of obesity. INFORM 11(2):160–171. 5. Morgan, K. J., 1983. The role of snacking in the American diet. Cereal Fds. World, 28(5):305– 306.

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6. Hegarty, V., 1995. Nutrition: Food and the Environment. Egan Press, St. Paul, Minnesota. 7. Deming, W. E., 1982. Quality, Productivity, and Competitive Position. Center for Advanced Engineering Study, Massachusetts Institute of Technology, Cambridge, Massachusetts. 8. Robertson, G. H., 1990. Quality Through Statistical Thinking: Improving Process Control and Capability. American Supplier Institute, Livonia, Michigan. 9. Imholte, T. J. and T. K. Imholte-Tauscher, 1999. Engineering for Food Safety and Sanitation: A Guide to the Sanitary Design of Food Plants and Food Plant Equipment, 2nd edn., Technical Institute for Food Safety, Woodinville, Washington 98072.

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CHAPTER 2

The Snack Industry: History, Domestic and Global Status JAMES A. McCARTHY

1. INTRODUCTION

S

is not a new phenomenon. Savory or salty snack foods, such as the potato chip and corn chip, are seen as relatively new because they were only commercialized in the last century and a half. Always evolving with new ﬂavors and styles, savory snack foods are considered uniquely “American.” They have become icons of the American lifestyle and symbols of the hard-charging, everchanging image most people of the world associate with the American style and spirit. Savory snack foods are multipurpose foods that can be eaten with a meal or on the go and are often associated with fun-ﬁlled events like picnics, barbecues, or sports, where an informal atmosphere reigns. Their association with fun reinforces the image of these foods as typically American to the rest of the world. NACKING

2. HISTORY Not all snacks were invented in the United States. The pretzel is said to have its origins sometime after 610 AD in southern France, where monks baked scraps of dough in the image of arms folded as in prayer to reward young children for learning their prayers. Tortilla chips have origins in Mesoamerica where corn masa has been used in tortillas and snack making for centuries; popcorn has been traced back as far as 3,000 BC. The success of snack foods worldwide, however, is attributed to American processing and marketing skills. The ingenuity of the early founders of this industry, now roughly $30 billion in annual global sales, is in many ways

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typical of the drive and spirit that has made American innovations the envy of the world. To illustrate, let us walk through the history of snacks in this country.

2.1. POTATO CHIPS, THE BEGINNING In 1853, railroad magnate Commodore Cornelius Vanderbilt was vacationing in Saratoga Springs, New York. One evening at dinner he sent his fried potatoes back to the chef, complaining that they were too thick. The chef, George Crum, decided Vanderbilt’s complaint deserved a sarcastic reply. So, he sliced potatoes paper thin, fried them in oil to a crisp, salted them and sent them back to the commodore. Commodore Vanderbilt loved them and called them “crunch potato slices.” Soon afterwards, “Saratoga chips” became a fad with the restaurant’s patrons [1]. Potato chips became very popular, but remained primarily a restaurant food item. By 1895, people like Cleveland, Ohio, businessman William Tappenden set out to make chips a household snack. Tappenden delivered chips to neighborhood stores in his horse-drawn wagon. He ﬁlled orders by cooking chips on his kitchen stove and, because of growing demand for the product, converted his barn into one of the ﬁrst potato chip factories. Potato chip companies soon sprang up across the United States. For many years, retailers dispensed potato chips in paper sacks from horse-drawn wagons, cracker barrels or glass display cases. In 1926, potato chip maker Laura Scudder had a fresh idea. Every evening she had women employees take home sheets of waxed paper and iron them into bags. The next day, workers would hand pack chips into bags, seal the tops with warm irons, and deliver them to retailers. The potato chip bag was born. The late 1920s and early 1930s gave rise to cellophane and glassine bags for chips. Today’s snack food packages are advanced polypropylene bags that keep chips fresh and crunchy for several weeks. The end of Prohibition in 1933 brought an increased demand for potato chips. Patrons of now legal bars and saloons liked salted snacks with their drinks. About the same time, Harvey Noss, the general manager of Noss Pretzel and Cone Company in Cleveland, Ohio, persuaded other potato chippers to join forces and establish the Ohio Chip Association in 1931 [2]. Six years later, Noss and his colleagues formed the National Potato Chip Institute (NPCI), forerunner to today’s Snack Food Association (SFA). The new association was founded to provide education to retailers and consumers on the use of potato chips and to develop product quality standards for potato chip manufacturers. A quality assurance package seal was adopted for members’ use. Today, the Snack Food Association symbol is seen on many snack packages around the world. In 1939, NPCI premiered its ﬁrst newsletter, titled The Chipper, at its annual convention in Harrisburg, Pennsylvania. This later became SFA’s SnackWorld magazine, with subscription circulation at 10,000 worldwide. In 1999, SFA

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joined resources with Stagnito Communications Incorporated, an MWC Company, Northbrook, Illinois, to launch Snack Food & Wholesale Bakery magazine with an expanded circulation. By agreement, the Snack Food Association publishes a monthly section in Snack Food & Wholesale Bakery and participates in developing the June State of the Industry Reports and the October Buyer’s Guides. With the advent of World War II, fats and oils became much in demand for manufacturing explosives and cellulose, the major ingredient of cellophane, for making gunpowder. As a result, NPCI members were faced with the threat of being forced out of business due to food rationing and possible declaration of potato chip as an “non-essential food.” However, NPCI prepared a document called “32 Reasons Why Potato Chips Are an Essential Food,” and convinced the government about the importance of this high-energy food. The document stressed that potato chips represented the most efﬁcient and economical way of packaging and shipping potatoes in a ready-to-eat form. This was the beginning of NPCI’s, and later SFA’s, successful tradition of petitioning the U.S. Congress on behalf of the industry. The success also made it clear to NPCI members that the association should be headquartered near the seat of the federal government in Washington, D.C., to make the industry’s presence and importance known to the government [3]. By 1956, NPCI’s membership had grown substantially and included nine international members. The addition of international members prompted NPCI to hold the ﬁrst international potato chip meeting in May 1958, at the Grosvenor House in London, England. This meeting also led to another change in the association’s name to the Potato Chip Institute International (PCII), reﬂecting the growth of popularity and interest in snack foods worldwide.

2.2. NEWER SNACK FOODS The 1960s and 1970s ushered in concerns about the effects of eating habits on health for most Americans. The industry as a whole faced the need to develop a positive message to consumers in the wake of various attacks on snack foods as junk food of little or no nutritional value. The industry mounted a successful public relations campaign pointing out the positive nutrients in potato chips and other savory snacks and started to respond to consumer demand for healthier, lower-fat snack products. The PCII changed its name again to the Potato Chip/Snack Food Association, initiated education about the positive nutrients in snacks, and helped develop advancements in snack manufacturing technology. In the 1980s and 1990s, public concerns about healthier foods continued to open new opportunities for fat-free and sodium-free snack products. Pretzels, which are naturally low in fat because they are baked, exceeded $1 billion in annual sales in 1993. While taste and “crunch” were still what the consumer

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demanded, a low- to no-fat snack became the industry’s “holy grail.” With the passage of the Nutrition Labeling and Education Act in 1990, additional products were introduced and manufacturers put nutrition information about snack foods at the consumer’s ﬁngertips. Although development of new baked snacks and fat-free oils has become a focus of snack food technology, as we enter the new millennium, sales of the traditional snacks continue to hold their ground. For example, the fried and salted potato slices Commodore Vanderbilt raved about in 1853 now account for over $5 billion annually in U.S. sales.

2.3. MAJOR ADVANCES Highlights in the development of the modern snack foods industry include: 1853 George Crum, cook on duty, prepares “crunch potato slices” for Commodore Cornelius Vanderbilt at Saratoga Springs Resort, New York. 1861 Julius Sturgis establishes ﬁrst commercial pretzel bakery in Lancaster County, Pennsylvania. The product had been introduced to the United States earlier by German and Austrian immigrants, who called it “bretzels.” 1885 Charles Cretors, Chicago, Illinois, develops a portable gasoline-powered corn popping machine, with a small peanut roaster, for street vendors. 1890s William Tappenden prepares potato chips at home and delivers them to neighborhood stores by horse-drawn wagon. 1906 Amedo Obici, Italian immigrant, develops process for commercially roasting shelled peanuts in oil; Planters Peanut Company formed with Marie Piruzzi in Wilkes Barre, Pennsylvania. 1926 Laura Scudder, Montgomery Park, California, invents ﬁrst potato chip bag by ironing sheets of waxed paper into bags. 1929 Freeman McBeth of J. D. Ferry Company invents ﬁrst continuous potato chip cooker and gives the device to Ross Potato Chip Company in Richland, Pennsylvania. Broad application delayed by the Depression years. 1933 Dixie Wax Paper Company, Dallas, Texas, introduces ﬁrst preprinted waxed glassine bag, which keeps potato chips fresh longer. New inks that don’t fade or bleed are developed. Reading Pretzel Machinery Company, Reading, Pennsylvania, introduces ﬁrst automatic pretzel-twisting machine. 1937 National Potato Chip Institute (NPCI) founded; initiates program to educate retailers and consumers about use of potato chips. 1943 Potato chip manufacture allowed to continue during World War II, but industry ﬁrmly conﬁned to rations of materials needed for production.

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1946 Adams Corporation, Beloit, Wisconsin, formed to market Korn KurlsTM , made on ﬁrst high-shear extruder patented in 1938, but marketing product was delayed until after World War II. Adams Corporation acquired by Beatrice Foods Company, Chicago, Illinois, in 1961. Early 1950s Pork rinds made commercially by frying cured pork skins. 1958 NPCI holds international potato chip meeting in London; later changes name to Potato Chip Institute International (PCII). 1961 Two of nation’s largest snack food companies, the Frito Company and the Lay Company, merge to become Frito-Lay. Initial main national products were FritosTM brand corn chips and CheetosTM brand extruded snacks. Lay’s Potato ChipsTM produced nationwide by end of 1961. 1964 DoritosTM tortilla chips (meaning “little gold” in Spanish) introduced by Frito-Lay Company; becomes largest-selling snack food in the world three decades later. 1970 U.S. potato chip sales top $1 billion mark. 1976 PCII changes name to Potato Chip/Snack Food Association (PC/SFA). 1978 PC/SFA moves headquarters from Cleveland, Ohio, to Washington, D.C., area. 1983 Thicker ridged chips introduced for dipping. Kettle-made potato chips again distributed widely. 1986 PC/SFA changes name to the Snack Food Association (SFA) and celebrates its golden anniversary. 1989 February declared National Snack Food Month by SFA and National Potato Promotion Board; leads to 41% increase in snack food consumption during February. 1995 Boom experienced in sales of low- and no-fat snack foods. Seventyﬁve percent of full-line snack foods companies responding to industry survey reported introduction of low- or no-fat products during this year. 1996 Website, http://www.sfa.org, established to inform public about snack foods. 1997 Flavor technology developments lead to broadened variety of snack food products.

3. THE DOMESTIC SNACK FOOD MARKET The June 2000 issue of Snack Food & Wholesale Bakery includes snack sales data provided by the Snack Food Association, Information Resources, Inc.

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and A. C. Nielsen Company [4]. Domestic sales of 6.17 billion pounds of snack foods for a total of $19.37 billion are reported for 1999. Sales in dollars increased by 4.4% in weight and 6.2% in dollars over the previous year. These numbers represent commercially made and traded products. Snack foods prepared in small scale in restaurants, quick food service stores and by street vendors are not included and the actual amount of snack foods consumed by the U.S. public is underestimated. Potato chips still are the sales leader, commanding $4.69 billion (24.3%) of the market. Tortilla and corn chips take second place at $3.75 billion (19.3%), snack nuts are third at $1.69 billion (8.7%), meat snacks fourth at $1.32 billion (6.8%), pretzels ﬁfth at $1.22 billion (6.3%), microwaveable popcorn sixth at $1.16 billion (6.0%), and pretzels sixth at $1.16 billion (6.9%). With an estimated U.S. population of 274 million, this equates to a 5.62 lb annual per capita consumption of potato chips worth $17.11; 5.23 lb tortilla and corn chips worth $13.68; 1.61 lb snack nuts worth $6.18; 2.21 lb pretzels worth $4.45; 1.55 lb microwaveable popcorn worth $4.22; 0.35 lb meat snacks worth $4.82; and 22.5 lb total savory snacks worth $70.71. In 1998 [5], supermarkets accounted for approximately 42.7% of total snack food sales, followed by 13.6% sales at convenience stores and 12.4% at mass merchandisers. Grocery stores, warehouse clubs, drugstores, vending machines and other businesses accounted for the remaining sales. In recent years, percent sales at convenience stores and mass merchandisers have grown rapidly at the expense of other outlets.

4. THE GLOBAL MARKET No reliable mechanism exists for estimating worldwide sales of prepared snack foods. But it is fair to say that the worldwide market is at least double the size of the U.S. market. Therefore, a rough working estimate of $30–35 billion worldwide annual sales, including the United States, seems reasonable. Overseas exports of U.S. snack food machinery are growing, and some domestic companies have established divisions or joint ventures overseas. Many snack food products are ﬁrst exported to evaluate overseas acceptance before production is started in the respective country.

5. THE SNACK FOOD ASSOCIATION The Snack Food Association (SFA) is an international trade association dedicated to advancing the snack food industry and improving the quality of its products. SFA’s headquarters is located at 1711 King Street, Suite One, Alexandria, Virginia 22314-2720, U.S.A., telephone 703–836–4500, facsimile 703–836– 8262. SFA’s services are available to its members worldwide. Domestically, it monitors pending legislation that may impact snack foods and organizes

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presentations and petitions to the federal government on behalf of the industry. SFA also conducts employee training sessions for its members, cooperates with universities in additional education programs, and organizes SNAXPO, the largest annual trade show in the world devoted exclusively to snack foods. SFA news, industry calendars, services for its members, and information about snack foods for the public are available at the website: http://www.sfa.org.

6. REFERENCES 1. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, Alexandria, Virginia, pp. 10–12. 2. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, Alexandria, Virginia, p. 30. 3. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, Alexandria, Virginia, p. 75. 4. SF&WB (June), 2000. State of the Industry Report 2000. Snack Food & Wholesale Bakery, 80(6):SI-1–SI–74. 5. SF&WB (June), 1999. State of the Industry. Snack Food & Wholesale Bakery, 88:(6):SI-1–SI-82.

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SECTION II

INGREDIENTS AND GENERAL EQUIPMENT

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CHAPTER 3

Food Quality of Corn

L. W. ROONEY E. L. SUHENDRO

1. INTRODUCTION

M

or corn (Zea mays L.) is the third most important crop worldwide with a total production of 576 million metric tons in 1997–1998. Nearly 41% of the total production is in the United States. Other major producers include China, Brazil, Mexico, Argentina, Central America and many African countries [1]. Maize grows well in hot, humid areas of the world and responds to fertilizer and moisture by producing large quantities of grain. However, it does not grow as well in hot, dry areas of the world where sorghum (Sorghum bicolor L. Moench) is raised. Sorghum is similar to corn in many respects and can also be used for snack food production. Corn is processed into a wide variety of products and traditional foods, i.e., porridges, tortillas, arepas, empanadas, atoles, polenta and many snacks [2–6]. Utilization of corn for food and industrial products has increased rapidly in the United States, using nearly 20% of the annual corn crop of 225 million metric tons with the balance going to animal feed. The largest users are wet millers, who produce sweeteners, glucose, starches, starch derivatives, alcohol, oil and other products, with considerable growth recently in sweeteners and alcohol. The U.S. snack food industry produced nearly $6 billion of corn-based snacks in 1998. Corn with soft, ﬂoury endosperm is desirable for wet milling because it requires less steeping time and yields high recoveries of starch containing less than 0.3% protein. Hard food corns require extended steeping times to achieve the desired starch purity. Further, broken kernels and improperly dried corn cannot be wet milled efﬁciently. U.S. environmental conditions favor production AIZE

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of soft corn. Thus, dry milling and snack food industries must make special efforts to obtain harder corn suitable for processing. Critical factors that affect food corn quality for dry milling and snacks are discussed in this chapter. Key indices and measurements of food corn quality are described, and a section on sorghum is included. Nixtamalization (alkaline cooking) of corn is discussed in Chapter 4.

2. TYPES OF CORN Flint, dent, ﬂoury, sweet or sugary, popcorn, waxy, multicolored and other types of corn are grown throughout the world, with color, size, kernel shape and other attributes varying signiﬁcantly. The production of yellow corn predominates in the United States, Brazil and China. However, white corn is preferred in Africa, Central America and Northern South America because of its sweeter, more ﬂavorful products. Mexican-type foods in the United States are increasingly made with white corn. The production of identity-preserved, value-enhanced corn hybrids has been increasing in the United States recently [7]. These include white, waxy, high-oil, hard-endosperm, nutritionally dense, and low-temperature dried corn that have improved properties over commodity corn. Physical properties and composition are shown in Figures 3.1, 3.2(A), and Table 3.1 [7]. Most white corns in the United States are harder than yellow corns, have excellent properties for processing and are grown primarily for use in food. About 3 million metric tons (120 million bushels) of this specialty corn is grown in the United States annually. Prices for white corn generally are 40–50 cents per bushel higher than for yellow corn, but prices are volatile depending on crop

Figure 3.1 Mean test weights (bulk densities) of U.S. yellow dent corn in elevators and export shipments, 1995–1999 [7].

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Figure 3.2 (A) left to right, ears of yellow dent feed corn, white food corn, yellow food corn, blue corn and popcorn; (B) dent corn with tight shuck (left) and loose shuck (right) on the ears; (C) diagram of corn kernel structure.

supplies and export demands in Southern and East Africa, Mexico, Colombia and Venezuela. Typically, domestic white corn is grown under contract for food corn suppliers or processors, who specify the hybrids desired for their operations. White corn must be grown in isolation to avoid cross-pollination from yellow corn. Yields of white corn per acre relative to yellow corn, have increased but are not yet equal in the United States. Few white corn hybrids, genetically modiﬁed by recombinant DNA techniques, are grown, and essentially none is expected to be produced in 2001 and beyond. Currently, white corn is the most reliable source of non-GMO (non-genetically modiﬁed organism) corn in the United States. Several million acres of high-oil content, non-GMO corn are grown domestically each year. It is used predominantly by the broiler industry because of its higher energy level from the increased oil, and slightly improved protein quantity and essential amino acids balance. Growers, seedsmen, handlers, and feeders have proﬁted from the development of high-oil corn, but its production

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Composition and Properties of Value-Enhanced Dent Corn Grown in 1998 in the United States Corn Belt [7].a

Number of samples Moisture, % BCFMd , % Total damage Test weight, lb/bue True density, g/cm3(e) 1,000-k weight, ge Kernel volume, cm3(e) Thins, % thru 20/64 Total stress cracks (%) Stress crack index Protein, % (d.b.) Oil, % (d.b.) Starch, % (d.b.) Fiber, % (d.b.) a

44 14.2 0.2 1.5 61.1 1.32 338 0.26 17.7 23 60 9.3 4.1 72.4 2.1

Waxy 37 14.2 0.8 1.7 59.9 1.30 309 0.24 33.1 31 113 9.3 4.4 70.7 2.2

High Oil

44 14.0 0.2 0.7 60.9 1.30 339 0.26 22.6 15 45 9.2 4.1 72.1 2.3

29 14.6 0.4 1.6 56.8 1.26 306 0.25 27.9 7 17 9.5 6.9 68.1 2.9

Nutritionally Dense 14 12.9 0.4 1.3 59.9 1.28 289 0.22 47.2 4 9 10.2 4.8 70.1 2.4

LowTemperature Dried 43 14.9 0.6 1.3 58.1 1.29 331 0.26 21.7 18 52 9.1 4.1 72.1 2.3

Elevatorb 175 14.3 1.3 1.9 57.4 1.28 328 0.26 22.8 44 176 9.0 4.1 72.2 2.3

White, waxy, hard endosperm, high oil, nutritionally dense, and low-temperature dried corns are value-enhanced corns with special end uses. Samples were taken from grain elevators in the Corn Belt. c Samples were taken from samples of exported corn. d Broken corn and foreign material. e Reported on ‘‘as is” moisture content. b

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Hard Endo

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slowed in the year 2000 because of reduced prices for feed-grade fats used in the broiler industry. Waxy corns are used speciﬁcally for starch production, and also to improve the texture of baked snacks. Waxy maize starch is all amylopectin, which signiﬁcantly affects extrusion and expansion properties of corn snacks. Low-temperature drying of corn signiﬁcantly reduces stress cracks in kernels compared to typical elevator and export corns. As a result, dry milling properties are signiﬁcantly improved in hard-endosperm, low-temperature dried corns. The corns described thus far were developed by conventional, rather than recombinant DNA, breeding techniques. Food sorghums, certiﬁed GMO-free, are available. They have a light color and a bland ﬂavor. The marketing of corn with enhanced value is a recent development and will increase as long as farmers, handlers, suppliers and end users proﬁt from it. Over the long term (ﬁve years or more), the acceptance of biotechnology will increase, especially for expediting the development of grains with enhanced value for processing and improved nutrition [8].

3. CORN GRADES, STANDARDS AND SPECIFICATIONS Six grades of corn and three classes are recognized in U.S. Grades and Grade Requirements Table 3.2 [9]. Moisture content is also determined and reported, but is not a part of the grade. Speciﬁcations for food corns usually indicate Number 1 Grade, yellow or white dent corn, with added requirements as needed. Typical speciﬁcations and variations for corn used in alkaline cooking or dry milling are shown in Table 3.3. Tighter speciﬁcations command higher prices TABLE 3.2.

U.S. Grades and Grade Requirements for Corn [9]. Maximum Percent Allowed

Grade

Minimum Test, Weight/Bushel (Ib)

Heat-Damaged

Total

Broken Corn and/or Foreign Material

56.0 54.0 52.0 49.0 46.0

0.1 0.2 0.5 1.0 3.0

3.0 5.0 7.0 10.0 15.0

2.0 3.0 4.0 5.0 7.0

U.S. No. 1 U.S. No. 2 U.S. No. 3 U.S. No. 4 U.S. No. 5

Damaged Kernels

U.S. sample grade is corn that: (a) does not meet the requirements for the grades U.S. No. 1, 2, 3, 4, or 5; (b) contains 8 or more stones that have an aggregate weight in excess of 0.20% of the sample weight, 2 or more pieces of glass, 3 or more crotalaria seeds (Crotalaria spp.), 2 or more castor beans (Ricinus communis L.), 4 or more particles of an unknown foreign substance(s) or a commonly recognized harmful or toxic substance(s), 8 or more cockleburs (Xanthium spp.) or similar seeds singly or in combination, or animal filth in excess of 0.20% in 1,000 grams; (c) has a musty, sour, or commercially objectionable foreign odor; or (d) is heating or otherwise of distinctly low quality.

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Standard

Measurement

Moisture (11−15%)

Electronic moisture meter, NIR, standard oven method

Foreign material (none) Breakage/damaged kernels (5−10% maximum) Fissures/stress cracks (<30%) Kernel size and shape (uniform)

Sieving and hand picking Sieving/hand picking

Dead germ (<0.1%)

Look at germ−−standard FGIS procedure for heat damage ELISA, HPLC

Hybrids Sampling FGIS = Federal Gain Inspection Service.

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Candle with a light box Subjectively evaluate or use screens Determine acceptable levels

Experience/testing for application Small pilot cooking tests Proper samples, probes or other methods

Provides a useful baseline to ensure minimum quality. Relates to plumpness and conditions of the kernel. Higher test weights indicate sound corn with properly matured kernels. As high as possible. Related to dry matter and storage quality. Dry corn requires special care to rehydrate, breaks during handling and requires longer alkaline cooking time. Buy it cleaned or clean it. Use levels allowed in No. 1 corn. Cracked, broken kernels should be removed during cleaning. Possible to have less than 2−3% damage in corn. Stress cracks critically affect dry milling. For alkaline cooking, stress cracks are not as important. Uniformity is highest when kernels from each end of the ear are removed. Increases cost of corn significantly. Mutual agreement with supplier is needed. Heat-damaged kernels indicate gross abuse of the sample; unfit for processing. Aflatoxins less than 20 ppb, specify 5 ppb or less to be safe. Fumonisins limit not set, probably 4.0 ppm. Sampling is a major problem. Identify acceptable quality hybrids for the process, contract with farmers to produce those hybrids. Retain representative sample in closed container held in freezer until corn products are declared okay.

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Mycotoxins (aflatoxins <20 ppb; fumonisins <4.0 ppm)

a

Corn Speciﬁcations and Their Relation to Processing Quality.

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for the corn. Speciﬁcations are necessary, but they must be developed for the speciﬁc region in which the user will be purchasing the corn used in the process. Unrealistically high speciﬁcations are a detriment to securing corn of consistent quality. In practice, food corn suppliers and customers agree on realistic speciﬁcations and premiums. For example, cleaning to remove odd-shaped and smaller kernels improves uniformity, but increases the cost of the corn signiﬁcantly. Broken and damaged kernels must be carefully cleaned from food corn, or the processor must expect reduced yields, poor-quality products and increased sewage treatment expenses [10]. Heat-damaged and moldy corn, caused by improper drying, ventilation inadequate for respiration, and heating, should not be used for food purposes. Corn that does not germinate should be rejected outright. White corn can contain up to 2% colored kernels, and yellow corn can contain up to 5% kernels of other colors. In practice, food corn users usually specify reduced levels of broken and chipped kernels and require guarantees that the aﬂatoxin content is below 20 ppb. Establishment of maximum permissible fumonisin levels is expected within the next year. Each processor should have a plan to obtain corn with consistent quality and can do so by developing a relationship with one or more reputable suppliers. Communication must be ongoing to minimize serious problems that may result from variations in the corn supply. A reliable food corn supplier will tell the processor that the corn is different ahead of delivery so adjustments to machinery and the process can be anticipated. It is impossible to supply corn of identical quality consistently. The crop is different each year, and aging during storage causes changes in cooking and processing characteristics. New corn hybrid varieties are constantly being developed by seed companies and research agencies. They typically replace older varieties because they have improved agronomics, disease and/or insect resistance, or produce higher grain yields. Food corn suppliers must constantly update their lists of acceptable hybrids by working with hybrid seed corn companies.

4. CORN KERNEL STRUCTURE AND COMPOSITION The corn kernel is a caryopsis—a single seed in which the fruit coat (pericarp or skin) adheres strongly to the true seed [Figure 3.2(C)]. The kernel consists of the pericarp or skin, germ or embryo, and the endosperm. The type of dent is related to the ratio of hard to soft endosperm and signiﬁcantly affects processing properties. The germ, pericarp and endosperm typically comprise 12%, 6–8% and 82% of dry kernel weight, respectively. The pericarp protects the kernel and resists penetration by water. Once it is broken [Figure 3.3(C)], water can move rapidly into the corn kernel. Hence, chipped, broken or cracked kernels overcook easily and lose their soluble solids

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Figure 3.3 (A) corn kernels varying in texture from soft (1) to hard (5); (B) corn kernels viewed with transmitted light. Opaque (soft, ﬂoury) top left and hard kernels bottom right; (C) chipped, broken and ﬁssured (F) kernel viewed with transmitted light; (D) standards for pericarp removal. Kernels were cooked and stained; No. 1 had excellent pericarp removal.

as discharge to the sewer. The pericarp contains mainly ash, ﬁber, and oil, with very little starch or protein. The germ is high in oil, protein, sugars, vitamins and minerals with little starch. Proper nixtamalization does not remove the germ. The aleurone is a single layer of cells that contain large quantities of oil, protein, minerals, ash, vitamins and enzymes. The internal composition of normal corn changes across the kernel. The peripheral and hard endosperm cells have the highest protein content (50–15%), while the center ﬂoury endosperm cells contain 4–5% protein [Figures 3.4(A), (C), and (E)]. Starch content is highest in the ﬂoury endosperm cells, and decreases as protein content increases. Starch granule size and shape change from small, polyhedral granules with indentations in the hard endosperm, to larger spherical granules in the ﬂoury endosperm cells. The composition of corn is affected by genetics and environment and varies signiﬁcantly. Environmental conditions greatly affect the quality and composition of the corn for processing. Yellow and white dent corns grown in the United States contain about 8–10% protein, 3.5–4.5% fat, 1.5–2.0% ash, 1.5– 2.1% crude ﬁber, 1.4–2.0% soluble sugars, 10–15% water and 65–70% starch. The endosperm contains all the starch and 70% or more of the protein. The ﬁber and ash are concentrated in the pericarp, and the germ contains higher levels of fat and protein. The aleurone of blue corn is purple, and the endosperm of yellow corn contains carotenoid pigments. Corn endosperm mutants that affect composition exist. All (100%) of the starch in waxy endosperm mutants is in the branchedchain (amylopectin) form.

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Figure 3.4 Corn structure: (A) longitudinal section of kernels showing ﬂoury (Fl), intermediate (Int), hard (H) endosperm sections; (B) hard endosperm cells; (C) soft endosperm cells; (D) starch granules from a hard endosperm cell; (E) starch granules from a soft endosperm cell. (SG—starch granules, PB—protein body, PM—protein matrix, CW—cell walls.)

Quality protein maize (QPM) is a hard endosperm corn that contains 100% more tryptophan and 70% more lysine than normal dent corn [11]. QPM hybrids and open-pollinated varieties have excellent grain yields, kernel properties and processing attributes. High-producing QPM varieties and hybrids have been developed in Brazil, Ghana, China, South Africa, Central America, Mexico and other countries. Dry milling and tortilla production from QPM are comparable to normal dent corns [12,13]. Consumption of QPM signiﬁcantly reduces human malnutrition and improves the feeding efﬁciency of swine and poultry production. Food processors produce more nutritious tortillas by using QPM corn [13]. Large, ﬂoury endosperm kernels are preferred for production of snacks (CORNNUTSTM ) and posole. Blue corn is used to produce dark-black or blue products with unique ﬂavor and natural color. Popcorn is discussed in Chapter 14.

5. AFLATOXINS AND FUMONISIN Aﬂatoxin, fumonisin and other mycotoxins sometimes are present in corn, and must be controlled to avoid problems with animal and human health [14]. Aﬂatoxins are potent carcinogens produced by Aspergillus species, especially

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in corn maturing during hot dry conditions. Much of the aﬂatoxin from infected kernels is removed by solubilization into the wastewater during alkaline cooking. The remainder (approximately 30%) is inactivated by the alkali but reforms under the acidic conditions of the stomach. Recently, sound-appearing kernels have been found contaminated with aﬂatoxin, which means it may not be removed by standard cleaning and cooking procedures. Black light is used to screen corn for the presence of components that absorb ultraviolet light and ﬂuoresce, which indicates that aﬂatoxins may be present. If the sample glows, the corn must be analyzed for the presence of aﬂatoxins. Most food corn suppliers monitor mycotoxin levels in the ﬁeld prior to harvest, often using enzyme-linked immunoassay (ELISA) tests. The fumonisins are a family of mycotoxins present in corn grain that has been attacked by Fusarium species, which causes ear rot. Fumonisins are widely distributed in corn and cause toxicity problems in horses, swine and other animals. They have also been linked to human health problems, but their effects have not been clearly determined. The U.S. Food and Drug Administration (FDA) has established advisory levels for fumonisins of 4 and 2 ppm maximums in whole corn and dry-milled corn products, respectively. Fortunately, fumonisins are water soluble; during alkaline cooking, 50–70% are lost in the steep liquor and wash water. Signiﬁcant amounts of fumonisins are removed during cleaning and degermination in dry milling. Aﬂatoxins and fumonisins form in corn as it matures in the ﬁeld, with fumonisins being more ubiquitous. Sophisticated HPLC (high-performance liquid chromatography) analytical techniques and ELISA tests are available for monitoring aﬂatoxins and fumonisins, respectively. Constant vigilance of corn supplies is required to minimize problems with mycotoxins. Sampling problems cause signiﬁcant variations in analytical results, and many corn buyers set speciﬁcations of 5 ppb maximum for aﬂatoxin because a “zero” speciﬁcation is unrealistic.

6. GENETICALLY MODIFIED ORGANISMS (GMOS) Genetic engineering has constituted an important component of crop improvement programs since civilization began. Early humans selected for improved types of animals and plants and for increased yields. Plant breeding has signiﬁcantly altered the composition and properties of food and feed crops. Modern biotechnology developed insertion of genes from other species into plants and animals using recombinant DNA (r-DNA) techniques. Currently, the public is often misled into thinking that genetic engineering and biotechnology always involve r-DNA, which is not the case. Currently, many yellow corn hybrids in the United States contain non-corn genes, which have been inserted to improve the hybrid. For example, Bt corn has greater resistance to

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corn earworms, which improves its food processing quality because reduction of earworms reduces the level of damaged kernels and, in turn, less mycotoxins are formed. Nutrient-dense GMO corn hybrids are nearing commercial production. Their development will revolutionize corn utilization and will be necessary to feed the world population in the future. Currently, European and other countries are expressing signiﬁcant concerns about the safety of GMOs. As a result, many domestic food companies are considering labeling or avoiding sales of foods containing GMOs. Some grain companies are selling corn that is certiﬁed GMO-free, although acceptable techniques for measuring GMOs efﬁciently, and criteria for what constitutes signiﬁcant GMO contamination, have not been developed. GMO contamination of nonGMO corn is difﬁcult to prevent because only a few GMO kernels in a truckload of nonGMO corn can cause “signiﬁcant contamination” test results. Certiﬁcation programs similar to those for organic foods appear to be the most reliable means of controlling GMOs in food corn. The increased costs would be passed on to consumers demanding GMO-free foods. The GMO issue is complex, and involves trade and political concerns along with human health. There has been little if any evidence that GMOs constitute any risk to human health [8].

7. FOOD CORN QUALITY ATTRIBUTES In this chapter, food corn quality means the attributes of corn for dry milling and alkaline cooking (nixtamalization). Requirements for both uses generally are similar. Corn that has a rounded crown, a smooth dent, a high proportion of hard endosperm, an easily removable pericarp, a clean bright color, and a kernel with tolerance to damage during handling, is desirable. Kernel size should be medium to large, with uniformity in the batch a key attribute. Broken kernels of corn, kernels with cracked or chipped pericarp and multiple stress cracks in the kernel are undesirable. Corn should have a clean fresh aroma, bright color, and be free of mold and insect or heat damage. Corn that has good alkaline cooking properties also has improved dry milling properties. Even harder corns will be preferred for dry milling in the future. Hard, ﬂint kernels are not acceptable for nixtamalization because they take too long to cook, and their meal requires additional time to hydrate in the preconditioner when extruding corn puffs. A corn hybrid with a tan or colorless hilum would be welcomed by dry millers to eliminate black hilum specks from milled fractions. Both genetics and the environment affect the quality, composition and physical properties of corn. Kernel quality is also greatly affected by harvesting, grain handling and storage practices. A signiﬁcant interaction exists between environment and corn hybrids. All corn hybrids do not behave similarly in the

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same environment, and no hybrid produces corn acceptable for processing in all environments. Maturity is critically important. Immature corn is soft and often has a pericarp that is difﬁcult to remove and an altered composition that creates problems during alkali cooking and processing. It tends to cook quickly with high total solids losses and development of off-color caused by higher levels of sugar, phenols, amino acids and soluble proteins. The corn crop in 1992 was difﬁcult to process in part because of an abnormally cool growing season and poor maturation. Progress has been made in developing tests related to dry milling and alkaline processing properties. Some of these properties, and how they are measured, are reviewed in this section.

7.1. MOISTURE CONTENT The moisture content of corn is important because it determines the amount of dry matter purchased, required storage and handling procedures, cooking properties and processing conditions. Corn above 14–15% moisture must be dried for safe long-term storage, while dry corn (6–10%) requires slow rehydration prior to cooking or dry milling. Moisture migrates in stored corn. Dry corn is brittle, breaks easily during handling and requires the addition of moisture over a longer time to allow penetration into the endosperm. Moisture above 14% in corn stored for a short time in a hot, humid environment results in signiﬁcant spoilage. Moisture content of whole grain usually is determined using electronic moisture meters. The time-proven Motomco moisture meter is durable and inexpensive [Figure 3.5(B)]. Increased moisture content is directly related to increased electrical conductance. Near-infrared (NIR) instruments also are utilized for determining moisture in whole and ground grain samples. Several modern computerized models effectively measure moisture as well as the protein and fat content of corn. Infrared moisture balances are available for analyzing processed products [Figure 3.5(A)]. These methods are calibrated against standard oven methods.

7.2. COLOR 7.2.1. Factors Affecting Color Subtle differences in kernel color can help predict the overall quality of alkaline-cooked products. Kernels should be a clean, bright white or yellow. Orange, reddish or other off-yellow colors are unacceptable for alkaline cooking because they affect the appearance as well as the ﬂavor of fried tortillas or chips. High xanthophyll pigment content in the kernel produces chips with an acrid

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Figure 3.5 (A) infrared moisture balance; (B) electronic moisture meter; (C) a color meter; (D) and (E) equipment for measuring test weight; (F) consistometer for measuring viscosity of slurries; (G) equipment for measuring volume and true density; (H) tangential hardness device for measuring resistance of corn to abrasion; (I) ﬂoatation of kernels in standard sodium nitrate solution; (J) rapid ViscoTM Analyzer for measuring hardness and cooking properties; (K) cooking corn in nylon bags in a large steam kettle for pericarp removal or optimum cook time.

odor because the carotenoid pigments degrade during frying. Further, white kernels with a lemon or off-white color produce chips with an unattractive dull, dirty, gray hue. Ferulic acid and related phenolic compounds exist in the cell walls of the corn kernel. They have blue autoﬂuorescent properties. These compounds are thought to affect the color and possibly the ﬂavor of alkaline-processed products.

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Some corn hybrids react adversely to insects, disease, and even cold weather, by producing kernels with greater levels of phenolic pigments. Sometimes these kernels are called “red banded” or “red streaked.” The phenolic pigments in the pericarp produce off-colors when they react with the alkali and affect product color when the pericarp is incompletely removed. Many compounds in corn develop color when the pH is increased above 7.0. White corn products appear yellow at high pH. The pH has a major effect on the color of blue and red corn tortilla chips. The weathering of corn affects color. For example, hybrids with tight shuck covers are more resistant to insects, moisture uptake and molding [Figure 3.2(B)]. Several years ago, heavy rains in South Texas at corn harvest time caused signiﬁcant discoloration of grain in a hybrid with a very loose shuck, while a similar food corn hybrid with a tight shuck cover yielded bright grain [Figure 3.2(B)].

7.2.2. Cob Color The cob can be red, pink or white in common U.S. corn hybrids, depending on genetics. Red pigments from the cob can give a dirty off-color to ﬁnished products and a white cob is preferred for alkaline-cooked food corns. Cob color is not important for dry milling. The most common yellow food corn hybrids, which yield the most grain today, have red cobs. However, white cob hybrids should be selected in improvement programs to broaden the potential usefulness of corn in foods.

7.2.3. Determination of Grain Color A good method for determining corn color is to measure it subjectively on the cob in the ﬁeld. This gives a general overview of the color, and any crosspollinated kernels can be eliminated at that time. An experienced corn breeder can evaluate cob and grain color very effectively in the ﬁeld. Photos or actual ears of standard samples can be used as standards for acceptable colors on a 1- to -5 basis. Additionally, trained observers using standard plates from soil color reference tiles, or color tiles from the paint industry, are effective. Good light should be available for such evaluations. Evaluation of shelled kernel color is more difﬁcult than that of corn on the cob. Several colorimeters express color in terms of L, a and b values to objectively measure the color of grains [Figure 3.5(C)]. However, they lack the ability to distinguish between white and off-white, lemon, or ash-gray kernels, which have visually detectable differences in whiteness. Correlations between L, a and b values and subjective evaluation of corn color were reported to be nonsigniﬁcant for white corns, but excellent for yellow corn [15].

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7.2.4. Hilum or Black Layer Effects The black layer is located beneath the tip cap of the kernel and darkens at physiological maturation of the kernel. The black melanoidin pigments do not leach during cooking, and black specks from the hilum result in product with a distinctive appearance that has been perceived as positive or negative by consumers. For example, corn and tortilla chips containing the hilum are readily accepted, whereas dry-milled products with black specs are highly unacceptable. In some instances, dry masa producers have added black specs to their ﬂour to mimic a whole-cooked corn appearance. In other cases, consumers have preferred tortillas made from dry masa ﬂours because they do not have the black specs of freshly cooked corn products. As often happens, the ﬁrst product accepted by consumers sets standards for later products of similar type.

7.3. HARDNESS 7.3.1. Texture The texture of a corn kernel is related to the proportions of hard (“horny”) and soft (“ﬂoury”) endosperm present. These are often referred to as hard or soft “starch” in industry [Figure 3.4(A)]. Hard kernels with a rounded crown and a shallow, smooth dent are desirable for alkaline cooking and dry milling. Rating kernel appearance on a 1- to -5 scale, based on known standards, is a quick and efﬁcient method of selecting for food corn quality in breeding and evaluation programs. When selections are made for hardness or texture in dent corn, the type of dent is an effective method to evaluate corn on the cob for relative levels of hardness [Figure 3.3(A)]. Texture is highly related to the hardness of corn kernels. It is positively correlated with density and test weight and negatively correlated with ﬂoatation values. A quick, effective method of measuring texture (hardness) subjectively is to look at the kernels with transmitted light to rate them on a 1- to -5 basis [Figure 3.3(B)]. Again, appropriate reference samples should be used to facilitate comparisons. Some methods to evaluate the relative areas of individual kernels, or to dissect the soft ﬂoury endosperm and weigh it, have been proposed, but are tedious, time-consuming and have limited application on a practical basis. Individual kernels of corn vary signiﬁcantly in hardness. Although many methods have been proposed to evaluate corn hardness [16,17], none measures true hardness. Several methods that relate to hardness are used, but they are affected by kernel size, shape, density, ﬁssures and stress cracks, moisture and previous history of the corn sample. The hardness values or indices usually

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reported are based on some standardized empirical method that is repeatable and related to end-use properties important to the respective processor.

7.3.2. Test Weight (Bulk Density) The weight of a quart container ﬁlled with grain is expressed in pounds per bushel [Figures 3.5(D) and (E)], and typically is 50–63 lb/bu. Test weights of 60 lb/bu (74 kg/hl) or more are preferred. It may be impossible to consistently obtain corn with 60 lb/bu test weight in northern areas of the United States because of the short growing season. Kernel size, shape, pericarp slickness, moisture content, foreign material, broken kernels and speciﬁc gravity affect bulk density. Higher test weights indicate that the corn has plump, well-ﬁlled kernels with a higher proportion of hard endosperm. Low test weights often indicate the corn did not mature properly. Test weights within a given hybrid provide more information than comparisons across hybrids. Higher test weights, within hybrids of similar hardness and kernel attributes, indicate better milling properties provided stress cracks are minimal. Some dry milling companies pay premiums based on test weight, lack of stress cracks, moisture content and U.S. grades to farmers who produce speciﬁc hybrids for dry milling. It is a quick, efﬁcient, inexpensive, repeatable and desirable method for practical selection and premium marketing programs. Moisture content and other kernel quality factors must be standardized. These programs work because the milling company accepts only certain corn hybrids that have been tested for dry milling efﬁciency. Kernel size and shape, hardness and other properties have already been set genetically, and the method actually measures the effects of environment. The level of ﬁssures measures the effect of improper drying.

7.3.3. Density Kernel density has been measured by displacement methods using alcohol, air, helium or nitrogen gas. The volume of a speciﬁed weight of corn is measured and expressed in grams per cubic centimeter (g/cm3 ). Corn varies from 1.18 to 1.4 g/cm3 in density. Harder corns have higher values because the endosperm is more tightly organized without air spaces [18]. In the soft endosperm, starch granules are incompletely dispersed in protein and many air spaces or voids exist. Density is highly correlated to the hardness and texture of corn. The alcohol method generally gives lower values than gas displacement procedures. New instruments for quickly and accurately measuring density are available. Alcohol is inexpensive and can be effective, but care should be used in interpreting the values. A density of 1.3 g/cm3 or greater, measured by gas displacement methods [Figure 3.5(G)], is preferred for food corn. This may be too high to achieve consistently in the northern Corn Belt and other areas in the world.

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7.3.4. Floaters The percentage of kernels that ﬂoat in a sodium nitrate solution of 1.275 speciﬁc gravity is a useful index of corn properties [Figure 3.5(I)]. It is simple and can be applied quickly and accurately for monitoring corn density. Originally developed by The Quaker Oats Company as a quick index of dry milling quality, the “ﬂoaters test” is used by some processors to predict alkaline cooking time in their processing lines. Trichloroethylene was used in the past, but has been abandoned because it is a reported carcinogen. The nitrate (NaNO3 ) solution method is safer, less expensive and works equally well. It is well suited for situations requiring analysis of only a few samples, but is difﬁcult to automate for large numbers of samples. Sometimes, two or three solutions varying in speciﬁc gravity are used to classify incoming corn in food plants. A solution at 1.275 speciﬁc gravity is not always optimum depending on the environment and type of corn.

7.3.5. Tangential Abrasive Dehulling Device (TADD) The tangential abrasive dehulling device [TADD, Figure 3.5(H)] is used for determining hardness based on the amount of material abraded from a 40 g corn sample subjected to abrasive milling for 10 min. It measures the resistance of corn kernels to the abrasive action of a horizontal aluminum oxide wheel surface rotating at a constant speed. The amount removed is an index of hardness. The results are very reproducible; however, wear on the surface of the stone causes the abrasive action to change over time. Therefore, development of a correction factor, based on a standard sample of corn, is required. In the TADD method, the hardest corn samples have the lowest values. For example, the author’s standard hard corn has a value of 32%, while for standard soft corn it is 60%. Flint corns have values of 25% or less. Corn samples are equilibrated to 11.5 ± 0.5% moisture content by storage in an air-conditioned laboratory before testing.

7.3.6. Stenvert The Stenvert hardness method is based on the principle that the time to grind a sample is directly related to corn hardness. Thus, a higher value means a harder corn. In practice, the values have a narrow range when commercial corn samples are evaluated. The TADD method has a greater spread in values from hard to soft corn. Kernel size, shape, pericarp toughness, dent characteristics, relative proportion of hard to soft endosperm, moisture content and other factors affect these grinding methods signiﬁcantly. Other hardness methods include kernel crushing strength and standardized grinding techniques followed by sieving to determine the amount of ﬁnes

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produced. Accurately measuring corn kernel hardness is essentially impossible. However, these indicators can be useful when applied consistently. In practice, the combination of hardness indices with densities, test weight, kernel weight and subjective evaluation is a useful measurement of corn quality. Reference standards of good- and poor-quality corns must be included in the testing program. It is undesirable to use only one measurement for evaluating corn quality. However, if only one method could be used, either test weight or the ﬂoatation test should be top priority.

7.3.7. Rapid ViscoTM Analyzer (RVA) Hardness The Rapid ViscoTM Analyzer (RVA, Newport Scientiﬁc Pty. Ltd., Australia) [Figure 3.5(J)] is an effective instrument used to characterize a wide variety of starch-based products for cooking properties and related information. The RVA measures the viscosity developed during cooking and stirring a sample of ground corn during a preprogrammed temperature change. A cooking curve, related to the relative rate of hydration and starch gelatinization of the sample, is developed. The harder the corn, the slower the development of viscosity and the lower the viscosity. The solids level, time, temperature and speed of stirring can be varied inﬁnitely to develop a repeatable procedure that can distinguish among corn samples varying in hardness [Figure 3.6(A)] [19,20]. The RVA is widely used for quality control of ingredients or to determine why certain changes occur during processing.

7.4. BROKEN, CRACKED AND CHIPPED KERNELS A representative sample of corn is screened to remove broken kernels using standard sieves, and the remaining corn is examined on a light box for broken kernels. The corn is stained with fast green dye to more easily detect kernel cracks within the pericarp and chipped kernels [21]. The percentage of broken, cracked and chipped kernels is then calculated. Cracked and broken kernel content should be as low as possible, and not exceed 5–10% in food corns. This does not include stress cracks or ﬁssures inside the corn endosperm. The contents of cracked and broken kernels are solubilized during cooking, resulting in increased dry-matter losses and sewage charges, and in reduced yield and quality of the ﬁnal products [22].

7.5. STRESS CRACKS Stress-cracked kernels result from improper drying and handling of corn, which leads to ﬁssures or hair line cracks inside the endosperm. Stress cracks are determined by using a light to “candle” each of the kernels [Figures 3.3(B) and (C)]. Single or double ﬁssures do not cause major problems, but multiple ﬁssures can signiﬁcantly affect cooking properties.

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Figure 3.6 (A) rapid ViscoTM Analyzer (RVA) curves for ground whole hard, soft and intermediate corn samples; 18% solids; (B) modiﬁed RVA curves for corn meals with good and poor extrusion properties, using a high solids concentration and pasting to 65◦ C. In “A” 18% solids; in “B” 65◦ C. Modiﬁed from Reference [28] with permission.

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Selection of the correct hybrid with careful attention to harvesting, handling, drying and storage reduces kernel damage problems. With proper management, it is possible to produce food corns with 3% or lower kernel damage. The popcorn industry carefully controls kernel damage because popping percentage is the most important quality criterion.

8. PROPERTIES OF CORN FOR ALKALINE COOKING

8.1. PERICARP/HULL REMOVAL Pericarp thickness and ease of removal vary signiﬁcantly among corn hybrids and are affected by environment and genetics [23]. Insufﬁcient removal of pericarp causes darkening and off-color in the cooked product. Most snack food producers remove the pericarp (skin) of the kernel during lime cooking. However, table tortilla producers incorporate dissolved pericarp into the masa because the pericarp gums improve tortilla quality. Some chip producers do not remove pericarp. One method for evaluating pericarp removal includes cooking the corn in small nylon bags in a steam kettle [Figure 3.5(K)] containing lime and water for 20 min. The samples are rinsed lightly, stained with green dye and subjectively evaluated on a 1- to -5 basis [Figure 3.3(D)]. Standard samples, with known good and poor hull removal, must be included with each set of experimental samples. The test distinguishes differences in pericarp removal that are known to exist in alkaline cooking. For example, Pioneer Hybrid 3192, an old, obsolete food corn hybrid, requires extra cooking to remove its pericarp and consistently has poor ratings (4.0 to 4.5) using the hull removal test. Alkali concentration and quality affect the test signiﬁcantly. Aged lime is often ineffective. Improper lime storage or agitation during corn cooking and washing affect the pericarp removal values. Reference samples retained in a freezer for several years have shown little or no change in hull removal.

8.2. WATER UPTAKE The absorption of water and alkali during cooking and steeping of the kernel depends on type of corn, cooking and steeping methods, temperature proﬁles, and concentration and quality of alkali. Sound dent corn kernels absorb water through distinct pathways, which involve movement of the water through the tip cap into the cross and tube cells, and around the kernel, until it reaches the dent where the structure is disrupted and the water moves into the soft endosperm. Another pathway is around the hilum into the germ, and through it into the soft ﬂoury endosperm cells. In sound kernels, very little water penetrates through the aleurone layer or the pericarp. In contrast, water penetrates easily into the

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endosperm of cracked kernels, causing overcooking and excessive losses of dry matter. In practice, a soft, ﬂoury corn cooks most rapidly; however, the pericarp is not removed. In such corn, cooking to remove the pericarp increases dry-matter losses and produces overcooked masa. A harder corn requires more time to cook but, because of the endosperm structure, can be abused during handling and overcooked without serious loss of quality in the ﬁnished product. A hard corn loses less dry matter if its pericarp removal is the same as for a soft corn; thus, optimum kernel hardness is desired for alkaline cooking. A ﬂint corn is too hard for cooking and grinding, and reduces processing line productivity because of the longer cooking time required. It is possible to make products from extremely soft corns, but the process must be adjusted carefully. Often, dry masa ﬂour must be blended with sticky overcooked masa made from soft corn. Blends of hard and soft kernels create special problems in both dry and alkaline cooking processes.

8.3. OPTIMUM COOKING TIME AND DRY-MATTER LOSSES Methods to determine optimum cooking time and dry-matter losses have been developed using 100 g of corn cooked in nylon bags in lime for various times: 0, 15, 30 and 45 min [24]. The cooked corn is steeped overnight, then moisture content and dry-matter losses are determined. From these values, linear regression equations are developed to calculate optimum cooking time and expected dry-matter losses at optimum cooking time. Optimum cooking is directly related to the hardness of the kernel. This method does not measure the cooking time required to remove the pericarp from soft corns.

8.4. PILOT PLANT ALKALINE COOKING A laboratory procedure to evaluate alkaline cooking properties using 3 to 5 kg (6.6 to 12.5 lb) of corn to produce tortillas or tortilla chips provides useful information [24]. The corn is cooked in alkali, steeped, washed and stone ground on 12 in. lava stones. The masa is sheeted, formed into chips, and baked in a small commercial triple-pass oven, cooled and fried for tortilla chips. Yields of tortillas, color and texture of the tortillas, and processability of the corn relate well to performance of the same corn in industrial plants. This technique is especially helpful for evaluation of experimental corn hybrids for alkaline cooking prior to their use in large-scale plant trials.

8.5. ALKALINE COOKING QUALITY ATTRIBUTES OF CORN A corn averaging 300 mg/seed, 1.3 g/cm3 density, test weight of 60 pounds per bushel, a hardness value of less than 40 by the TADD, and easily removed pericarp with outstanding grain yields and agronomic properties, would be ideal.

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The majority of U.S. commercial corn hybrids do not meet these speciﬁcations. However, a sufﬁcient number of yellow and white food corn hybrids have been developed that meet these speciﬁcations.

9. HANDLING FOOD CORN

9.1. FOOD CORN SUPPLIERS Food corn suppliers specialize in working with producers to grow, clean, store and merchandise corn with improved properties for dry milling and alkaline cooking. Practices differ, but reputable suppliers specify hybrids they will accept and establish purchasing standards for corn including broken and chipped kernels, test weight, color, insect and mold damage and aﬂatoxin content. In practice, the corn processor speciﬁes the desired corn quality, and premiums must be paid to farmers for growing speciﬁc hybrids. The type of harvesting, drying and handling is speciﬁed. Food corn producers usually use rotary combines during threshing. Aﬂatoxin levels are speciﬁed and carefully monitored during harvesting and handling in the elevators. Once the corn is received by the food corn company, it is recleaned to remove small broken kernels and foreign material. Drying of corn is done carefully to avoid stress cracking and kernel breakage. The special corns are cleaned, stored, blended, and sold to different segments of the breakfast cereal and snack food industries. In some cases, the odd-shaped and -sized kernels are removed to improve uniformity. A reliable food corn supplier strives to provide corn of consistent cooking quality to his customers year round. Many snack food manufacturers rely on food corn suppliers and pay the price to secure a corn of consistent quality. Processors who buy cheap corn often end up paying more in lost dry matter, inconsistent food product quality, lost manufacturing time and reduced yields of saleable product. Good food corn costs more than feed corn. Buying from a reputable food corn supplier is an insurance policy to secure the best possible corn and careful monitoring for acceptable mycotoxin levels. However, food processors should periodically check the quality of corn received to assure themselves that their speciﬁcations are being met.

9.2. HANDLING OF FOOD CORN BY PROCESSORS High-quality processing corn results from buying the correct variety or hybrid, grown in an appropriate environment. Quality must be maintained by proper harvesting, drying, storing, cleaning and handling from the storage bin to the food processor’s equipment. Many corn processors depend on food corn

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suppliers to deliver grain as needed, while others secure and store their annual supply of corn. Proper moisture content in the grain must be maintained and managed during storage, along with control of insects. Failure to control these factors can create signiﬁcant problems. Often, these are related to improper handling of corn after receipt from the supplier. Faulty conveyors from the corn storage tank to the cookers often break the corn. Every aspect of corn handling at the processor’s facility must be considered to maintain corn quality. Corn ages, and moisture content typically decreases during storage. The resulting endosperm changes increase cooking time and affect extrusion properties as well. Corn with low moisture content requires a longer time to absorb moisture, necessitating adjustment of tempering time for dry milling and longer alkaline cooking time.

10. INDUSTRIAL DRY CORN MILLING About 2% (4 million tons annually) of U.S. corn production is dry milled [6]. Although there are many small dry corn mills in 22 states, several large millers produce a high percentage of dry-milled products. An array of food, feed and industrial corn products is produced. Major uses include baking, batters, dry mixes, fast foods, snack foods, breakfast cereals and brewing.

10.1. PROCESSES Corn is dry milled in two ways by: (1) stone grinding the kernels to produce hominy grits and whole meals rich in bran and germ; and (2) degermination. The latter process produces highly reﬁned grits, meals, and ﬂours with longer shelf lives. Fresh whole corn meals have rich ﬂavor because of their high oil and germ content. Some meals are bolted to remove coarse particles of bran and germ. Watson [25] reports the average chemical composition of these products. Whole or bolted meals have a shorter shelf life because the oil becomes rancid quickly. Generally, white corn is preferred for production of whole meals, especially in the southern United States. Watson [25] and Alexander [26] have described the tempering-degerming process for corn [Figure 3.7]. About 25% (30 million bushels) of corn dry milled in 1997–1998 was white. The objective of dry milling is to produce the maximum percentage of clean grits, containing minimum fat, ﬁber and specks from the hilum and to recover the maximum percentage of clean germ with maximum oil content and largest particle size. The corn is thoroughly cleaned by combinations of sieving, aspiration, washing in water, electrostatic separation and other methods [Figure 3.7]. All mills carefully examine incoming lots of corn for aﬂatoxins,

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Figure 3.7 A simpliﬁed scheme of essential operations in dry milling of corn using degermination. Modiﬁed from Reference [25].

fumonisins, grain molds, herbicides and pesticide residues. The clean corn is conditioned to 20 to 23% moisture and placed in a tempering bin for 1–3 hr. The objectives of conditioning are to toughen the germ and bran to facilitate subsequent separations. Tempering hydrates the kernel so maximum grit yields with minimum ﬂour are achieved. Modiﬁcations of tempering conditions are used depending upon corn attributes. Degermination is the key to efﬁcient dry milling. The most common degerminator is the Beall, ﬁrst introduced in 1906. It consists of a conical knobbed rotor and a stator shell that is knobbed on the lower convex surface and slotted on the upper surface. Most of the germ and pericarp are removed with the Beall degerminator. The degerminator is set to produce large, clean pieces of endosperm known as “hominy tails.” This endosperm fraction is dried to 15% moisture, cooled and reprocessed to obtain ﬂaking grits, medium and ﬁne grits, meal and ﬂour. Reduction of the large endosperm pieces is done with roller mills, followed by sifting and aspiration to remove bran particles from the grits. Then, gravity tables separate germ pieces from the endosperm particles. Endosperm fractions are ﬁnished in puriﬁers designed to remove ﬁne pieces of pericarp and are packaged at a moisture content of 12%. Typical yields, composition and properties of dry-milled fractions are shown in Table 3.4 [26].

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TABLE 3.4.

Composition (% Dry Basis) U.S. Standard Sieve

Coarse grits Regular grits Coarse meal Dusted meal Flour 100% meal Fine meal Brewers grits Snack mealb Snack gritsc Corn conesd a

Through

Over

Diameter (<µm)

Yield (%)

Moisture (%)

Protein N×6.25

Fat

Crude Fiber

Ash

10 14 28 50 75 28 50 12 ----40

14 28 50 75 pan pan 80 30 ----80

2,000 1,410 638 297 194 638 297 1,680 -------

15 23 3 3 4 10 7 30 -----

13.0 13.0 12.0 12.0 12.0 12.0 12.0 13.0 12.5 13.5 13.0

8.4 8.0 7.6 7.5 6.6 7.2 7.0 8.3 7.5 7.5 7.5

0.7 0.8 1.2 1.0 2.0 1.5 1.6 0.7 0.9 1.0 2.0

0.5 0.5 0.5 0.5 0.7 0.6 0.6 0.5 0.6 0.5 0.6

0.4 0.5 0.6 0.6 0.7 0.6 0.7 0.5 0.6 0.6 0.7

Adapted from Reference [26]. Yields based on corn weights. Fractions are combined and yields do not sum to 100%. Distribution of 2, 18, 75−95, and 5% max, over U.S. No. 20, 25, 30, 40, 50 sieves, respectively. 2% max in pan. Distribution of 9, 20−45, 50−75, 10% max, 3% max, and 1% max over U.S. No. 16, 20, 35, 50 sieves and 1% max in pan, respectively. d 15% max through the U.S. No. 80 sieve. b c

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The main coproducts of the dry milling industry are germ and bran. In most cases, germ is pressed and/or solvent extracted to yield crude oil and defatted corn germ meal. Dry-milled corn germ has excellent nutritional value and has been proposed for human foods. Corn bran fractions are used in prepared foods to increase dietary ﬁber content. Different particle sizes, from coarse to ultraﬁne, are manufactured for speciﬁc applications. The most desirable bran product is relatively high in total dietary ﬁber and low in oil, protein, and starch.

10.2. FOOD USES OF DRY-MILLED FRACTIONS Endosperm products from corn dry milling, ranging from large grits to ﬂour (Table 3.4), are widely used by brewers, and snack food and breakfast cereal processors. Corn endosperm fractions are cooked to varying degrees with different types of equipment to obtain many different products and intermediate ingredients.

10.3. CORN GRITS Corn grits are particles of endosperm that pass through a 1.19 mm sieve (U.S. No. 14) and ride on a 0.59 mm sieve (U.S. No. 28). They are low in ﬁber and contain less than 1% oil (Table 3.4). Corn meal has a smaller granulation than grits (0.59 to 0.193 mm; U.S. sieves Nos. 28 to 75). Meal has less than 1% oil, low ash and ﬁber content, long shelf life and bright color without black specks. Corn meal is used extensively to produce corn puffs, curls and other expanded products that are fried or baked, ﬂavored and packaged. Corn curls are popular around the world, and are formed by lowcost single-screw extruders or sophisticated twin-screw extruders. Chemically leavened baked and fried products like corn bread, mufﬁns, pancakes, corn sticks, fritters, hush puppies, and spoon bread are popular. Hush puppies are produced from a chemically leavened dough that contains cornmeal, wheat ﬂour, eggs, milk, salt, onions and tomato. Pieces of dough are deep fat fried for 2 to 3 min. Corn cones are a special fraction containing spherical particles from the hard endosperm of the corn kernels. Cones impart unique ﬂowability to powders. For example, in production of extruded potato ﬂour snacks, 10% or more corn cones or special meal fractions are used to impart ﬂowability, improve extrudate properties and reduce costs.

10.4. SPECIFICATIONS FOR DRY-MILLED CORN PRODUCTS Speciﬁcations of meal for extrusion vary depending on the type of product desired and the type of extruder used (Table 3.5) [27]. Single-screw extruders require a meal that does not contain any ﬂour or ﬁne particles, while

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TABLE 3.5.

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Corn Meal Speciﬁcations for Extruded Snacks.a Baked

a

Granulation

Fried

Soft

Crunchy

16 20 25 30 40 50 60 80 Pan Moisture % Fat %

0 0--2 2--10 25--50 45--65 0--8 0--2 0 0 11--13 1.0

0.0 0.0 0.0 0.0 0.7 47.5 30.1 15.4 6.3 13.0 0.9

--50.5 22.4 8.1 2.1 0.4 0.0 0.0 0.4 12.7 0.7

Modified from Reference [27].

twin-screw extruders tolerate more ﬁnes in the meal. Particle size distribution, oil content, moisture, hardness of the particles, color and freedom from dark specs are important criteria. Moisture content affects expansion; excessively dry meal requires more time to rehydrate during extrusion and might require longer preconditioning. Oil content above 1% acts as a lubricant and may cause insufﬁcient cooking and poor expansion. The upper level of acceptable oil depends on the process and other ingredients in the blend. Particle-size distribution affects the ease of cooking and thus the expansion and relative crunch of the products. Ash reﬂects the relative degree of reﬁning during milling, and is related to the color of the meal and the resultant products. Protein is an index of starch—the higher the protein the lower the starch—and can affect expansion at higher levels. Meals that meet all typical specs (Table 3.5) often expand differently during extrusion. This relates to the structure and hardness of the corn endosperm particles (Figure. 3.8). Hard particles [Figure 3.8 (B)] require longer hydration time and thus “cook” differently during extrusion and expand differently, significantly affecting product quality. Often preconditioning is required to eliminate grittiness and improper expansion in extremely hard, slow-to-hydrate corn meal particles. Corn hybrid, the environmental conditions during maturation of the corn, hardness of the kernels, details of the milling process, and storage time and temperature for corn and meal affect meal quality signiﬁcantly. Meal from hard endosperm varieties, and from corn maturing in cool, moist conditions, has signiﬁcantly different extrusion properties even though meal composition and particle size are similar. Corn matured under cool, moist conditions is

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Figure 3.8 Environmental scanning electron microscope micrographs of good (top) and poor corn meals (bottom). These meals are similar to those in Figure 3.6 (B), but with signiﬁcantly different extrusion properties. SG—starch granules.

signiﬁcantly softer and cooks more rapidly than harder corn maturing normally. Hard particles often do not hydrate properly and cause gritty, glassy particles in the cell walls of the snacks—a defect that signiﬁcantly affects consumer acceptance. Desired cornmeal extrudate characteristics vary among countries and between ethnic groups within a country. For example, corn puffs that barely hold together and melt into discrete particles in the mouth are preferred in some areas, while others like crunchy, harder texture. Consistent meal quality

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is required to produce each of these products once the appropriate extrusion conditions are established. The Rapid ViscoTM Analyzer (RVA) effectively measures corn cooking and hydration times. RVA curves for corn meal with good and poor extrusion cooking properties show large differences [Figure 3.6(B)] [28] when high concentrations of meal are pasted to the critical temperature of 65◦ C or slightly higher. These curves provide excellent information on corn-meal cooking properties, which is used to predict extrusion properties. For control purposes, the hydration properties of meal can be measured by quick tests in which corn meal is cooked in excess water for an established time. Then, the relative viscosity of the blend can be measured with a Bostwick consistometer [Figure 3.5(F)]. With experience, the test can be used to predict differences among meal samples. This instrument is also used to measure viscosity and extent of cooking of pregelatinized corn meal and dry masa ﬂours [29]. This technique is inexpensive and works effectively once it is set up properly.

10.5. EVALUATION OF DRY MILLING Kernel hardness and freedom from stress cracks are the major quality criteria for corn used in dry milling. High-temperature drying creates stress cracks, which lead to breakage during handling. Dry-milling quality decreases linearly with increasing drying temperature. Kirleis and Stroshine [30] found that hard hybrids had better milling characteristics than soft counterparts. The physical property of corn most closely related to milling yields is density. For high yields of ﬂaking grits, corns with high test weight and hardness are recommended [30]. Kirleis and Stroshine [30] developed a laboratory procedure for evaluating dry milling yield potential based on 1.3 kg of grain. The milling evaluation factor (MEF) is a useful method for estimating the production of large grits— the higher the MEF value, the greater the potential value of the corn for use in dry milling. The MEF factor is highly related to kernel hardness indices, speciﬁc gravity, test weight and ﬂoatation values. The MEF of corn hybrids is signiﬁcantly affected by location, with the highest milling efﬁciency for hybrids grown in southern areas. This has been observed consistently in the national yellow and white food corn trials over several years. Flint corns are ideal for producing maximum yields of large corn grits for corn ﬂakes. However, the meal may be too hard and difﬁcult to hydrate. Thus, dry millers want hard dent corns to enhance milling yields of large grits while producing meal that has acceptable extrusion properties.

11. DRY MASA FROM DRY-MILLED CORN FRACTIONS Some corn millers produce dry masa ﬂour (DMF) by cooking dry-milled corn fractions with moderate levels of water and 0.1–0.2% lime, followed by

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drying, grinding, sieving and reblending to obtain the desired particle size distribution. These dry masa ﬂours usually have properties signiﬁcantly different from the traditional DMF [31]. Some of them produce excellent tortilla chips and taco shells although the texture is different. These DMFs can have brighter colors and are used effectively for snacks but are less acceptable for table tortillas [32]. Instant arepa ﬂours are available in Colombia and Venezuela. They are not alkaline cooked, but are made from dry-milled endosperm particles that are precooked, dried, ground and formulated into the proper size distribution. Water is added to produce masa. These precooked ﬂours are sometimes confused with DMF. The term “corn ﬂour” can refer to different products. To the alkaline cooking industry, “corn ﬂour” means alkaline-cooked (nixtamalized) dry masa ﬂour, which is made by cooking and soaking whole-kernel corn in lime and water, removing the pericarp, grinding and drying. To dry corn millers, “corn ﬂour” means raw starchy endosperm particles of a certain maximum size made from corn. Precooked corn ﬂours do not contain alkali.

12. SORGHUM UTILIZATION IN SNACK FOODS Sorghum is certiﬁed GMO-free and can be used in alkaline-cooked and extruded snacks. It is used alone or in combination with maize for tortillas and tortilla chips in some areas of Honduras, Nicaragua, Guatemala, El Salvador and Mexico [33]. Compared to corn, sorghum nixtamalization requires a shorter cooking time and reduced levels of lime [34–36]. Acceptable table tortillas and snacks have been made from sorghums that have tan plant color, white pericarp, intermediate endosperm texture without a subcoat, and low levels of color precursors [36–39]. Recently released sorghum varieties and hybrids have excellent food processing characteristics. New photosensitive tan plant sorghums have replaced some of the “criollo” sorghums of Central America, which have a purple plant color that causes off-color products. Special black, brown and red sorghums produce tortilla chips with deep black or blue to brown color [40]. They have unique ﬂavor and texture. Decorticated sorghum can be used to produce acceptable tortillas and tortilla chips, and the meal can be extruded into snacks. Decortication reduces color by removing many pigments from the grain. Decorticated sorghum cooks more quickly with reduced levels of lime and may not require washing [35,36]. However, it is easily overcooked and can produce a sticky masa, yielding tortillas and chips with poor texture. Blends of maize and sorghum have been processed into acceptable tortilla chips [38,39]. Meal and grits from food sorghums [33,41] are easily extruded to produce white or light-colored, bland-tasting products that can easily be colored and ﬂavored. Corn has a strong ﬂavor that can signiﬁcantly interact with snack food

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seasonings, but sorghum does not have that problem. The expansion capabilities of sorghum endosperm are equivalent to those of corn grits or meal. Usually, sorghum is less expensive to purchase than corn. However, the proper sorghum must be obtained since some varieties contain bitter, off-tasting components. Food sorghum is compatible with a wide variety of ingredients and gives a different ﬂavor that is desirable in snacks and related products.

13. ACKNOWLEDGMENTS We appreciate the hard work and creativity of numerous graduate students, postdoctorates and colleagues, who facilitated our continued efforts during the past 25 years to understand corn quality. The Snack Foods Association, Tortilla Industry Association, Texas Corn Producers Board, Texas Agricultural Experiment Station, and numerous private companies and technical organizations have ﬁnancially supported our research.

14. REFERENCES 1. FAO, 1999. Food Agriculture Organization, http//apps.fao.org. 2. Inglett, G. E., ed., 1970. Corn: Culture, Processing, Products. AVI, Westport, Connecticut. 3. Rooney, L. W. and S. O. Serna-Saldivar, 1987. Food uses of whole corn and dry milled fractions. In Corn Chemistry and Technology. S. A. Watson and P. E. Amsted, eds. American Association of Cereal Chemists, St. Paul, Minnesota. 4. Serna-Saldivar, S. O., M. H. Gomez, and L. W. Rooney, 1990. The technology, chemistry and nutritional value of alkaline cooked corn products. In Advances of Cereal Science and Technology, Vol. 10. Y. Pomeranz, ed. American Association of Cereal Chemists, St. Paul, Minnesota. 5. Bressani, R., 1990. Chemistry, technology, and nutritive value of maize tortillas. Food Rev. Int., 62:225–263. 6. Faga, B., 1998. Dry Milling—A Variety of Products. 1998 Corn Annual Report. Corn Reﬁners Association, Washington, D.C. 7. Anon. (a), 2000. Value-Enhanced Grains Quality Report. U.S. Grains Council, Washington, D.C, 123 pp. 8. Persley, G. J. and J. N. Siedow, 1999. Applications of Biotechnology to Crops: Beneﬁts and Risks. Issue Paper # 12. Council for Agr. Sci. and Technology, Ames, Iowa, 8 pp. 9. Anderson, K., P. Keukel, R. Fredrich, and T. Herman, 1999. Corn Kernel Damage (L-59). Oklahoma State University, Stillwater, Oklahoma. 10. Pﬂugfelder, R. L., R. D. Waniska, and L. W. Rooney, 1988. Dry matter losses in commercial corn masa production. Cereal Chem., 65:126–132. 11. Anon. (b), 1999. Quality Protein Maize Progress Report. International Maize and Wheat Center (CIMMYT), El Batan, Mexico, 13 pp. 12. Serna-Saldivar, S. O. and L. W. Rooney, 1994. Quality protein maize processing and perspectives for industrial utilization. Proceedings of the International Symposium on Quality Protein Maize. Sete Lagoas, Brazil, 1994.

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13. Sproule, A. M., S. O. Saldivar, A. J. Bockholt, L. W. Rooney, and D. A. Knabe, 1988. Nutritional evaluation of tortillas and tortilla chips from quality protein maize. Cereal Foods World, 33: 233–236. 14. CAST, 1989. Mycotoxins: Economic and Health Risks. Task Force Report # 116. Council for Agricultural Science and Technology, Ames, Iowa, 89 pp. 15. Floyd, C. B., L. W. Rooney, and A. J. Bockholt, 1995. Measuring Desirable and Undesirable Color in White and Yellow Food Corn. Cereal Chem., 72(5):488–490. 16. Stenvert, N. L. J., 1974. Grinding Resistance, A Simple Measure of Wheat Hardness. Flour, Animal Feed, Milling, 156:24–25, 27. 17. Tran, T. L., J. M. DeMan, and V. F. Rasper, 1981. Measurement of corn kernel hardness. Can. Inst. Food Sci. Technol. J., 14:42–48. 18. Hosney, R. C., 1994. Principles of Cereal Science and Technology, 2nd edition. American Association of Cereal Chemists, St. Paul, Minnesota. 19. Almeida-Dominguez, H. D., E. L. Suhendro, and L. W. Rooney, 1996. Factors Affecting Rapid ViscoTM Analyzer Curves for the Determination of Maize Kernel Hardness. J. Cereal Sci., 25:93–102. 20. Almeida-Dominguez, H. D., E. L. Suhendro, and L. W. Rooney, 1997. Corn alkaline cooking properties related to grain characteristics and viscosity (RVA). J. Food Sci., 62(3):516–523. 21. Jackson, D. S., L. W. Rooney, O. R. Kunze, and R. D. Waniska, 1988. Alkaline processing properties of stress cracked and broken corn (Zea mays, L.). Cereal Chem., 65:133–137. 22. Almeida-Dominguez, H. D., G. G. Ordo˜nez-Dur´an, and N. G. Almeida, 1998. Inﬂuence of kernel damage on corn nutrient composition, dry matter losses, and processability during alkaline cooking. Cereal Chem., 75:124–128. 23. Serna-Saldivar, S. O., H. D. Almeida-Dom´ınguez, M. H. Gomez, A. J. Bockholt, and L. W. Rooney, 1991. Method to evaluate ease of pericarp removal of lime-cooked corn kernels. Crop Science, 31(5):842–844. 24. Serna-Saldivar, S. O., M. H. Gomez, H. D. Almeida-Dominguez, A. Islas Rubio, and L. W. Rooney, 1993. A method to evaluate the lime cooking properties of corn (Zea mays). Cereal Chem., 70:762–764. 25. Watson, S. A., 1988. Corn marketing, processing and utilization. In Corn and Corn Improvement. Agronomy Series No. 18. G. F. Sprague and J. W. Dudley, eds. Am. Soc. Agro., Crop Sci. Soc. Am., and Soil Sci. Soc. America, Madison, Wisconsin. 26. Alexander, R. J., 1987. Corn dry milling: processes, products and applications. In Corn Chemistry and Technology. S. A. Watson and P. E. Ramstad, eds. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 351–376. 27. SFA, 1992. Corn Quality Assurance Manual. Snack Food Association, Alexandria, Virginia. 28. Whalen, P. J., 1999. Detecting differences in snack ingredients quality by rapid visco-analysis. Cereal Foods World, 44:24–26. 29. Lobeira, R., H. D. Almeida-Dominguez, and L. W. Rooney, 1998. Methods to evaluate hydration and mixing properties of nixtamalized corn ﬂours. Cereal Chem., 75(4):417–420. 30. Kirleis, A. W. and R. L. Stroshine, 1990. Effect of hardness and drying air temperature on breakage susceptibility and dry-milling characteristics of yellow dent corn. Cereal Chem., 67:523–528. 31. Gomez, M. H. L. W. Rooney, R. W. Waniska, and R. L. Pﬂugﬂelder, 1987. Dry corn masa for tortilla and snack food production. Cereal Foods World, 32:372–377. 32. Almeida-Dominguez, H. D., M. Cepeda, and L. W. Rooney, 1996. Properties of commercial nixtamalized corn ﬂours. Cereal Foods World, 41:624–630.

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33. Rooney, L. W. and R. D. Waniska, 2000. Sorghum food and industrial utilization. In Sorghum: Origin, History, Technology and Production. C. W. Smith and R. A. Frederiksen, eds. John Wiley & Sons, New York, pp. 689–729. 34. Almeida-Dominguez, H. D., S. O. Serna-Saldivar, and L. W. Rooney, 1991. Properties of new and commercial Sorghum hybrids for utilization in alkaline cooked foods. Cereal Chem., 68(1):25–30. 35. Bedolla, S., M. Gonzalez de Palacios, L. W. Rooney, K. C. Diehl, and M. N. Khan, 1983. Cooking characteristics of sorghum and corn for tortilla preparation by several cooking methods. Cereal Chem., 60:263–268. 36. Choto, C. E., M. M. Morad, and L. W. Rooney, 1985. The quality of tortillas containing whole sorghum and pearled sorghum alone and blended with yellow maize. Cereal Chem., 62(1): 51–54. 37. Khan, M. N., L. W. Rooney, D. T. Rosenow, and F. R. Miller, 1980. Sorghums with improved tortilla-making characteristics. J. Food Sci., 45:720–722, 725. 38. Serna-Saldivar, S. O., A. Tellez-Giron, and L. W. Rooney, 1988. Production of tortilla chips from sorghum and maize. J. Cereal Sci., 8:275–284. 39. Quintero-Fuentes, X., C. M. McDonough, L. W. Rooney, and H. D. Almeida-Dominguez, 1999. Functionality of rice and sorghum ﬂours in baked tortilla and corn chips. Cereal Chem., 76:705–710. 40. Zelaya, N., H. Yeggy, E. L. Suhendro, X. Quintero, and L. W. Rooney, 1990. The Effect of grain color and pH on sorghum tortilla chips. AACC 84th Annual Meeting, October 31–November 3, Seattle, WA, Cereal Foods World, 44(7): 347. 41. Rooney, L. W. 1996. Attributes of improved quality sorghums for value-added marketing. ASTA Proceedings of the Fifty-First Annual Corn & Sorghum Research Conference. December 10, Chicago, Illinois, pp. 112–124.

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CHAPTER 4

Alkaline-Cooked Corn Products

CASSANDRA M. McDONOUGH MARTA H. GOMEZ LLOYD W. ROONEY SERGIO O. SERNA-SALDIVAR

1. INTRODUCTION

T

chapter summarizes the science and technology of producing alkalinecooked corn products. Speciﬁcally, ingredients and product quality, traditional and current processes and physicochemical changes occurring during production of alkaline-cooked products are covered. Aside from their traditional use in North and Central America, corn and tortilla chips are becoming popular in other parts of the world. Processing plants have been initiated in Australia, Brazil, India, China, Korea, Europe and other countries. The chemistry, technology and nutritional status of nixtamalized products have been extensively reviewed by several authors [1–3]. HIS

2. TRADITIONAL CORN PRODUCTS Dishes are produced from corn in many traditional ways in Latin America. Tortillas and arepas are the most important corn-based foods for people in North America (Mexico), Central America and South America (Venezuela and Colombia). In Mexico, nearly 72% of the corn produced is used for food, mainly in the form of nixtamalized (alkaline-cooked) products. In particular, the lower socioeconomic groups depend on tortillas as their main source of calories and protein. Paredes-Lopez and Saharopulos-Paredes [4] estimated that the average annual per capita consumption of corn in Mexico was 120 kg, mainly in the form of tortillas. Krause [5], likewise, found that Guatemalan Indian women

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Figure 4.1 Traditional tortilla making process.

consumed an average of 579 g tortilla per day, which contributed 33 g protein, 642 mg calcium, and 1,164 kcal to their diets. The traditional method of processing corn into tortillas, nixtamalization, was developed by ancient Mesoamericans. Water, containing lime (calcium oxide) or leachate of wood ashes is used to cook the grain for 5 to 50 min, followed by steeping for 8 to 16 hrs (Figure 4.1). The lime-cooked corn, called nixtamal, is washed by hand to remove excess lime and pericarp tissues, and then ground with a stone metate to form a dough called masa. Traditional products, like tamales, pozol, atoles, tortillas, tostadas, totopos, and others, are made from masa. In Central America and Mexico, small portions of masa are hand-shaped into ﬂat disks that are baked on a hot griddle or clay comal for 30 to 60 sec on each side [3]. Over 90% of the tortillas consumed in Guatemala are prepared

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using this method [5]. In Mexico, a table tortilla is thin and puffs during baking, whereas in Central America most tortillas are thick and unpuffed. Tortillas generally are consumed in combination with beans, various meats, cheeses, and vegetables. In Mexico, tostadas are fried from stale tortillas. Arepas, the national corn bread of Venezuela and Colombia, are traditionally produced by cooking the grain in water to soften it. The cooked corn then is ground into a dough with smooth texture. The dough is hand shaped into ﬂat disks approximately 7.5 cm in diameter and 1 cm thick and baked. Arepas are cut in half and stuffed with meat, cheese, butter, jellies and other ﬁllings. Stuffed arepas are sometimes fried to produce hallaquitas, hallacas, empanadas and other dishes. Hopi Indians from the Southwestern United States still consume traditional foods prepared with 12 to 14 different types of corn, in 70 different ways [6]. Many dishes are based on corn containing blue anthocyanin pigments in the aleurone layer. Blue corn tortillas, chips, pozole and other products are sold in many restaurants and some supermarkets. In addition to the color, blue corn products have a unique ﬂavor. Indians in Mexico use blue and red corn. The early settlers of North America cooked corn in lye or wood ashes to produce hominy. The process was ﬁrst used by American Indians, who taught the colonists how to use wood ashes. The alkali effectively removes the pericarp, enhances the palatability and nutritional value of the corn kernels, and transforms the hard raw kernels into a soft, chewable product that can be stored relatively safely [7]. In the United States, canned hominy is produced from white and yellow corn by using lye, which produces a different ﬂavor than that of hominy prepared with lime. Corn for use in hominy is dried and handled carefully to avoid stress cracks. In Mexico, hominy (nixtamal) is commonly used in preparing pozole. The use of corn for tortilla chips and ethnic Mexican prepared foods has increased rapidly in the United States. A similar situation is occurring in many other developed countries due to availability and affordable cost of corn, feasibility of alkaline cooking and diversity of the products. Snacks based on corn are sold as retail products, and offered in restaurants, delis, amusement parks and convenience stores (Chapter 1). Corn snacks are relatively inexpensive and easier to process with greater ﬂexibility and proﬁtability than potato chips. Compositions of lime-cooked corn products are compared with those of wheat bread and ﬂour tortillas in Table 4.1.

3. INGREDIENTS Corn, lime and water are the basic ingredients used in alkaline cooking for making snacks and tortillas. Product quality and processing parameters depend on the corn characteristics (Chapter 3). However, oil, salt and seasonings used

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TABLE 4.1.

Nutritional Composition of Flour Tortillas, Lime-Cooked Corn Products and Table Bread (100 g. Serving).

Nutrient Water (g) Energy (kcal) Digestible energy (kcal) Protein (g) Digestible Protein (g) Fat (g) Ash (g) Total dietary fiber (g) Dietary insoluble fiber (g) Dietary soluble fiber (g) Starch (g) Calcium (mg) Phosphorus (mg) Magnesium (mg) Sodium (mg) Potassium (mg) Iron (mg) Zinc (mg) Copper (mg) a b

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Lime-Cooked Products

Wheat Flour Tortillas

Table Tortillas

Corn Chipsa

Tortilla Chipsb

Bread

29.3 351.3 331.2 7.2 6.4 9.8 2.2 --------42.2 77.0 84.8 573.0 99.0 1.5 0.6 0.8

41.9 238.3 223.5 6.5 5.4 2.5 0.9 7.4 6.3 1.1 44.9 92.8 162.6 69.7 13.3 205.3 2.5 2.5 0.07

0.9 573.1 --6.3 --36.6 1.9 --------105.0 177.5 76.1 1091.1 211.2 2.9 2.5 0.09

1.6 514.3 487.0 7.6 6.2 23.9 1.1 12.4 9.0 3.1 59.9 124.0 208.6 89.4 ----3.5 3.0 0.11

35.8 274.0 --8.7 7.7 3.9 1.9 2.7 ------126.0 87.0 21.7 494.8 103.0 2.6 0.6 0.14

Salted corn chips. Unsalted tortilla chips. Salted tortilla chips contain approximately 774 mg sodium/100 g.

for making deep-fried snacks have the greatest effect on mouth feel, taste and acceptability.

3.1. LIME Food-grade lime, such as quicklime and hydrated lime, consists principally of calcium oxide and generally contains less than 5% magnesium oxide. The concentration of lime used most frequently in alkaline cooking is 1.0% based on corn weight. Cooking temperatures range from 85 to 100◦ C (185–212◦ F) with varying cooking times. Cooking time, temperature, lime concentration and method of cooking interact. The addition of lime facilitates pericarp removal during cooking and steeping, controls microbial activity and affects texture, ﬂavor, aroma, color, shelf life, and nutritional value of tortillas and snacks [1–3]. Long-term storage of lime results in poor pericarp removal; thus, the lime must be kept fresh. Lime also affects the amount of solids that goes into the processing plant’s sewage system. Only a small quantity of lime (less than 0.2%) is retained by the grain, with the remainder being discharged into the

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Figure 4.2 Effects of cooking and steeping times on nixtamal moisture, calcium content and drymatter losses. Adapted from Reference [2].

plant efﬂuent. Higher lime concentrations used during cooking increase total dry-matter losses from corn (Figure 4.2) [2,8], which reduces product yields and increases costs of efﬂuent treatments. Lime affects the corn kernel by breaking the bonds that hold hemicelluloses together in the cell walls and allows the pericarp to be easily removed. The degraded pericarp acts as a hydrocolloid and imparts desirable properties to corn tortillas. For chips, the pericarp is usually removed by washing until the corn is “squeaky” clean; however, some processors do not remove the pericarp. Incomplete pericarp removal causes darker-colored chips and may adversely affect grinding.

3.2. WATER The lime is partially solubilized in water during cooking. For the production of fresh masa, corn typically is cooked with 1–3 parts water and 1% lime, based on grain weight. Kernels absorb about 28–30% water during cooking and 5–8% more during steeping (Figure 4.2) [2]. The corn must always be covered by the lime/water solution during cooking and steeping. Current water: corn ratios are 1:1 based on the volume of grain, with more water added as needed to keep the grain covered. Additional fresh water (2–4%) is also added to the

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masa during stone grinding. The amount of water absorbed depends on the extent of cooking, which varies with the type of product and the desired masa texture. The pH of the water, and the minerals it carries, can affect the color of the ﬁnal product. Moisture is a key critical control point in the processing operations and also regulates oil uptake during frying and subsequent quality of the snacks.

3.3. OIL Frying oil is the second major ingredient after corn in deep-fried snacks. The selection of frying oil depends on cost, availability, stability and ﬂavor (Chapter 6). Soybean, cottonseed and sunﬂower oils are the most popular in the snack industry. Peanut oil, although more expensive, is often blended with other oils to improve product ﬂavor. Frying oils are partially hydrogenated to improve stability and to prevent ﬂavor reversion in the case of soy oil. The shelf life of frying oils depends on the oil composition and manufacturing practices. Regular ﬁltering and maintenance of proper oil frying temperatures improve oil performance and increase shelf life of the products. Oil uptake depends on the type of fryer, product moisture content, frying temperature, residence time and oil quality. The turnover time (8 hrs) of oil in large industrial fryers is critically important (Chapter 6).

3.4. OTHER INGREDIENTS Salt and ﬂavoring agents are added to corn and tortilla chips at different levels to improve ﬂavor and appearance, depending on need. Salt is a non-aromatic ingredient, while ﬂavoring agents include cheese, spices, chili peppers and a wide array of other ingredients. Nacho cheese, barbecue, cool ranch and hot pepper ﬂavors are popular in the Southwestern United States. Seasonings are discussed further in Chapters 19 and 20.

4. PREPARING AND USING FRESH MASA The alkaline cooking process involves several unit operations, including cooking and steeping, grinding, kneading, sheeting, molding, cutting, baking and frying. A general ﬂow sheet summarizing typical end uses of masa is shown in Figure 4.3 [2] and examples of the products produced in each step during nixtamalization are presented in Figure 4.4. The cooking, steeping, grinding and other operations are optimized for each of the ﬁnal products in commercial operations. The types of corn and corn blends used also differ, depending on the desired product.

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Figure 4.3 Overall masa preparation and uses for industrial products. Adapted from Reference [2].

4.1. COOKING AND STEEPING Corn cooking is more art than science, although standardized cooking procedures are followed as closely as possible. Corn is said to “cook” whenever the temperature is 65◦ C, 149◦ F, or above the average gelatinization temperature of corn starch. Thus, corn-cooking procedures must be carefully controlled to ensure that the rise time, the cooking (simmering) time and the times for temperature decrease are the same for all batches. The variables that must be

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Figure 4.4 Views of corn processing. 4A, Raw corn. 4B, Nixtamal. 4C, Grinding stone with masa. 4D, Masa. 4E, Sheeting/forming masa. 4F, Tortillas. 4G, Tortilla chip.

carefully controlled to achieve uniform cooking from one batch to another are the mass of the corn, amount of stirring or agitation, lime concentration and suspension. Thus, a cook time of 10 minutes usually means that the corn is held at a given temperature for 10 minutes, although actual cooking begins when it

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reaches 65◦ C and continues until it cools below 65◦ C. The temperature in the middle of the corn batch is usually recorded from the time heating begins until the corn mixture has returned to room temperature. Large quantities of corn retain heat and cook long after the cooking time is completed and the steam or energy source turned off. Records of cooking cycle temperatures and times are important in determining why certain samples of cooked corn, also called “nixtamal,” have different grinding properties than others. The extent of cooking, i.e., whether the corn is “done” or not, depends on the endosperm characteristics of the corn, the interaction of temperature, time and lime concentration, size of the cooking vessel and the frequency of agitation. Optimum cooking and steeping are determined subjectively by evaluating the extent of pericarp removal, kernel softening, water uptake and overall appearance of the nixtamal. Moisture content is an excellent index of the extent of cooking. Longer cooking times are required for table tortillas, and the nixtamal is steeped without quenching. Nixtamal for corn and tortilla chips is cooked to a lesser extent either by decreasing cooking time or by quenching the steeping liquor to less than 65◦ C. During quenching, cool water quickly cools the kernels below the starch gelatinization temperature range and avoids overcooking in hot spots that develop in large cooking vessels. Corn is industrially cooked using three basic types of equipment. Open vats generally are used by small processors in the United States, and are the most common type of equipment used in Mexico. The method is energy-inefﬁcient and labor-intensive because the cooking vat is open, and the mixture is manually agitated. Heating is accomplished with gas burners, but sometimes steam injector tubes are used to improve cooking efﬁciency. Cooking vessel capacity ranges from 180 to 900 kg of grain [2]. Steeping, usually overnight, occurs in the same container. Two more advanced systems are the Hamilton-type kettle and the vertical cooker. Hamilton or other steam-jacketed kettles are heated indirectly by steam and agitated mechanically. Corn is generally cooked just below boiling temperatures and immediately transferred to tanks for steeping. Vertical cookers use direct steam injection to heat and agitate the corn and lime solution, with cooking and steeping done in the same tank. Compressed air may be injected for additional agitation. In vertical cookers, the grain is generally cooked with 1.5 to 3 parts water and 1% lime (varying from 0.8 to 5% lime) based on corn weight (Figure 4.1). Vertical cookers are designed to cook at temperatures well below boiling (i.e., 85◦ C, 185◦ F). The cooking time generally is longer than in steam kettles and varies from a few minutes to 1.5 hrs, with 15 to 45 min cited most often. Capacities of steam kettles and vertical cookers range from 136 to 270 kg and 1,360 to 2,730 kg, respectively. Temperatures are controlled, and these two systems provide consistent results with high efﬁciency, provided the agitation is sufﬁcient to prevent hot spots.

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A continuous cooking process was designed and patented to overcome cooking variations between batches and to produce nixtamal in less time with greater control of moisture content and greater product uniformity. Clean corn kernels were continuously fed into a stationary tank containing a heated lime solution (80◦ C, 176◦ F) at pH 11–12. The lime solution was introduced under pressure into the bottom of the tank and ﬂowed upward through the kernels. The cooked corn was discharged from the bottom of the tank at a controlled rate and washed to remove the pericarp. Then, the nixtamal, with a moisture content of about 50%, was ground into masa. This procedure required 5–7 hr and less equipment, labor and ﬂoor space than conventional processing. In addition, the process recycled the lime solution, reducing efﬂuent treatment costs. Despite these advantages, continuous cooking processes are seldom if ever used because they do not provide sufﬁcient modiﬁcation of the corn kernel in a uniform manner. After cooking, the nixtamal is steeped for several hours. Steeping or soaking increases moisture uptake and distributes moisture and lime uniformly throughout the kernel. The nixtamal is either steeped in the cooking tank (at small tortillerias) or pumped to holding tanks in larger manufacturing plants and steeped.

4.2. WASHING After steeping, the nixtamal and steeping liquor are pumped or dropped by gravity, into mechanical washers. The steep liquor nejayote is drained into an efﬂuent treatment system. Most commercial washers are rotating barrels or drums that rinse the nixtamal with pressurized water to remove the pericarp and excess lime. Pumping increases dry-matter losses of the nixtamal during washing, especially when poor quality, stress-cracked corn has been used. Washing in commercial processes is done using either of two types of equipment, the drum washer or the lowboy system. A drum washer consists of a conveyor that transports the nixtamal into a rotating perforated cylinder with internal ﬂights and water sprayers located within the drum. The nixtamal next passes onto a draining conveyor, where excess water is removed. The lowboy system consists of a receptacle equipped with internal screens and sprayers. The washed nixtamal is continuously removed from the bottom of the receptacle by an inclined belt conveyor. In both systems, a conveyor transports the washed, drained nixtamal into a hopper, which feeds the stone grinder. Washing removes the lime, lowers the pH and removes most of the pericarp [Figure 4.4(B)], which enhances chip color. Recovery of corn dry matter lost during cooking, steeping and washing is critical. The common practice is to screen the liquor to remove insoluble solids and then further reduce the level of suspended solids using various methods.

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4.3. GRINDING Next, the clean nixtamal is ground using a system of two matched carved stones: one stationary and the other mechanically rotated at 500 to 700 rpm. Volcanic [Figure 4.4(C)] and synthetic (aluminum oxide) stones are widely used by the industry. Synthetic stones last longer and require less maintenance; however, they cannot be “dressed” (resurfaced) at the tortilla plant. The typical stone is 10.2 cm thick, 40.6 cm in diameter, and is carved radially. Commercial grinders use stones ranging from 25 to 46 cm (10–18 in.) in diameter. The grooves become progressively shallower as they approach the perimeter of the stone. Grinding starts when a screw conveyor at the base of the hopper forces the nixtamal through a central opening and into the gap between the stones, where shearing occurs. The ground nixtamal is cut, kneaded, and mashed while moving outwards between the stones. Masa particle-size reduction is directly related to the size and depth of the grooves, and is the result of several interacting factors: (1) degree of nixtamal cooking; (2) design of the stone-grinding surface (groove size and depth); (3) gap setting or pressure between the grinding stones; (4) amount of water used during milling; and (5) corn type. For the production of table tortillas, the nixtamal is cooked more thoroughly, the grinding stones have shallower grooves and the gap between the stones is smaller so that more pressure is applied during grinding. Grinding stones carved for corn and tortilla chips contain fewer and deeper grooves. Water added during milling cools the stones, prevents excessive wear, and reduces the masa temperature. About 0.6–1.2 L of water per minute is added for a grinder with a capacity of 600 kg/hr. This amount of water raises the masa moisture content to optimum levels for sheeting, which depend on the product being made. Synthetic aluminum oxide stones are often used for grinding corn (Chapter 11). They have longer milling times and do not require dressing as frequently as lava stones. A new stainless steel attrition mill has recently been developed and works efﬁciently. In some processes, especially taco shell masa production, the nixtamal is cut into particles by an Urschel mill. These particles must be subjected to additional attrition milling to obtain optimum masa texture. The attrition process breaks down gelatinized starch granules and forms a continuous phase holding the masa particles together.

4.4. KNEADING, SHEETING, CUTTING The masa becomes plastic and cohesive upon further kneading [Figure 4.4(D)]. This occurs as it is conveyed from the grinder to the sheeter using a masa feeder. In smaller operations, the masa is mixed and formed into loaves (logs), which are conveyed manually to the sheeting rolls. In the United States, two rotating

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smooth, teﬂon-coated rolls automatically press the masa into a thin sheet. The gap between the rolls determines product thickness, weight, and ultimate use; i.e., table tortillas typically have a diameter of 15 cm and weigh 28–30 g. The resulting sheet of masa is cut into disks by an attachment located underneath the front roll [Figure 4.4(E)]. Different interchangeable cutter conﬁgurations are used for production of various products, varying from disks to triangles in shape. Sheeting heads that cut up to eight rows of tortillas exist [2]. A set of cutting wires helps dislodge the masa disks onto the conveying belt that feeds the oven. Sheeters without wires have been used recently. In Mexico, most tortillas are formed by the Celorio machine, which consists of a mixer, extruder and former. The extrusion system forces the masa through a slot at the bottom of the unit. A gate cutter controls the discharge and regulates the shape and size of the masa product. This machine is exclusively used for table tortillas and requires a ﬁnely ground masa. Tortillas extruded and formed with the Celorio machine puff during baking and retain optimum texture longer [2]. However, when fried, these tortillas produce tostadas that are quite ﬁrm and often oily with many blisters in the skin. This typically happens to table tortillas during frying because they have ﬁne particle sizes conducive to pillowing.

4.5. BAKING AND COOLING The newly formed masa disks are baked into tortillas [Figure 4.4(F)] or tortilla pieces destined for frying [Figure 4.4(G)] in a triple-pass gas-ﬁred oven at temperatures ranging from 350 to 480◦ C (660 to 890◦ F) for 20 to 40 sec. The moisture content of the masa is reduced by about 10–12% during baking to yield tortillas containing 38–46% moisture. The baked tortillas or pieces are cooled for 3 to 20 min in a series of opentier conveyors that discharges into the fryer. The hot, baked tortilla pieces have different levels of moisture. Equilibration time permits some of the moisture inside the chip to migrate to the surface and evaporate, effectively lowering oil uptake during frying. The equilibrium within baked chips prior to frying critically affects oil content, color, texture and appearance of the ﬁnal product. Cell structure and pore size of the chips are affected during frying because moisture escapes in a different fashion when baked tortilla pieces are adequately equilibrated. Surface pores of chips affect light refraction, which relates to appearance and color. “Pillowing” and other defects are reduced by proper equilibration. Baked tortillas are equilibrated for 12 hrs or more at 4◦ C (39◦ F), before frying many types of restaurant-style chips. Refrigeration facilitates retrogradation in the tortilla pieces, which signiﬁcantly improves the texture of the fried products. In some cases in Mexico, special tostadas are made by drying baked tortillas in ambient air to remove part of the water prior to frying [9]. These tostadas have reduced oil content and good texture with less pillowing.

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Figure 4.5 Production of coarse masa for corn and tortilla chips. Adapted from Reference [2].

4.6. FRYING AND SEASONING The majority of lime-cooked corn snacks in the United States are consumed in fried form. However, baked and baked/fried snacks are sold in the healthy snacks segment. The two most popular products, tortilla chips and corn chips, are made from coarse masa. In contrast to table tortillas, the corn is cooked for less time and/or quenched immediately after cooking. They are then ground into a coarse, lower-moisture content masa (Figure 4.5) [2]. For corn chips, the masa is formed by extrusion, or sheeted and cut into strips, and fried directly (Figure 4.6) [2]. In making tortilla chips, masa pieces are baked before frying to reduce their moisture content so they absorb less oil and have a ﬁrmer texture and a stronger alkaline ﬂavor than corn chips. Different product conﬁgurations exist. Tostadas, chalupas, taco shells and baskets are tortillas produced from coarse masa and fried ﬂat, folded, or in a basket form. These products are ﬁlled/topped with meat or vegetables and served in restaurants and fast food establishments. Corn chips contain more oil (32–38%) than tortilla chips (21–24%). This large difference is due to the moisture content of the product before frying. Masa strips for corn chips contain at least 48–50% moisture, whereas the baked

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Figure 4.6 Production of tortilla chips and related products. Adapted from Reference [2].

tortilla chips contain 36–42% moisture. For production of taco shells, tostadas, baskets, and related products, the tortillas made from coarse masa are either bent or formed into the desired conﬁguration using special forming devices and then fried [2]. The fryers are designed to maintain uniform temperature and make products with acceptable color and low moisture content (<2.0%). Most commercial fryers are continuous with direct or indirect heating elements, gas-ﬁred tubes, or

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high-pressure steam tubular heaters. Frying temperature and product residence time depend on the type of product. Masa or tortilla pieces from yellow maize require lower frying temperatures than pieces from white maize or blends [1–9]. Most corn chips are made from blends of white and yellow corn to improve their frying characteristics. The carotenoids of yellow corn degrade at high temperatures into beta-ionones, which adversely affect the ﬂavor of the products. Seasonings are applied immediately after frying in rotating tumblers or drums equipped with auger, venturi or electrostatic dispensers (Chapter 20). Levels of salt and other seasonings vary from 0 to 1.5%. After seasoning, the fried products are immediately packaged in moisture-proof bags to avoid loss of crispiness due to moisture uptake.

5. BAKED AND REDUCED-FAT PRODUCTS Many processors have developed reduced-fat products for speciﬁc markets by modifying manufacturing procedures in which the product is baked or toasted (Figure 4.7) [2]. For production of reduced-oil snacks, moisture is removed from the shaped masa or baked tortilla chip by further baking or toasting (180◦ C, 356◦ F, for about 3 min) or baking/ﬂash frying (207◦ C, 405◦ F, for 7–10 sec) to yield a product with less than 2% moisture [9]. Sometimes, baked tortilla chips are sprayed with oil to increase the fat content to 7–8% and enhance ﬂavor and texture.

Figure 4.7 Production of low-fat baked snacks.

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Waxy ﬂours (rice, corn, sorghum) increase the acceptability of baked tortilla chips by making them more porous (with smaller air pores formed during baking) and friable [10]. In the same study, inclusion of gelatinized ﬂours enabled the chips to expand earlier in the baking process to produce increased pufﬁng in the product. Waxy corn requires a signiﬁcantly lower cooking time and special grinding conditions to prevent formation of sticky masa [11]. Baking produces sticky raw tortilla chips which, upon frying, yield a spongy-textured chip with improved fragility and texture compared to chips made with nonwaxy corn. OleanTM , a nondigestible frying oil, has been used to produce tortilla and potato chips. Signiﬁcant sales occurred at ﬁrst, but demand appears to be decreasing rapidly. The higher cost of OleanTM chips, accompanied by subtle differences in ﬂavor and texture (mouth feel), have been difﬁcult problems to overcome. Some small niche companies, producing low-fat chips by various methods, have failed due to decreased sales of low-fat products.

6. PREPARING AND USING DRY MASA FLOURS Dry masa ﬂour (DMF) production has increased signiﬁcantly during the past 10 years along with consolidation of the industry. The two largest companies are based in Mexico with signiﬁcant operations in the United States. Both produce a wide variety (20–30) of DMFs that vary in color, particle size distribution, pH, content of preservatives, level of carboxymethylcellulose (CMC) and expected end use (Table 4.2) [12,13]. DMFs have improved signiﬁcantly in quality, consistency and availability [12]. The largest manufacturer has nearly 30 dry masa plants in Mexico, the United States and Central America. Dry masa producers, using whole corn, place great emphasis on selecting the best corn hybrids for their process and work closely with hybrid seed company personnel. Hybrids are tested, and acceptable varieties listed for growing by producers or for purchasing by companies to meet speciﬁcations (Chapter 3). Several methods are used to produce DMF. The most common method is to cook the clean, intact whole kernels in lime by injecting steam in a continuous screw conveyor for a relatively short time (30–60 min) (Figure 4.8) [2]. The cooked corn is allowed to equilibrate for a short time, then rinsed to remove some of the pericarp, and ground using a specially designed hammer mill. The ground particles are ﬂash-dried, sieved, the coarse particles are reground and sieved, and the fractions reformulated into particle-size distributions needed for speciﬁc DMFs. Drying is critically important since additional cooking and some expansion occur in the particles. Other methods use batch cooking, steeping and stone grinding. These procedures produce different-quality ﬂours [14].

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Density (g/cc)

Moisture (% as is)

Starch (% d.b.)

Proteinc (% d.b.)

36.8 19.3

14.2 7.4

11.2 11.2

5.9 7.9

8.7 1.3

1.4 0.1

9.4 0.7

71.7 4.2

9.1 1.2

FRESH MASA: TABLE TORTILLAS (2 samples) Av. 11.3 14.2 11.0 3.2 S.D. 1.6 0.3 0.3 0.5

3.0 0.3

5.2 1.0

46.7 0.9

-----

-----

-----

75.6 1.1

11.8 0.5

20.3 8.4

10.3 5.4

8.6 4.4

5.6 4.6

6.8 1.9

1.3 0.4

8.9 2.6

67.5 19.7

8.5 2.5

FRESH MASA: TORTILLA CHIPS (2 samples) Av. 37.6 4.6 3.1 1.0 S.D. 1.3 0.9 0.5 0.5

1.0 0.5

3.9 0.6

35.5 4.3

-----

-----

-----

72.6 0.6

10.5 0.4

DMF: CORN CHIPS (2 samples) Av. 14.6 19.3 S.D. 10.0 9.6

24.8 7.2

17.7 7.5

8.4 4.5

6.8 4.5

4.8 4.7

6.3 1.7

1.3 0.3

9.2 2.2

70.3 16.0

8.4 2.2

DMF: TACO SHELLS (2 samples) Av. 15.9 15.6 S.D. 9.8 5.1

21.1 6.6

17.3 8.1

10.0 5.4

7.0 3.7

5.2 4.3

6.1 2.1

1.2 0.4

8.6 2.8

66.2 21.2

7.5 2.4

DMF: TABLE TORTILLAS (16 samples) Av. 0.5 2.4 29.7 S.D. 1.9 3.0 9.2

DMF: TORTILLA CHIPS (10 samples) Av. 9.7 17.5 25.4 S.D. 7.1 11.2 6.9

Adapted from References [12,13]. a <325 for fresh masas. b Particle Size Index. c Nx6.25.

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Figure 4.8 Production of dry masa ﬂour. Adapted from Reference [2].

Using dry masa ﬂour, a chip or tortilla maker can produce products by simply rehydrating the selected masa with water, sheeting, molding, baking and frying as required by the product. This greatly reduces labor, capital outlay for processing equipment, problems of corn acquisition, cooking, wastewater treatment, and provides considerable ﬂexibility in the products made. Disadvantages include the high price of dry masa, the reduced number of manufacturers due to consolidation and subtle differences in ﬂavor and texture

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of fresh vs. dry masa products. For processors cooking corn, proﬁtability is optimized along with improved quality. Often, dry masa is used in conjunction with fresh cooked masa. In Mexico, for example, dry masa is often added to overcome problems when fresh masa is too sticky. This results when only poor-quality maize is available for processing. DMF particles are quite different from those of fresh masa [15–17]. Fresh masa particles include signiﬁcant quantities of free starch granules with low protein content, while DMF has particles that contain starch and protein at levels similar to the original corn endosperm. This results from the different methods of processing. The highly hydrated nature of nixtamal for fresh masa means that starch granules are freed from the protein matrix during grinding and therefore function differently in subsequent processing. In dry masa, the particles are obtained by hammer milling lower-moisture nixtamal without separating starch from the other components. The differences in processing corn into fresh masa and DMF are marked. For example, during steeping of cooked nixtamal the starch granules undergo annealing, which affects the properties of the masa. During drying of dry masa, the gelatinized starch molecules retrograde and form a structure that only partially rehydrates during dough mixing. It is well known that rehydrated masa (from DMF) has a signiﬁcantly greater viscosity than similar fresh masa, and more power is required to sheet/mold masa from DMF than fresh masa. This partially explains why DMF products cannot be the same as those from fresh masa. However, it does not mean that DMF products are necessarily inferior. Dry masa quality is more consistent than ever before, but variations that signiﬁcantly affect product quality still exist. Particle-size distribution is critically important and is determined by sieving. The pH, water absorption and viscosity of the masa are also important. Subjective evaluation of water absorption is an effective way to evaluate the ﬂour. Viscosity methods include use of the Bostwick consistometer, Rapid Visco Analyzer (RVATM ), visco-amylograph, penetrometer and various proprietary tests. Viscosities of DMF differ depending on the end use, and differences can be detected with both the RVA and the Bostwick consistometer (Figure 4.9) [18]. Use of the mixograph and farinographs may be helpful in certain applications [19]. DMFs are produced by some traditional corn dry millers using dry-milled fractions that are treated with lime, partially cooked and formulated to produce proper particle size and water uptake, for use mainly in tortilla chips, taco shells and other fried products. Some of these DMF products produce excellent tortilla chips and taco shells. The ﬂavor, color and texture may be slightly different, but are quite acceptable. Sometimes, the color is brighter than products made from traditional whole-corn DMFs. However, DMF products made from dry-milled fractions do not make acceptable table tortillas. Signiﬁcantly more research is required to overcome this hurdle.

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Figure 4.9 Methods of assessing viscosity of dry masa ﬂour products. (A) RVA curves of 6 dry masa ﬂour products showing diversity among the samples. (B) Bostwick consistometer values for the samples in “A.” Adapted from Reference [18].

The future is bright and DMFs will be extremely useful as Tex-Mex and related cuisine penetrates international markets. Improved quality control and new products will likely fuel the expansion of corn snacks and other foods. Both fresh masa and DMFs will be used. The recommended rehydration of DMFs is about 10 min in a sigma blade mixer at 15–25 rpm. Mixing rehydrates the solids without causing stickiness

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due to excessive mechanical work or shear. The amount of water required to rehydrate masa ﬂour for tortilla production is 1.0–1.2 L per kg of ﬂour. DMFs for tortilla chips require 0.9–1.0 L of water per kg of ﬂour. The rehydrated masa should be rested for 5–10 min after mixing to allow water equilibration.

6.1. ALTERNATIVE PROCESSES FOR PRODUCING DRY MASA FLOURS Alternative methods that attempt to produce nixtamalized corn masa ﬂours continuously, faster and more efﬁciently in utilizing labor, energy, and ﬂoor space have been proposed [20]. Extrusion cooking has also been proposed (see Chapter 12). Excessive starch gelatinization and extrudate pufﬁng are avoided by controlling grit size, moisture content, screw conﬁguration, speed and heat input. Generally, corn grits are mixed with 0.2–0.3% lime and water to reach a moisture content of 34%. The tempered blend is continuously fed into the extruder and exits at a moisture content of approximately 18–20%. An additional 10% moisture is reduced by continuous drying at 65◦ C, 149◦ F. The extrudate, containing 10% moisture, is hammer-milled into ﬂour, which is further classiﬁed by particle size and reblended [21,22]. These processes do not produce high-quality dry masas. The use of a drum drier to produce corn masa ﬂour was proposed by Molina et al. [23]. Whole-corn ﬂour was mixed with water and lime and simultaneously cooked and dried on a double-drum dryer with a gap of 0.007 in. and an internal pressure of 110–183 kg/m2 at 2–4 rpm. Micronization (dry heat treatment using infrared burners) of corn grits, previously tempered with dilute lime solution, has been used for making corn masa ﬂour. The tempered grits were cooked, ﬂaked, cooled and ground into ﬂour [14]. Hart [24] patented the production of masa ﬂour by micronization of ground whole corn. A similar process was developed by Villalba [25], in which corn kernels tempered in a lime solution were dry cooked with a jet-sweep impingement oven. In general, the quality of these ﬂours was inferior to that of conventional dry masa ﬂours. These processes are not used on a commercial basis to any extent.

7. PHYSICOCHEMICAL CHANGES IN ALKALINE–COOKED PRODUCTS

7.1. COOKING, STEEPING AND WASHING Water and calcium uptake occurs during cooking and steeping, and the moisture content of the grain increases from 10–12 to 48–50% (Figure 4.2) [2]. The grain absorbs water rapidly during the ﬁrst 15 min of cooking [26].

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Trejo-Gonzalez et al. [27] reported rapid initial water uptake during nixtamalization of a Mexican corn variety. Water uptake of corn cooked in calcium hydroxide solution was 15–20% higher than water uptake of corn cooked in water [28]. Steeping of cooked grains further increases moisture content by 4–7 % (Figure 4.2) [2] and distributes the water more evenly throughout the kernel [26]. Changes in composition during alkaline cooking are shown in Table 4.3 [2,8,13,16,29–33]. Moisture content increases as cooking, steeping and grinding progress, then declines partially after baking and dramatically after frying. On a dry weight basis, protein and starch levels are stable prior to frying, but decrease signiﬁcantly as moisture is replaced by oil during frying. The damaged starch, presented as enzyme-susceptible starch (ESS) values, increases as the extent of cooking increases. Ether extract remains stable until frying, then increases dramatically as expected. Dietary and crude ﬁber levels appear variable, but are documented by only a few analyses. The most evident effect of alkaline cooking on the gross structure of the kernel is loosening and removal of most of the pericarp. The pericarp separates from the kernel below or through the endocarp layer, above the aleurone, in both corn and sorghum [15]. The alkali facilitates separation of the pericarp from the kernel as the peripheral endosperm cell walls and middle lamellae are degraded or solubilized. Corn that is severely overcooked without alkali retains the pericarp [Figure 4.10(A)], while pericarps of samples cooked with alkali are removed [Figure 4.10(B)]. Physical agitation or abrasion are required for complete removal. The pericarp is the primary component of the 3–9% corn dry-matter losses found in wastewater of commercial alkaline processing plants [29]. Degradation of the cuticle and other pericarp layers occurs during the cooking and steeping processes [4]. As the pericarp breaks down, gums are formed and become a component of the continuous phase “glue” that holds the ground masa together. Nixtamalized kernels exhibit swelling and hydration of the starch granules and protein [Figures 4.11(A) and (B)]. The starch granules absorb water and swell, ﬁlling the entire area within each endosperm cell. When nixtamalized kernels are broken for microscopic examination, the starch granules are released from the cell, but remain packed in the original form of the endosperm cells. This structure is seen with both scanning electron microscopy (SEM) and ﬂuorescence microscopy, indicating that the weakened cell walls in the endosperm are the most susceptible place for breakage, even under slight pressure. The protein matrix adheres to the cell walls in a smooth, honeycomb pattern, and the protein bodies remain embedded in the matrix, even when the cell wall separates from the cell contents. The cell walls of the ﬁrst 1–2 layers of the peripheral endosperm ﬂuoresce brightly before alkaline cooking [Figure 4.12(A)]. The inner lamella between the cell walls loses ﬂuorescence ﬁrst during cooking, followed by a substantial

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Ash %

Dietary Fiber %

Crude Fiber %

12.0--14.4 12.6 4 49.1--50.5 49.7 3 51.0--54.0 52.5 2 8.0--9.7 8.6 5 38.2--47.1 42.9 8 1.2--2.1 1.7 6 0.1--0.9 0.9 3

9.6--11.1 10.2 10 10.3--11.1 10.6 4 9.1--10.8 9.7 3 8.3--10.9 9.6 2 9.5--11.2 10.5 7 7.2--7.9 7.6 5 6.3--6.6 6.4 3

65.0--84.0 74.3 5 73.2--84.3 78.8 3 72.6--79.0 75.7 4 70.5--73.9 72.3 5 75.0--89.0 82.4 6 63.3--78.8 67.1 4 63.5--64.5 54.0 2

50--240 138 4 272--420 346 2 475--624 550 2 221--365 299 5 584.596 590 2 768 768 1 ---

3.9--5.3 4.8 8 3.1--4.9 4.3 7 3.7--5.6 4.8 3 ---

1.1--1.4 1.3 4 1.5 1.5 3 1.7--1.9 1.8 3 ---

12.7--13.9 13.3 2 11.8 11.8 1 ---

1.5--1.7 1.6 2 0.8 0.8 1 ---

---

---

1.5--4.4 2.7 6 22.0--25.7 24.2 6 33.9--37.0 35.8 3

1.5--2.5 1.7 6 1.1--3.6 2.3 5 1.9--2.7 2.2 3

7.4--10.7 9.1 2 10.5--12.4 11.5 2 ---

1.1--2.4 4.8 3 0.8--1.1 0.9 4 0.8--1.0 0.9 2

a

Compiled from References [2,8,13,16,29,30,32,33]. Expressed as oven dry weight basis; analyses were performed on defatted samples. ESS = enzyme-susceptible starch. d Ether extract values determined prior to defatting. b c

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Summary of Compositions of Alkaline-Cooked Products.a,b

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Figure 4.10 Pericarp removal in alkaline cooked corn. (A) corn cooked without alkali and stained; pericarp is stained dark blue and remains on the kernel. (B) corn cooked with alkali; pericarp has been removed and the aleurone layer is exposed. P: pericarp; A: aleurone.

loss of ﬂuorescence in the endosperm cell walls. The same mechanism, causing the breakdown of the cell wall tissues that attach the pericarp to the kernel, is responsible for loss of ﬂuorescence in the peripheral endospem cell walls. The lime helps solubilize the hemicellulose in the cell walls, resulting in a decrease in ﬂuorescence. Fluorescence of proteins in the endosperm does not decrease during processing. However, small areas of protein in the peripheral endosperm, and occasionally in the corneous (hard) endosperm, appear to have only a continuous protein matrix and no protein bodies. This is caused by hydration and swelling of protein bodies to the point that the edges disappear. Since alkaline processing

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Figure 4.11 Environmental SEM views of products through the alkaline cooking process. (A) raw corn. (B) nixtamal. (C) masa, showing formation of the continuous phase, “glue” network. (D) interior of a tortilla. (E) surface of a tortilla. (F) cross-section of a fried tortilla chip with oil present in air tunnels. CW: cell wall, S: starch granule, G: glue, V: vent hole, O: oil, A: air tunnel.

dramatically changes the physical appearance of the protein bodies in some areas of the kernel, chemical changes also might be occurring. Prolamines, found primarily in the protein bodies, decreased during alkaline processing [34], but much of the germ tissue is retained during nixtamalization, which positively affects the protein quality of these products [4]. Raw corn displays intense ﬂuorescence around the edge of the starch granules, which decreases after alkaline cooking. The presence of alkali in the processing water reduces the ﬂuorescence of the external surface of the starch granule. Gelatinized starch granules have a doughnut shape when viewed while still hydrated by environmental scanning electron microscopy (ESEM) [Figures 4.13(A) and (B)]. Raw starch is round or angular depending on the area where it originates within the kernel, but after gelatinization the swollen granules have depressed or collapsed centers. These same granules, when viewed with traditional SEM, appear little different from raw starch samples. Corresponding

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Figure 4.12 Fluorescence of cell walls in alkaline-cooked products stained with calcoﬂuor. (A) raw corn. (B) tortilla. Al: aleurone, CW: cell wall, P: protein bodies.

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Figure 4.13 Gelatinization and birefringence in raw corn and tortillas. (A) raw corn, showing intact ungelatinized starch granules. (B) gelatinized, doughnut-shaped starch granules in a baked tortilla. (C) raw cornstarch granules showing strong birefringence. (D) cornstarch granules corresponding to those in “B” showing the extent of gelatinization.

samples, when viewed under polarized light, show that nixtamalized starch granules exhibit birefringence, but the “Maltese crosses” are wider and more diffused than those in the raw grain. The absence of birefringence in the center corresponds to granules that have depressed centers in the ESEM photos [Figures 4.13(C) and (D)]. The decrease in relative crystallinity determined by X-ray diffraction is signiﬁcantly correlated with enzyme-susceptible starch values (r = 0.92 and 0.99; P > 0.01) (Table 4.4) [30]. Starch crystallinity decreases 15–25% during the cooking phase. Only limited starch gelatinization takes place during nixtamalization due to the hydrothermal treatment and also some stabilization of starch granules due to calcium ions [35].

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TABLE 4.4.

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Relative Crystallinity (RC) and Enzyme Susceptible Starch (ESS) Values of Corn and Sorghum Products.a

Grain

Treatment

Relative Crystallinity (%)

Enzyme-Susceptible Starchb (mg glucose/g starch)

Corn

Raw Nixtamal Masa Tortilla Raw Nixtamal Masa Tortilla

100.0 86.3 87.2 42.3 100.0 75.1 62.5 43.5

240 420 475 584 252 393 458 614

Sorghum

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Values are means of 2 replicates. The least significant difference ( p = 0.05) value for RC was 4.0. Values from Reference [30] are means of 3 replicates on dry weight basis. The least significant difference ( p = 0.05) value for ESS was 32.0.

Dry matter is lost from corn as water and calcium are taken up (Figure 4.2) [2]. The losses depend on the processing conditions and the type and soundness of the corn. The liquor from a typical cooking-steeping process consists of 2.8% solids, of which 60% is soluble and 29% is ash, mostly lime [27]. In commercially processed corn, the total dry-matter losses are distributed between cooking-steeping (2.8–10.7%) and washing (1.6–2.0%) [29]. Total dry-matter losses of 8.4% are reported in corn steam-cooked for 60 min, quenched to 68◦ C (155◦ F), and steeped for 8 hr; 70% of the losses occur during lime cooking; the rest during steeping [36]. Solids losses are more related to cooking temperature and lime concentration than to cooking and steeping times per se [37]. Corn with a high percentage of damaged kernels is very susceptible to overcooking, and can result in increased solids and nutrient losses [38]. The structure of the native starch granule is partially disrupted during cooking, resulting in a less organized X-ray pattern [39]. Steeping, however, changes the pattern to resemble that of native starch. Alterations in starch crystallinity caused by cooking are partially restored by recrystallization or annealing during steeping. The reassociation of starch molecules affects the rheological properties of masa. The amylose:amylopectin ratio, determined by spectroscopic analysis, decreases from 0.72 (after 20 min cooking) to 0.50 (after 20 min cooking and 5 hr steeping). Both amylose and amylopectin are less water extractable after 5 hr steeping; however, amylose is the controlling factor. The annealing process at 50◦ C, (122◦ F) permits the realignment of starch chains in the amorphous phase and additional crystallization of starch molecules [40]. This affects the texture of the masa and ultimately fried chip texture and oil content. Nixtamalization has a positive effect on the availability of niacin in the diet. In the corn kernel, the greatest concentration of bound and free niacin is in the aleurone layer and the embryo/scutellum, respectively. Alkaline cooking

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releases part of the bound niacin and increases the amount available in the diet. Raw corn contains 26 ␮g of niacin per gram but only 0.4 ␮g as free nicotinic acid, whereas tortillas contain 11.7 ␮g of free nicotinic acid per gram, even though niacin is lost during cooking and washing [41].

7.2. CHANGES DURING GRINDING When nixtamal is ground into masa, the kernel is physically torn apart by the mechanical cutting and shearing action of the grinding stones. Water is added to the masa to reduce heat generation from the grinding operation and to obtain optimum texture in the masa. The starch granules and protein components are hydrated slightly by the water added during grinding. Grinding also causes the starch granules to be subjected to additional heat from friction, resulting in additional starch gelatinization. The degradation and/or weakening of the cell walls caused by alkaline cooking and steeping facilitate grinding, and result in the particle size distribution of the masa. Masa is composed of several coarse fractions (pericarp, germ and peripheral endosperm pieces), intermediate-sized pieces of corneous endosperm and the ﬁne fractions, which include free starch granules. Grinding raw or undercooked corn, in the absence of alkali, or with shortened heating/steeping times, does not produce sufﬁcient disruption of the kernel structure necessary for acceptable masa texture. Masa contains 52–54% moisture, 12–25% small endosperm and germ pieces, 19–31% free starch granules and cell wall fragments, and 3–4% dispersed solids and free lipids [8]. The masa is held together in a cohesive, nonsticky state by the glue-like mixture of dispersed solids in water (3–4% of total wet masa), which consists of gelatinized starch, hydrated protein, lipids and ions [Figure 4.11(C)]. When an acceptable masa is fractionated [8], and the fractions are recombined without the aqueous soluble and dispersed solids or the free lipid fractions, the resulting masa has unacceptable texture and reduced waterholding capacity. The reconstituted masa is moist but non-cohesive [16]. Water added during grinding also aids in the distribution, solubilization and adhesion of starch granules, protein, cell walls and lipids to each other. Cohesiveness of masa is due to amylose and amylopectin that leach from the physically disrupted gelatinized starch granules. The masa particles examined with ﬂuorescence microscopy consist of small endosperm pieces with 3–6 intact cells, strips of aleurone with 1–2 layers of peripheral endosperm attached, and small sections of germ. There is no reduction in the ﬂuorescence of the structural components of the masa due to grinding. Approximately 4–7% of the starch granules lose birefringence during alkaline cooking, steeping and milling operations [8]. X-ray diffraction patterns reveal a 1–10% loss of crystallinity during nixtamal grinding (Table 4.4). Many of the starch granules appear irregular in shape, compared to raw and nixtamalized samples, and often only part of the granule (<60–70%) exhibits birefringence.

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The insoluble solids in masa consist of large, intermediate and small particles. The large particles (more than 850 microns in diameter) are pieces of remnant pericarp, peripheral endosperm, tip cap and germ. Intermediate and ﬁne particles are mostly corneous (hard) endosperm and germ pieces. Chemically, the large particles contain most of the protein-rich parts of the kernel (germ, aleurone and peripheral endosperm); the ﬁner particles are almost pure starch. The fat content of the insoluble solids gradually decreases as the particle size decreases, depending on the distribution of germ tissue after grinding. The mineral components’ “ash,” including the absorbed calcium, are uniformly distributed in the masa fractions after grinding.

7.3. BAKING When the masa is baked into a tortilla, the changes in microstructure are due primarily to intense heat (>240◦ C, 464◦ F). The thin tortilla is exposed to heat on both sides, and the starch is further gelatinized in the interior. However, due to limited water availability and short residence time, the starch is not completely gelatinized on the surface of the tortilla (Figures 4.11(D) and (E). The center of the tortilla remains relatively moist, and more water is available for gelatinization than on the surface. As a result, the starch granules on the surface of the tortilla display more birefringence than those in the interior [39]. Starch granules on the surface are rounder and less distorted than those in the center of the tortilla. Up to 15% of birefringence in the free starch fraction is lost and the polarization crosses are thick, indicating that 50% or more of the crystalline areas of the granule are damaged. The loss of crystallinity is in agreement with enzyme-susceptible starch values for nixtamalized products [30]. Approximately 35–40% of the total starch crystallinity is lost during the baking process. As the tortilla bakes in the oven, water from the interior is released in the form of steam that vents through the surface, resulting in the formation of large- and small-diameter holes, with a network of tunnels and cavities in the interior. Large gaps form around endosperm and cell wall pieces in the center of the tortilla. The larger masa particles disrupt the continuity of the gelatinized starch phase. Their presence is necessary to reduce pillowing and to impart a friable texture to the chips after frying. Cell walls in the peripheral endosperm completely lose ﬂuorescence after baking (Figure 4.12(B)]. The hard (ﬂinty) endosperm cell walls retain some ﬂuorescence, but it is less intense than in the masa. The edge of the starch granules still ﬂuoresce, although the intensity is much lower, and the granules are distorted in appearance. The calcium ions react at the surface of the starch granules, causing them to swell and inhibit the supply of water to the interior portions of the granule; with limited water availabilty, gelatinization is delayed. Calcium hydroxide is adsorbed or attached to the starch granules during cooking and steeping [27].

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The protein is further modiﬁed by heat during baking and becomes a component of the amorphous sheets of material surrounding the starch granules. Very few protein bodies are visible on the outer edges of tortillas. Some are obscured by the continuous phase, and some of the protein becomes part of the continuous phase. The effect of heat on tortilla edges is severe enough to disrupt the spherical structures of protein bodies. Heat effects are not as severe in the center of the tortilla, and intact protein bodies are visible. Small chunks of endosperm cells are visible in the corn tortilla and, even at the ﬁnal product stage, the processing conditions are not severe enough to completely disrupt endosperm cells.

7.4. FRYING Frying essentially volatilizes the water in the masa and replaces it with oil. When the tortilla chip is immersed in hot oil, the moisture content drops from 34% to 10–11% after 15 sec frying, whereas the oil content rises from 2% to 21% (Figure 4.14) [11]. Moisture leaves the chip as steam, and creates tunnels and air pockets that give the tortilla an extensive sponge-like network of small, uniform air tunnels [Figures 4.11(F) and 4.15(A)]. As the air tunnels in the interior expand and steam leaves the chip, some oil enters the interior [Figure 4.15(B)]. The oil content reaches 21% within 15 sec, then gradually increases to 23% in tortilla chips fried for 1 min. On the surface of the chip, any moisture remaining is instantly evaporated, the starch granules retain their birefringence and shape, and vent holes where steam left the chip become visible [Figure 4.15(C)]. The surface is also covered with oil [Figure 4.15(D)]. Tortilla chips initially absorb the frying oil at a rapid rate. Chips viewed after 15 sec of frying contain oil in the outermost areas of the chip closest to the surface [Figure 4.15(B)]. After 1 min of frying, the tunnel network is more

Figure 4.14 Relationship between oil and moisture content in tortilla chips during frying. Unpublished data from Reference [11].

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Figure 4.15 Fried tortilla chips viewed with SEM and environmental SEM. (A) SEM view of the cross-section of a tortilla chip fried for 15 sec, showing tunnel network that develops during frying. (B) cross-section of a tortilla chip viewed with ESEM, showing oil on the surface and entering the tunnel network after frying. (C) SEM view of surface of tortilla chip fried for 1 min, showing intact starch granules and vent holes where steam escaped during frying, (oil was extracted). (D) similar view as “C” with oil on the surface of the chip, viewed with ESEM. T: air tunnel, O: oil, V: vent hole, S: starch granules.

extensive and vents in the surface of the chip allow oil to enter the interior [42]. In ESEM comparisons of chips fried for 15 sec vs. those fried for 1 min, the chips had equilibrated, and some of the surface oil had entered the chips by capillary action during cooling. Some of the frying oil is bound to the starch in tortilla chips during frying, especially to the amylose fraction [39]. The texture of a tortilla chip becomes harder and more uniform as starch is gelatinized and water is released. Starch chains, protein and lipids begin to interact to form a continuous phase that ﬁrms as moisture content decreases. When the chip structure sets due to fast dehydration during frying and amylose/lipid interactions, the molecular dispersion of starch in water at l00◦ C is reduced [39]. The starch reorients itself into a retrograded structure during deep fat frying [11]. Starch granules inside some of the larger particles are fully gelatinized, but retain their individual shape. Starch damage increases from 81% to 87% of the total starch available. The extent of birefringence indicates that the ungelatinized starch remains only on the surface of the chip. After 1 min frying time, water that is bound to gelatinized starch evaporates, and the moisture content is extremely low at this point (∼1.0–1.5%). The oil

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content is stable at 23%. Starch damage levels off at ∼95% of the total starch. The surface remains coated with oil as before. Eddies and currents in the oil within the chip are visible when activated by the electron beam and ﬂow through the tunnel networks can be documented. As the chip is further dehydrated, the continuous phase of starch becomes ﬁrmer. The texture/friability of the chip depends in part upon the particle size of the masa, the size of air tunnels/pores in the chip and the strength of the continuous phase after it becomes ﬁrm. When chips are overfried, the steam vent holes present in the surface become larger in diameter, and the chip can become more fully saturated with oil after cooling. The interior tunnels also are larger and more irregular after extensive frying. The level of starch damage in the chip is unchanged; the limitation of water inside the tortilla chips during the extended frying time (from 1 min to 2 min) does not allow for further starch damage. The chip has a tough, hard texture and, when broken, snaps cleanly and smoothly. Corn chips have a higher moisture content before frying and absorb more oil during frying than tortilla chips, but the relationship between oil and moisture demonstrated in Figure 4.14 holds true for corn chips as well. Fried corn chips contain up to 37% oil. The interior structure of a corn chip is similar to that of tortilla chips in that a tunnel system and pores develop within the starchy continuous phase. However, the tunnel system is less interconnected and the pores that ﬁll with oil during and after frying are much larger than those found in tortilla chips. Instead, the oil is found pooled inside the large pores and tunnels after cooling. The texture of corn chips depends on development of the pore network, the friability of the starchy continuous phase and the amount of oil absorbed during frying.

7.5. CALCIUM The concentration of calcium is high in the pericarp of nixtamalized kernels [43], indicating that a relationship exists between calcium content and cell wall degradation. Calcium ions are carried into corn by water through the tip cap, germ and pericarp. Calcium absorption follows a trend similar to that of water absorption (Figure 4.2) but is much slower [27,39]. Most of the calcium is retained in the germ and pericarp of the nixtamalized grain (Figure 4.2). Calcium binds to the starch granules when they come into contact; approximately 2.9 times more calcium is found in starch isolated from lime-cooked kernels than that isolated from untreated grains [27]. The protein bodies and proteinaceous material in the germ absorb the calcium more readily throughout cooking and steeping. Calcium also appears in the aleurone occasionally, but is not generally observed in the starchy endosperm [43]. Phytin bodies are found in the form of inclusions within protein bodies in the aleurone and germ of raw corn. Calcium complexes with phytin during nixtamalization. The phytin in nixtamal cooked without alkali loses 60% of its ﬂuorescence after 20 min of cooking and 100% after 70 min. However, 20 min

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cooking in alkali results in a total loss of ﬂuorescence of the phytin, indicating that the calcium becomes bound to the phytin molecule [43].

7.6. PROTEINS Lime cooking alters the solubility patterns of maize proteins. Lime cooking and tortilla baking decrease the salt water-soluble proteins (albumins and globulins) and alcohol-soluble proteins (prolamins) and increase the amount of unextractable proteins [44,45]. Lime cooking alters the molecular weight distribution of the different protein fractions, as seen in electrophoretic patterns where the loss of several protein bands and the lighter intensity of other bands are observed. Frying tortillas into chips further decreases the solubility of albumins, globulins, prolamins and glutelins. The electrophoretic bands from fractions extracted from tortilla chips are considerably less intense than those from raw grain. The sequential heat treatments applied during processing cause hydrophobic interactions, protein denaturation, and cross-linking of proteins. These chemical changes are responsible for the lower protein solubility and the higher amounts of insoluble protein recovered in the residue.

7.7. LIPIDS Little information is available about the role of lipids during nixtamalization. One to two percent of the masa dry weight is comprised of free lipids distributed throughout the continuous phase of the masa [46]. This lipid fraction is mainly composed of partially emulsiﬁed lipids located in the aqueous phase of the masa and free lipids that interact with both peptides and carbohydrates, altering the masa properties. In raw corn and sorghum, the lipids in the germ and aleurone ﬂuoresce yellow. The ﬂuorescence increases in intensity when grain is cooked without alkali, but disappears after the addition of alkali [43]. The heat from cooking may release or expand the lipid bodies, freeing more material to ﬂuoresce. Further research is needed to evaluate the relationship between lipids, masa machinability and texture, and the texture, ﬂavor and staling rate of tortillas.

8. QUALITY OF ALKALINE-COOKED PRODUCTS

8.1. FRESH MASA The quality of masa products depends on the soundness and characteristics of ingredients and the manufacturing practices. A useful quality control guide for the production of nixtamalized foods is included in the Corn Quality Assurance

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Manual edited by the Snack Food Association [47]. Some suggested processing parameters and quality control guidelines for tortilla chips and corn chips are presented in Tables 4.5 and 4.6. Variations of this information are used in industry. In practice, each plant develops its own speciﬁc procedures and parameters to produce a particular product. The major parameters controlled during tortilla production are: (1) the temperature and relative humidity of corn silos and storage rooms for ingredients and products, (2) the cooking, steeping, baking, and frying times and temperatures, (3) the types of grinding stones and their adjustment during milling, (4) the moisture content of the corn, nixtamal masa, tortillas and related products, and (5) operating conditions of the equipment, such as the cooking and holding tanks, sheeters, cutters, oven bands, conveyor belts, tumblers, and so on. The most important factor to control during alkaline cooking is the degree of cooking. Most processors subjectively evaluate the degree of cooking by observing the condition of the cooked-steeped nixtamal. A strong correlation exists between the degree of cooking and water uptake in corn tortillas [26]; the best way to control this parameter is to monitor the amount of moisture absorbed by the nixtamal. Plasticity, cohesiveness and stickiness are some of the subjective rheological properties of masa used to judge optimum cooking conditions [47]. Analytical approaches that have been used include tests for enzyme-susceptible starch [48], loss of birefringence [46], amylograph peak viscosity and Instron shear force [49]. Moisture can be rapidly estimated for quality control purposes with infrared devices [19] or a microwave oven [50]. The stickiness of masa, which affects machinability, can be rapidly evaluated with a mechanical device [19]. However, most tests are not practical for routine monitoring. Subjective hand “feeling” of masa, based on experience, is often still the most effective method. Two important considerations in stone grinding are the degree of grinding (masa particle size) and the amount of water applied per unit of time. The degree of grinding or particle distribution of the masa can be determined by the masa fractionation scheme ﬁrst proposed by Pﬂugfelder et al. [8] and modiﬁed by Gomez et al. [39]. Frequent monitoring of products is required to adjust settings for the greatest product uniformity. Oven residence time and temperatures in the drying tiers should be constantly monitored, because the ﬁnal moisture content of baked chips and the oil content are greatly inﬂuenced by baking.

8.2. FRIED PRODUCTS Near-infrared instruments can be used to continuously monitor oil, moisture and color of fried chips. Color, crispness, texture of corn and tortilla chips, and the amount of oil absorbed are inﬂuenced by masa moisture content, thickness

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Tort Chip >200◦ F

(93◦ C)

Corn Chip >200◦ F

(93◦ C)

Tort Chip

Corn Chip

4--10 min Quickly 8--24 hr 2--10 min Add water --<5 min

15--45 min Quickly 8--24 hr 2--10 min No water Promptly ---

<150◦ F (65◦ C) 115--140◦ F (46--60◦ C) 50--70◦ F (10--21◦ C) <100◦ F (37.7◦ C) --Room temp

<150◦ F (65◦ C) 115--140◦ F (46--60◦ C) 50--70◦ F (10--21◦ C) <100◦ F (37.7◦ C) Room temp ---

>29% >29% >45% >45% 52--54% --52--54%

42--44% 42--44% 50--52% 50--52% 50--52% 50--52% ---

12--18 sec 2--30 min

-----

750--900◦ F (399--482◦ C) <90◦ F (32◦ C)

-----

+40% +38%

-----

2 min

1.5 min

355◦ F (179◦ C)

410◦ F (210◦ C)

1--1.2%

1.0--1.5%

Adapted from Reference [47].

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Corn Chip

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Corn cook Cooling Corn soak Wash/drain Corn milling Extrusion Masa sheeting and forming Bake oven Cooling and equilibration Frying time

Tort Chip

Moisture (%)

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Steps

Temperature

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Time

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Summary of Typical Corn and Tortilla Chip Processes.

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TABLE 4.5.

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TABLE 4.6.

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Suggested Quality Control Guidelines for Corn and Tortilla Chips.

Test Masa Moisture Tortilla chip Corn chip Oil Content Tortilla chip Corn chip Salt Content Tortilla chip Corn chip Chip Moisture Tortilla chip Corn chip Defects Tortilla chip

Corn chip

Free Fatty Acids, Oil Tortilla chip Corn chip

Target

Control Limit(s)

Shutdown if:

51% same

48--54% same

<48% same

22.5% or more 37%

>26% 34--40%

<20% <34%

1.0% 1.5%

0.8--1.3% 1.2--1.8%

<0.7% <1.0%

1.0--1.2% same

<1.4% same

>1.5% same

7% or less with 5% or less puffed chips 0% pillowing, ragged edges, burnt

15% or less with 6% or less puffed chips 10% total defects, 1% burnt

more than 15% total or more than 6% puffed >15% defects

<0.40% same

<0.55% same

>0.56% same

Adapted from Reference [47].

of the chips, frying temperature and residence time. A hydraulic press can be used to estimate oil content [47]. Chips are placed in the press and the oil pressed out is related to a calibration chart standardized for a given product. The factors that affect oil degradation are oil temperature (during operational and slack periods), type of oil, frequency of ﬁltration and frying practices, which greatly affect the shelf life of both the oil and the ﬁnished product. The free fatty acid (FFA) content, peroxide value, polymer development, change in viscosity and heat transfer capacity of the oil, smoke point, and Oil Stability Index (OSI), or the Active Oxygen Method (AOM), determine the condition and stability of oil and fried products [47]. Tests for these should be incorporated in a quality control program. The FFA content is the factor most commonly evaluated in quality control of frying oils. Fresh frying oils contain <0.05% FFAs; the FFA content rises to a maximum accepted level of 0.4–0.5% for corn and tortilla chip manufacturing (Table 4.5). Rapid methods for evaluating oil quality have been developed and are currently used by some processors. These include test strips for FFAs and methods to determine peroxide values (resulting from fat oxidation) and development of

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polar compounds. The amount of salt and seasoning applied to fried products can be analyzed by procedures suggested by the Snack Food Association [47].

8.3. DRY MASA FLOURS Particle-size distribution, water absorption, color and pH are critically important parameters of dry masa quality [12]. Processors can determine the particle size distribution by sieving [49], water absorption index (WAI) [49,51] and pH of the dry ﬂour prior to purchasing. Water uptake and dough consistency can be determined subjectively. Methods to measure the consistency of a masa water slurry can be related to quality attributes of DMF for certain purposes [18]. The Rapid Visco-AnalyzerTM can be used to evaluate starch properties of DMF.

9. SHELF LIFE OF CORN PRODUCTS Fried products have long shelf lives because of their low moisture content (1–2%). However, oil oxidation (formation of aldehydes) or rancidity (formation of free fatty acids) limits shelf life. The main factors affecting autoxidation are: (1) the degree of unsaturation and the condition of the frying oil; (2) product storage conditions; (3) packaging materials characteristics such as light transmission rate and moisture and oxygen permeabilities; and (4) use of inert gases. Antioxidants and chelating agents effectively prolong the shelf life of fried products, but are generally avoided because of consumer preference for “natural foods.” Moisture absorption causes tough, chewy, undesirable chips. Moisture is rapidly absorbed by chips unless they are properly packaged and stored. Corn snack consumption will continue to increase around the world because they are relatively convenient to produce and market compared to alternatives. Nixtamalization in some modiﬁed form will be used to produce numerous products with varying tastes, textures and uses. Hybridized nixtamalization procedures will be and, indeed, are already in use combining new techniques with traditional methods. The use of whole ground corn treated with moisture and chemicals using microwaves and other technologies will be accepted as high-quality masa for snacks.

10. ACKNOWLEDGMENTS Partial ﬁnancial support from The Snack Foods Association, industrial companies, and the Texas Agricultural Experiment Station has provided long-term support for numerous graduate students and staff. The graduate students have

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made major contributions to our understanding of nixtamalization and snack food processing and we are indebted to them.

11. REFERENCES 1. Rooney, L. W. and S. O. Serna-Saldivar, 1987. Food uses of whole corn and dry-milled fractions. In Corn: Chemistry and Technology. S. A. Watson and P. E. Ramstad, eds. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 399–429. 2. Serna-Saldivar, S. O., M. H. Gomez, and L.W. Rooney, 1990. The technology, chemistry and nutritional value of alkaline cooked corn products. In Advances of Cereal Science and Technology, Vol. 10. Y. Pomeranz, ed. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 243–307. 3. Bressani, R., 1990. Chemistry, technology, and nutritive value of maize tortillas. Food Rev. Int., 62:225–263. 4. Paredes-Lopez, O. and M. E. Saharopulos-Paredes, 1983. Maize: A review of tortilla production technology. Bakers Digest, 57(September):16–21. 5. Krause, V. M., 1988. Rural-Urban Variation in Limed Maize Consumption and the Mineral Content of Tortilla in Guatemala. Unpublished report, Center for Studies of Sensory Impairment, Aging and Metabolism, Guatemala City, Guatemala. 6. Kuhnlein, H. V., D. H. Calloway, and B. F. Harland, 1979. Composition of traditional Hopi foods. J. Am. Diet. Assoc., 75:37–42. 7. Hardeman, N. P. 1981. Shucks, Schocks and Hominy Blocks. Louisiana State University Press, Baton Rouge, Louisiana. 8. Pﬂugfelder, R. L., L. W. Rooney, and R. D. Waniska, 1988. Fractionation and composition of commercial corn masa. Cereal Chem., 65:262–266. 9. Moreira, R. G., E. M. Castell-Perez, and M. A. Barrufet, 1999. Deep-Fat Frying Fundamentals and Applications. Aspen Publishers, Gaithersburg, Maryland. 10. Quintero-Fuentes, X., H. D. Almeida-Dominguez, C. M. McDonough, and L. W. Rooney, 1999. Ingredient functionality in baked tortilla and corn chips. Cereal Chem., 76(5):705–710. 11. Lee, J. K., 1991. The Effects of Processing Conditions and Maize Varieties on Physicochemical Characteristics of Tortilla Chips. Ph.D. dissertation. Texas A&M University, College Station, Texas. 12. Almeida-Dominguez, H. D., M. Cepeda, and L. W. Rooney, 1996. Properties of commercial nixtamalized corn ﬂours. Cereal Foods World, 41:624–630. 13. Gomez, M. H., 1986. Physicochemical Characteristics of Fresh Masa from Alkaline Processed Corn and Sorghum and of Corn Dry Masa Flour. Ph.D. dissertation. Texas A&M University, College Station, Texas. 14. Johnson, B. A., L. W. Rooney, and M. N. Khan, 1980. Tortilla making characteristics of micronized sorghum and corn ﬂours. J. Food Sci., 45:671–675. 15. Gomez, M. H., C. M. McDonough, L. W. Rooney, and R. D. Waniska, 1989. Changes in corn and sorghum during nixtamalization and tortilla baking. J. Food Sci., 54(2):330–336. 16. Gomez, M. H., L. W. Rooney, R. D. Waniska, and R. L. Pﬂugfelder, 1987. Dry corn masa ﬂours for tortilla and snack food production. Cereal Foods World, 32:372–377. 17. Suhendro, E. L., H. Almeida-Dominguez, L. W. Rooney, and R. D. Waniska, 1998. Objective rollability method for corn tortilla texture measurement. Cereal Chem., 75(3):320–324.

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18. Lobeira, R., H. D. Almeida-Dominguez, and L. W. Rooney, 1998. Methods to evaluate hydration and mixing properties of nixtamalized corn ﬂours. Cereal Chem., 75(4):417–420. 19. Ramirez-Wong, B., V. E. Sweat, P. I. Torres, and L. W. Rooney, 1993. Development of two instrumental methods for corn masa texture evaluation. Cereal Chem., 70(3):286–290. 20. Gomez-Aldapa, C., F. Martinez-Bustos, J. D. C. Figueroa, and F. C. A. Ordorica, 1999. A comparison of the quality of whole corn tortillas made from instant corn ﬂours by traditional or extrusion processing. Int. J. Food Sci. Technol., 34(4):391–399. 21. Almeida-Dominguez, H. D., 1984. Development of Maize-Soy Sesame and Sorghum Soy Tortilla Flour Using Extrusion and Nixtamalization. Master’s thesis. Texas A&M University, College Station, Texas. 22. Bazua, C. D., R. Guerra, and H. Sterner, 1979. Extruded corn ﬂour as an alternative to time heated corn ﬂour for tortilla preparation. J. Food Sci., 44:940–941. 23. Molina, M. R., M. Latona, and R. Bressani, 1977. Drum drying for the improved production of instant tortilla ﬂour. J. Food Sci., 42:1432–1436. 24. Hart, E. R., 1985. Cereal Processing. U.S. Patent 4,555,409. 25. Villalba, A., 1989. Development of a Dry Cook Process for Corn and Dry Masa Flour. Ph.D. dissertation. Texas A&M University, College Station, Texas. 26. Serna-Saldivar, S. O., A. Tellez-Giron, and L. W. Rooney, 1988. Production of tortilla chips from sorghum and maize. J. Cereal Sci., 8:275–284. 27. Trejo-Gonzalez, A., A. Feria-Morales, and C. Wild-Altamirano, 1982. The role of lime in the alkaline treatment of corn for tortilla preparation. In Modiﬁcation of Proteins: Food, Nutritional and Pharmacological Aspects. Adv. Chem. Ser. No. 198. R. E. Feeney and J. R. Whitaker, eds. American Chemical Society, Washington, D.C. 28. Slade, L. and H. Levine, 1991. Beyond water activity: Recent advances based on an alternative approach to the assessment of food quality and safety. CRC Crit. Rev. Food Sci. Nutr., 30:2, 3, 115–359. 29. Pﬂugfelder, R. L., L. W. Rooney, and R. D. Waniska, 1988. Dry matter losses in commercial corn masa production. Cereal Chem., 65:127–132. 30. Bedolla, S., M. Gonzalez de Palacios, L. W. Rooney, and M. N. Khan, 1983. Cooking characteristics of sorghum and corn for tortilla preparation by several cooking methods. Cereal Chem., 60:263–268. 31. Sproule, A. M., S. O. Saldivar, A. J. Bockholt, L. W. Rooney, and D. A. Knabe, 1988. Nutritional evaluation of tortillas and tortilla chips from quality protein maize. Cereal Foods World, 33(2):233–236. 32. Serna-Saldivar, S. O., D. A. Knabe, L. W. Rooney, and T. D. Tanksley, 1987. Effects of lime cooking on energy and protein digestibilities of maize and sorghum. Cereal Chem., 64(4): 247–252. 33. Rooney, L.W., H. D. Almeida-Dominguez, E. L. Suhendro, and A. J. Bockholt, 1995. Critical factors affecting the food quality of corn. Proceedings, 49th Annual Corn and Sorghum Research Conference of the American Seed Trade Association, Dec. 7–8, 1994, Chicago, Illinois, pp. 80–96. 34. Vivas, N. E., R. D. Waniska, and L. W. Rooney, 1987. Effect of tortilla production on proteins in sorghum and maize. Cereal Chem., 64:384–389. 35. Robles, R. R., E. D. Murray, and O. Paredes-Lopez, 1988. Physicochemical changes of maize starch during the lime-cooking treatment for tortilla making. Int. J. Food Sci. Technol., 23: 91–98. 36. Serna-Saldivar, S. O., S. J. Richmond, M. H. Gomez, A. J. Bockholt, and L. W. Rooney, 1988. Methods to evaluate the alkaline cooking properties and pericarp removal of sorghum and maize. Cereal Foods World, 33:673–676.

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37. Sahai, D., J. P. Mua, M. O. Buendia, M. Rowe, and D. S. Jackson, 2000. Dry matter loss during nixtamalization of a white corn hybrid: Impact of processing parameters. Cereal Chem., 77(2):254–258. 38. Almeida-Dominguez, H. D., G. G. Ordonez-Duran, and N. G. Almeida, 1998. Inﬂuence of kernel damage on corn nutrient composition, dry matter losses and processability during alkaline cooking. Cereal Chem., 75(1):124–128. 39. Gomez, M. H., J. K. Lee, C. M. McDonough, R. D. Waniska, and L. W. Rooney, 1992. Corn starch changes during tortilla and tortilla chip processing. Cereal Chem., 69(3):275–279. 40. French, D., 1984. Organization of starch granules. In Starch: Chemistry and Technology. L. H. Whistler, J. N. BeMiller, and E. F. Paschall, eds. Academic Press, New York, pp. 198– 247. 41. Wall, J. W. and K. J. Carpenter, 1988. Variation in availability of niacin in grain products. Food Technol., 42(10):198–204. 42. McDonough, C. M., M. H. Gomez, J. K. Lee, R. D. Waniska, and L. W. Rooney, 1993. Environmental scanning electron microscopy evaluation of tortilla chip microstructure during deep-fat frying. J. Food Sci., 58(1):199–203. 43. McDonough, C. M., A. Tellez-Giron, M. H. Gomez, and L. W. Rooney, 1987. Effect of cooking time and alkali content on the structure of corn and sorghum nixtamal (Abstr.). Cereal Foods World, 32(9):660. 44. Ortega, E. I., E. Villegas, & S. K. Vasal, 1986. A comparative study of protein changes in normal and quality protein maize during tortilla making. Cereal Chem., 63:446–451. 45. Vivas-Rodriquez, N. E., S. O. Serna-Saldivar, R. D. Waniska, and L. W. Rooney, 1990. Effect of tortilla chip preparation on the protein fractions of quality protein maize, regular maize and sorghum. J. Cereal Sci., 12:289–296. 46. Pﬂugfelder, R. L., 1986. Dry Matter Distribution in Commercial Alkaline Cooking Processes for Production of Tortillas and Snack Foods. Ph.D. dissertation, Texas A&M University, College Station, Texas. 47. SFA, 1992. Corn Quality Assurance Manual. The Snack Food Association, Alexandria, Virginia. 48. Khan, M. N., L. W. Rooney, D. T. Rosenow, and F. R. Miller, 1980. Sorghum with improved tortilla making characteristics. J. Food Sci., 45:770–775. 49. Bedolla, S. and L.W. Rooney, 1984. Characteristics of U.S. and Mexican instant maize ﬂours for tortilla and snack preparation. Cereal Foods World, 29:732–735. 50. Jackson, D. S. and L. W. Rooney, 1987. Rapid determination of moisture in masa with a domestic microwave oven. Cereal Chem., 64:196–198. 51. Anderson, R. A., H. F. Conway, V. F. Pfeifer, and E. I. Grifﬁn, Jr., 1969. Roll and extrusioncooking of grain sorghum grits. Cereal Sci. Today, 14:372–375, 381.

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CHAPTER 5

Starches for Snack Foods

DAVID P. HUANG LLOYD W. ROONEY

1. INTRODUCTION

S

is abundant in nature, surpassed only by cellulose as a naturally occurring organic compound. It accounts for approximately 70–80% of edible weight of the major cereal grains on a dry-matter basis, 64% of dry ﬁeld beans and peas and 78% of potato. Starch is located in the endosperm of cereals, cotyledons of some legumes and the storage cells of many root and tuber crops. It is the adhesive that holds non-gluten-based snack foods together. Starch exists inside the storage cells surrounded by protein or other components. Procedures to extract and produce starches from the major crops differ depending upon the type of starch. Cornstarch is usually isolated by a wet-milling process in which the whole kernels are steeped in dilute sulfurous acid followed by milling and separation of the starch granules from the gluten, ﬁber and germ fractions. Rice starch is isolated after steeping in dilute alkali, and wheat starch is obtained by washing it out from a ﬂour-water dough. It is important to remember that isolated starch behaves differently from that enclosed in the structure of its plant’s storage system. The Corn Reﬁners Association estimates that total world production of starch in 1997 was approximately 42.1 million short tons (2,000 lb, 907.44 kg). Corn dominates the production of starch (80%), followed by wheat (8%), potato (7%), tapioca/cassava/manioc (4%) and other crops (1%). The United States produced about 57% of the world’s starch, followed by the European Union at 17%, Japan at 7%, and the rest of the globe accounting for 18%. Approximately 82% of the cornstarch produced in the United States was converted to corn sweeteners. Various books and chapters on starch chemistry, production, modiﬁcation and TARCH

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use are available [1–5]. The Corn Reﬁners Association, at www.corn.org, is a quick source of information. This chapter provides only a limited introduction to starch chemistry and a brief description of starch products currently used in preparing savory snack foods.

2. STARCH GRANULES Starch exists in discrete, semicrystalline entities called starch granules. The size, shape and structure of these granules vary substantially among botanical sources. Granule diameters generally range from less than 1 ␮m to more than 200 ␮m; shapes vary from elliptical to spherical to angular (Figure 5.1).

Figure 5.1 Starch granule shapes and sizes for wheat, corn, rice, and potato viewed with scanning electron microscopy. (Courtesy of C. McDonough, Cereal Lab, Texas A&M University, College, Station,TX.)

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Granules are simple (wheat, corn) or compound (rice, oats). Wheat, barley, triticale and rye granules have bimodal granule distributions. Corn, starch, viewed with the environmental scanning electron microscope, is shown in Figure 4.13 (Chapter 4). The small (3 ␮m) and large granules (35 ␮m) of wheat starch have different shapes. The compound granules of oats and rice have many small, individual granules bound together into a compound granule (Figure 5.1). Much diversity occurs in the structure and characteristics of native starch granules, including signiﬁcant variation among granules of a given species. The native starch granule is cold-water insoluble, but swells reversibly when put in cold water. Tuber starches swell more than cereal starches, while waxy cereal starches swell more than non-waxy starches. Native starches rotate the polarized light plane and show birefringence [Figure 5.2 and Figure 4.13 (Chapter 4)]. Native starches are white, dense, resist digestion by amylase enzymes and contain small quantities of proteins and lipids that are part of the granule. Each species has its characteristic shapes, sizes and birefringence patterns. With exception of the oilseeds, most plants store energy in the form of starch, which is a glucan composed of D-glucose held together by alpha-1–4 linkages (amylose). Amylopectin has a few alpha 1–6 branch points while most glucose chains are alpha 1–4 links (Figure 5.3). The ratio of amylose to amylopectin in the starch signiﬁcantly affects its properties for use in food applications. Starches vary from nearly 0 to 80% or more amylose content (Table 5.1).

2.1. AMYLOSE Amylose is essentially a linear polymer composed almost entirely of a-1, 4-linked D-glucopyranose (Figure 5.3), although some branches are present on the amylose polymer. Amylose is often represented as a straight chain structure, but it usually exists in a helical form, which permits it to complex with free fatty acids, mono-and diglycerides, linear alcohols and iodine. Because of its long chains, amylose stains purple with iodine, undergoes retrogradation readily and forms strong cohesive gels. The formation and structural integrity of amylose-lipid complexes are affected by temperature, pH, mixing of the amylose polymers with the “guest” molecule and structure of the fatty acid or glyceride. The resulting complex often alters the properties of the starch. Amylose mono- and diglyceride complexes affect starch gelatinization temperatures, texture and viscosity, and limit retrogradation.

2.2. AMYLOPECTIN Amylopectin, the predominant molecule in most typical starches, is a branched polymer that is much larger than amylose (Figure 5.3). Amylopectin is

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Figure 5.2 Bright ﬁeld (left) and polarized light (right) photographs illustrating the process of starch gelatinization from 60–90◦ C. (Courtesy of C. McDonough, Cereal Lab , Texas A&M, University, College, Station, TX.)

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Figure 5.3 Amylose (top) and amylopectin (middle) chains. Bottom—amylopectin structure showing the clusters of chains, which form crystallites in the starch granule.

composed of alpha-1,4-linked glucose segments connected by alpha-1,6-linked branch points. About 4–6% of the linkages within an average amylopectin molecule are alpha-1,6 linkages [2]. This small percentage produces more than 20,000 branches in an average molecule, although the branches themselves are not large. A bimodal size distribution of small and large polymer chains [4,5] probably exists. The small chains have an average degree of polymerization (DP) of about 15 glucose units, while the larger chains consist of about 45 TABLE 5.1.

Approximate Amylose and Amylopectin Contents of Major Starches.

Starch Type Corn Waxy corn High-amylose corn Potato Rice Waxy rice Tapioca/cassava/manioc Wheat Sorghum Waxy sorghum Heterowaxy sorghum a

Amylose (%)

Amylopectin (%)

GTR, ◦ Ca

25 <1 55--70 (or higher) 20 19 <1.0 17 25 25 <1.0 <20

75 >99 45--30 (or lower) 80 81 >99 83 75 75 >99 >80

62--72 63--72 70--95+ 50--60 68--78 68--77 52--61 58--63 65--74 64--73 64--73

GTR = Gelatinization temperature range.

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glucose units. This unique conﬁguration contributes to the crystalline nature of amylopectin and an ordered arrangement of amylopectin molecules within the starch granule. The branched chains of amylopectin exist in helical form, but they are relatively short and are brownish-red when complexed with iodine. The molecular weight of amylose is less than 500,000, while that of amylopectin ranges from 10 to 500 million. Because of the highly branched nature of amylopectin, its properties differ from those of amylose. For example, retrogradation is slowed, and gel formation is delayed or prevented. Pastes from waxy starches are considered non-gelling, but typically have a cohesive, gummy texture. Amylopectin pastes are signiﬁcantly stickier than pastes containing amylose. For example, waxy rice (99% amylopectin) is called “sticky rice” because it is very adhesive after cooking. Waxy or glutinous rice ﬂour is often preferred for breadings when the batter must adhere strongly to the food. Waxy rice is preferred for production of rice crackers that have a light texture, while high amylose rices are preferred for heavier crackers and rice noodles. The amylose retrogrades and forms a ﬁrm structure in the noodle or cracker, which causes it to resist breakdown during cooking in water or mastication. Increasing the amylose content of extruded snack formulas results in ﬁrmer, crispier products but reduces expansion; increasing the amylopectin fraction increases product expansion and softness. Unless chemically stabilized, amylopectins break down more rapidly than amyloses under high-shear conditions. The ratio of amylose to amylopectin within a given type of starch affects its functionality in foods, including the cooking and eating qualities of rice. Highamylose-content rice varieties cook intact and form dry, ﬂuffy kernels, while low-amylose varieties are sticky when cooked. Starches, which vary in amyloseto-amylopectin ratios, can be produced from most species. For example, waxy wheat starches are under development currently. Waxy varieties of rice, millet, sorghum, barley, maize and other cereals originated in China.

2.3. STRUCTURE OF THE STARCH GRANULE Amylopectin is responsible for starch granule structures, which consist of crystalline (crystallites, micelles, organized areas) and noncrystalline (amorphous, noncrystalline, gel phase) areas (Figures 5.3 and 5.4). The amorphous areas (low in crystallites) of starch granules are degraded ﬁrst by the entry of water and enzyme and acid action. The crystallites are composed of large numbers of glucose chains that undergo hydrogen bonding to form areas difﬁcult for water and enzymes to penetrate. Heat, or energy, and water are required to cause these crystallites to irreversibly lose their organization in the process called gelatinization. When native starch is heated in water, the granules swell until their structure eventually disintegrates, and amylose and amylopectin are released as an aqueous suspension. The loss of organization occurs over different temperature ranges for various starches (Table 5.1).

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Figure 5.4 Scanning electron micrograph of half a kernel of sorghum incubated with hog pancreas alpha-amylase. The partially hydrolyzed starch granules demonstrate the crystallites remaining in the starch granules.

Compared with crystalline areas, amorphous areas of the granule generally are degraded more easily by acid and enzymes, such as alpha-amylase. Granules exhaustively treated with puriﬁed alpha-amylase demonstrate a typical ringed pattern (Figure 5.4). This pattern indicates that crystalline and amorphous areas of the granule alternate. The radially oriented amylopectin clusters probably associate with amylose molecules, which are interwoven throughout the crystalline and amorphous areas. Thus, the lack of amylose in waxy starch granules explains why they swell more rapidly and are more easily hydrolyzed by amylases than nonwaxy starches of the same species. The starch granule is considered to be a glassy polymer by modern starch chemists and technologists. Starch is believed to exist in the glassy state until it

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Figure 5.5 Conceptual representation of changes in starch granules during heating and cooling in water. Tg = glass transition temperature; Tm = melting temperature. (Modiﬁed from Reference[5]).

reaches the glass transition temperature (Tg ) where the molecules lose organization and the polymer becomes rubbery. Eventually it reaches the temperature (Tm ) at which the starch granules melt and lose their organization completely. Water is a plasticizer that signiﬁcantly affects the Tg and Tm temperatures of the starch granules. As swelling and melting occur, the granules are said to undergo gelatinization, pasting, dispersion, and ﬁnally retrogradation, when the material is allowed to cool. These changes (Figure 5.5) are affected by temperature, water content, mechanical energy and other factors. The texture of baked or fried chips is crisp below 3% moisture, but the chips become rubbery and have a tough, chewy texture at higher moisture levels because the Tg is reduced by the water molecules.

3. DEFINITIONS Starch chemistry and technology utilize numerous interchangeable terms that are rather loosely deﬁned and often have different meanings to various interest groups. Some terms are deﬁned based on a recent AACC handbook [2] and modiﬁed per our experience: —Birefringence—A phenomenon that occurs when polarized light interacts with a highly ordered structure like a crystal. A diffraction pattern referred

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to as a “Maltese cross,” is created by rotation of polarized light by a crystalline or highly ordered region, such as that found in starch granules. —Cookup starch—Any granular starch that requires water and heat to gelatinize and paste. —Cornstarch—Common cornstarch composed of approximately 25% amylose and 75% amylopectin. —Degree of polymerization (DP)—The molecular size of a polymer. In this case, it refers to the number of alpha-1,4-linked D-glucopyranose units in a starch chain. —Dextrose Equivalent (DE)—A measure of the proportion of dextrose (glucose) units in starch with reducing ends compared to the complete starch granule. It is related inversely to the degree of polymerization by the equation DE = 100/ DP. Solubility and sweetness of corn products increase with DE as starch is hydrolyzed, typically by acids or enzymes. The DE of intact starches theoretically is “”; maltodextrins, DE under 20; corn syrup solids, 20–60 DE; and corn syrups, DE higher than 60. A completely hydrolyzed corn sugar has a theoretical DE of 100. —Gel—A colloidal system that has a solid continuous phase with a liquid dispersed phase. —Gelatinization temperature—A narrow temperature range at which starch granules begin to swell, lose crystallinity and impart viscosity to the cooking medium. —Gelation—The process of a colloidal sol changing to a gel. —High-amylose cornstarch—Starch isolated from specialty corns that contains greater than 40% amylose. Some high-amylose cornstarches now contain as much as 90% amylose. —Native starch—Any granular starch that has been isolated from the original plant source, but has not undergone subsequent modiﬁcation, i.e., unmodiﬁed starch. —Paste—Starch in which a majority of the granules have undergone gelatinization, giving it a viscosity-forming ability. Pasting involves swelling and exudation of the components of the granule. The terms “pasting” and “gelatinization” are often used interchangeably. Usually pasting involves high concentrations of starch in water and occurs after the initial loss of organization. —Sol—A colloidal system with a solid phase dispersed in a liquid phase. —Syneresis—The separation of a liquid from a gel; weeping caused by reordering of the starch molecules in a gel. —Viscoelastic paste—A paste that possesses properties of both a viscous (liquid-like) and an elastic (solid-like) substance. —Waxy starch—The term “waxy” describes the appearance of the endosperm of mutant corn kernels, which contain homozygous recessive wxwxwx

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genes. Waxy varieties occur in corn, rice, sorghum, proso millet and barley. The amylopectin content of waxy starches approaches 99% or more.

4. CHANGES IN STARCH Relationships between water, starch content, shear and chemical additives affect cooking viscosity, moisture retention and expansion signiﬁcantly. In most extrusion situations, water is limiting, and the mechanical energy added to the system by friction cooks the starch and associated materials. The hot melt then is allowed to expand directly, or is cooled and forced through the die to shape it. The structure is set by cooling and/or drying, which facilitates retrogradation of the starch chains and formation of a new ordered structure. The ratio of amylose to amylopectin has a major effect on extrudate properties.

4.1. GELATINIZATION Gelatinization is the disruption of molecular order within the starch granule. It (1) depends on temperature and moisture content; (2) is irreversible; (3) initially increases the size of granules (i.e., causes granular swelling); (4) results in increased solution or suspension viscosity; (5) varies with cooking conditions (e.g., pH and solids); and (6) varies with starch granule type (botanical source). The temperature at which starch begins to undergo irreversible changes is called the “initial gelatinization temperature.” The gelatinization temperature range is narrow and varies with the source of the starch. In general, the gelatinization temperature ranges of tuber and root starches such as potato and tapioca are lower than those of cereal starches (Table 5.1) (Chapter 9). Granular starch is essentially insoluble in cold water, and even when added to water at room temperature, little happens until heat is applied. The combination of heat and water causes un-cooked granules to undergo dramatic and irreversible changes, the most dramatic of which are (1) disruption of the semicrystalline structure, as evidenced by a loss of birefringence; and (2) increase in granule size. As these changes occur, viscosity in the starchwater system increases. When a majority of the granules have gelatinized, the starch is considered to be pasted or cooked out. Functionality of starches as a food ingredient often results from its pasting (i.e., viscosity-forming) ability. Heating of starch in water causes disruption of the hydrogen (H) bonds between polymer chains, thereby weakening the granule. The initial swelling probably takes place in the amorphous regions of the granule where hydrogen bonds are less numerous and the polymers are more susceptible to dissolution. As the structure begins to weaken, the granule imbibes water and swells. Because not all the granules gelatinize simultaneously, different degrees of structural disruption and swelling exist.

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Figure 5.6 A typical Rapid ViscoTM Analyzer (RVA) proﬁle illustrating viscosity and setback readings for sorghum starch.

4.2. PASTING As heating continues and more and more granules become swollen, the viscosity of the medium increases. The paste viscosity reaches a maximum when the largest percentage of swollen, intact granules is present; this is referred to as the “peak viscosity” (Figure 5.6). Continued heating of native starches eventually results in decreased viscosity as granules dissolve and polymers are solubilized (Figure 5.7). The Viscoamylograph (C. W. Brabender, Hackensack, NJ, USA) and the Rapid ViscoTM Analyzer (RVA) (Newport Scientiﬁc Pty. Ltd., Warriewood, NSW, Australia) are used to produce “pasting curves” (Figures 5.6 and 5.7). A speciﬁed weight of starch is dispersed in a speciﬁed volume of water, and viscosity changes are recorded as temperatures are varied while stirring. Important measurements on the curves are: —Pasting temperature—the initiation of paste formation, which varies with starch type, modiﬁcation and additives present in the slurry. —Peak viscosity—the maximum viscosity obtained during cooking; gives an indication of the viscosity that can be expected for a given starch.

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Figure 5.7 Typical changes in starch granules as they are heated in water and changes in viscosity occur as measured with a viscosity analyzer.

—Viscosity at 95◦ C—indication of the ease of cooking the speciﬁc starch. —Viscosity after stirring 1 hr at 95◦ C—indication of paste stability when the starch is held at 95◦ C under relatively low shear. —Viscosity at 50◦ C—indication of the extent of retrogradation that occurs in the cooled paste. —Viscosity after 1 hr at 50◦ C—indication of the stability of the cooled, cooked paste under low shear. Viscosity curves are used as ﬁngerprints of the hydration and cooking characteristics of starchy materials. Changes in viscosity proﬁles often explain how new processes affect the starch properties. They are extremely useful in measuring variation among starch-based ingredients (Chapters 3 and 4), and can be used to indicate changes in retrogradation during drying, frying and other unit operations. Staling of products is related to amylopectin retrogradation and can be followed by viscosity changes. The RVA instrument has nearly unlimited variables of concentration, heating and stirring rates. It is relatively fast and can be used to promptly provide information on hydration rates of starch-based ingredients and adjustment of cooking times and conditions to produce consistent products. Viscosity measurements

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Figure 5.8 Generalized curves showing the cooking behaviors of potato starch, waxy cornstarch, normal dent cornstarch, stabilized dent cornstarch, and moderately cross-linked and stabilized dent cornstarch. Modiﬁed from Reference[5].

can also be used to determine the effects of other ingredients in the formula on cooking and hydration properties. Sometimes, pasting is deﬁned as the state following gelatinization of starch. It involves granular swelling, exudation of molecular components from the granule, and, eventually, total disruption of the granules. For all practical purposes, gelatinization and pasting are considered together, and it is impossible to separate one from the other. Sometimes pasting refers to high levels of starch in the cooking system. For most starches, the texture and viscosity of the paste change during cooling. Either a viscoelastic paste or a gel usually is formed, depending on the amylose content and concentration of solids. In general, the higher the amylose content, the more likely a ﬁrm paste or gel. Figure 5.8 shows pasting curves for ﬁve starches. Potato starch has the greatest viscosity of the ﬁve initially, followed by a signiﬁcant reduction during holding because the granules are fragile, but the paste forms a strong gel during cooling. Normal cornstarch requires a longer cooking time to reach maximum peak viscosity than waxy maize starch because of its higher amylose content. The amylose undergoes strong retrogradation, producing a much higher ﬁnal viscosity than obtained with the same amount of waxy starch. Waxy cornstarch has a high peak viscosity, which breaks down upon stirring and does not retrograde upon cooling to any extent. Waxy and normal starches are often cross-linked (Figure 5.9) to improve their shear stability during cooking, pumping and use at low pH [6]. Cross-linked and stabilized cornstarches show signiﬁcantly different properties than their parent normal cornstarch.

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Figure 5.9 Structure of a gelatinized cross-linked starch granule; each C refers to a covalent bond formed by a cross-linking agent between and among starch chains. Modiﬁed from Reference[2].

4.3. RETROGRADATION In a sense, retrogradation is the opposite of gelatinization. Solubilized starch polymers and the remaining insoluble granular fragments reassociate after heating (Figure 5.5). Retrogradation results in formation of crystalline aggregates, which affect texture. Linear amylose molecules have a greater tendency to reassociate and form hydrogen bonds than the larger, highly branched amylopectin molecules. As retrogradation occurs, the starch paste becomes increasingly opaque and forms a gel. With time, this gel becomes rubbery and has a tendency to release water. These changes occur extensively during and after extrusion, baking, frying and other processes. They signiﬁcantly affect the texture and other properties of snacks. Dehydration removes water, increasing the extent of retrogradation. Thus, the ﬁlms that are formed depend on the relative amounts of water, the type of starches and their interaction with other ingredients in the system. Retrogradation is involved in drying, frying, baking, extrusion and other processes involved in snack production. Extensive retrogradation of amylose produces strong retrogrades that are resistant to enzymes. Retrogradation of amylopectin in baked products is related to staling. In snacks, it produces a light, crisp texture.

4.4. EFFECTS OF SHEAR, pH AND OTHER INGREDIENTS Shear dramatically affects starch behavior. Unmodiﬁed starches, which are normally susceptible to granular disruption and viscosity breakdown, are even more vulnerable when subjected to shear during gelatinization and pasting processes. Shear from stone grinders, mixers, pumps, homogenizers and extruders signiﬁcantly changes starch properties.

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The effect of pH on starch properties is an important consideration. In general, pH extremes have a negative impact on viscosity by hydrolyzing bonds and disrupting the molecular integrity of the starch granule, actually cleaving the alpha-1–4 and 1–6 links in the starch chains. Acid hydrolysis can lead to degradation of starch into products with lower molecular weights, especially during heating. The net result of acid hydrolysis is signiﬁcant viscosity loss. In alkaline cooking, the high pH causes quicker gelatinization and produces partially charged starch chains that slow retrogradation, which is why high pH tortillas retain freshness for a longer time. Fats, sugars, proteins and salts affect starch gelatinization, pasting and retrogradation. In general, any ingredient that interacts (e.g., coats, binds, or complexes) or competes with the granule for available water, has a negative impact on viscosity. For example, fat has a tendency to interact with the starch granule and prevent complete hydration, resulting in lower viscosity development. Fat serves as a lubricant and reduces the mechanical energy imparted to the system during extrusion for example. Sugar and other solids limit gelatinization and pasting by competing for available water. Other food ingredients, like proteins and salts, alter starch properties and therefore must be considered when foods containing starch are formulated.

4.5. MODIFIED STARCHES Native and physically modiﬁed starches from any source are generally recognized as safe (GRAS). Chemically modiﬁed food starches are food additives, and limits of their modiﬁcation, use and labeling, deﬁned in the U.S. Code of Federal Regulations (21CFR 172.892); 9CFR 318.7, should be consulted regarding use in non-meat and meat products. The Code of Federal Regulations can be accessed at www.cfr.gov. Pregelatinized starches are used in many food applications. They are made by cooking the starch in water, drying and grinding. Often, drum drying or spray drying may be combined with agglomeration technology in starch production. These starches do not require cooking to absorb water and develop desirable rheological properties. The methods of drying and grinding affect the performance properties of pregelatinized starches. Cross-linked starches have covalent bonds between hydroxyl groups on the same or different starch polymers. These covalent bonds hold the structure together and stabilize the starch during processing (Figure 5.9). Phosphate cross– linked starches are used in many food applications. Starches can be speciﬁcally designed to resist shear and develop the functionality required. Low levels of cross-linking increase viscosity, while higher levels of cross-links can produce starch that requires extensive shear, pressure and heat to paste (Figure 5.10) [1].

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Figure 5.10 The effect of cross-linking waxy cornstarch with trimetaphosphate on viscosity proﬁles. Modiﬁed from Reference [6].

Dextrins (starch adhesives) are used to tack water-soluble ﬂavors to low-fat baked snacks. They are made by pyroconversion—controlled heating of dry acidiﬁed starch in a reactor with good agitation. The products have high water solubility, low viscosity and good ﬁlm-forming ability [7].

5. STARCH INGREDIENTS FOR SAVORY SNACK FOODS

5.1. PARTICLE SIZE OF FLOUR, GRITS AND MEAL Endosperm particles, instead of isolated starches, are used in snack food processing. Thus, the particle size of the endosperm particles, and how they were treated during processing, signiﬁcantly affect the starch transformations described earlier in this chapter. The hardness of the endosperm affects the way the particles absorb water and the time and energy required to produce a continuous gelatinized melt of starch and other components in the extruder. Competition for water among the various ingredients affects the cooking properties signiﬁcantly. This is also reviewed in Chapters 3 and 4 on corn quality and nixtamalization, respectively, and illustrated by the viscosity curves of different corn meals and dry masa ﬂours. The rate of water hydration is critically important in these processes because it affects changes in the starchy components that ultimately affect the texture of fried or baked snacks (Chapter 9). Other ingredients in the formula also compete for the same water. Lipids may coat the starch and frustrate its hydration and swelling. Or, the lipids may

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lubricate the extruder and decrease the amount of energy applied to the system, which will signiﬁcantly reduce the expansion ratio. Despite their limitations, viscosity proﬁles are often the best techniques available to evaluate the properties of starchy materials.

5.2. EXTRUSION PROPERTIES OF CEREALS Moist starchy ingredients, heated and sheared at high temperatures and pressures, produce a melted, putty-like dough that puffs when the pressure is released. Corn, sorghum, pearl millet and rice have excellent extrusion properties, whether as isolated starches or as meal from the endosperm. They have signiﬁcant expansion and produce excellent extrudates, although the ﬂavors are different. Pearl millet extrudates have a strong but acceptable ﬂavor; corn has its characteristic aroma and ﬂavor. Decorticated white food-type sorghum produces extrudates with exceptionally bland ﬂavor, equaling or surpassing rice, which is also characterized by a bland ﬂavor. White food sorghum is a recent development that has excellent extrusion properties and competes with rice for producing light-colored, bland extrudates that serve as the carrier for mild ﬂavors (Chapter 3). Corn ﬂavor often masks subtle ﬂavors. These sorghums compete with rice since they are signiﬁcantly lower in price. Waxy versions of these cereals, with varying amylose levels, provide interesting possibilities for different product textures. Depending on the variety, wheat, rye, oats and barley ﬂours or meals may produce extrudates with strong ﬂavors and usually have darker colors. Blends of the two groups of cereals produce excellent extrudates and processed products.

5.3. STARCHES Many U.S. snack foods are made from corn or its starch. Tapioca (cassava, manioc) and potato starches or ﬂours are available (Chapter 9). In the Far East, Brazil and other areas, cassava starches or manioc ﬂour is widely available and used in snacks. Isolated starches sometimes are used for special products where the high starch content provides the continuous phase for making products like snack pellets. The combination of isolated starches with meal, and other sources of ﬁber, allows producers to prepare multigrain snacks with added ﬁber and other components. The addition of isolated starch to a formula adds a component that hydrates and cooks more quickly and often improves the ease of processing and/or the quality of the extrudate. It is common to utilize 5–10% potato, cassava or waxy starches blended with cereal meals or ﬂours to improve expansion and extrudate quality.

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5.4. SNACK PELLETS Corn meal and tapioca or potato starches are often used in formulating “half products” or pellets. The most common way to make these types of products is by using an extruder to cook the starch and cereal blends; then, the dough is formed into pellets, which are slowly dried under controlled humidity (Chapter 12). The pellets can be stored and shipped for expansion by frying, microwave or hot-air oven baking at the point of use. Potato or cassava starches have longer starch chains in the amylopectin molecules that are thought to improve the “seal” on the outside of the pellet, which enables more consistent expansion by frying or baking. Sometimes, potato starch or chemically modiﬁed cereal starch is added to rice meal to produce extrudates with desired texture and other properties. Isolated starches are expensive, and they are used only when necessary to improve functionality.

5.5. EXTRUDED OR FRIED SNACK FOODS Starches and starch derivatives have a long history of use in snack foods, especially as functional ingredients to help achieve various textural attributes. Starch selection is critical for controlling the ratio of amylose and amylopectin content. In addition, starch granule shape and amylose:amylopectin ratios differ among starches, and the expansion property of each starch is unique. For example, in expanded or puffed snacks, the target texture can be obtained by adjusting the amylose:amylopectin ratio by selecting combinations of high-amylose and high-amylopectin starches. Cornstarches with 55% and 70% amylose are available. These starches are used when increased crunchiness and strength are required. In the opposite direction, waxy maize starch, which is essentially 100% amylopectin, can be used to increase the expansion of the expanded or puffed snacks and increase the crispiness of snacks. Potato starch has the largest granules of all commercial starch types, and also the greatest swelling capacity. However, a dough made with high-swelling starch is sometimes difﬁcult to roll into thin sheets of uniform thickness. Thus combinations of different starches and meals are used. Native starches, especially the waxy type, generally are not resistant to the high temperatures and shear processing conditions experienced in producing extruded snacks. Disruption of the starch granules negatively affects texture and tooth packing in the mouth. Cross-linked starches are used to provide resistance to shear and excessive heat during processing. Excessive cross-linking lowers the swelling capacity of the starch, resulting in a snack that has reduced expansion with non-uniform poor texture. Use of the proper cross-linked waxy cornstarch in the formula controls the expansion of puffed snacks and provides uniform products.

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Amylose is especially receptive to hydrophobic compounds, including monoand diglycerides and lipids. High-amylose formula starches, or sometimes coatings, are used to reduce oil absorption during frying because of their strong ﬁlm-forming characteristics.

5.6. BAKED LOW-FAT SNACKS Pregelatinized waxy corn starches are used to produce low-fat snacks that are made by baking or by indirect expansion processes (low-shear extrusion followed by microwaving, baking, or frying). Pregelatinized waxy cornstarch is necessary because the temperature rises slowly in the dough and raw starch does not have sufﬁcient time to gelatinize. Pregelatinized starches are cookup starches that have been precooked in water and then dried; they require no further cooking for functionality. This is an important feature for baked expanded snacks because, by the time a raw cookup waxy starch gelatinizes, most of the water vapor has escaped from the dough. Pregelatinized waxy cornstarch allows the expansion process to begin as soon as water starts vaporizing. For indirectly expanded products (example: half products), pregelatinized starches are often used because of limited moisture and heat in the formulation and process. However, the pregelatinized starches must have granular integrity to avoid development of sticky, gummy doughs that do not form well and do not retain their shape during processing. Pregelatinized starches that maintain their granular shape improve the handling and forming properties of dough used to make indirectly expanded products. In addition, high-amylose starches are used to prevent oil absorption in fried snacks because they form a strong ﬁlm, which ﬁrms up the texture and reduces oil uptake.

5.7. STARCH-BASED LIQUID ADHESIVES Fat and oil have traditionally been used for attaching seasonings to the surface of cereal-based snacks. The development of low-fat and fat-free snacks has increased the need for new adhesives that can attach seasonings. Many manufacturers have evaluated gum-based solutions to replace fat or oil for adhering seasonings. Disadvantages of using gum systems include: (1) difﬁculty in spray applications because of excessive viscosity; (2) when cooled, the spray solution forms a gel and plugs the spray nozzle; and (3) postseasoning application drying is required. A starch-based coating (dextrin) at 30% solids, with a high degree of tackiness, has effectively attached seasonings to cereal-based snacks. The starchbased coating solution is sprayed onto snacks to adhere both seasonings and particulates like salt, and dries quickly. It is available as a powder, dissolves easily in water, or can be mixed with glycerin and water. The solution is easy to spray, even at high solids concentrations of 30–40% due to its low viscosity

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characteristics. An advantage of the starch-based coating is that it can be applied cold or hot, and the stability of both solutions prevents the application nozzles from plugging. Starch-based liquid adhesives have shown many beneﬁts in snack and cereal applications. They work well on RTE cereals, tortilla chips and corn chips, pretzels, baked chips, nut products, crackers and granola bars. The adhesive can also seal the ends of egg rolls and burritos.

5.8. STARCH-BASED HOT MELT SYSTEM Hot melt technology used in the adhesives industry has been adapted for tacking ﬂavors and seasonings to snack foods. The new starch-based hot melt system is a free ﬂowing, oil- and water-free, preblended, dry powder. The powder is applied to the hot snack (121–150◦ C, 250–300◦ F), which melts the powder in less than 30 seconds. The seasonings adhere to the products. Since no liquids are used, there is no need for heating, and the snack retains its dryness and crisp mouth feel. The powder is very stable at temperatures below 93◦ C, 200◦ F. The starch-based hot melt system provides greater tackiness than canola and other vegetable oils. Based on many laboratory tests, it outperforms oil alone as an adhesive for seasonings.

5.9. FUNCTIONAL FIBER-RESISTANT STARCH Resistant starches are unique. Although technically starches, they are part of the total dietary ﬁber (TDF) content when assayed using approved AOAC methods for ﬁber analysis [8]. In the United States, this enzymatic-gravimetric method is required by the Nutrition Labeling and Education Act (NLEA) to support ﬁber–content claims. Marketing of commercial resistant starches has created new interest in increasing the dietary ﬁber content of foods. Resistant starch, billed as a functional ﬁber, contributes up to 40% or more total dietary ﬁber as analyzed by the approved AOAC method for ﬁber analysis [9]. It is well suited for snack applications, because resistant starch allows “good source” or “high ﬁber” nutritional claims. It also imparts excellent texture without compromising quality. Unlike traditional sources of dietary ﬁber, which hold signiﬁcant moisture and impart a gritty mouth feel and characteristic ﬁber taste, resistant starch has low water-holding capacity, small particle size and bland ﬂavor. Commercial resistant starch is a special high-amylose starch that has been modiﬁed by biochemical and/or physical processing to maximize its total dietary ﬁber content. Resistant starch provides snack processors the opportunity to produce high-quality ﬁber-fortiﬁed snacks for health conscious customers.

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6. SELECTION OF STARCHES The use of native and modiﬁed starches in snacks enables production of an array of products with different properties for various applications. The type of starches chosen will depend on their cost, availability, functionality and the quantity used. The best way to obtain information and samples of starches and related products is by contacting technical service personnel from starch and hydrocolloid suppliers. Starches with different functional properties are available, and suppliers can recommend the types of starch required for speciﬁc types of processes. A major food starch processor may offer several dozen or more products (including crude, pregelatinized and modiﬁed versions) for each starch species handled. In addition, many starch suppliers are willing to develop modiﬁed starches for speciﬁc end uses if warranted by potential sales volume.

7. CONCLUSIONS Starches in meals, ﬂours and whole grains can effectively provide texture and acceptable taste in a wide variety of snacks. Combinations of starches and meals or ﬂours from different cereals provide great variation in products. Amylose and amylopectin dominate the functionality of starches and starchy ingredients for extrusion and other processes. Specialty starches can provide a number of functional beneﬁts in making snack products, including: increased expansion, improved crispness, reduced oil pickup and better overall eating quality. The use of starch-based coatings and adhesives to replace fat or oil in low-fat baked snacks will increase their taste and appeal. Dry hot melt starch-based adhesives provide cost-effective tacking agents with good ﬂavor release, compatibility with a range of processes and friendly labeling as corn syrup solids. Commercial resistant starch provides opportunities for snack manufactures to develop high-quality ﬁber-fortiﬁed snacks. It is easily incorporated into a formulation, does not mask ﬂavors, provides a light, crispy texture and can be used alone as a ﬁber source or as a functional complement to other types of ﬁber.

8. ACKNOWLEDGMENTS Thanks to Ms. C. McDonough, research scientist, and Ms. Pamela A. Littlejohn, word processor, for their critically important assistance with the manuscript.

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9. REFERENCES 1. Cecil, J. E., 1992. Small-, Medium- and Large-Scale Starch Processing. Food and Agriculture Organization of the United Nations, Rome. 2. Thomas, D. J. and W. A. Atwell, 1999. Starches. American Association of Cereal Chemists, St. Paul, Minnesota. 3. Zobel, H. F., 1984. Gelatinization of starch and mechanical properties of pastes. In Starch Chemistry and Technology, 2nd, edition. R. L. Whistler, J. N. BeMiller and E. F. Paschall, eds. Academic Press, Inc., New York. pp. 285–307. 4. Whistler, R. L. and BeMiller, J. N., 1997. Carbohydrate Chemistry for Food Scientists. American Association of Cereal Chemists, St. Paul, Minnesota. 5. Waniska, R. D. and Gomez, M. H., 1992. Dispersion behavior of starch. Food Technology, 46(6):110–123. 6. Schoch, T. J., 1965. Starch in bakery products. Bakers Digest, 39:April, 251–259. 7. Bemiller, J. N., 2000. Starch. In Encyclopedia of Food Science and Technology, 2nd edition, Vol. 4. F. J. Francis, ed., John Wiley & Sons, Inc., New York, pp. 2203–2209. 8. Huang, D. P., 1995. New perspectives on starch and starch derivatives for snack applications. Cereal Foods World, 40:528–531. 9. Ranhotra, G. S., J. A. Gelroth and S. D. Leinen, 1999. Resistant starch in grain-based foods. Cereal Foods World, 44:357–359.

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CHAPTER 6

Oils and Industrial Frying

DON E. BANKS EDMUND W. LUSAS

1. INTRODUCTION

O

is used as a heat transfer agent for frying the vast majority of savory snacks and becomes part of the products. Its functions include cooking, expanding (pufﬁng) certain products, dehydrating them to crispiness and assisting in the formation of desirable ﬂavors and color. The material to be fried may be raw, nixtamalized (alkali-cooked), or previously extruded and partially dried (half products, pellets). Once the oil has been readied by heating, frying is the most rapid way of cooking food and gives a unique ﬂavor and texture unmatched by any other process. Additionally, oil remaining on the surface of fried snacks, or applied as spray, acts as a tacking agent to bind salt and seasonings to snack pieces and as a carrier for oil soluble ﬂavors. With consideration for protecting product crispiness by packaging in moisture-barrier materials, the protection of oil from degradation, from receipt through ﬁnal usage, is the most important consideration for producing high-quality savory snacks. Oil is the most expensive component of many fried snacks. Numerous references on processing and utilization of oils are available [1–8]. Additionally, the Journal of the American Oil Chemists’ Society, INFORM, Lipids, Food Technology and Journal of Food Science report research on oils extraction and processing, utilization, quality problems and nutritional implications. Often, industry personnel learn and apply specialized information before it is documented in research reports or books. This chapter summarizes the basics of oil chemistry, extraction and reﬁning, oil selection, the frying process and oil management, and presents an overview of the fats and oils industry as it relates to the preparation of savory snacks. IL

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Details are included to alert frying oil processors and buyers where problems may originate.

2. WORLD OIL SUPPLY

2.1. PRODUCTION Approximately 82 million metric tons (MMT) of major edible vegetable oil are produced in the world annually, an amount currently increasing by slightly more than 2 MMT yearly. The major oilseed crops are shown in Table 6.1 [9]. The 1998/1999 production is the sum of the fall harvest in the northern hemisphere plus the harvest in the southern hemisphere occurring in the early months of the succeeding calendar year. The world’s major oils, in diminishing order, are: soybean, palm, rapeseed/canola, sunﬂower, peanut, cottonseed and coconut.

2.2. AVAILABILITY OF OILS Many factors affect the availability of edible oils in speciﬁc markets. On an astraded moisture basis, oil contents of seeds vary from about 18.5% for soybeans and 20% for cottonseed, to 41% for canola, 42% for sunﬂower seed and 45% for shelled peanuts. Some crops, including oil palm, rapeseed/canola, sunﬂower and coconut, are grown primarily for their oil. However, signiﬁcant amounts of soybean, corn and cottonseed oils are produced as secondary coproducts. For example, the major return from processed soybean in most years is from its highquality protein used in poultry, swine, aquaculture and other animal feeds. Yet, even with an oil-to-meal yield ratio of less than 1:4, soybean is the world’s major source of edible oil. Because of its ready availability, it has a pronounced effect on prices for all edible and inedible vegetable oils and animal fats throughout the world. Other oils have to offer distinct beneﬁts to users to compete directly or warrant premiums over soybean oil. Corn oil is another example of a signiﬁcant secondary product. Dent corn contains about 4–5% fat, of which about 83% is concentrated in the germ [10]. Yet, because of the large production of starches, corn sweeteners and ethanol by the domestic corn reﬁning industry, corn oil (1.02 MMT in 1997) is currently the second major oil produced in the United States after soybean (7.41 MMT) [11]. Global trade in oilseeds and their products has a patchworkquilt appearance. The United States produces 46.8% of the world’s soybeans. Approximately 29.2% of its crop is exported as whole soybeans. An additional 18.3% of its crushed soybean meal and 13.2% of its soybean oil also are exported. In contrast, Brazil exports 28.4% of its soybeans whole and 61.1% and 38.2% of its meal and oil, respectively. Argentina exports 16.2% of its soybean

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(%)

159.35 --26.18 35.98 33.03 30.08 4.40 ----5.62 294.64

38.48 --4.27 9.35 0.96 1.29 0.25 ----0.06 54.65

24.1 16.3 26.0 2.9 4.3 5.7

1.1 18.5

MMT

106.22 --10.42 19.52 11.50 5.97 1.48 --5.74 2.96 163.79

39.07 --3.65 4.03 0.60 0.31 0.71 --0.31 2.55 54.28

Export Trade

(%)

World Production

MMT

(%)

36.8 --36.5 5.3 5.2 5.2 48.0 --5.7 86.1 33.1

24.47 19.27 9.18 12.05 3.63 4.61 2.69 2.54 1.11 2.44 81.99

8.01 12.32 3.80 2.89 0.15 0.27 1.30 1.07 0.63 1.15 31.58

32.7 63.9 41.4 24.0 4.1 5.9 48.3 42.1 56.8 47.1 38.5

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Soybean Palm Sunflower Seed Rapeseed/canola Cottonseed Peanut Copra/coconut Olive Fish Palm kernel TOTAL

Export Trade

World Production

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Estimated Annual World Supply and Trade of the Major Oilseeds, Meals, and Oils and Fats, Million Metric Tons (MMT) [9]

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crop as whole soybeans and 95.7% and 97.5% of its meal. During the last two decades, Brazil and Argentina, producing 19.6% and 12.5% of the world’s soybean crop, respectively, each has moved into exporting signiﬁcantly more soybean meal and oil tonnage than the United States [9]. With modern automation, not as many jobs are created by importing whole seeds for local processing as previously, but many countries still encourage the establishment of domestic oil extraction plants and reﬁneries. The local tax base is increased; broader options become available for buying seed on the open market; and food and feed supplies are more stable. Many international companies also ﬁnd advantages in establishing extraction and reﬁning facilities within the expected sales regions, for example, in the European Community. Some oil crops, such as oil palm fruit, are highly perishable. Consequently, the oil must be extracted from the soft pulpy tissue near the growing site. Cottonseed is an example of a crop currently undergoing signiﬁcant change. It was the ﬁrst oil whose processing technology was developed during the Industrial Revolution of the late 1800s and early 1900s. Prior to that time, the Old World edible fats were primarily olive and sesame oils, and (pork) lard and (beef) tallow, although peanut, rapeseed and other oils were also produced. Many principles of seed preparation, hydraulic and screw-press extraction, alkali reﬁning, bleaching, winterization, hydrogenation and deodorization were ﬁrst perfected by cottonseed oil processors. Large-scale growing of soybeans, sunﬂower seed, and rapeseed/canola came later. A driving force for development of the cottonseed oil industry was the need to ﬁnd a use for the piles of cottonseed left to decompose after ginning cotton. Initially, the seed was free for the taking but contained gossypol, a brown-green pigment toxic to non-ruminants, which also darkens the oil. Cottonseed oil was ﬁrst used for illumination, and then in edible applications as processing technology improved [12]. Development of the potato chip industry and edible-quality cottonseed oils occurred at about the same time. The timing was fortunate, because cottonseed oil develops a slightly nutty ﬂavor during the early stages of oxidation that can enhance the ﬂavor of potato chips. As a result, cottonseed oil became generally recognized as the gold standard for frying potato chips, a reputation that continues to have support today. But there are also some limitations associated with cottonseed. The supply is dictated by the world market for cotton ﬁber and is inelastic to oil prices. After ginning, seed handling is more difﬁcult compared to other grains and oilseeds due to linters that restrict ﬂow and necessitate storage in aerated seed houses or piles, rather than silos. Thus, relatively little whole U.S. grown seed is exported (∼3%). However, cottonseed has become recognized for its nutritional beneﬁts (metabolizable energy, protein content and increased butterfat production) in feeding of whole seed to dairy cattle, a cost-effective application that can use up more than half the available seed in a given year.

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The ﬁrst soybeans processed in the United States were imported from Manchuria in 1911 [13]. Soybean production increased by 700% between 1929 and 1939 when the crop exceeded 91 million bushels. Initially, soybean oil was used as a substitute for linseed and other drying oils, but as processing technology improved and demands for oils increased, soybean oil began to compete with cottonseed oil. This coincided with needs for a more reliable feed protein source than ﬁshmeal, whose production has greatly ﬂuctuated because of climatic effects of Los Ni˜nos off the western coast of South America and Las Ni˜nas in the eastern equatorial Paciﬁc. U.S. public health concerns in the 1970s led to increased preferences for vegetable oils over animal fats, which are secondary products in meat production. Only 0.173 MMT of edible lard and 0.676 MMT of edible tallow (a total of 0.849 MMT of edible animal fats exclusive of butterfat) were produced in the United States in 1997 [11]. Malaysia, the world’s leading exporter of palm oil, imports and crushes soybeans. The meal is kept for its rapidly growing poultry, swine and aquaculture industries, and the crude soybean oil is exported. Plants in Singapore and Portugal extract soybeans “in transit” and reexport crude oil and meal. The climate in northern Europe is too severe for growing soybeans, and sunﬂower seed can be produced only in southern areas. Europe is a major importer of soybeans for processing into animal feeds and edible oil, and exports a signiﬁcant amount of rapeseed/canola grown in its relatively cool climate.

2.3. OILSEEDS MODIFICATION Fatty acid compositions of oilseeds have been modiﬁed by selective breeding and recombinant DNA techniques. Crops from the latter approach have become known as “GMOs”(genetically modiﬁed organisms), which can include genes modiﬁed within a plant as well as genetic material transferred from one organism to another. Although potentially necessary to ensure sufﬁcient food in the future for the increasing human population, GMOs have encountered considerable emotional resistance, and some countries are seeking to ensure the oilseeds they import are GMO-free. GMO technology is progressing rapidly and diplomatic efforts currently are in process to resolve issues. Successes in modifying oilseeds by traditional selective breeding techniques include: r Rapeseed/Canola. Erucic acid, a 22-carbon fatty acid found in fatty deposits

in hearts, skeletal muscles and adrenals of laboratory animals fed rapeseed oil, was essentially eliminated from the crop by Canadian breeders during the mid-1950 to mid-1970 era. Rapeseed with low erucic acid content was initially identiﬁed by the acronym LEAR. During the same period, the glucosinolates in rapeseed were also reduced. These compounds are

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precursors of isothiocyanates and other active sulfur-containing compounds that interfere with uptake of iodine by the thyroid gland, have negative growth effects on animals, contribute to liver disease in poultry, and poison nickel and other catalysts used for hardening (hydrogenating) oils. “Canola” is the trademarked name designating products derived from low-erucic acid, low-glucosinolate rapeseed varieties. Maximum permissible levels for these compounds are part of the Canola Council of Canada standards for canola varieties [14]. HEAR (high-erucic acid rapeseed) varieties are still grown for food use in some parts of the world, as well as for industrial purposes. Buyers should inquire about erucic acid and glucosinolate contents when seeing the name “rapeseed.” Improvement of canola has continued. When erucic acid, which comprised approximately 50–60% of the fatty acids in HEAR varieties, was removed, the resulting fatty acids proﬁle of the oil shifted to approximately 55% oleic acid, 21% linoleic acid and 11% linolenic acid. The latter fatty acid is highly susceptible to oxidation and was present in quantities slightly higher than in soybeans. Canola varieties containing 65–75% oleic, 10–20% linoleic and 3–5% linolenic are now available and possess improved frying stability. Domestic public health concerns about the role of saturated fatty acids in the formation of arterial plaque deposits (atherosclerosis) led to increased use of polyunsaturated oils (containing linoleic and linolenic acids) in the 1960–1970s. Concerns then shifted to the role of oxidized cholesterol and polyunsaturated fatty acids in arterial plaque formation, and to antioxidants as protectors of dietary and nervous system lipids. Currently, the Mediterranean diet is in favor. Because the world supply of olive oil (containing ∼80% monounsaturated oleic acid) is limited, interest has turned to development of canola, sunﬂower seed and safﬂower varieties containing 65–80+% oleic acid. The reduced oxidative tendency of high-oleic acid oils results in longer frying life and in fried products with extended shelf life. r Sunﬂower. Traditional sunﬂower oil contained approximately 20% oleic acid and 65% linoleic acid. In the 1970–1980s, varieties containing 80–90+% oleic acid, which have excellent potential for frying applications and as an industrial source of oleic acid, were developed by traditional breeding techniques. However, a sustainable market has not yet developed for high-oleic acid sunﬂower oil, apparently due to price structure and patent issues. Currently, mid-oleic sunﬂower varieties, containing about 65% oleic acid, are being commercially developed. r Soybeans. Soybean breeders were effective in reducing the linolenic acid content of soybean oil by approximately one half (from 9% to 4.5%) by traditional breeding techniques in the early 1980s, and more recently to less than 3% linolenic acid. This appreciably increases the ﬂavor stabilities of frying oil and supports better oxidative stability of fried products.

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r Improved oilseeds. Additional soybean, canola, sunﬂower, cotton and

peanut cultivars, with oil compositions modiﬁed for speciﬁc uses, have been developed or are nearing release to growers. Some of the changes are the result of traditional breeding, others come from recombinant DNA techniques. But availability of special seed does not automatically ensure availability of their oils in the marketplace. Seed companies naturally want to recover the development costs of the new varieties. Farmers must be able to earn a reasonable return, particularly for growing oilseed varieties/crops that may have reduced yields (“yield drag”) and riskier markets than for established varieties. But global trade of soybeans has traditionally been speculative—at the time of purchase, the trader does not know where or how a speciﬁc lot of seed will be used. The system works well when all soybeans are essentially interchangeable. But, unlike the wheat milling industry, which manages to keep six or more types of wheat segregated, an extensive trading system for keeping different types of soybeans segregated does not exist yet. However, the industry is now positioned and prepared to develop the necessary infrastructure to handle different types of soybeans as warranted by market demand.

3. OIL CHEMISTRY

3.1. DEFINITIONS Some terms are used in a general manner in the edible oils industry. Lipids include triglycerides, waxes, sterols, phosphatides, and other fatty-like substances that are soluble in organic solvents. A few, like the phosphatides and emulsiﬁers, may also be partially soluble in water. Oils are mixtures of triglycerides that are liquid at room temperature. Fats are mixtures of liquid and crystalline triglycerides that are solid or semisolid at room temperature. Frying oils usually refers to liquid triglycerides, which may have been slightly hydrogenated to improve stability and sometimes contain oil-soluble additives; but some commercial fryers also use the term to include higher-melting fats that are stored as heated liquids. A consensus deﬁnition for shortenings, as applied to frying, does not exist. For convenience in this chapter, they are deﬁned as oils that have been processed to prolong frying life and product shelf life, modify the melting proﬁle, and are semisolid or contain crystals at room temperature.

3.2. FATTY ACIDS Deﬁnitions are closely adhered to when addressing the chemical aspects of fats and oils. Fatty acids, hydrocarbon chain structures that have a terminal carboxyl group (–COOH), are the primary subunits of triglycerides—the major constituents of fats and oils. Short, medium and long chain fatty acids contain

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4–10, 12–14, and 16+ carbon atoms, respectively. Frying oils are triglycerides, compounds consisting of a glycerol backbone with three attached (esteriﬁed) fatty acids, whose individual characteristics are collectively reﬂected in the assembled molecule. Carbon atoms form four linkages (covalent bonds) with other atoms, oxygen two, and hydrogen one. When arranged in a straight chain, carbon atoms with attached hydrogens form an extremely stable (nonreactive) alkane hydrocarbon. If hydrogen atoms are removed from two adjacent carbon atoms and a carbon-to-carbon double bond is formed, the hydrocarbon is an alkene. The double bonds in alkenes are unsaturated with respect to hydrogen and are much more reactive than alkanes. Carbon chains with more than one unsaturated bond are polyunsaturated. Important end-chain and mid-chain structures are shown in Figure 6.1 to refresh the reader’s memory of organic chemistry. The oxidation level (and reactivity) of carbon chain ends is: carboxyl group> aldehyde/ketone>alcohol>methyl group. Basically, two types of organic carbon compounds exist: aliphatics—which include the fatty acids that are the principal components of oils; and aromatics— cyclic compounds (including sterols, pigments, oil-soluble vitamins and antioxidants) that have benzene-like structures. The original meanings of the terms “aliphatic” and “aromatic” were “fatty” and “fragrant,” respectively, but either type can display odors depending on composition and volatility. Most of the stability problems in oils are associated with double bonds, whether in aliphatic or aromatic structures. Several conventions are used for naming fatty acids. Systematic names are derived from alkane/alkene names for the respective number of carbon atoms [15]. The alkane chain consisting of 18 carbons (common to edible fats and oils) is called “octadecane.” If the chain has a carboxyl end, and is saturated, the systematic name is “octadecanoic acid.” The existence of an unsaturated linkage in a fatty acid containing 18-carbons is signaled by the name “octadecenoic” acid. A chemist would further want to know “How many double bonds?” and “Where are they in the chain?” The presence of one unsaturated bond is indicated by “mono,” two by “di,” and three by “tri.” Organic chemists traditionally count carbon positions starting with the carbonyl (acid) carbon as “1.” Biochemists often use the “omega, ␻ system,” and count from the other end of the chain with the methyl carbon as “1.” Each convention is useful to its respective specialty. Octadecanoic acid is the saturated member of the 18-carbon family of vegetable oil fatty acids, and has the common name “stearic acid.” The once-unsaturated member of the family oleic acid has the systematic name 9-octadecenoic acid, meaning an 18-carbon chain with one unsaturated bond after the ninth carbon. In like manner, the twice unsaturated member of the family linoleic acid is 9,12-octadecadienoic acid, and the triunsaturated member, linolenic acid, is 9,12,15-octadecatrienoic acid (Table 6.2) [15,16].

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CHEMISTRY TERMS - I MID CHAIN GROUPS

CHAIN END GROUPS O

O

H

H

Methyl --------CH3

Alcohol “-ol” -C(H)2OH

=

-C-O-H

-C

-C H

O-H

Aldehyde Acid “-al” “carboxyl” -CHO - COOH

O

H

O-H

=

H

=

H -C-H

-C-

-C-

-C-

H

H

“Methylene “Hydroxyl carbon” carbon” -C(H)2 -CHOH-

Ketone “keto” -CO-

The carbonyl group includes aldehydes and ketones. SYSTEMATIC NAMES: If a straight chain hydrocarbon ends with a carboxyl group, it is called: “-anoic acid” if all carbon-carbon bonds are saturated: -C-C-. “-enoic, -dienoic, -trienoic acid” if 1, 2 or 3, double bonds, -C=C-, occur.

GENERAL FORM OF FATTY ACIDS CARBOXYL E ND

METHYL END

O

H

= H-O-C-…...-(CH2)n-……-C-H

H Carbon “1” Systematic

Carbon “1” Omega, N,

System; count to right.

System, count to left.

18 CARBON FATTY ACIDS 1 1 1 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8

Stearic Acid (18:0) HOOC-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-CH3 Oleic Acid (18:1, n-9) = Linoleic Acid (18:2, n-6) = = Linolenic Acid (18:3, n-3) = = = (Only introduction of = changes within the family) Saturated fatty acid, no = bond; monounsaturated, 1=; polyunsaturated, 2+ =. Figure 6.1 Depictions of fatty acid terms (I).

Table 6.2 includes an abbreviation system of numbers for identifying common fatty acids.The abbreviation for linolenic acid is 18:3 (n-3), where “18” represents the number of carbon atoms in the chain, “3” indicates the number of unsaturated bonds, and “(n-3)” means the ﬁrst unsaturated bond occurs after the third carbon counted from the omega end. Oil chemists, familiar with the structure of 18-carbon fatty acids know that, with few exceptions, the ﬁrst

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Ethanoic Butanoic Hexanoic Octanoic Decanoic Dodecanoic Tetradecanoic Hexadecanoic 9-Hexadecenoic Octadecanoic 9-Octadecenoic 9-Octadecenoicb

Acetic Butyric Caproic Caprylic Capric Lauric Myristic Palmitic Palmitoleic Stearic Oleic Elaidic

2:0 4:0 6:0 8:0 10:0 12:0 14:0 16:0 16:1 18:0 18:1 (n-9) 18:1 (n-9)

--−7.9 −3.4 16.7 31.6 44.2 54.4 62.9 −0.5 69.6 16.3 43.7

--B H Oc D La M P Po St O ---

11-Octadecenoicb 9,12-Octadecadienoic 9,12,15-Octadecatrienoic 6,9,12-Octadecatrienoic Eicosanoic 5,8,11,14-Eicosatetraenoic Docosanoic 13-Docosenoic

Vaccenic Linoleic α-Linolenic γ -linolenic Arachidic Arachidonic Behenic Erucic

18:1 (n-7) 18:2 (n-6) 18:3 (n-3) 18:3 (n-6) 20:0 20:4 (n-6) 22:0 22.1 (n-9)

44.0 −6.5 −12.8 --75.4 −49.5 80.0 33.4

--L Ln ----An --E

Reference [15]. Trans fatty acids. All others are cis form.

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Typical Source --Butterfat Butterfat Coconut oil Coconut oil Coconut oil Butterfat, coconut oil Most fats and oils Many plant and animal fats Most fats and oils Most fats and oils Ruminant fats, partially hydrogenated vegetable oils Butterfat Most vegetable oils Soybean oil, canola oil Soybean oil Peanut oil Lard, animal depot fats Peanut oil Rapeseed oil, crambe oil

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Common Name

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unsaturated bond is located after the ninth carbon, the second unsaturated bond occurs three carbons later, and the third unsaturation after yet another three carbons. Alternatively, this is shown as 18:3␻3 in the omega system. Delta () sometimes is used to indicate the bond after a speciﬁc carbon (counted from the carboxyl carbon). For example, 9 means “the bond after the ninth carbon.” The melting points of saturated fatty acids, rigidly linear, increase with chain length Table 6.2. The longest saturated common fatty acid, which will melt in the human mouth (at 98.6◦ F/37◦ C) is 10 carbon decanoic (capric) acid with a melting point of 84.5◦ F/31.6◦ C. Heat is synonymous with molecules in motion. Individual molecules are able to move freely in gases and somewhat less in the liquid state. Introduction of an unsaturated bond in a fatty acid increases three-dimensional “ﬂex” in the carbon chain and lowers the melting point, with the greatest lowering occurring if the bond occurs midpoint in the chain. Increasing the number of double bonds adds more complexity to the fatty acid chain structure and further lowers the melting point. Stearic acid (18:0) melts at 157◦ F/69.6◦ C, oleic acid (18:1 [n-9]) at 62◦ F/16.3◦ C, linoleic acid (18:2 [n-6]) at 20◦ F/-6.5◦ C, and linolenic acid (18:3 [n-3]) at 9◦ F/-12.8◦ C (Table 6.2). Unsaturated bonds normally are in the cis form in plant oils, depicted in two-dimensional drawings by two carbons linked by a double bond, with the adjacent hydrogens on the same side of the bond (Figure 6.2). The cis conﬁguration in fatty acids results in a non-linear structure and supports a ﬂuid nature. It is not possible to make margarines or plastic shortenings from liquid oil alone. The most common way of hardening oils (creating solids) is by catalytic hydrogenation, which also increases the resistance of the oil to oxidation. If hydrogenation of a mixture of homologous fatty acids (18:0, 18:1, 18:2 and 18:3) is carried through to completion in a batch reactor, the ﬁnal product will be stearic acid (18:0), melting at 157◦ F/69.6◦ C. Partial hydrogenation is an alternative in which some trans forms of fatty acids are produced with intermediate melting points. Trans bonds are depicted by two carbons linked by a double bond, but with the adjacent hydrogens on opposing sides of the bond, indicating restricted ﬂexing of the chain at that point (Figure 6.2). They are called “geometric isomers” if they occur in the former cis position, and “positional isomers” if locations of the bonds in the chain have changed. Oleic acid (18:1 n-9) is a cis isomer form and melts at 62◦ F/16.3◦ C. Its saturated homolog stearic acid (18:0) melts at 157◦ F/69.6◦ C. Shifting the cis bond of oleic acid to 18:1 (n-6) results in a positional isomer with a melting point of 91.4◦ F/33◦ C. Elaidic acid (18:1 n-9) is a geometric (trans) isomer of oleic acid (18:1 n-9) and melts at 111◦ F/47.3◦ C [5]. In addition to catalytic hydrogenation, trans geometric isomers are also created by rumen microorganisms (bacteria and protozoa) in cattle, sheep and goats. In the rumen, triglycerides are hydrolyzed and the freed glycerin is rapidly metabolized. Liquid fatty acids are toxic to microorganism cells, and

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CHEMISTRY TERMS - II HYDROGENATION, BIOHYDROGENATION H H

HH H2

-C=C-

H

-C-C-

Catalysts, Rumen Microorganisms

+

-C=C

HH

Unsaturated cis Form

H trans Form, Geometric Isomer

Saturated

Nonconjugated Bonds

Conjugated Bonds

-C=C-C-C=C-

-C=C-C=CConjugation can move in either direction. Resulting bond can be cis or trans.

TRIGLYCERIDE SYNTHESIS Glycerol + 3 Fatty Acids

H

O

H-C-O-H + H-O-C-(CH2)n-C-H O

H

H

O

O

=

=

3, γ

H-C-O-H +

H

H-C-O-C-R1

O H-O-C-R2

H

=

H-C-O-H +

H-O-C-R1

O

H-C-O-C-(CH2)n-C-H + 3 H2O

=

2, β

H

=

1, α

Triglyceride + 3 Molecules Water Ester Linkage

=

Glycerol Carbon Position

Plant Enzymes

H-C-O-C-R2

H

H Glycerol

Fatty Acids

Triglyceride

Water

FREE FATT Y ACID HYDROLYSIS Triglyceride + Water

Alkalis, Enzymes

Free Fatty Acids + Mono-, Diglycerides.

Waxes = Ester-linked product of long chain (single -OH) alcohols and fatty acids.

Figure 6.2 Depictions of cis/trans bonds, conjugation, triglyceride synthesis/hydrolysis (II).

(70–90%) are biohydrogenated to trans forms by enzymes in their cell walls, apparently to limit their uptake. The trans fatty acids are later absorbed in the small intestine and may be assembled as components of triglycerides. Rumen microorganisms have been reported to completely synthesize trans fatty acids de novo (in place, starting from shorter carbon units) [17]. Animal sources of dietary trans-monoenes, as a percentage of total fatty acids, have been reported as follows: milk fat, 7.5%; butterfat, 5.0–9.7 beef (depot), 2–12%; calf (depot), 1–17.3%; and sheep (depot), 11–16% [18].

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TABLE 6.3.

Relative Rates of Oxidation and Hydrogenation of Fatty Acid Chains. Modiﬁed from: Beckman, H. J., 1983. J. Am. Oil Chem. Soc., 60(2):234A-242A [19]. With permission.

Fatty Acid Stearic (18:0) Oleic (9cis-18:1) Linoleic (9cis,12cis-18:2) Linolenic (9cis,12cis, 15cis-18:3)

Iodine Value

Relative Oxidation Rate

Relative Hydrogenation Reactivity

0 90 181 274

1 10 100 150

0 1 20 40

The relative reactivities of fatty acids in oxidation and hydrogenation (terms to be described later) increase with the number of unsaturated bonds present (Table 6.3) [19].

3.3. TRIGLYCERIDES Triglycerides often are depicted in two-dimensional representations as a large letter E conﬁguration, turned right or left, where the stem represents a glycerin backbone, and each arm is an ester-linked fatty acid. A “chair” structure is also used, usually in connection with crystallography. Esteriﬁcation, also called “acylation,” is a dehydration reaction in which one of the hydroxyl groups of glycerin is joined to the hydroxyl arm of a fatty acid’s carboxyl end with elimination of a molecule of water and resulting in an ester linkage (Figure 6.2). The resulting compound is a monoglyceride if one linkage has occurred, a diglyceride if two, and a triglyceride if all three of the glycerin’s hydroxyls have been linked to fatty acids. Modern textbooks reﬂect IUPAC’s (International Union of Pure and Applied Chemistry) technical preference for calling these compounds “monoacylglycerols,” “diacylglycerols” and “triacylglycerols,” respectively; however, the sufﬁx “glyceride” has a long history of usage in the industry. Glycerol is water-soluble, and its polarity (attraction for water) decreases as more fatty acids are substituted for hydroxyl groups. Monoand diglycerides and their derivatives are produced commercially for use as emulsiﬁers. The type employed depends on whether the emulsion is oil-inwater or water-in-oil. Waxes are long-chain monohydroxy alcohols ester-linked to fatty acids and function as barriers to moisture loss in leaves and seeds. It is desirable to know which fatty acids are present in the triglyceride, and their speciﬁc location in the structure. In the early R/S system, priorities were assigned to each fatty acid, and the acids then assigned to the E with the top arm designated as “position 1.” Typically, the longest saturated fatty acid was shown in the “1“ position, and the shortest in the “3,” but with no conﬁrmation of which fatty acid was where. As analytical procedures improved, the stereospeciﬁc

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numbering (sn) method was established. Locations on the glycerol are still numbered top to bottom, but the presence of the notation sn indicates that the identity of the fatty acid in the indicated position is known. For example, a triglyceride named 1-stearoyl-2-palmityl-3-lauryl-sn-glycerol has stearic acid in the 1 position, palmitic acid in the 2 position and lauric acid in the 3 position. The compound could also be identiﬁed as sn-StPLa or as sn-18:0–16:0–12:0. The Greek letters ␣ (alpha), ␤ (beta) and ␥ (gamma) are sometimes used in place of 1, 2, and 3, respectively. The 2 or ␤ position is very important in oil chemistry. Many lipases cleave either 1, 3 position fatty acid linkages, or 2fatty acid linkages; also, the type of fatty acid in the 2 position signiﬁcantly affects the triglyceride’s melting point. Returning to the sn system, the notation ␤-StPLa indicates that palmitic acid is known to be in the 2 position, but the location of the other fatty acids is not known [15]. It is not necessary to draw the complete triglyceride molecule, including all atoms and bonds, each time it is depicted. Chemists use various abbreviations, for example CH3 (CH2 )14 COOH is a structural formula for palmitic acid. Sometimes, a fatty acid is designated by –OOCRn , with Rn numbered to identify its position in the triglyceride when the focus is not on the speciﬁc fatty acid (Figure 6.2). Fatty acid compositions of major oils are shown in Table 6.4 [16], although considerable variation can occur as described later.

3.4. PHOSPHOLIPIDS In addition to two fatty acids, glycerol may be ester-linked to a phosphate group, which in turn is linked to choline, ethanol amine, inositol or serine. The corresponding proper names of the phosphatides are diacylphosphatidyl choline, diacylphosphatidyl ethanolamine, diacylphosphatidyl inositol and diacylphosphatidyl serine, with the fatty acids additionally identiﬁed if relevant (Figure 6.3). After separation from oil, crude lecithins may be processed by several methods, including oil reduction and separation into alcohol-soluble and insoluble fractions, to make a variety of commercial products. The phosphatides participate in synthesis of triglycerides, in absorption of fatty acids in the small intestines of animals, and as components of other biological compounds. The presence of phosphatides in oils is determined from phosphorous analysis and the relationship [20]: % phosphatides = 30.0 × % phosphorous content

3.5. SYNTHESIS OF VEGETABLE OILS 3.5.1. Synthesis in Plants and Animals Synthesis of vegetable oils is similar to that of animal fats in that fatty acids are constructed ﬁrst and then acylated to glycerol to form triglycerides. The

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10:0

18:0

20:0

16:1

18:1

24 27 4 26 9 11 22 26 13 45 8 11 7 7 11 7 4

19 12 2 34 3 2 3 14 3 4 3 2 2 2 4 5 5

4 2

43 29 62 34 6 28 19 44 71 40 15 48 13 78 24 19 65

14:0

Beef tallowa Butterfatb Canola oil Cocoa butter Coconut oil Corn oil Cottonseed oil Lard Olive oil Palm oil Palm kernel oil Peanut oilc Safflower oilc High-oleic safflower oil Soybean oil Sunflower oil Mid oleic sunflower oil a

4

Mono-unsaturated

2

1

3

3

3 11

1

8

6

47

18 1 2

3

4

48

1 16

Beef tallow typically contains C15:0 plus C17:0 at about 2% and C14:1 plus C17:1 at about 2% of total fatty acids.

b

Butterfat typically contains C15:0 plus C17:0 at about 3% of total fatty acids.

c

Peanut oil typically contains C22:0 plus C24:0 at 4--5% of total fatty acids.

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18:3

3 2 22 3 2 58 54 10 10 10 2 32 78 13 54 68 26

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Typical Fatty Acid Composition of the Principal Vegetable and Animal Fats and Oil in the United States (% of total fatty acids). Modiﬁed from: Food Fats and Oils 1999, Eight Edition, Institute of Shortening and Edible Oils, Washington, D.C. [16]. With permission.

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CHEMISTRY TERMS - III PHOSPHOLIPIDS, “LECITHINS” CH2-O-R1 CH-O-R2 = “beta” Form

=

O X CH2-O-P-O-R3 = “alpha” Form OWhere

Phosphatide Name

R1 = Fatty Acid R2

----3

= Fatty Acid or R (beta)

-----

R3 = CH2-CH2-N+(CH3)3 Diacylphosphatidyl choline “ = CH2-CH2-N+H3

Diacylphosphatidyl ethanolamine

“ = CH2-CHN+H3

Diacylphosphatidyl serine

COO“ = C6H6-(OH)6

Diacylphosphatidyl inositol

“ = H+

Diacylphosphatidyl acid

X = Phospholipase-D cleavage site, where complexing /crosslinking with divalent cations (Ca ++, Mg++, etc.) occurs to form non-hydratable phosphati des (NHPs).

SUCROSE FATT Y ESTERS - Up to 8 fatty acids (R groups). CH2OR O RO

ROCH2 O

OR O OR

O

RO

CH2OR

OR

R = Fatty acid. Ester linkages can be formed between carboxyl ends of fatty acids and hydroxyl groups o f sugars as if they were alcohols.

Figure 6.3 Depictions of phosphatides and sucrose fatty esters (III).

combination is a highly efﬁcient form for storing energy at slightly more than 9 calories/gram instead of 4 as with carbohydrates. Many of the same synthesis mechanisms are involved in both kingdoms. However, plants do not have adipocytes—cells specialized for synthesis and storage of triglycerides—nor a circulatory system that can transport fatty acids as lipoproteins. Instead, fatty acids are synthesized, acylated to triglycerides and stored primarily in fat bodies in the cytosol of cells concentrated in the seed germ, where the oil will be available for providing energy to initiate germination and support early cell

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growth of the young plant. In the grass family (Gramineae), including maize and wheat, the germ lies along the side of the endosperm (starch energy supply). In most oilseeds, the entire hull contents (meats) is the germ, and includes a rootlet (hypocotyl) and two cotyledons (leaves), which are pushed above the soil and unfold at germination. The raw material for synthesizing vegetable oils is sucrose, formed by photosynthetic ﬁxing of absorbed atmospheric carbon dioxide by chloroplasts and conversion in the plant’s canopy leaves, then transported through the vascular system to the site where oil is synthesized. There, it becomes several metabolites, from which even-numbered fatty acids are assembled, two units at a time until 16:0 (palmitic fatty acid) is produced [21,22]. Another set of enzymes is employed for further elongation to 18:0 (stearic acid) and longer fatty acids. Very speciﬁc desaturases work with the elongases to produce unsaturated bonds at speciﬁc locations on the fatty acid chain. Delta-9 desaturase abstracts two hydrogens between the ninth and tenth carbon atoms of 18:0 to produce 9cis-18:1 (oleic acid). Delta-12 desaturase, acting on oleic acid, forms 9cis,12cis-18:2 (linoleic acid); and, sequentially, 15 desaturase forms 9cis,12cis,15cis-18:3 (linolenic acid) [21,22]. However, microorganisms sometimes start the chain with a 3-carbon base, to which two carbons are added at a time to produce fatty acids with odd carbon numbers (typically 15 or 17) [17]. These fatty acids occur in butterfat and tallow as a result of rumen microbial synthesis, followed by absorption in the small intestine and esteriﬁcation into triglycerides by ruminant fat. Mammals require linoleic, linolenic and arachidonic (5cis,8cis,11cis,14cis20:4) essential fatty acids for synthesis of prostaglandins, prostacylins, thromboxanes and other hormone-like compounds. They do not have desaturases able to establish double bonds after 9 , but, given linoleic acid, are able to elongate and modify it to synthesize arachidonic acid. Linoleic and linolenic fatty acids must be supplied in the diet. The National Academy of Science’s Food and Nutrition Board has established a Recommended Daily Allowance (RDA) for linoleic acid of 1–2% of dietary calories. The RDA for linolenic acid is not deﬁned, but generally is considered to be about 0.5% of calories [23].

3.5.2. Fatty Acid Compositions The fatty acid composition of a seed is affected by the genetics of the species, variety or hybrid and, in some cases, by climatic temperature at the time of oil synthesis. Nature apparently ensures that oils in non-dormant plants, and in coldblooded animals that feed on plants, remain liquid in their natural environment. Overall, oils with the most saturated fatty acids, such as coconut and palm oil, are produced near the equator, and plant and ﬁsh oils become increasingly polyunsaturated as the North and South Poles are approached. The linoleic acid content in sunﬂower oil is inversely related to the temperature of seed maturation

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and oleic acid content—demonstrated by planting the same seed in northern and southern locations for typical growing seasons, and by planting the same seed for spring and winter growth in southern Texas [24,25]. Differences in oleic-linoleic acid contents of sunﬂower seed grown at different maturation temperatures have been signiﬁcant, shifting by as much as 40% each. Oil processors have exploited this difference by selecting northern-grown sunﬂower (high polyunsaturated) oils for sale as salad oils and southern-grown oils (high-oleic acid content) for frying uses [26]. Although the same soybean seed may not ﬂower if planted over wide latitudes because of the plant’s narrow daily photoperiod requirements, modest increases in oleic acid content have been observed in soybeans grown in southern regions of established maturity group belts compared to their northern limits, and in seed produced in hot summers compared to cooler years. Recent advances in plant genetics now enable growing high-oleic acid varieties/hybrids of various species in northern climates.

3.5.3. Triglyceride Structures Tables 6.2 and 6.4 show that signiﬁcant amounts of saturated fatty acids, with melting points higher than human body temperature, exist in various oils (for example, over 25% in cottonseed oil). They are kept in liquid state in their normal habitat by esteriﬁcation onto triglycerides with lower-melting mono- and polyunsaturated fatty acids. Molecules of even lower-melting polyunsaturated triglycerides additionally act as solvents for the higher-melting triglycerides. Nature makes efﬁcient use of the lower-melting fatty acids in constructing liquid triglycerides. When scarce, unsaturated fatty acids in vegetable oils generally occur in the 2 (␤) position, with the saturated fatty acids in the 1 and 3 positions. As availability of unsaturated fatty acids increases, they can also be found in the 1 and 3 positions. This phenomenon is shown in Table 6.5, which compares theoretical (random) patterns based on total fatty acid composition TABLE 6.5.

Theoretical (Random) and Actual (Found) Distributions of Saturated (S) and Unsaturated (U) Fatty Acids in Soybean Oil, %. Modiﬁed from: List, G. R. et al., 1977. J. Am. Oil Chem. Soc., 54(10):410–413 [27]. Glyceride Class SSSa SUS USSb USU UUSb UUU

a

Theoretical

Found

0.4 2.1 4.2 11.2 22.4 59.7

0.07 5.2 0.4 0.7 35.0 58.4

S = saturated, either palmitic or stearic; Unsaturated = oleic, linoleic or linolenic. is identical with SSU and UUS is identical with SUU.

b USS

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TABLE 6.6.

Melting Points of Original and Rearranged (Randomized) Triglycerides. Modiﬁed from: O’Brien, R. D., 1998. Fats and Oils: Formulating and Processing for Applications. Technomic Publishing Co., Lancaster, Pennsylvania [5]. With permission Original Fat or Oil

◦

F

Randomized ◦

C

◦

F

◦

C

Natural oils: Soybean oil Cottonseed oil Lard Palm oil Palm kernel oil Coconut oil

19.4 50.9 109.4 102.9 82.9 77.9

−7.0 10.5 43.0 39.4 28.3 25.5

41.9 93.2 109.4 108.9 80.4 82.8

5.5 34.0 43.0 42.7 26.9 28.2

Hydrogenated oils: Hydrogenated palm kernel oil Hydrogenated coconut oil

113.0 100.0

45.0 37.8

93.9 88.9

34.4 31.6

with actual patterns found in soybean oil [27]. “S” and “U” represent saturated and unsaturated fatty acids, respectively. Only four or ﬁve fatty acids comprise 95+% of most vegetable oils, but over two dozen different arrangements have been reported for soybean and cottonseed oils. Table 6.6 [5] compares original oils to oils whose fatty acids locations have been randomized (rearranged) by interesteriﬁcation. Nature’s positioning efforts have reduced the melting point of soybean oil by 22.5◦ F/12.5◦ C, and by 42.6◦ F/23.5◦ C in cottonseed oil compared to random arrangement.

3.6. ANALYTICAL METHODS Various analytical methods are used in oilseeds breeding, monitoring seed during storage, crude oils trading, control of oils reﬁning and reﬁned oils sales/purchasing speciﬁcations. Increasing use is being made of rapid, nondestructive and on-line continuous methods because of lower cost and availability of information in time to adjust processes. Many trading contracts provide that, whenever a legal dispute regarding compliance with purchasing speciﬁcations occurs, the buyers and sellers defer to AOCS-Certiﬁed Chemists and the Ofﬁcial Methods and Recommended Practices of the AOCS [28]. The National Oilseeds Processors Association, NOPA, [29] speciﬁes the following analyses in its typical trading contracts for crude soybean oil: free fatty acids content, unsaponiﬁable matter, moisture and volatile matter, insoluble impurities, phosphorous, bleachable color and ﬂash point. The National Cottonseed Products Association, NCPA, [30], which also establishes standard trading rules for peanut oil, speciﬁes free fatty acids content in cottonseed, and free fatty acids, bleaching test color, moisture and volatile matter and ﬂavor

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for oil. These analyses are always conducted, and discounts applied for substandard seed or crude oil. Processor/purchaser speciﬁcations for reﬁned frying oils commonly include color, free fatty acid, peroxide value, iodine value, cold test, ﬂavor, an oxidative stability test, melting point and often a solids melting proﬁle. Purchasers may add further speciﬁcations as needed to meet speciﬁc requirements. Brief descriptions of assays that typically would be conducted as oilseeds move to ﬁnished oil [28] follow: r NIR Moisture, Oil and Protein. Modern near-infrared analyzers enable

r

r

r

r

simultaneous analyses of ground seed or extracted meal for moisture, protein and oil. Results can be obtained within a matter of minutes; however, instrument calibration is critical and re-calibration is essential if major changes occur in the materials analyzed. The method can provide rapid results for screening large numbers of samples, but some extraction plants (oil mills) prefer to analyze individual samples by traditional methods for closely controlled operations. Aﬂatoxins. Cottonseed, peanuts and corn (germ) are susceptible to infection by Aspergillus species with production of aﬂatoxins, recognized carcinogens. Alkali reﬁning removes aﬂatoxins, resulting in safe oils. But oil millers need to know which lots of seed contain aﬂatoxins to ensure segregated binning, and to anticipate treatment or disposal of extracted meals if maximum amounts of aﬂatoxins permitted in animal feeds are exceeded. Seed Grade. Seed grade is the basis for determining payments to the selling party, and its determination is a sensitive issue. The general industry philosophy is to minimize rejections at the receiving dock to avoid losing the supplier in the future, but to recover the increased costs of processing substandard seed by discounting the price paid. Additional speciﬁcations may be established by the oil mill. For example, charges are made for drying high-moisture seeds to levels where they can be stored without spoilage. U.S. Department of Agriculture inspectors typically grade soybeans for the domestic and export markets. Regarding other seeds, many oil mills sample trucks at the receiving dock according to prescribed procedures and send the samples to a third neutral party (independent laboratory) for grading. Moisture and Volatiles (M&V). This analysis employs a forced-draft oven. The assay requires at least four hours. Since it is impossible to separate volatiles in this method, moisture essentially means M&V. Preparation techniques vary with seed species. If the need occurs for determining low levels of water speciﬁcally, the more complex Karl Fischer titration method may be used. Fat (EE). Fat is extracted from the seed using petroleum ether. The method is commonly know as “ether extraction” to distinguish it from other fat analysis methods.

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r Free Fatty Acid (FFA). Extracted fat is titrated with dilute alkali to

r

r

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r r r

r

r

neutrality, and the FFA content of the oil is commonly calculated as oleic acid. Only the free fatty acids that are not bound to triglyceride structures are measured. This method is used for oil in seeds, extracted and reﬁned oils, and for quantifying breakdown in frying oils. Iodine Value (IV). This is a measure of unsaturation (double bonds) in fats and oils. The technique is also used to monitor progress during hydrogenation. Typical IV values are coconut oil, 6–11; corn oil, 107–128; cottonseed oil, 100–115; olive oil, 74–94; palm oil, 50–55; palm kernel oil, 14–21; peanut oil, 86–107; rapeseed (HEAR), 94–120; rapeseed/canola (LEAR), 100–116; safﬂower, 136–148; soybean oil, 124–139; sunﬂower, 118–145; and high-oleic acid sunﬂower, 80–92 [31]. Peroxide Value (PV). PV is a measurement, in terms of milliequivalents per 1,000 grams of oil, of all substances that oxidize potassium iodide under conditions of the test. The reactants are assumed to be peroxides or similar products of fat oxidation. p-Anisidine Value. The para-anisidine method estimates the amount of aldehydes (principally 2-alkenals and 2,4-dienals) present in animal fats and vegetable oils by spectrophotometer absorbance at 350 nm. Anisidine values are higher in oils from damaged seed, and are interpreted by many as indicative of performance risk due to the accumulation of secondary oxidation products. p-Anisidine values are included in frying oil purchase speciﬁcations of some snack food processors. Insoluble Impurities. These consist of dirt, meal and other foreign substances in oil that are insoluble in kerosene or petroleum ether. Unsaponiﬁable Matter. This consists of substances soluble in oil that cannot be hydrolyzed to free fatty acids by alkali. Long-chain alcohols, sterols, pigment, and possibly contaminants are included. Flash Point. This refers to the temperature at which a heated oil will ﬂash (ignite) when a test ﬂame is applied to the vapor. The ﬂash point of solvent-extracted crude oil, typically above 250◦ F, 121◦ C is inﬂuenced by residual hexane. The ﬂash point of fully processed oils, typically above 575◦ F, 302◦ C, is related to the presence of breakdown products resulting from the splitting of fatty acids and oxidation during frying and other uses. Gas chromatographic methods are now being used to determine residual hexane in oils received from solvent extraction plants. Neutral Oil and Loss. Column chromatography is used for predicting the amount of saleable oil that may be obtained from a lot of crude oil. Oil that passes through the column is considered neutral (saleable) and the polar compounds that are adsorbed to the column packing are indicative of reﬁning loss. Bleaching Test. This speciﬁc reﬁning and bleaching procedure is used to predict Lovibond color after full-scale processing of a crude oil lot. Loss of

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oil and bleaching earth consumption during bleaching of reﬁned oil are estimated. Oil Color. The color of oil, in red and yellow values, is determined using speciﬁed instruments calibrated to AOCS or Lovibond standards. Phosphorous. Phosphorous content indicates the presence of phosphatides in oil. When determined on laboratory-degummed oil, the assay measures the remaining non-hydratable phosphatides (NHPs) content and provides the basis for calculating the amount of phosphoric/citric acid addition needed to convert NHPs to hydratable form. Oxidative Stability. Several methods are used to predict the resistance of oil to oxidation by bubbling warm air through a sample of oil. In the now surplus Active Oxygen Method, AOM value was the number of hours required to reach 100 milliequivalents of peroxides/kg in the heated oil. The Oil Stability Index, OSI value, determines the number of hours required to reach an inﬂection in a baseline curve derived by plotting changes in conductivity as volatile oxidation products are collected in distilled water. Some interpret this as the point where all components protecting the oil against oxidation are depleted. Refractive Index. This light refraction technique monitors progress in hydrogenation. Research has also been reported on its use to monitor degradation of frying oils. Melting Point. Most fats and oils do not have sharp melting points but change from solid to liquid state over a temperature range. Several methods are used and should be speciﬁcally referenced since results are method-dependent. The current leading methods are (Mettler) dropping point and capillary melting point. Cold Test. This procedure measures resistance of the sample to “clouding” (crystallization on cooling) and is commonly used as an index of the effectiveness of winterization and stearine removal processes. Solids Analysis. These measures of fat solids in a sample commonly are determined at 3–5 standardized temperatures. Two systems exist. The Solid Fat Index (SFI) is a method based on dilatometry that was developed in the United States in the 1950s and is applicable to oils containing <50% solids at 50◦ F/10◦ C. Solid Fat Content (SFC) is a NMR (nuclear magnetic resonance) method applicable to fats containing <95% solids, which was developed later for the palm oil industry and is used throughout the rest of the world. SFI/SFC curves indicate changes in fat solids content with temperature because of incremental melting as the temperature increases. Changes in solids content of fats in the 92–104◦ F range have a signiﬁcant effect on the perception of oiliness/greasiness of fried products. Polar Compounds. In fats and oils, these include free fatty acids, monoglycerides, diglycerides, aldehydes, ketones, other oxidation products

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and polymers, and can be collectively measured by column chromatography. Limitations on polar compound content of fats and oils in restaurant fryers exist in some European countries.

3.7. CHEMISTRY OF OIL PROCESSING AND DEGRADATIONS 3.7.1. Hydrolysis, Lipolysis Splitting a triglyceride ester linkage to produce a free fatty acid is called “hydrolysis” or “lipolysis.” Heat is also produced during the reaction in seed, crude and reﬁned oils, or frying (Figure 6.2). Lipolysis is accelerated by moisture and heat, which activate enzymes, by alkalis and metallic ions, and by partially degraded components like monoglycerides, which increase the wetting and reactivity of triglycerides. Sodium hydroxide, in excess of the amount needed for neutralization in alkali reﬁning, increases hydrolysis as does residual soap after cleaning a fryer.

3.7.2. Conjugation of Unsaturated Fatty Acids Oils chemistry is complex and involves a number of intricate details. As described earlier, two types of fatty acid isomers exist—in geometric isomerization, one or more double bonds change from cis to trans form; in positional isomerization, locations of double bonds shift. Conjugation of fatty acids has been known for many years [19], but it took the current interest in conjugated linoleic acid (CLA) by the medical community for specialists to reexamine the role of shifting bonds in hydrogenation, biohydrogenation and oxidation [32]. The most common polyunsaturated fatty acid is linoleic acid, 18:2 (n-6). Its natural form in oilseeds is 9cis,12cis-18:2. Catalytic hydrogenation and biohydrogenation are traumatic to the fatty acid chain and result in partial conversion of 9 and/or 12 cis isomers to the trans conﬁgurations. In addition, the two double bonds can move from the −C9 =C10 −C11 −C12 =C13 − conﬁguration in either direction to a conjugated conﬁguration −C=C−C=C−, in which doublebonded carbons are no longer separated by a −CH2 − group, and −C8 − and −C14 − carbons can become involved. After partial hydrogenation, the double bonds may or may not return to their original positions, resulting in six or more residual positional isomers. Kramer et al. [33] have reviewed the history of CLAs, which essentially coincide with development of analytical techniques for their separation and identiﬁcation, and make the valid point that emphasis on the potentials of CLAs in medicine may have obscured an even greater phenomenon. Conjugation has been shown to occur in triunsaturated fatty acids and shifting of bonds in monounsaturated fatty acids. The ﬁnding of up to 6% CLAs in

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meat, milk and cheese fats should raise questions about earlier explanations that rumen-modiﬁed fats are simple trans forms. The realization that some of the CLAs formed in catalytic hydrogenation of linoleic acid are identical with natural biohydrogenated forms, found beneﬁcial in medical research, should also be addressed in assessing dietary trans fats.

3.7.3. Fat Oxidation Autoxidation and photooxidation of fats and oils have been studied for many years, and scientiﬁc understanding is still evolving. In considering the linoleic acid molecule: HOOC−(CH2 )7 −CH=CH−CH2 −CH=CH−(CH2 )4 −CH3 the potential origins of 9, 3 and 6 carbon degradation fragments can be recognized. Indeed, nonanal and 3-carbon atom fragments are found, and hexanal generation is highly correlated with ﬂavor degradation. But well over 250 additional compounds, with a wide variety of carbon numbers, also have been identiﬁed in linoleic acid degradation alone, indicating the effects of conjugation and possibly creation of artifacts during analysis. A modern explanation of autoxidation of unsaturated fatty acids focuses on allylic hydrogen, which is hydrogen bonded to carbon adjacent to a −C=C− bond [15]. A fatty acid with one double bond has four allylic hydrogens as shown here: −C−H2 C−C=C−CH2 −C−. Allylic hydrogen has a relatively low bond dissociation energy and can readily be abstracted by a free radical r (X ). Free radical abstraction of hydrogen is the initial step in the chain reacr tion sequence of autoxidation. The resulting allyl radical (HC–C=C ), which can undergo double bond shifting, reacts with oxygen and forms a peroxyl r radical (–COO ). The peroxyl radical then abstracts an “available” hydrogen r (RH), forming another free radical (R ) and a hydroperoxide (–COOH). The hydroperoxides formed during autoxidation subsequently decompose, yielding additional free radicals and secondary oxidation products that accumulate and cause rancidity. Fatty acids with more than one double bond have an increased number of allylic hydrogens. In addition to regular allylic hydrogen, linoleic, linolenic and other polyunsaturated fatty acids contain methylene hydrogens, which are allylic with respect to two double bonds (–C–C=C–CH2 –C=C–C–) and are particularly susceptible to free radical abstraction. Various studies with methyl oleate, methyl linoleate and methyl linolenate have shown the relative autoxidation rates to be 1:12:25, respectively [19,34–36]. For oleic acid, the simplest unsaturated C18 fatty acid, hydrogen can be abstracted at carbons 8 or 11, resulting in formation of either of two allylic

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radical intermediates leading to an isomeric mixture of 8-, 6-, 10-, and 11allylic hydroperoxides: r r −C8 −C9 =C10 −C11 − → − C8 −C9 =C10 −, −C8 =C9 − C10 −, r r −C9 =C10 − C11 −, − C9 =C10 −C11 − → −C8 OOH−C9 =C10 −, −C8 −C9 −C10 OOH−, −C9 =C10 −C11 OOH−, −C9 OOH=C10 −C11 −

Each of these peroxides could be in the cis or trans conﬁguration; however, autoxidation predominantly yields the trans form. In addition to geometric isomerization, autoxidation of polyunsaturated fatty acids causes positional isomerization; essentially all of the hydroperoxides formed contain conjugated double bonds [15]. Hydroperoxides are moderately stable but rapidly decompose when subjected to heat, light, trace metals or other types of stress. Decomposition of unsaturated fatty acid hydroperoxides results in chain cleavage at either side of the double bond to form a wide range of alkanes, alkenes, aldehydes, ketones, short chain fatty acids, carbonyl compounds and other oxidation products. The accumulation of secondary oxidation products that have objectionable ﬂavors and aromas leads to rancidity. Photons or quanta of light energy, particularly in the near-ultraviolet range, can signiﬁcantly accelerate oxidation of unsaturated fats and oils. In photooxidation, light energy is absorbed by a sensitizer, such as chlorophyll, pheophytin, porphyrin, or riboﬂavin, and either transferred to a substrate to produce free radicals (Type I) or transferred to oxygen, leading to formation of singlet oxygen (Type II). The Type I mechanism involves the same free radical reactions associated with autoxidation, but also includes the direct decomposition of hydroperoxides, which signiﬁcantly accelerates the overall rate of oxidation [35]. In Type II photooxidation, molecular oxygen is energized to the strongly electrophilic singlet state and reacts directly with either carbon in a –C=C– bond to form hydroperoxides. Singlet oxidation is very rapid, with reaction rates at least 1450 times faster than autoxidation [37] and possibly even faster [36]. Due to direct reaction with double bonds, Type II photooxidation shows only modest differences in relative reaction rates for oleic, linoleic and linolenic fatty acids, which are 1.1, 1.9, and 2.9, respectively [35], as compared to autoxidation. Photooxidation can be controlled in savory snack and other fried foods by use of packaging that provides adequate protection from light. Efforts to provide protection from photooxidation by reducing chlorophyll, pheophytin and other photosensitizers in oil to the extent possible can provide beneﬁts to oil per se, but will not necessarily protect fried foods. Essentially all plant and animal foodstuffs, as well as seasonings and colorants, contain photosensitizers; thus, use of proper packaging provides the most reliable protection from photooxidation.

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3.7.4. Hydrogenation Hydrogenation is the process of catalytic saturation of carbon-to-carbon double bonds by addition of hydrogen gas under controlled heat, pressure and agitation. If complete hydrogenation is achieved, the three C18 fatty acids become C18:0. Partial hydrogenation of soybean oil can result in production of 30 or more different linolenic, linoleic and oleic esters, whose cis and trans (and positional) forms potentially could produce 4,000 different triglycerides [19,38]. The main objective in preparing soybean frying oil is reduction of linolenic acid content, with some reduction of linoleic to oleic acids, to extend fryer life of the oil and the shelf life of fried products. Selective hydrogenation catalysts and techniques, which favor hydrogenation of 15 bonds over 12 bonds, over 9 bonds, are used to reduce Iodine Value by 15–25 units for soybean frying oils. Conditions are chosen to avoid appreciable increase in saturated or trans fatty acids; the process sometimes is called “brush hydrogenation.” In producing margarine or shortenings base stocks for some products, conditions are chosen to control trans fatty acid content as needed to achieve desired solids melting proﬁles.

3.7.5. Polymer Formation Fat polymers are degradation compounds resulting from three-dimensional cross-linking of triglycerides, fatty acids, and derivatives at their double bond and carbonyl sites. Polymer development in frying oil can be monitored by increases in the viscosity during use.

4. OIL EXTRACTION AND REFINING

4.1. SEED HANDLING AND STORAGE A general ﬂow sheet of oil extraction processes is presented in Figure 6.4. Modern technology is shown, and may include steps not implemented in some installations. Exposure of mature seed to moisture initiates the sprouting sequence, with a rise in free fatty acids—even in the ﬁeld in wet falls and during storage. It is essential that seed be coaxed into dormancy by drying and cooling at the farm, elevator or processor’s site before storage. Fuel-heated air dryers, or forced circulation of ambient air, are used. Field trash, including leaves and stems, is removed ﬁrst because it preferentially holds moisture. Seed held for long-term storage is dried to 75% or less relative humidity (measured in the air space above an equilibrated sample); in some cold-weather climates storage at 65% or 70% maximum RH is used. Oil does not attract water or affect relative humidity; thus, high-oil content seeds are dried to lower moisture levels

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Figure 6.4 General ﬂow sheet for extracting oil from row crop seeds.

than low-oil-content seeds. Maximum moisture content levels that have been proposed for safe storage of seed (70–75% RH) are: cottonseed, 10%; palm kernel, 8.0%; peanut, 11%; rapeseed, 7%; safﬂower seed, 11%; soybean, 13%; and sunﬂower, 8.5% [39]. Moisture and heat result in increased FFA content in stored seed. Of the two, moisture has the greatest effect. It activates enzymatic hydrolysis, resulting in production of heat and water, which initiate a chain reaction and can result in spontaneous combustion of piled cottonseed, or charring of soybeans in storage tanks. Removing moisture slows the reaction, and evaporation of water cools the seed. In the oilseed milling industry, the words “drying” and “cooling” are sometimes used interchangeably. Answers to the question: “Why the concern about free fatty acids so early in post-harvest handling when they will be removed from the oil by reﬁning?” include: (1) FFA reduces the amount of saleable oil that can be made per ton of seed processed and therefore its value and price; and (2) For every free fatty acid produced, a molecule of diglyceride also is made, which cannot be easily removed in the reﬁnery but will reduce the stability and frying life of the oil.

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Cracking or breakage always occurs in moving seed and can result in increased moisture absorption and enzymatic action. Gentle methods should be used, and dropping from great heights minimized (especially for soybeans).

4.2. SEED PREPARATION Prior to extraction, seed is cleaned again to remove any clumps that may have formed during storage. Next, it is tempered, which includes adjustment to room temperature in freezing weather and increasing the moisture content of very dry seed. Both reduce brittleness and shattering during subsequent dehulling. The seed is cracked into 4–6 pieces, and the hulls removed by aspiration. Hulls are separated primarily to increase the throughput capacity of the solvent extractor and may be returned to the meal after extraction to adjust the protein content for animal feed. Depending on the species, part of the hulls may be left with the seed to improve screw traction if oil is removed by pressing. The dehulled seed then is heated (“cooked”) to plasticize it for ﬂaking. The industry recognizes the importance of cooking as a means of inactivating (fatty acid splitting) lipases, phospholipases (which produce non-hydratable phosphatides) and lipoxygenases (which make the oil more susceptible to oxidation and ﬂavor reversion, resulting in green, beany notes in soybean oil). Solvent extraction is essentially an anhydrous (waterless) process, conducted at about 135◦ F/57◦ C for hexane, or at least 10–15◦ F/5.6–11.1◦ C below the boiling point of the solvent. Water in the system remains mainly absorbed by the meal. Moisture assists heat inactivation of enzymes, but the only opportunities for increasing moisture (to about 12–13%) are during tempering, cooking (by heated contact surfaces and steam injection) and by extrusion using an expander. However, rupturing the seed makes the oil more available to enzymes, whose activity increases with temperature before their inactivation at about 185+◦ F/85+◦ C. Some oil mills solve this problem by: (1) heating and ﬂaking at less than 135◦ F/57.5◦ C (below the temperature of enzyme activation); (2) heating and ﬂaking above 185+◦ F/85+◦ C (after inactivating many enzymes); or (3) heating and ﬂaking at an intermediate temperature and rushing seed to the expander to limit the time available for enzyme activity. Even though the seed may be homogenized later by an expander, ﬂaking is still considered necessary to disrupt the structure of the seed. Flaking roll pairs turn at differential speeds, creating a smearing action on the ﬂake, which disrupts oil bodies in individual cells and enhances screw pressing and solvent extraction. The expander, an extruder with an interrupted (“cut”) ﬂight screw, was introduced domestically in the late 1970s for homogenizing seed and forming a porous crude collet for solvent extraction. With the exception of hard press operations, it has been readily accepted in domestic cottonseed solvent extraction and has generally replaced prepress operations. Expanders are used in the

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majority of soybean extraction plants, although not yet exclusively. The expander has essentially doubled the throughput of solvent extractors and improved solvent drainage in the extracted meal, thus reducing the energy costs of desolventization. Early inactivation of enzymes in the expander, at temperatures in the 220–230◦ F/104–110◦ C range, has been credited with lower p-anisidine values in crude and reﬁned oils. The ﬁrst step in adapting expanders to handling high-oil-content seeds (canola/rapeseed, sunﬂower and peanut) was installing an oil removal cage in the barrel to reduce oil content of exiting materials to <28% and enable production of cohesive collets. With recently improved screw and discharge end designs, expanders are replacing prepresses in preparing high-oil-content seeds for solvent extraction. Special discharge heads also increase oil yields in hard pressing, including soybeans. Rapeseed/canola is not dehulled before extraction. Sunﬂower seed may be dehulled if a local market exists for higher protein-content meal. Wax content of the oil is higher when undehulled seed is solvent-extracted and typically requires a dewaxing process if salad (table) oil is produced. Early heat treatment, as by expander or high-temperature cooking, is necessary for inactivating myrosinase, the enzyme in rapeseed/canola that liberates thioglucosinolates and undesirable sulfur compounds.

4.3. PRESS AND SOLVENT EXTRACTION Screw presses and solvent extractors have been the traditional means for separating oil from meal. Well-run hard screw press operations are able to reduce residual oil contents of seeds to 5–6%. Residual oil contents for direct-, prepress-, or expander-solvent extracted oilseeds typically are under 1%. Generally, commercial screw-press operations are smaller, less costly to build and can be operated on a one-shift/day basis, but have high labor and maintenance costs for press repair and resurfacing of screws. Hexane is essentially the only solvent currently used for oil extraction worldwide. Commercially, it is a mixture of straight, branched, and sometimes cyclic compounds, varying in carbon number, blended from different petroleum reﬁnery streams to have a uniform boiling temperature. The solvent has a ﬂash point of approximately −25.6F/−32◦ C and a boiling range of 149–156◦ F/65–69◦ C. Extraction plants must be designed to meet various governmental and insurance company safety standards, and require more expensive, knowledgeable operators for safe operation. A solvent extraction plant includes distillation equipment for recovering hexane from the miscella (oil-solvent mixture) and steam sparging equipment to strip solvent from the extracted meal (marc) for recovery and recycling. Either screw presses or solvent extractors can produce good-quality crude oil for later reﬁning. Traditionally, soybean oil has been extracted by the following sequence: clean, temper, dehull, heat, ﬂake, solvent extraction, solvent recovery. A

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delintering operation is inserted before dehulling when processing cottonseed. In hard press operations, ﬂaked seed typically is “cooked”—actually a drying operation to reduce moisture content to approximately 5%—which also denatures cell walls and makes them brittle and easier to rupture during pressing. In later years, ﬂakes at higher moisture level were ﬁrst prepressed to produce a cake containing ∼17% oil; the cake then was crumbled and solvent extracted to less than 1% oil residual. Domestically, prepressing of cottonseed has been replaced by expanders, and oil cage-equipped expanders with special discharge heads now are replacing prepresses for the high-oil-content seeds. Expelled or solvent-extracted crude soybean oil contains phosphatides, which can become hydrated by the accompanying water and precipitate in storage tanks and ship’s holds, causing unloading problems. The National Oilseed Processors Association requires that traded crude soybean oil contain no more than 0.02% (200 ppm) phosphorous to avoid such problems. Partial degumming is accomplished by hydrating the phosphatides with water to form gums removed by centrifugation, and drying the oil before storage. Commercial lecithin in the United States is primarily produced from phosphatides that are water extracted from crude soybean oil. Crude oils from other major oilseeds also contain phosphatides, but in lesser quantities. Cottonseed oil is unique because it often is miscella-reﬁned. Sufﬁcient alkali is mixed with the miscella to neutralize the free fatty acids, which, with occluded phosphatides and other components, are removed by centrifugation. Miscella reﬁning at the extraction plant also removes gossypol and prevents color ﬁxation, which can occur if crude cottonseed oil is not processed soon after extraction. Reﬁning in the presence of solvents enhances centrifugal separation because of viscosity reduction. Minimal ﬂoor space is required. The oil may be sold as “once-reﬁned oil” to other reﬁneries. Some extraction plants rely on miscella reﬁning as the single step for neutralization of FFAs and degumming, and have installed the additional equipment to produce reﬁned, bleached, winterized, deodorized (RBWD) oil suitable for frying snack foods and table oil use. The separated soapstock-gums-gossypol mixture is spread over meal in the desolventizer toaster to recover the hexane and enable selling the soapstock with animal feed. Locating oil reﬁning facilities on the same properties as extraction plants simpliﬁes disposal of soapstock and unneeded crude lecithin in the case of soybeans, and has reduced the number of stand-alone reﬁneries in the United States to essentially those owned by independent operators. Stand-alone reﬁneries can make good-quality oil products, but have to ﬁnd other means for soapstock disposal.

4.4. EXTRACTION PLANT MANAGEMENT The ﬁrst step in producing good-quality oil is to begin with good-quality oilseeds. If mature, intact seed is harvested, stored at the proper moisture content,

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and care is taken to avoid physical damage, the oil in the seed will remain stable for an extended period. Controlling stored oil temperature and limiting its aeration are of primary importance in producing good-quality crude oil. High pressure is needed to achieve good oil yield in expeller operations, but excessive pressure (overpressing), which can generate enough heat to scorch oil, is to be avoided. Exposure of oils to atmospheric oxygen should be minimal after it leaves the extractor, including avoiding splashing oil when ﬁlling empty tanks and agitators that incorporate air. After desolventizing, the oil should be cooled to near ambient temperature before transfer to storage. NOPA trading rules have set a maximum of 0.02% phosphorous [29]; the degumming process typically will remove ﬁnes (particles of meal) that contribute to sludge formation in crude soybean oil. Other crude oils may require decanting and ﬁltering to prevent shipping of ﬁnes and phosphatides that settle in tank bottoms as sludge.

5. OIL PROCESSING “Reﬁning” initially meant alkali reﬁning, the conversion of free fatty acids into soaps by reaction with added caustic (sodium hydroxide) solution, and their subsequent removal by settling or centrifugation followed by water washing and drying. More recently, reﬁning has come to mean removal of free fatty acids by any means, including steam distillation as used in deodorization/physical reﬁning. To some people, reﬁning means the many operations occurring in a reﬁnery between receipt of crude oils and their shipment as useable products. A general ﬂow sheet of modern oil reﬁnery processes is shown in Figure 6.5. The ﬁrst step after receiving a shipment of crude oil is to estimate the amount of saleable oil that can be produced from it. Previously described analyses, like Neutral Oil and Loss, Free Fatty Acids, Moisture and Volatiles, Unsaponiﬁable Matter, Bleach and Color, and others, are run. Before processing begins, a “day tank” of oil is mixed to ensure a uniform feedstock throughout the run. Free fatty acids are determined by titration, and phosphorous and other metal contents by ICP (inductively coupled plasma spectrometry). The tests are rapid enough that treatments can be calculated before processing begins and processes can be monitored while in progress. Other slower phosphorous tests are available, but do not afford the same degree of control.

5.1. DEGUMMING The phosphatides (Figure 6.3) discolor oil at high temperatures (deodorization and frying) and, acting as surfactants, accelerate the breakdown of frying oil. Their presence in crude oil varies with the species and method of oil extraction: soybean, 1.8–3.2%; cottonseed, 1.3–2.7%; sunﬂower seed, 0.5–1.0%;

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Figure 6.5 General ﬂow sheet of reﬁnery operations.

peanut, 0.3–0.4%; rapeseed, 0.2–0.5; linseed, ∼1.8%; and corn 1–2% [3]. The major commercial source of lecithin in the United States is crude soybean oil; corn oil lecithins also have been produced. Phosphatides are recovered from sunﬂower oil in Eastern European countries. Cottonseed oil is not used as a source of phosphatides because of the presence of gossypol. The phosphorous content in soybean oil can be higher than 600 ppm, and typically is reduced to under 4 ppm in preparation of edible oils. Phosphatides may be separated for commercial use by hydration in the soybean oil with 1–3% added water, mixing and centrifugation. However, this does not remove all of the phosphorous because of prior phospholipase-D activity, which splits choline, ethanolamine, inositol, or serine from the phosphatide chain beyond the phosphorous, forming a highly dissociating diacylphosphatidyl acid (Figure 6.3). Divalent cations (calcium, magnesium, iron and others) then bind to the phosphate site, or create a bridge between two diacylphosphatides, to

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form water-insoluble (nonhydratable phosphatides, NHPs). Phospholipase-D activity and divalent cations cause the problem, and measurement of residual phosphorous in water-degummed oils merely conﬁrms the presence of NHPs. Addition of phosphoric acid, citric acid or other chelating agents complexes the divalent cations and renders diacylphosphatides water-soluble again. Inactivating phospholipases while preparing seed for extraction, and using only deionized water in processing oil, help reduce the problem. Phosphatides for commercial use cannot be obtained from soapstock, nor from acid-treated oils, and are hydrated only by water when saved. Even though phosphatides will not be saved, many soybean oil reﬁners degum to facilitate downstream processing.

5.2. CAUSTIC NEUTRALIZATION In caustic neutralization, a calculated amount of caustic solution (typically sodium hydroxide, but sometimes potassium hydroxide or sodium silicate), sufﬁcient to convert the free fatty acids into sodium salts (soaps), is added to oil, reacted for sufﬁcient time, and the soapstock and other occluded components are separated by centrifuges. Water used in the process is also sufﬁcient for solubilizing hydratable phosphatides. An initial degumming step is often bypassed in oils other than soybean, but chelators often are added in the neutralization step to solubilize any nonhydratable phosphatides. Basically, two types of mixer-reactor processes are used—short mix and long mix. The short-mix process, developed in Europe, was intended to minimize reﬁning loss when processing oils with higher free fatty acid content. Crude oil, at 186◦ F/90◦ C, is mixed with high-concentration caustic solution for less than a minute, and then centrifuged. In the long-mix process, derived from earlier U.S. processes, crude oil at ambient temperature is mixed with a lower concentration of caustic solution, held for 15 minutes, heated to 165◦ F/70◦ C to reduce viscosity, then centrifuged [40]. The additional holding time is built into the equipment and allows for more thorough and complete reaction. U.S. soybean oil processing specialists generally endorse the long-mix process. In the author’s experience with soybean oil, the long-mix process supports the production of oil with improved ﬂavor and enhanced stability. Various neutralization systems are used throughout the world, including variations of early batch/kettle reﬁning, which rely on cooling and gravity to separate the soapstock, although reﬁning losses are much higher in the absence of a centrifuge. Many reﬁneries in former Soviet Union countries use a neutralization process in which small droplets of oil are allowed to rise through a column of caustic solution. This is similar to a process ﬁrst developed in Sweden, and the Zenith ProcessTM offered worldwide by a Canadian equipment manufacturer [41].

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5.3. ADSORPTIVE PROCESSES Soap is an inactivator of bleaching earths, a poison for hydrogenation catalysts, and leads to oil degradation during deodorization and frying. Every effort should be made for its early removal in oil processing operations. Traditionally, neutralized centrifuged oil has been washed once or twice to remove soapstock and vacuum dried before proceeding to the bleaching step. Costly mixing and centrifugation equipment is required for each wash, and disposal of the wash, water has become an increasing concern. One of the more innovative developments in reﬁning technology during the last 15 years has been the introduction of the waterless modiﬁed caustic reﬁning process using silica hydrogel adsorbents. Silicas remove considerably more soaps and phospholipids than an equal weight of bleaching clay, leaving the clay for adsorbing chlorophyll, other pigments, catalytic metals like iron and copper, and oil oxidation products including peroxides [42]. The term “bleaching” is somewhat of a misnomer. Color is reduced during the process but other important beneﬁts [43] also occur. These include: (1) adsorbing of soaps, phosphatides and trace metals; (2) acting as a catalyst surface for decomposing peroxides and removing secondary oxidation products, and (3) adsorbing chlorophyll, carotenoids and other pigments. In modern operations, bleaching is conducted under vacuum (50 mm Hg) to avoid oxidation. From this point forward throughout the remainder of processing, storage, loading shipping, and ﬁnal use in frying, extreme care is taken to minimize the aeration and oxidation of oil.

5.4. HYDROGENATION The role of hydrogenation is to increase the stability of frying oils, extend the shelf life of fried products, and in some cases to alter the solids proﬁle to modify the eating and/or handling attributes of fat products. Alteration of the melting proﬁle is monitored by the Solid Fat Index or Solid Fat Content, later described in mouth feel considerations when selecting frying oils. Methods to limit formation of trans isomers and saturated fats during hydrogenation are being developed, and the industry is making good progress in achieving reductions. Historically, the trans isomer content of moderately hydrogenated frying oil has ranged around 15–25%. Current progress in hydrogenation technology indicates that it will be possible to reduce the trans content of traditional products by half or more. For example, moderately hydrogenated frying oils with 9–15% trans fats are now being produced. With current technology, partially hydrogenated frying oils should have essentially no aroma or ﬂavor. Anything other than a slightly sweet character requires veriﬁcation that the oil was processed from good-quality crude, that reﬁning and bleaching were properly conducted, and especially that the

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hydrogenation feed stock was free of peroxides and secondary oxidation products [44,45].

5.5. CHILL FRACTIONATION The objective of chill fractionation, also sometimes called “winterization” or “fractional crystallization,” is to remove the higher-melting triglycerides naturally present in the oil or created during partial hydrogenation. The process was initially developed to ensure that cottonseed salad oils would remain clear when stored in household refrigerators. The process was later adapted for use with partial hydrogenation to produce liquid oils with improved oxidative stability. Stearine, the general term for the higher-melting component from fractionation, is commonly used in manufacture of margarine, shortenings and confectionery products. Palm oil is commonly chill fractionated to produce palm olein, a liquid or semiliquid oil, that is convenient to handle in frying applications. The process consists of slowly stirring and gradually cooling oil to encourage selective crystallization of higher-melting components, which subsequently are removed by ﬁltration. Continuous belt ﬁlters have been used in high-capacity applications like palm oil processing, but have generally been replaced by inﬂatable bladder plate and frame presses, which separate more liquid from the crystals. A centrifuge may be used if only a small amount of oil is to be chill fractionated, but the equipment is expensive and yields a dilute crystals-oil steam for which uses have to be found. Chill fractionation also removes waxes that solidify in the process. Sunﬂower and corn oils have the highest wax contents of the row crop oils, and can be chill dewaxed before bleaching to prevent wax haze (micro-crystals) in the ﬁnished oil. One process version employs residual soap from reﬁning as a detergent to help separate wax from chilled sunﬂower oil by centrifugation. Water and residual soaps must then be removed before bleaching [24]. Another dewaxing process consists of rapidly chilling a mixture of oil and bleaching earth, followed by ﬁltration [46]. Typical wax contents of crude oils are: sunﬂower, 0.2–3.0%; corn, 0.5–1.0%; safﬂower, ∼0.5%; and canola, 0.2% [5].

5.6. DEODORIZATION/PHYSICAL REFINING The ﬁnal step in oil processing is deodorization, a process for removing volatile components from oils by steam distillation, conducted under high vacuum. Stripping of the compounds to be removed is aided by formation of azeotropes, which boil at a lower temperature than either water or the compound to be removed. A variation of deodorization is used to strip cholesterol from lard, tallow and butter oil. The word “deodorization” is descriptive but is not a comprehensive term for the process. Volatile components are removed from the oil, but other important beneﬁts include reduction of free fatty acids, destruction of some oxidation

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products including peroxides and aldehydes, and heat bleaching of yellow pigments. Deodorization is conducted within the broad ranges of 1–6 mm Hg vacuum, and 410–525◦ F/210–274◦ C, with less rigorous treatment given to heat-sensitive oils [47]. Fatty acids contents of chemically neutralized oils are reduced to 0.02–0.05% [48]. Relatively little material is removed from the oil weightwise (generally less than 1%), and duration of heating depends on whether a continuous or a batch process is used. Typically, citric acid (50–100 ppm) is added to the oil during cooling to serve as a chelator for catalytic metal ions, speciﬁcally copper and iron. An effective deodorization process will reduce peroxides to undetectable levels, but peroxide development will resume immediately if the oil is exposed to air/oxygen. “Don’t deodorize until the oil is sold and ready to ship!” is a rule of thumb in the oil processing industry [47]. Blending of base stocks, if required to achieve desired fat solids melting proﬁles, is done before deodorization. It is critical that post-deodorization aeration/oxygenation of the oil be kept to a minimum. Nitrogen sparging is recommended for oil in batch deodorizers or during removal from continuous deodorizers. Approved antioxidants may be added, consistent with allowed usage (i.e., <0.02% of fat) if desired by the customer, immediately after deodorization. Physical reﬁning is a version of the process that relies on the deodorizer to reduce the free fatty acids from 0.05–6.0% to 0.02–0.05% [44]. It is used in processing palm, coconut and other oil, which contain few phosphatides, but the oils are still prepared by drying, bleaching and hydrogenation if required. Removal of the phosphatides has been the major problem in applying physical reﬁning to row crop oils. Various domestic companies have tried physical reﬁning of row crop oils with limited success because yields and energy costs generally have favored traditional processes. The volatiles from deodorization/physical reﬁning are condensed as deodorizer distillates, and have a ready market for extraction and puriﬁcation of tocopherols—the natural antioxidants in vegetable oils. These are sold for commercial use as natural antioxidants and also in capsule form as nutraceuticals. Approximately 20–40% tocopherols are removed in typical deodorization processes, and temptation exists to maximize their stripping because of the high prices obtainable for distillates. Tocopherol content is important to snack processors who maintain “non-additives” product ingredients listings, and some companies use purchase speciﬁcations to ensure optimum concentrations. Soapstock, spent bleaching earth and deodorizer distillate are the three routes for removing mycotoxins, pesticides, herbicides and other agrochemicals from crude oils. Proper care should be exercised in their handling, disposal, or further processing. The oil exiting the deodorizer is known as RBD (reﬁned, bleached and deodorized) and RBWD (reﬁned, bleached, winterized and deodorized). Scientists have long used the rule of thumb that the speed of many chemical reactions doubles for each 10◦ C/18◦ F increase in temperature, although exceptions

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occur. Heat is an enemy of oil quality. Crude oils, as coming from a pressing or solvent-extraction operation, and RBD oils, should be cooled to ambient temperatures before storage, even if purchase of heat exchangers is required. Temperatures of hydrogenated fats, which are kept melted for shipping, storage and transfer by pump, should be no higher than needed to facilitate ease of handling, and nitrogen protection should be employed as needed.

5.7. PALM, OLIVE AND COCONUT OILS Palm [49] and olive [50] oils are distinctly different from row crop oilseed oils and are derived from the fruit or ﬂesh surrounding a hard seed. Each crop has its unique machinery, technology and terminology, which the reader is advised to review. Olive oil is pressed from macerated olives and may only be ﬁltered or subjected to various degrees of reﬁning. The residual oil is extracted by solvent and, after reﬁning, is sold as olive pomace oil. Composition of the oil in palm kernel seed is quite different from oil that comes from the pulpy fruit. The white ﬂesh inside the coconut shell is dried by sun or fuel to copra, from which coconut oil is removed by screw pressing [51].

5.8. OPTIONAL ADDITIVES Reﬁneries offer processed frying oils and shortenings that have been developed for speciﬁc common applications. The already-mentioned citric acid (or phosphoric acid) chelating agent, antioxidants (0.02%, 200 ppm, in total, maximum), and polydimethylsiloxane (0.5–2.0 ppm), antifoaming agent, are the most common additives and are dispersed in the oil while warm. Snack food processors, who buy sufﬁcient quantities, can order oils/shortenings prepared to meet their own speciﬁcations. Frying fats are shipped in standardized size packages, or in bulk (tank truck or railroad car) quantities. Tank trucks are usually insulated and maintained at temperatures just sufﬁcient for oils to be liquid and pumpable on receipt. Railroad tank cars do not move as rapidly as trucks, and are typically equipped with steam coils to melt the fat for unloading. Heating procedures, designed to avoid degrading oil during unloading and storage, should be closely monitored.

6. THE FRYING PROCESS

6.1. OVERVIEW The origins of deep-fat frying are not known, but it is a universal method used for cooking food by almost all cultures around the world. Deep-fat frying consists of placing the food to be cooked in hot oil and removing it when it is

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Figure 6.6 Changes occurring during deep fat frying. From: Fritsch, C. W., 1981. J. Am. Oil Chem. Soc., 58(3):272–274 [52]. With permission from American Oil Chemists’ Society.

“fried” as determined by the experience of the cook. The process is rapid and yields products with delectable texture, ﬂavor and eating qualities unique to fried foods. Although the procedure is not complicated, the chemistry is complex and involves extensive changes in both the frying oil and the food being fried. The dynamics of frying are illustrated in Figure 6.6 [52]. Fryers operate in the range of 300–425◦ F/148.9–218.3◦ C, just slightly below temperatures of deodorization, and at atmospheric conditions rather than under vacuum. Chemical reactions can be rapid and detrimental to the oil and product. Many of the conditions that have been cautioned against in oil extraction and reﬁning occur during frying. Introduction of food to the fryer, also brings in: (1) oxygen, which can contribute to oil oxidation, resulting in the development of volatile and polymeric compounds; (2) water, which can contribute to fat hydrolysis and increases in fatty acids, mono- and diglycerides, and glycerin—all more easily degradable than triglycerides; (3) leachable metals and color compounds that remain in the

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oil; and (4) enzyme systems, which may complete some degradation reactions even though inactivated rapidly. However, the high temperature and available moisture also act beneﬁcially to steam distill some of the volatile degradation products formed during frying. Selection of oils/shortenings, selection and operation of equipment operation, and management of fat use are reviewed here from two different perspectives—industrial (continuous) frying and food service (batch) frying.

6.2. FRYING EQUIPMENT Industrial fryers consist of a heat source to heat the oil, various conveying devices for moving the product through and a hood to exhaust steam and vapors. Raw products typically sink to the bottom of the oil and then rise to the top as internal moisture turns to steam. Paddle wheels sometimes repeatedly dunk the product, or submergers of various types are used to ensure that product does not ﬂoat on the surface of the frying oil. Some products are form-fried using conveyor belts containing molds that hold the product in a speciﬁc shape during frying. Fryers, which are directly heated by gas burners in a ﬁrebox under the fryer pan, are in common use. These direct-ﬁred fryers are not as efﬁcient as fryers with heat exchangers, but they are more economical to purchase. Some of the smaller industrial fryers utilize ﬁre tubes in the oil bath through which a gas-air ﬂame circulates; or coils containing thermal ﬂuid or steam may be placed in the oil. Larger fryers usually use remote heating systems in which oil is circulated by pump through tubes in a ﬁrebox, a thermal ﬂuid heat exchanger, or a highpressure steam chamber, and then returned to the fryer just before cocurrent introduction of the product [53]. Advantages of remote heating systems include: improved control of the frying temperature, avoidance of dead space under ﬁre tubes or heating coils where ﬁnes collect and pyrolyze, and opportunity to pass the oil through an in-line ﬁlter to remove ﬁnes. Vacuum fryers are sometimes used to fry heat-sensitive products. The technology supports rapid moisture reduction, which enables frying at lower temperatures. The resulting products are lighter in color than those processed in atmospheric fryers. The fried product is conveyed from the fryer oil pan onto a sloped belt for draining the oil. The amount of fat retained with the product mainly depends on product orientation and handling at this stage. Too short a drainage time results in more oil remaining with the product as it moves on to seasoning and packaging. Oil reduction units designed to remove surface oil from products exiting a fryer, primarily utilizing high-velocity dry steam, are available from several manufacturers. In producing fried snack foods, the fryer is the most critical piece of equipment and therefore the heart of the operation. The fryer should be speciﬁcally sized for each operation. The best-quality products are produced when fryers

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are operated continuously and at full capacity. Operating above the rated capacity changes the frying temperature proﬁle, which can adversely affect ﬂavor and quality, and necessitates excessive heat input, which leads to early equipment failure. Operating below the rated capacity reduces oil turnover, resulting in accumulation of degradation products. Some allowance is needed in fryer sizing to provide ﬂexibility in production and potential future growth, but production planning should be based on the designated capacity of the fryer [54]. Food service (fast food shop, restaurant, hotel and institutional) fryers are far simpler in design. Countertop fryers often consist of a ﬂat-bottom pan capable of holding a 2.5 gallon (9.5 liter) charge of oil, and a thermostatically controlled electrical heating element. Many fast food shops use gas-ﬁred batch fryers with a V bottom (open pot design), or a broader bottom, which heats the oil by several immersed ﬁre tubes [7]. The designs provide a cold zone in the bottom of the fryers to limit charring of crumbs, but beneﬁts have to be balanced against a slower rate of oil turnover, which results from the additional oil volume. The product to be fried is lowered into the hot oil in baskets and removed after frying, either manually or with the aid of an automatic basket lift. Achieving consistent quality manually requires good judgment by the operator and careful attention to frying and drain times.

6.3. CHANGES IN FOOD DURING FRYING Frying food involves a series of stages: (1) fryer entry; (2) case hardening; (3) surface ﬁrming; (4) cooking/moisture reduction; (5) ﬁnish frying; and (6) oil absorption [54]. r Fryer Entry. When raw product is ﬁrst immersed in hot oil, starch on the

surface is rapidly gelatinized and the product is soon uniformly covered with small steam bubbles as surface moisture begins to vaporize. Steam evolution and surface bubbling increase rapidly and help keep product pieces from sticking together. Rapid steam evolution also limits the product temperature to the boiling point of water and restricts oil penetration [54]. r Case Hardening. The outer layer cells on the surface of the product dehydrate and ﬂatten into a veneer-like structure. Slight changes in steam evolution may be noted as case hardening continues, with some surface sites bubbling more rapidly than others. As surface moisture diminishes, the internal moisture is converted to steam and ruptures channels through the product structure. At this point in frying, dehydration has not led to the development of a crisp surface texture, but a degree of structural integrity has occurred. For example, a potato chip at this stage in frying can still be twisted or bent and will return to its original shape [54]. r Surface Firming. Additional layers of surface cells begin to dehydrate and add to the developing crust structure. Products that are fried at high

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temperature will have thin, light-textured crusts, while frying slowly at lower temperature supports the development of a thicker crust and crunchier texture. The cell structure below the crust layer is disrupted and the resulting pillared, cavernous, interior substructure continues to be inﬂuenced by frying temperature. At this stage, crust and internal structure formation is far from complete, but the elements that will strongly inﬂuence texture in the ﬁnished product have been established [54]. r Cooking/Moisture Reduction. The primary emphasis in the cooking phase is on heat penetration and reduction of moisture [54]. Uniformity in piece size of products being fried is the key to maintaining proper fryer load, product time/temperature proﬁle and cooking. r Finish Frying. During the ﬁnal stage of frying, the surface temperature of the product rapidly approaches that of the oil. Low moisture content and high temperature support ﬂavor–producing reactions involving amino acids, proteins and carbohydrates. The rising temperature supports ﬁnal moisture reduction, development of crust with a crisp texture and rich color. The oil content of the product increases during ﬁnish frying, but most of the oil remains on the surface at this point. The ﬁnal stage has to be closely controlled, with precise timing of product removal from the oil to produce optimum quality fried product [54]. r Oil Absorption. The oil content of fried foods results from surface wetting, capillary action and vacuum absorption. The surface texture of the product inﬂuences initial wetting and capillary absorption during the early stages of frying, but steam evolution limits signiﬁcant absorption. During the latter stages of frying, some additional oil will be absorbed by capillary action as voids are created in the product. But much of the oil associated with the product is carried out of the fryer as surface oil. During cooling, water vapor within the product condenses, creating a partial vacuum, which expedites absorption of surface oil. Several methods are available for producing fried products with reduced oil contents as they leave the fryer, including centrifugal force used in small-scale operations and high-steam velocity treatment [54].

6.4. CHANGES IN THE OIL DURING FRYING r Fryer Oil Turnover. Two broad types of frying situations exist: (1) high fryer

oil turnover, where enough oil leaves the fryer as part of the product so that fresh oil has to be added continuously, precluding total oil degradation and the need for replacement; and (2) low fryer oil turnover, where, even though makeup oil is added periodically, turnover is insufﬁcient to prevent accumulation of breakdown products, thus necessitating the complete replacement of used oil with fresh oil periodically. Most industrial snack food companies design their frying operations to ensure that optimum oil

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and product quality will be maintained continuously. In contrast, most food service establishments only operate their fryers intermittently as needed to meet customer orders. As result, fryer oil degrades rapidly and has to be replaced on a regular basis. Fryer oil turnover is deﬁned as the number of hours required for the makeup oil added during frying to equal the total quantity of oil in the frying system: Fryer Oil Turnover =

Total Pounds of Oil in Frying System (% Oil in Product)(Fryer Output in Pounds/Hour)

Due to commingling of fresh oil and used oil, one turnover does not equate to replacing all of the oil in the fryer with fresh oil. After one turnover, one half of the original oil still remains in the fryer and is halved with each subsequent turnover. The turnover rate is a good indicator of the stress placed on the oil and is a primary consideration in selecting fryers. Industrial fryers commonly have oil turnover rates in the 5- to 10-hour range. Depending on the product, fryer design, and heating system, some frying systems operate successfully with oil turnover rates of 12 hours, while others have problems at 7 hours. Typically, fryer oil quality does not achieve a steady state until four or more turnover periods have been completed. To conduct meaningful oil tests and product evaluations in industrial operations, a steady state, consistent with normal continuous production, has to be achieved before samples are collected for assessment [54]. By contrast, oil turnover in food service kitchens commonly ranges around 20–35% per day, and both oil and product quality continually change throughout the useful frying life of the oil [5]. Modern reﬁnery processes produce oils that are almost completely bland, devoid of ﬂavor or aroma. When ﬁrst used, new frying oils contribute very little ﬂavor to fried products and can actually dilute ﬂavor. After a period of frying, oils begin to accumulate ﬂavors and aromas, which are primarily derived from the constituents being fried. Potato chips, corn chips, and other fried products have their own characteristic ﬂavors, even when fried in different oils. The ability of oils to absorb and preserve ﬂavors supports the unique characteristics of fried foods with little change during product shelf life. On extended frying, oils begin to show the effects of heat and moisture stress. If not turned over rapidly enough, breakdown products caused by hydrolysis, oxidation, polymerization and pyrolysis accumulate, resulting in oil darkening, increased viscosity, foaming, and smoking and in darkening of products and development of off-ﬂavors. r Hydrolysis. This is an important reaction in frying. Water provided by the food participates in splitting triglycerides into free fatty acids, mono- and diglycerides and glycerin. In the presence of heat, glycerin degrades to acrolein (CH2 CHCHO) which, with a boiling point of 126◦ F/52.7◦ C,

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rapidly volatilizes and is a major irritant in the rising smoke. It is also one of the compounds that condense and polymerize in the exhaust hood. Free fatty acids are more susceptible to oxidation and catalyze additional hydrolysis. The smoke point of oil is reduced by increases in free fatty acid, polyunsaturation and length of oil use. Free fatty acids, and mono- and diglycerides are surfactants, which reduce surface tension of the oil, increasing its ability to wet and adhere to the product. General-purpose shortenings with added mono- and diglycerides or lecithin should not be used for frying since these components are prime subjects for hydrolysis [55]. r Oxidation. During the early phases of oxidation, some oils develop characteristic ﬂavors. For example, cottonseed oil develops a slightly nutty ﬂavor, peanut oil begins to taste like roasted peanuts, corn oil develops popcorn ﬂavor, palm oil develops a sweet aroma similar to that of violets and soybean oil develops a grassy or beany ﬂavor. Polyunsaturated oils in frying applications generally support rapid product ﬂavor development, but are subject to continued oxidation and limited shelf life. Oils high in oleic acid, 18:1, require a longer conditioning period to develop optimum ﬂavor but are much more resistant to oxidation and support both long fry life and extended product shelf life. Polydimethylsiloxane, originally added to frying oils to inhibit foaming, was later found also to support improved resistance to thermal oxidation. Addition is approved in oils at up to 10 ppm, but the most effective results are achieved at about 0.5–2.5 ppm [5]. r Antioxidants. Autoxidation of carbon double bonds is a thermodynamically driven process. Plants require that their fats be liquid for survival and have evolved the ability to produce inhibitors, which either intercept free radicals or the energy quantums that initiate them, thereby protecting their oils [56]. People, by eating plant materials, also beneﬁt from the protective action of these compounds, which have become known as “antioxidants.” Natural or synthetic antioxidants, some of which also provide protection against photooxidation, typically include resonating phenolic or quinone structures. A number of these compounds have been investigated and reviewed [57–60]. r Monitoring Degradation of Frying Fats. Chromatographic separation and instrumental identiﬁcation of frying fat degradation products are the surest ways to quantitatively assess frying fats, but the procedures are time-consuming and expensive. Standardized procedures have been developed for polymers, polar compounds, oxidized fatty acids, conjugated dienes, fatty acid composition and other components. Traditional methods for deciding when to discard used frying fats include: color, free fatty acids, foaming, smoke point, viscosity, and ﬂavor. Quick tests include: dielectric constant, colorimetric tests, RAU test, strip test and Alkaline Contaminant Metals (ACM) [62].

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Tompkins and Perkins [63] observed signiﬁcant correlations of p-anisidine value of partially hydrogenated soybean oil frying oil with: overall odor intensity (r = 0.82), fried food odor (r = 0.53), and burnt odor (r = 0.43). Additionally, p-anisidine value was signiﬁcantly correlated with hexanal (r = 0.81), heptanal (r = 0.66), t-2-hexenal (r = 0.81), t-2-heptenal (r = 0.71), t-2-octenal (r = 0.92), t,t-2,4-decadienal (r = 0.86) contents and with polymers (r = 0.84). r Regulation of Used Frying Oils. Public health concerns have developed about safety issues that may be associated with heavily oxidized frying fats. Oil quality is rarely a problem in large-volume continuous commercial frying operations due to close monitoring and rapid oil turnover. In contrast, fryer oil quality can be a concern in food service situations, and batch frying operations have attracted most of the regulatory attention. Two signiﬁcant surveys of world practices for regulating use of frying fats in food service establishments have been conducted [64,65]. More than 400 different chemical compounds have been identiﬁed in deteriorated frying oils, of which about 220 are volatile [65–67]. Frying oils typically contain <0.05% free fatty acids and about 2–5% polar material when they leave the reﬁnery. European countries, which have established standards for used frying oils, typically have set acid value (deﬁned as free fatty acid content as oleic acid determined by the AOCS method, multiplied by 1.99) at 2.0 or 2.5% maximum, polar compounds content at 25 or 27% maximum, and/or fryer oil smoke point at 338 or 356◦ F (170 or 180◦ C) minimum. The 27% polar compound limit has been also found to coincide with the concentration at which triglyceride polymers precipitate [68]. Some countries do not permit the use of polydimethylsiloxane, and others have set 356 or 374◦ F (180 or 190◦ C) as maximum frying temperatures. Recent evaluations of methods, to determine fryer quality of palm olein used in industrial production of potato chips, rated alternative methods in the following order: changes in tocopherols content>dielectric constant>FFA content>changes in TBHQ content>anisidine value>Rancimat induction period. The ﬁrst three methods correlated well with total polar compounds level and dielectric constant, and FFA measurements were recommended for monitoring oil condition during frying [69].

7. SELECTION OF FRYING OILS

7.1. BACKGROUND The use of vegetable oils is well documented in ancient records. Early Egyptian papyruses reference olive, sesame, safﬂower, castor, radish seed and balanos oil [70], but it is unlikely that any were used for frying. The early oils were valuable for use as food and for lighting and formulating medications. In

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fact, oil was so important that, reportedly, it was included in marriage contracts, whereby a husband was obligated to provided his wife with a monthly quota of oil. Historical records do not document the origin of frying or the ﬁrst oil that was used. But some of the earliest records about frying use words derived from roasting, and it is possible that frying was discovered when a fatty piece of meat was being roasted. On that basis, meat fats would have been the ﬁrst frying oils [71]. Lard was the primary fat used for cooking and frying during the early industrial development of the United States. Later, as the beef industry developed, tallow also became a commercial fat. For many years, lard and tallow were the primary cooking fats used in hotels and restaurants. A number of vegetable oils were produced in the United States as commerce developed in the 1800s, including cottonseed, corn, peanut and others. When cottonseed oil initially entered the market, consumers did not readily embrace it. Oil processing was not well developed and cottonseed oil of the day, which had a strong ﬂavor and dark color, did not compete well with lard and tallow. But as caustic reﬁning, bleaching with Fuller’s earth, and high-temperature steam-vacuum deodorization were perfected, cottonseed oil began competing with animal fats and soon became a preferred product [72]. Development of the snack food industry, which was destined to have a major impact on the development of frying oils, occurred in the same time frame as improvements in oil processing. Potato chips were invented in 1853 and grew in popularity as a restaurant item for a number of years. In the early 1900s, the demand for chips led to commercial production in stand-alone operations that greatly increased demands for frying oil. By that time, good-quality cottonseed oil was available in quantity to meet the needs of the developing potato chip industry. Later, as demand increased, other oils that could be produced in large volume, notably soybean, also were needed. A number of factors, including functional, practical and institutional considerations, enter into the process of selecting frying oils.

7.2. CORPORATE POLICIES AND LEGAL CONCERNS Some snack food producers emphasize “clean labels” for speciﬁc product lines, or for all of their products. The ingredient listing is to be simple, and ingredients whose proper names might connote chemical or “artiﬁcial” to customers are avoided as a matter of policy. U.S. labeling laws require that all ingredients (with exceptions for Standards of Identity and some speciﬁc ﬂavors) be identiﬁed and generally shown in diminishing order in an Ingredients Statement on the food package label. This is partly to alert persons with known sensitivities to ingredients like wheat, peanuts, monosodium glutamate, FD&C Yellow No. 5 and others, that these components are present in the product.

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Allergens are protein-based compounds. Crude oil usually contains some protein from its parent seed and therefore can contain allergens, but it would be highly unusual to ﬁnd any proteinaceous material in oil that has been fully reﬁned and processed. However, the possibility of an exception is a concern that can deter product acceptance by some consumers. Consequently, food companies have to assess the performance and cost beneﬁts of using ingredients that may be directly or indirectly associated with allergens. Similar considerations of costs versus beneﬁts apply to company decisions regarding supervision for preparation of kosher foods and achieving approval for rabbinical seals. Consumer concerns about saturated fats and cholesterol have led to corporate policy decisions not to fry in animal fats, even though essentially cholesterolfree products are now available. “Tropical oils” raised concerns about saturated fats and serum cholesterol elevation about 20 years ago, and may still linger in the memory of some U.S. consumers. The nature of the frying fat may be reﬂected in the Nutrition Facts Statement of food labels to a greater degree than in the Ingredients Statement. At the time of this writing, the U.S. Food and Drug Administration is considering inclusion of trans fatty acid isomers (trans fat) in nutrition facts labeling as part of the saturated fat content, with an astrisk referencing the grams of trans fat in a product serving. A decision is expected on or before January 1, 2004, and could change domestic oils processing and utilization practices signiﬁcantly if trans fats content becomes a public focus. Margarine/spread and shortening applications, which require solid fats, would be affected more than the frying fats. The issue has already promoted signiﬁcant interest in reducing or eliminating trans fat by methods involving blending, interesteriﬁcation/rearrangement and seed breeding, as well as low-trans hydrogenation technologies.

7.3. OPERATING FACTORS Operating considerations typically are common sense economics. If a new snack is to be a line extension, rather than a completely new product, checking the suitability of already approved frying oils and other ingredients is expected because establishing and maintaining separate bulk handling systems increases manufacturing cost. The same principle applies to processing equipment— changes may have to be made to process all items in a product line or not made at all. The new product also has to be compatible with the snack food processor’s store delivery and expired product pickup policies, which typically are well established and strictly enforced.

7.3.1. Including Other Known Technologies Oil selection is important, but additional beneﬁts can sometimes be obtained by including other technologies. As an example, in an effort to increase market

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share in the 1980s, a snack food processor introduced a potato chip that was an immediate hit with the public because of its ﬂavor, crispiness and exceptional appearance. The product was fried in cottonseed oil, a traditional favorite, which can contribute a slightly nutty ﬂavor during the early stages of oxidation. Additionally, the product was packaged in metallized light, moisture and oxygenbarrier ﬁlm, and nitrogen ﬂushed before sealing. The negative effects of atmospheric oxygen and moisture on snack ﬂavor and crispiness had been known for years, as had principles of nitrogen packaging and other technological improvements, but had not previously been collectively used for a national product. Competitors were stimulated to incorporate similar technology and responded quickly. Today, potato chips with near-perfect appearance, packaged in lightprotective, gas-barrier bags with nitrogen protection are the standard in the industry.

7.3.2. Ensuring an Adequate Oil Supply The availability of some types of oil, especially those involving new crops, can be a problem. Finding suppliers who can meet speciﬁcations with a particular type of oil can be even more challenging. Thus, some large snack food processors hire specialists, or assign persons experienced in oil extraction and reﬁning on their staffs, to work with suppliers to incorporate equipment and operating changes as needed to gain a supply of a desired oil. Like many other food companies, snack processors often require at least two qualiﬁed suppliers before approving a new kind of oil or other ingredients. Trading in oilseeds with ﬂuctuating market prices can be more of a risk than oil processors or their customers are willing to take. Some large-volume buyerusers ﬁnd it beneﬁcial to arrange longer-term positions in the commodity market to lock in oil costs and provide protection against adverse price ﬂuctuations in the cash market.

7.4. FUNCTIONAL FACTORS After corporate and practical considerations have been addressed, attention focuses on the technical side of selecting fats for commercial frying. Frying oils can best be selected by developing a list of requirements that are needed for a speciﬁc operation and then prioritizing the list. Candidate oils can be chosen for testing and evaluated on a best-ﬁt basis. Some of the factors for such a list include: (1) product(s) to be produced; (2) historical oil usage; (3) competitive products; (4) product appearance and eating characteristics; (5) how the products will be packaged, distributed and consumed; (6) shelf life requirements; (7) fryer design; and (8) fryer oil usage/turnover. The types of fryers that will be used, the frying schedule, and the amount of product to be produced each day, are basic considerations. Product appearance,

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ﬂavor, aroma, eating characteristics, shelf life requirements and other attributes have to be assessed and balanced with due consideration for product economics.

7.4.1. Flavor The American Oil Chemists’ Society has formalized methods for correlating oil volatiles with ﬂavor scores of edible oils (Cg 1–83); panel evaluation of vegetable oils (Cg 2–83); assessing oil quality and stability (Cg 3–91); measurement of volatile organic compounds (VOC) in fats and oils by gas chromatography (Cg 4–94); and accelerating aging of oils by oven storage (Cg 5–97) [28]. Oil degradation processes and products are described in many publications and reviews [4,8,73]. When evaluating frying oils for ﬂavor contribution in continuous frying applications, it is essential to ensure that oil quality parameters have reached equilibrium and steady state conditions are maintained. Normally, four or more oil turnover periods are required. Continuous production is critical, since oil ﬂavor is directly impacted by oxidation and interruptions in frying change both the type and concentration of oxidation products formed. Fry tests conducted with batch fryers can provide preliminary information, but should only be used for general screening of oils in preparation for testing in commercial production. Test protocols that require batches of product to be fried without interruption during conditioning periods should be used. Conditioning should be continued until oil quality parameters most closely simulate commercial production. Samples for testing should then be taken within a short period to ensure representative product. Test protocols involving intermittent or periodic frying should not be used since they constitute more of a heat stress test than a frying test. When screening oils for use in food service applications, where batch frying is the norm, it is essential to recognize that oil quality does not equilibrate, but changes continually throughout its useful fry life. The stages of fry life can be viewed as: (1) fresh oil; (2) conditioning; (3) optimum frying performance; (4) declining quality/performance; (5) marginal; and (6) unacceptable. To obtain relevant results, test protocols designed for speciﬁc product/product mixes, frying schedules, oil handling and management have to be utilized. The useful fry life of the oil and related economics are usually major considerations inﬂuencing oil selection in batch frying operations. It is well accepted that increased numbers of double bonds per fatty acid is directly related to reduced oxidative stability. A preliminary indication about the stability of an oil can be estimated by determining its fatty acid composition and iodine value as shown in Table 6.7 [5]. Stability values in this table were calculated by multiplying the decimal fraction of each unsaturated fatty acid present by its relative oxidation rate, using 0 for saturated fatty acids, 1 for oleic acid (18:1), 12 for linoleic acid (18:2), and 25 for linolenic acid (18:3). Iodine

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TABLE 6.7. Calculated Fats and Oils Oxidative Stability Ratings. Adapted from: O’Brien, R. D., 1998. Fats and Oils: Formulating and Processing for Applications. Technomic Publishing Co., Lancaster, Pennsylvania, With permission [5]. Caution, for Illustrative Purposes Only. Not for Use as an Oil Selection Guide.

Rating Lower Stability

❄ Higher Stability

Fat and Oil Source

Relative Oxidative Stability

Total Double Bonds

Calculated Iodine Value

Safflower Soybean Sunflower Corn Cottonseed Canola Peanut Lard High-oleic sunflower Olive Palm High-oleic safflower Tallow Palm kernel Coconut

9.55 8.58 8.49 7.71 6.90 5.35 4.33 2.43 1.89 1.74 1.72 1.71 1.27 0.43 0.36

168.8 153.7 156.3 148.4 130.1 131.3 112.6 68.5 99.4 95.6 60.8 96.8 55.6 20.1 11.0

146.1 133.1 135.3 128.4 112.6 113.3 97.1 59.3 85.6 82.4 81.8 83.3 48.4 17.2 9.6

values were calculated in a similar manner based on the following theoretical IVs for pure triglycerides: oleic, 86.01; linoleic, 173.21; and linolenic, 261.61. But, as the author [5] points out, calculated stability values like these can be slightly misleading. The inherent stability of each lot of oil raw material is inﬂuenced by fatty acid composition, which can vary signiﬁcantly with variety/hybrid and environmental conditions. Also, other factors have to be taken into account. Consideration has to be given to the natural antioxidants remaining in the deodorized oil, which can vary with seed abuse and enzymatic activity during storage or processing. For example, animal fats (lard and tallow) do not contain natural antioxidants and have lower stability than vegetable oils with similar compositions. Conversely, some oils such as corn and sesame have been found to be more stable in frying applications than would be expected on the basis of their fatty acid composition and iodine values. Typical elements of frying oil speciﬁcations are shown in Table 6.8 and assays can be selected from the basic list as needed for most applications. Additional assays, as listed in the Optional Tests list, may be included as needed to ensure performance for speciﬁc applications. The limits to be used for a number of the assays will depend on the type of oil selected and the required functionality. The test methods to be used should be included as part of the speciﬁcation, such as AOCS Ca 5a-40 for free fatty acid. The listing of stability by both AOM and

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TABLE 6.8.

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Potential Components of Frying Oil Speciﬁcations.

Assay

Limit

Basic Color Flavor Free fatty acids (FFA), % Peroxide value (PV), Meq/Kg Chlorophyll (ppm) AOM/OSI/rancimat Iodine value (IV) Drop point/Cold test SFI/SFC Moisture (M&V), % Phosphorus, ppm Fatty acid distribution Performance requirement Optional Testsc Tocopherols, mg/kg Para Anisidine Value, p-A.V. Polymers, % Trace Metals, ppm Sodium Calcium Magnesium Iron Copper Triglycerides, % Monoglycerides, % Diglycerides, % Dimers, %

a

Test Method b

Bland 0.05 max 1.0 max 0.75 max a a a a

0.05 max <4.0 Typical As needed to ensure functionality

Limits are oil- and/or application-specific. test methods to be used should specifically stated, such as ‘‘AOCS Ca 5a-40 for free fatty acid”. Items for inclusion as needed to support frying oil performance or finished product quality. Limits are oil- and/or application-specific.

b The c

OSI can be expected in U.S. speciﬁcations as the industry transitions to the OSI method.

7.4.2. Oil Species Developments By far, the majority of frying fats used today are derived from traditional varieties of oilseeds, and are either: (1) reﬁned, bleached and deodorized; or (2) hydrogenated after bleaching to increase oxidative stability and/or solids content. Soybean oil, including RBD and RBHD, accounts for about 75% of the vegetable oil produced in the United States annually. On a global basis, soy is the volume leader by a moderate margin followed by palm, rapeseed/canola and sunﬂower oils. Over the past several years, palm/palmolein has been the growth

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oil in international trade. In the last ﬁve years, nearly twice as many utilization research articles have been published on palm oil compared to soybean oil. Development of improved dietary oils continues to attract much interest. There have been two major genetic thrusts: (1) development of new varieties/hybrids of essentially all row crops (except cottonseed) with higher oleic content; and (2) reduction of linolenic acid in soybeans and canola for frying applications. Beneﬁts of longer shelf life have also been realized with the development of high-oleic confectionery-type sunﬂower seed and high-oleic acid content peanuts. Genetically based increases in oleic acid content typically correspond to a reduction of linoleic acid. The ﬁrst high-oleic acid candidate mentioned in the literature was safﬂower in 1966. It contained 75–80% oleic acid and 12–20% linoleic acid, compared to averages of 14.0% and 76.0%, respectively, for the traditional crop. The AOM stability of high-oleic safﬂower at 40 hours is signiﬁcantly higher than the 10-hour AOM of the regular oil. Notably, lower polymer formation and smaller increases in viscosity were noted in high-oleic acid safﬂower oil compared to regular safﬂower oil after oxidation [74,75]. Open pollinated sunﬂowers, yielding high-oleic (80%) oil, were developed in 1974–1975 [76], followed by development of hybrid seed in the 1980s. Commercial production of high-oleic sunﬂower oil in the United States began in 1984, and oil from the ﬁrst crop was used to fry snack foods. To date, commercial production has been limited to about a hundred million pounds of oil a year, apparently due to price structure and patent issues. Currently sunﬂower varieties that yield mid-oleic (∼65%) oil are being developed. With strong support from the sunﬂower industry, production is increasing rapidly. Oxidative stabilities of high-oleic acid peanut oil (75.6% oleic, 4.7% linoleic and 0.03% linolenic acids) were compared to regular peanut oil (56.1% oleic, 24.2% linoleic and 0.03% linolenic fatty acids). Adaptations of the AOM and Schall oven tests indicated that onset of oxidation in traditional peanut oil occurred in one tenth the time, or less, than in high-oleic acid oil [77]. Wet-milled high-oleic acid corn oil (65.1% oleic, 23.0% linoleic, 0.6% linolenic) was compared with regular wet-milled corn oil (23.6% oleic, 62.5% linoleic, 0.6% linolenic) in french-fried potatoes by trained analytical sensory panelists. High-oleic acid corn oil showed lower total polar compounds increase after heating and frying and lower ﬂavor intensity in frying initially, which became higher than regular wet-milled corn oil after 17.5 hours of frying [78]. Frying experiences with high-oleic acid content canola oils have been mixed, partly because some of the early high-oleic acid varieties had higher linolenic acid contents than the so-called low-linolenic acid varieties [79,80]. At the same level of oleic acid content (∼66%), linolenic acid content was a critical factor and was inversely related to the sensory ranking of fried potato chips and oxidative stability as measured by color index, FFA, and total polar compounds content [81]. Low-linolenic acid (2.2%) canola oil was found to be

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equivalent to sunﬂower oil (54.4% oleic acid, 32.4% linoleic acid) and palm olein (30.1% palmitic acid, 40.1% oleic acid and 10.5% linoleic acid). The best ﬂavor stability has been experienced with high-oleic acid canola oils containing less than 3% linolenic acid [81,82]. Commercial development of soybean oils with higher oleic content has not progressed as rapidly as other row crop oilseeds at this time. A patented higholeic (80+%) oil has been developed but commercial production to date has been limited. More recently, soybean germ plasm that yields oil with about 60% oleic acid has been reported and may be developed into a new soybean variety in the near future. Progress in developing low-linolenic (∼3%) acid soybean oil has been more rapid and is now commercially available. Oxidized soybean oil (∼7.5%) linolenic acid content) is just discernable when mixed at 25% with other oils [83]. Trials comparing soybean oils with genetically reduced linolenic acid contents (1.7, 1.9 and 2.5%), compared with a 6.5% linolenic acid control, showed: (1) improved ﬂavor stability in accelerated storage tests at 140◦ F/60◦ C or under light (7,500 lux, 30◦ C); (2) less ﬁshy odor after 1 hour at 374◦ F/190◦ C; and (3) less acrid/pungent odor after 5 hours. The overall ﬂavor quality of potatoes fried in reduced linolenic acid oils at 374◦ F/190◦ C after 5, 10 and 15 hours of use was consistently better than potatoes fried in control oil. After 15 hours of frying, free fatty acid contents of all oils remained below 0.3% [84]. In a similar study, using oils from lowlinolenic acid (1.9 and 2.9%) soybeans, also developed by hybridization techniques but by a different group of researchers, the oils were subjected to more harsh abuse but also showed superior results compared with oil from standard varieties. Blending of oils can be beneﬁcial in some situations. Sensory panel studies have shown that up to 29% nonhydrogenated (7% linolenic acid content) soybean oil can be blended with 71% hydrogenated (∼0% linolenic acid) soybean oil without affecting stability. This results in about a 2% linolenic acid content in the blend and may be signiﬁcant as a cost-saving step in some operations [85]. Four oils: (1) low-linolenic acid soybean oil (2.3% 18:3, and 642 ppm gamma and delta, ␥ + ␦, antioxidant forms of tocopherols); (2) partially hydrogenated low-linolenic acid soybean oil (0.1% 18:3, 154 ppm ␥ + ␦); (3) cottonseedpartially hydrogenated soybean oil blend (1.4% 18:3, 557 ppm ␥ + ␦); and (4) liquid partially hydrogenated soybean oil (0.4% 18:3, 836 ppm ␥ + ␦), were evaluated in frying shoestring potatoes and chicken nuggets. Although differences in performance were relatively small, the partially hydrogenated low-linolenic acid oil appeared to have the best oxidative stability [86].

7.4.3. Fat Replacers Not all reduced-calorie fats and fat replacers are suitable for frying. Of approximately 8–10 groups of potentially useable lipid-based fat substitutes [87], the 6–8 fatty acid sucrose polyester (Figure 6.3) olestra has been developed the

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most commercially under the trade mark OleanTM by the Procter & Gamble Company. Details of composition, use, or nutritional properties of this product can easily be obtained by Internet browser using the search word “olestra,” or from sales representatives. Snack food processors should note that, although olestra may be indigestible, the fatty acids are still susceptible to oxidative degradation and ﬂavor deterioration. The olestra products currently being used by the snack food industry have high melting points. De-oiling units are commonly used to remove surface olean from chips after frying. Akoh [88] has reported that sucrose polyesters made with oleic and stearic fatty acids are more stable than those made from polyunsaturated fatty acids, and TBHQ can be added to enhance stability. Oxidative stability of fatty acids is not signiﬁcantly altered by esteriﬁcation with sucrose.

7.4.4. Added Antioxidants Antioxidants work in oils by absorbing active free radicals (or stabilizing the energy quantums that cause them) and disrupting the well-known chain reaction sequence of autoxidation. Antioxidants are sacriﬁced in the process, and after their depletion the oil becomes susceptible to attack. There has been controversy about use of antioxidants in consumer products, and snack producers who emphasize “clean labels” have been able to discontinue usage without adversely impacting the frying performance or product shelf life. The methods used include selection of appropriate oils, veriﬁcation of oil quality, and special procedures for oil receipt, storage, handling and usage. Near-steady fryer states have been described [89,90] where, with use of high-oleic acid oils without antioxidants and frequent turnover of fresh oil, no oil is discarded. Continuous use of frying oils, without added antioxidants or antifoaming agent, and without need for discarding oil, has been widely achieved domestically. Some industrial fryers prefer to use antioxidants and antifoaming agents, and these additives have been common in institutional frying. In comparison to natural antioxidants, synthetic antioxidants react faster and form more stable free radicals. They provide for longer induction periods under standard test conditions, delay oxidation of oil and protect natural antioxidants. The natural antioxidants are not fully preserved, but remain at higher concentrations than they would be otherwise. It should be noted that BHA, BHT and TBHQ add about 0.02% to FFA titrations due to their acidity. Synthetic antioxidants are not retained in oil during active frying. In the author’s experience, concentrations of the commonly used phenolic-type synthetic antioxidants are rapidly reduced from the allowable usage level to below 10 ppm in continuous commercial frying as result of distillation during frying, oxidation, and possibly by thermal degradation. But their inclusion can provide beneﬁts by protecting oils and shortenings from the point of manufacture, through shipping and storage and during initial use for frying.

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Differences exist between countries in permitted use of antioxidants. Use of the following is allowed in the United States: r Tocopherols. Nature’s fat-soluble antioxidants exist in four forms: alpha (␣),

r

r

r

r

beta (␤), gamma (␥ ) and delta (␦). Alpha tocopherol (vitamin E) is widely used as a dietary supplement and sold over the counter in drugstores and nutritional food stores. Studies generally show that the gamma and delta forms have stronger oil protection properties than the alpha and beta forms. The gamma and delta forms are sold as “natural antioxidants” for food processing applications. Early research did not distinguish between “vitamin E,” “alpha tocopherol” and the more active antioxidant forms—a factor to be considered when reviewing the literature. Mixed tocopherols and partially fractionated tocopherols are now offered to industry. However, tocopherols can act as antioxidants or prooxidants depending on concentrations, test conditions, stage of oxidation and method of testing. Laboratory testing indicates that 400–600 ppm mixed tocopherols provide optimum protection for soybean oil [35]. In the author’s experience, moderately higher concentrations can provide additional protection in some frying applications. Testing under production conditions is recommended to identify optimum concentrations for speciﬁc applications and to avoid excessive concentrations which could have a prooxidant effect. The U.S. Department of Agriculture limits addition of tocopherols to 0.03% in lard, and the Food and Drug Administration allows the amount required for the intended stabilization effect in most products, which typically is 0.02–0.06% of the fat content. Citric acid and ascorbic acid are often used as synergists [5]. Propyl Gallate. This is the n-propyl ester of 3,4,5,-tri-hydroxy benzoic acid. Its use is reduced by solubility problems and poor heat stability, and it has little carrythrough in frying operations. Reactions with iron result in purple or dark discoloration [5]. BHA (Butylated Hydroxyanisole). Its strong phenolic odor is noticed during initial heating of frying oils or shortenings. It can form a pink color when in contact with alkaline metal ions like sodium or potassium [5]. BHA is more effective than the tocopherols but is not as strong as other synthetic antioxidants in protecting vegetable oils from oxidation. BHT (Butylated Hydroxytoluene). Generally considered to be a stronger antioxidant than BHA, it is not as effective as TBHQ. Combinations of BHA, and BHT are synergistic [91] and beneﬁt by chelating agents like citric acid. TBHQ (Tertiary Butylhydroquinone). Developed relatively recently, it is widely used in the United States but has not been approved for use in some countries. It is the most effective antioxidant for unsaturated vegetable oils

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and has the following advantages: (1) good solubility in fats and oils; (2) effectiveness in poultry and animal fats as well as vegetable oils; (3) no discernable odor or ﬂavor imparted to oils and fats; (4) stabilizing effect on tocopherols; and (5) no discoloration in the presence of iron. TBHQ can develop pink color at alkaline pH, and with certain proteins or sodium salts. It has been found effective for protecting crude oils from extraction until deodorization, but is removed during deodorization and additional TBHQ has to be added to protect products leaving the reﬁnery [5]. In the United States, total antioxidants added to foods under FDA jurisdiction have long been permitted at 0.02% (200 ppm) on the basis of fat content. Periodic checking of the Code of Federal Regulations is recommended for new developments in food laws. It can be accessed by requesting “Code of Federal Regulations” on an Internet browser and following the indicated prompts. Animal product foods are contained in Title 9 and foods under FDA jurisdiction in Title 21. Synergistic protective effects of using rosemary and sage extracts, and citric acid, in frying potato chips in RBD palm olein have been reported [92]. Herbal extracts may contribute unwanted ﬂavors to some foods. It has long been known that browning reactions and pyrolysis of lipid-amino acid during frying produces antioxidants, but the subject has received relatively little quantitative research. Natural compounds more active than BHT have been reported [93]. Their effects normally are part of the background of both control and treatment samples.

7.4.5. Other Frying Oil/Shortening Additives r Polydimethylsiloxane (Methyl Silicone). A defoaming agent, it is credited

for making pourable liquid shortenings feasible in food service applications and can also be used in industrial frying oils and shortenings. Frying oil stability has reportedly been increased by 3 to 10 times over the original oil in laboratory tests. Smoke points of oils have reportedly been increased by as much as 25◦ F/13.9◦ C. Levels as low as 0.2–0.3 ppm have been found to be effective. Usage at 0.5–5 ppm levels has been reported. Tests conducted at the higher concentration show signiﬁcant reduction in oxidation and polymerization at elevated temperature. Dispersion of polydimethylsiloxane in oil is difﬁcult [5], requiring the use of high-shear blenders to make premixes that can then be added to bulk oil shipments. The use of polydimethylsiloxane is not permitted in all countries. r Synergists. The role of synergists includes: (1) sequestering (tying up) trace metals, which are fat-oxidizing catalysts, by forming chelates; and (2) increasing the effectiveness of the antioxidant or mixture. It is common

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practice to add citric acid 50–100 ppm at <302◦ F/150◦ C, during cooling of oil after deodorization (Figure 6.5). Phosphoric acid should not be added at greater than 10 ppm because higher levels can cause rapid free fatty acid development during frying.

7.5. MOUTH FEEL Melting points of frying fats inﬂuence product appearance, mouth feel and how quickly ﬂavors in the oil will be released during mastication. Liquid oils give fried products a shiny surface that brightens and enriches product color. During mastication, they provide a rich, juicy eating quality and immediate ﬂavor release. Fats that are semisolid at ambient temperature provide a creamy eating quality and a slight delay in releasing ﬂavor during mastication. Frying fats with higher melting points provide a dry or non-oily appearance and a drier eating quality. Flavor release of the base product will be delayed depending on the melting point of the fat used. The eating quality of frying fat should be matched to the product that is to be produced. A shiny or oily surface provided by liquid oil is expected and preferred by most customers in products like corn chips. For frying potato chips, a wide variety of frying fats, ranging from liquid oils to high-melting shortenings, are available to meet different customer needs. Most potato chips are fried in liquid oil, which supports a full, rich potato chip ﬂavor. But some customers prefer chips that do not have an oily appearance and choose “dry” chips even if they have lower ﬂavor intensity. Some snack foods, such as cheesecoated corn puffs, require a higher-melting fat to set and hold the coating on the surface of the product. Party mixes and similar snacks are expected to provide a good handling experience that does leave oil on the ﬁngers. Melting proﬁles of fats are commonly speciﬁed as Solid Fat Index (SFI) in the United States and Solid Fat Content (SFC) in other countries. When making temperature-proﬁled fats, it is common to produce and hold reserves of several base stocks, each with its own speciﬁcation (SFI/SFC, IV, etc.). Varying amounts of base stocks, plus RBD oil and often hard stocks—oils hydrogenated to IVs of 10 or less—can be blended together as needed to make numerous different margarine/spread, shortening, and specialty fats. SFI curves for soybean oil base stocks are shown in Figure 6.7 [5]. The reader is introduced to SFI applications technology by the buttermargarine/spread curves in Figure 6.8 [1,5]. Curve B-1 shows the SFI of butter. Curve M-2 is the proﬁle for a hard-stick margarine, which is softer than butter when refrigerated (50◦ F), but remains ﬁrmer than butter at ambient temperature (∼70◦ F). Three or ﬁve temperature points are usually shown in the SFI curve. The 100◦ F/37.8◦ C point is close to the normal mouth temperature and is an important consideration in foods. People differ in sensitivities, but may identify greasiness or a waxy feeling if more than 2–3% solids are present in

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Figure 6.7 Solid fat index (SFI) proﬁles of soybean oil hydrogenated to various iodine values. From: O’Brien, R. D., 1998. Fats and Oils: Formulating and Processing for Applications. With permission from Technomic Publishing Co., Lancaster, Pennsylvania [5].

Figure 6.8 Solid fat index (SFI) proﬁles of butterfat, selected margarines/spreads, and frying fats. From: O’Brien, R. D., 1998. Fats and Oils: Formulating and Processing for Applications. With permission from Technomic Publishing Co., Lancaster, Pennsylvania [5].

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margarines/spreads at mouth temperature. The threshold can be higher in baked goods and snacks depending on the fat content and nature of the product matrix. Curve M-3 is the proﬁle for oils used to make soft-stick margarines/spreads and M-4 shows solids content for a tub margarine. Figure 6.8 also shows SFI curves of some specialty fats. In bakery generalpurpose “doughnut” frying fats (S-5), the fat plays other important roles, such as preventing oil separation, sealing the doughnut against drying and assisting in sugar pickup. The “cloudy” effect in pourable cloudy shortenings (S-6) results from inclusion of high-melting beta crystals of fat, which are detectable as a ﬂat plateau in the SFI. Curves S-7 and S-8 represent two high-stability (∼200 AOM) frying fats and are included to show that high-stability frying fats with lower melting points are produced. However, product fried in S-8 shortening would more likely result in a waxy mouth feel as compared to S-7, depending on the nature of the product and the temperature at which it is served/ consumed.

7.6. FORMS OF OILS/SHORTENINGS Referring to Figure 6.5, chelating agents and antioxidants may be added to RBD oil during cooling after deodorization/physical reﬁning. Polydimethylsiloxane is usually added in a dedicated tank or during vessel loading to protect against residual transfer to other products. The oil/melted shortening can then be shipped by railroad car or insulated tank truck to the user. Shortening for food service frying is usually packaged in 40–50 pound plastic–lined cardboard boxes. To prevent separation of crystals after cooling, and to minimize leakage of the surface oil, packaged shortenings are texturized by scrape surface heat exchangers, as used for making margarine. Nitrogen injection during texturizing helps stabilize the fat and produces a soft texture, which aids fryer loading. However, when melting shortening in a batch fryer, cavities can form above heating surfaces and create a ﬁre hazard. Pourable shortenings were developed to facilitate batch fryer oil loading/heating and quickly gained food service acceptance. Two types of pourable (liquid) shortenings are produced—opaque and clear. The opaque version was introduced ﬁrst. It consists of 2–6% hard fat in the beta crystal form, suspended in 100–110 IV partially hydrogenated soybean oil. Clear version shortenings are hydrogenated to ∼88 IV and chill fractionated (winterized) to obtain a liquid oil of ∼92 IV [5].

7.7. FRYING AND PRODUCT SHELF-LIFE TESTS Factors entering into selection of a frying oil/shortening are complex, but not overly complicated. During new product development, it is not always clear how marketing objectives, product formulations and processing equipment will

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work together, or what adjustments will have to be made, until after completing frying tests and evaluating ﬁnished product shelf life. A list of candidate oils, selected from frying oils historically used by a company, and promising new oils available in the market, should be developed and screened for necessary physical and chemical attributes. Screening may include a number of the following: fatty acid composition analysis, melting point, solids analysis, oxidative stability, photooxidative stability, ﬂavor, heat-stressed ﬂavor and others. The better candidates pass on to batch frying tests designed to best simulate steady-state frying, and the most promising are selected for production-scale trials. In current testing, factors like free fatty acid content, p-anisidine value, polar compound development, polymer development and changes in Lovibond Red are monitored during the batch frying phase. Accelerated product stablity tests are conducted using the Schall oven test or a vesion of the OSI test to provide preliminary results, with subsequent testing being conducted to closely simulate market conditions.

8. FRYING OIL MANAGEMENT Most product development/improvement projects include establishing (1) ingredient purchase speciﬁcations; (2) a formula and process manual; and (3) a quality control manual. Additionally, a quality assurance/audit program is normally used to ensure that the product continues to be made as speciﬁed and meets compliance standards on receipt. Comprehensive oil management is essential for producing high-quality fried foods. The oil content in snacks typically is in the 15–40% range. With a good management program, the oil will enrich and enhance product quality. The choice is either to aggressively manage oil quality, or to default to product quality being controlled by the condition of the oil. Requirements for good oil management in various frying applications are similar in many respects, but can have a number of signiﬁcant differences. To ensure proper control, an oil management program, including detailed stepwise procedures, should be developed for each frying application.

8.1. OIL SPECIFICATIONS The volume buyers, who purchase oil in bulk shipments and use continuous fryers, buy oil directly from oil reﬁners and can develop strong business-tobusiness relations. Buyer-users should develop their own frying oil speciﬁcations. The development process involves a complete assessment of the oil in terms of composition, attributes and performance required for a speciﬁc application. The speciﬁcation

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should include a descriptive name, date of issue and revision number for proper oil identiﬁcation and tracking. The requirements for chemical attributes, physical traits and organoleptic qualities should be listed in separate sections with the required test methods identiﬁed. Performance requirements should be included as part of the speciﬁcations. Supplier responsibility for compliance with U.S. Food and Drug Administration regulations and assurance that the oil has been processed in accordance with good manufacturing practices (GMP) should also be included in the speciﬁcations. Traditionally, the composition of oil has been described by referencing the origin of each component present, such as 100% corn oil, or 75% partially hydrogenated soybean oil/25% partially hydrogenated cottonseed oil, along with any additives such as approved antioxidants or antifoaming agents. Descriptive composition statements provide a convenient reference, but to ensure compliance with current fatty acid labeling requirements, the typical fatty acids composition of the oil should also be included. Frying oils are purchased based on their ability to provide acceptable performance in speciﬁc applications. In unusual circumstances, oils may meet the analytical requirements but still fail to provide acceptable performance. Including a performance requirement in the speciﬁcations and stating that the frying oil is to provide acceptable performance for its intended use will support appropriate recourses in the event of a failure.

8.2. SUPPLIER QUALIFICATION AND APPROVAL When volume buyers have their own oil speciﬁcations, purchasing ﬂexibility and competitive bidding are signiﬁcantly enhanced. Branded products that meet the speciﬁcations may be used; but, in addition, oil may be purchased from any supplier that can meet the product speciﬁcation and successfully complete the qualiﬁcation testing. Careful screening and prior approval of suppliers, including inspection of production facilities, is essential for processors who operate on a just-in-time delivery basis. With close inventory control, oil may occasionally have to be used within a matter of hours after receipt. Timing may not allow for completion of some analyses such as stability testing or solids evaluation. To resolve issues with timing and ensure compliance with oil speciﬁcations, supplier selfcertiﬁcation is being increasingly incorporated as part of the supplier approval process. When a supplier is self-certiﬁed, oil receipts are sampled and screened, but the analysis provided by the supplier is essentially accepted as if the buyer had conducted the tests. Extensive documentation of the supplier’s processing, sampling, testing and quality control procedures, including veriﬁcation that an effective Hazard Analysis Critical Control Point (HACCP) program exists, is required to achieve self-certiﬁed supplier status. Self-certiﬁcation is becoming a common business practice, which supports product quality and enhances business relationships.

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8.3. OIL ORDERING The oil inventory should be closely controlled to ensure an adequate supply for production requirements but avoid excessive quantities, which would have to be stored for an extended period. Oil should not be ordered on the basis of storage capacity, but on the basis of projected usage, with consideration of current inventory and any oil that may be in transit. Quality problems should rarely be experienced when shipments are received from a self-certiﬁed supplier and the oil inventory is rotated rapidly.

8.4. OIL RECEIVING At the time of shipment, a representative sample should be forwarded to the buyer along with the supplier’s analysis of the oil. When the shipment is received, product identiﬁcation should be veriﬁed, including lot and batch numbers, to ensure the origin and manufacturer of the oil can be tracked if needed for future reference. The physical condition of the shipment should be noted and the transit time reviewed to identify any irregularities. Bulk shipments should also have a certiﬁcate of sanitation verifying that the vessel was inspected before loading, and was clean, dry, sanitary, and in compliance with prior cargo requirements (i.e., National Institute of Oilseed Products Trading Rules—Prior Cargo Lists). After the paperwork is in order, a formal procedure should be followed to ensure the oil is properly sampled and tested. If the oil is from a self-certiﬁed supplier, testing primarily consists of screening to ensure that no major changes have occurred in transit—typically FFA, PV and ﬂavor/appearance—before the shipment is approved for unloading. A preplanned procedure to control temperature and avoid overheating should be developed and followed for oils that require melting before unloading. After acceptance for unloading, the oil is transferred to storage using proper bulk storage practices and facilities.

8.5. BULK STORAGE When oil is received frequently and stored at proper temperature without aeration, little if any analytical change should occur during the ﬁrst week. The PV should remain below 1.0 meq/kg. During the second week, a moderate increase in peroxide can be expected with the PV remaining below 2.0 meq/kg. During the third week, peroxide development can be expected to increase at a faster rate. Practices should be adapted for each operation; but, as a general rule, if bulk oil is to be stored for longer than two weeks, nitrogen protection should be provided when the oil is ﬁrst received. The peroxide value (PV) of oil in bulk storage is a good indicator of the new oil’s storage quality and should be monitored on a regular basis. The quality

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and quantity of oil in storage always should be checked before adding fresh oil to the tank. Adding fresh oil to storage oil is generally not a problem if both oils meet quality standards; but it is a good practice to limit commingling to 15% or less of stored oil. A PV limit should be established to deﬁne the maximum value allowed in the stored oil to avoid accelerated degradation of the commingled fresh oil. Action standards should also be established to direct handling and usage of stored oil when the PV reaches speciﬁc values, including a rejection limit.

8.6. FRYER OIL LOADING AND PRODUCTION STARTUP Fryers should not be ﬁlled with oil until it is time to begin preheating in preparation for start of production. As soon as preheating (to remove the residual moisture from the fryer) has been completed, the oil should be heated directly to frying temperature. Production should be started at the full capacity of the fryer as soon as the oil reaches the required temperature and maintained at capacity throughout production. Loading the fryer earlier than required subjects the oil to unnecessary abuse and degradation. Unfortunately, it is not unusual for fryers to be ﬁlled with oil and heated to frying temperature several hours before starting production. Checking equipment is the reason usually given for the delay, which causes extensive oil oxidation and initiates polymerization. This practice is unnecessary. All of the equipment, with exception of the oil heating and circulation system, can and should be checked before oil is placed in the fryer.

8.7. OIL TURNOVER Fresh oil is added on a continuous basis to replace oil absorbed by the product during frying. Continuous fresh oil addition is an essential factor in maintaining fryer oil quality. Operating a fryer at its designed capacity provides for the maximum rate of oil turnover and provides the best beneﬁts for oil quality. Many factors, including frying temperature and the product being fried, are involved but, in general, an oil turnover of eight hours or less supports good oil quality and provides for recovery in the event of a problem. Turnover rates of 8–10 hours are common and support normal oil quality. As the rate of turnover becomes protracted, stress on the oil is proportionately increased, and opportunities for recovery in the event of a problem are correspondingly decreased. Commingling of fresh and fryer oil during production, and the extended time required for complete oil replacement, provide good insight as to why oil quality is slow to recover after a problem such as high free fatty acid has occurred. A portion of the abused oil remains in the fryer through several turnover periods.

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8.8. INTERRUPTIONS IN PRODUCTION Hot oil degrades rapidly in quality when exposed to aeration without the beneﬁts of either steam stripping or oil turnover that accompany continuous frying. Any interruption in production is a period of high risk for oil quality. Interruptions in production that are not necessary, such as stopping during a shift change, should be avoided. Planned interruptions that cannot be avoided, such as scheduled equipment or product changes, should be targeted for 15 minutes or less to limit accumulation of oil oxidation products. When unscheduled production interruptions occur, the downtime should be limited to 15 minutes or less to the extent possible. If it becomes apparent that the downtime will extend beyond 30 minutes, steps should be taken immediately to discontinue heating and limit oil aeration and oxidation. A formal procedure to reduce oil stress, consistent with engineering requirements for fryer operation, should be available and used when needed.

8.9. FRYER SHUTDOWN Fryer shutdown is another period when the oil is hot and product is not being fried. A shutdown procedure is needed to specify: (1) the earliest time that oil heating is to be discontinued as production is concluded; and (2) the highest temperature, allowed by the fryer manufacturer, at which oil circulation is to be discontinued to stop unnecessary oil aeration and oxidation.

8.10. FRYER OIL STORAGE The oil may be left in the fryer if production is scheduled for the following day. Otherwise, the oil should be transferred to a fryer oil holding tank. The transfer should occur as soon as possible after shutdown, consistent with safe handling practices. Fryer manufacturers usually stipulate the temperature at which oil can be removed from the fryer. Nitrogen protection is recommended to control oxidation of fryer oil during storage.

9. REFERENCES 1. Erickson, D. R., ed., 1995. Practical Handbook of Soybean Processing and Utilization. AOCS Press, Champaign, Illinois. 2. Hui, Y. H., 1996. Bailey’s Industrial Oil and Fat Products, 5th edition, Vols. 1–5. John Wiley & Sons, New York. 3. Bockish, M., 1998. Fats and Oils Handbook. AOCS Press, Champaign, Illinois. 4. Lusas, E. W., 2000. Oilseeds and oil bearing materials. In Handbook of Cereal Science and Technology, 2nd edition, K. Kulp and J. G. Ponte, Jr., eds. Marcel Dekker Inc., New York.

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5. O’Brien, R. D., 1998. Fats and Oils: Formulating and Processing for Applications. Technomic Publishing Co., Lancaster, Pennsylvania. 6. Perkins, E. G. and M. D. Erickson, eds. 1996. Deep Frying: Chemistry, Nutrition, and Practical Applications. AOCS Press, Champaign, Illinois. 7. Moreira, R. G., M. E. Castell-Perez, and M. A. Barrufet, 1999. Deep-Fat Frying: Fundamentals and Applications. Aspen Publishers Inc., Gaithersburg, Maryland. 8. Min, D. B. and T. H. Smouse, eds. 1989. Flavor Chemistry of Lipid Foods. American Oil Chemists’ Society, Champaign, Illinois. 9. FASonline, 2000. Oilseeds: World Markets and Trade, June 2000 edition Foreign Agricultural Service, U.S. Department of Agriculture, Washington, D.C., www.fas.usda.gov/ oilseeds/circular, June 2000. 10. Watson, S. A., 1987. Structure and composition. In Corn Chemistry and Technology. S. A. Watson and P. E. Ramstad, eds. American Association of Cereal Chemist, St. Paul, Minnesota, pp. 53–82. 11. U.S. Census Bureau, June 2000. Fats and Oils: Oilseed Crushings, M311J(00)–5. U.S. Department of Commerce, Washington, D.C. www.census.gov. 12. Jones, L. A. and C. C. King, 1996. Cottonseed oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2., Y. H. Hui, ed. John Wiley Sons, New York, pp. 159–239. 13. Dies, E. J., 1943. Soybeans: Gold from the Soil. The Macmillan Co., New York. 14. Shahidi, F., ed., 1990. Canola and Rapeseed: Production, Chemistry, Nutrition and Processing Technology. AVI-Van Nostrand, Reinhold, New York. 15. Nawar, W. W., 1996. Lipids. In Food Chemistry, 3rd edition, O. R. Fennema, ed. Marcel Dekker, Inc., New York, pp. 225–319. 16. ISEO, 1999. Food Fats & Oils, 8th edition. Institute of Shortening and Edible Oils, Washington, D.C. 17. Wiseman, J., ed., 1984. Fats in Animal Nutrition. Butterworths, London. 18. Applewhite, T. H., 1993. The role of dietary fat in health and nutrition. In Proceedings of the World Conference on Oilseed Technology and Utilization. T. H. Applewhite, ed. AOCS Press, Champaign, Illinois, pp. 96–106. 19. Beckman, H. J., 1983. Hydrogenation practice. J. Am. Oil. Chem. Soc., 60(2): 234A– 242A. 20. Erickson, D. R., 1995. Degumming and lecithin utilization. In Practical Handbook of Soybean Processing and Utilization. D. R. Erickson, ed. AOCS Press, Champaign, Illinois, pp. 174–217. 21. Stryver, L., 1988. Biochemistry. 3rd edition, W. H. Freeman and Company, New York. 22. Voet, D., J. G. Voet, and C. W. Pratt, 1999. Fundamentals of Biochemistry. John Wiley and Sons, New York. 23. NRC, 1989. Recommended Dietary Allowances, 10th edition, National Academy Press, Washington, D.C. 24. Robertson, J. A., Morrison, W. H. III, and R. L. Wilson, 1979. Effects of Planting Location and Temperature on the Oil Content and Fatty Acid Composition of Sunﬂower Seeds. USDA Agric. Results ARR-S-3. U.S. Depart. Agriculture, Washington, D.C. 25. Robertson, J. A. , 1975. Use of sunﬂower seed in food products. Crit. Rev. Food Sci. Nutr., 6:201–240. 26. Davidson, H. F., E. J. Campbell, R. J. Bell and R. A. Pritchard, 1996. Sunﬂower oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 603–689.

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27. List, G. R., E. A. Emken, W. F. Kwolek, T. D. Simpson and H. J. Dutton, 1997. “Zero trans” margarines: properties of interesteriﬁed soybean oil-soy trisaturate blends. J. Am. Chem. Soc., 54(10): 408–413. 28. Firestone, D., ed., 1998. Ofﬁcial Methods and Recommended Practices of the AOCS, 5th edition, American Chemical Society, Champaign, Illinois. 29. NOPA, 1999. Yearbook & Trading Rules, 1999–2000. National Oilseed Processors Association, Washington, D.C. 30. NCPA, 1999. Trading Rules, 1999–2000. National Cottonseed Products Association, Memphis, Tennessee. 31. AOCS, 1996. Ofﬁcial Methods and Recommended Practices of the American Oil Chemists’ Society, Physical and Chemical Characteristics of Oil, Fats and Waxes, Section I. AOCS Press. Champaign, Illinois. 32. Yurawecz, M. P., M. M. Mossoba, J. K. G. Kramer, M. W. Pariza, and G. N. Nelson, eds. 1999. Advances in Conjugated Linoleic Acid Research, Vol. I. AOCS Press, Champaign, Illinois. 33. Kramer, J. K. G., N. Sehat, J. Fritsche, M. M. Mossoba, K. Eulitz, M. P. Yurawecz, and Y. Ku, 1999. Separation of conjugated fatty acid isomers. In Advances in Conjugated Linoleic Acid Research, Vol. I. M. P. Yurawecz, M. M. Mossoba, J. K. G. Kramer, M. W. Pariza, and Gary N. Nelson, eds. AOCS Press, Champaign, Illinois, pp. 83–109. 34. Sonntag, N. V. O., 1979. Reactions of fats and fatty acids. In Bailey’s Industrial Oil and Fat Products, 4th edition, Vol. 1. D. Swern, ed. John Wiley & Sons, New York, pp. 99–175. 35. Frankel, E. N., 1998. Lipid Oxidation. The Oily Press, Dundee, Scotland, United Kingdom. 36. Gunstone, F. D., 1984. Reaction of oxygen and unsaturated fatty acids. J. Am. Oil Chem. Soc., 61:441–447. 37. Rawls, H. R. and J. P. Van Santen, 1970. A possible role for singlet oxygen in the initiation of fatty acid autooxidation. J. Am. Oil Chem. Soc., 47:121–125. 38. Hastert, T., 1996. Hydrogenation. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vo1. 4. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 213–300. 39. Gustavson, E. H., 1976. Loading, unloading, storage, drying, and cleaning of vegetable oilbearing materials J. Am. Oil Chem. Soc., 53:248–250. 40. Erickson, D. R., 1995. Neutralization. In Practical Handbook of Soybean Processing and Utilization. D. R. Erickson, ed. AOCS Press, Champaign, Illinois, pp. 184–202. 41. Cavanaugh, G. C., 1990. Neutralization II. Theory and practice of non-conventional caustic reﬁning by miscella reﬁning and by the Zenith process. In World Conference Proceedings. Edible Fats and Oils Processing: Basic Principles and Modern Practices. D. R. Erickson, ed. American Oil Chemists’ Society, Champaign, Illinois, pp. 101–106. 42. Welsh, W. A., J. M. Bogdanor, and G. J. Toeneboehn, 1990. Silica reﬁning of oils and fats. In Edible Fats and Oils Processing: Basic Principles and Modern Practices. D. R. Erickson, ed. American Oil Chemists’ Society, Champaign, Illinois, pp. 189–202. 43. Taylor, D. B., 1993. Adsorptive puriﬁcation. In Proceedings of the World Conference on Oilseed Technology and Utilization. T. H. Applewhite, ed. AOCS Press, Champaign, Illinois. pp. 152– 165. 44. Wiedermann, L. H., 1978. Margarine and margarine oil, formulation and control. J. Am. Oil Chem., 55:823–929. 45. Erickson, D. R. and M. D. Erickson, 1995. Hydrogenation and base stock formulations. In Practical Handbook of Soybean Processing and Utilization. D. R. Erickson, ed. AOCS Press, Champaign, Illinois, pp. 218–238.

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46. Strecker, L. R., M. A. Bieber, A. Maza, T. Grossberger and W. Doskoczynski, 1996. Corn oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 125–158. 47. Zehnder, C. T., 1995. Deodorization. In Practical Handbook of Soybean Processing and Utilization. D. R. Erickson, ed. AOCS Press, Champaign, Illinois, pp. 239–257. 48. Carlson, K. F., 1996. Deodorization. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 4. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 339–390. 49. Basiron, J., 1996. Palm oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 271–376 50. Firestone, D., D. Fedeli, and E. W. Emmons, 1996. Olive oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2. Y. H. Hui, ed., John Wiley & Sons, New York, pp. 241–270. 51. Canapi, E. C., Y. T. V. Agustin, E. A. Moro, E. Pedrosa, Jr. and M. L. J. Bendaro, 1996. Coconut oil. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 2. Y. H. Hui, ed. John Wiley & Sons, New York, pp. 97–124. 52. Fritsch, C. W., 1981. Measurements of frying fat deterioration. J. Am. Oil Chem. Soc., 58(3):272–274. 53. Unknown, 1999. Heating industrial frying oils. Oils & Fats International, 51(2):44, 45. 54. Banks, D., 1996. Industrial frying. In Deep Frying: Chemistry, Nutrition, and Practical Applications. E. G. Perkins and M. D. Erickson, eds. AOCS Press, Champaign, Illinois, pp. 258–270. 55. O’Brien, R., 1993. Food service use of fats and oils. INFORM, 4(8): 913–915, 918–921. 56. St. Angelo, A. J., 1996. Lipid oxidation in foods. Crit. Rev. Food Sci. Nutr., 36(3):175–224. 57. Frankel, E. N., 1999. Antioxidants and hydroperoxides: from soybean oil to red wine. INFORM, 10:889–896. 58. Haumann, B. F., 1990. Antioxidants: ﬁrms seeking products they can label as “natural.” INFORM, 1:1002–1013. 59. Bravo, L., 1998. Polyphenols: chemistry, dietary sources, metabolism, and nutritional signiﬁcance. Nutrition Reviews, 56(11):317–333. 60. Decker, E. A., 1995. The role of phenolics, conjugated linoleic acid, carnosine, and pyrroloquinoline quinone as nonessential dietary antioxidants. Nutrition Reviews, 53(3):49–58. 61. Chung, K-T., T. Y. Wong, C-I. Wei, Y-W. Huang and Y. Lin, 1998. Tannins and human health: A review. Crit. Rev. Food Sci. Nutr., 38(6):412–464. 62. Orthoefer, F. T. and D. S. Cooper, 1996. Evaluation of used frying oil. In Deep Frying: Chemistry, Nutrition, and Practical Applications. E. G. Perkins and M. D. Erickson, eds. AOCS Press, Champaign, Illinois, pp. 285–296. 63. Tompkins, C. and E. G. Perkins, 1999. The evaluation of frying oils with the p-anisidine value. J. Am. Oil Chem. Soc., 76:945–947. 64. Firestone, D., 1996. Regulation of frying fat and oil. In Deep Frying: Chemistry, Nutrition, and Practical Applications. E. G. Perkins and M. D. Erickson, eds. AOCS Press, Champaign, Illinois, pp. 323–334. 65. Paul, S. and G. S. Mittal, 1997. Regulating the use of degraded oil/fat in deep-fat/oil food frying. Crit. Rev. Food Sci. Nutr., 37(7):635–662. 66. Perkins, E. G., 1996. Volatile odor and ﬂavor components formed in deep fat frying. In Deep Frying: Chemistry, Nutrition, and Practical Applications. E. G. Perkins and M. D. Erickson, eds. AOCS Press, Champaign, Illinois, pp. 43–48. 67. Takeoka, G., C. Perrino, Jr. and R. Buttery, 1996. Volatile constituents of used frying oils. J. Agric. Food Chem., 44:654–660.

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68. Tasioula-Margari, M., G. Marquez-Ruiz, and M. C. Dobarganes, 1996. Fractionation of oligomeric triacylglycerides and the relationship to rejection limits for used frying oil. J. Am. Oil Chem. Soc., 73:1579–1584. 69. du Plessis, L. M. and A. J. Meredith, 1999. Palm olein quality parameter changes during industrial production of potato chips. J. Am. Oil Chem. Soc., 76:731–738. 70. Sandy, D. B., 1989. The Production and Use of Vegetable Oils in Ptolemaic Egypt. Scholars Press, Atlanta, Georgia. 71. Banks, D., 1996. Introduction. In Deep Frying: Chemistry Nutrition and Practical Applications. E. G. Perkins and M. D. Erickson, eds. AOCS Press, Champaign, Illinois, pp. 1–3. 72. Weber, G. M. and C. L. Alsberg, 1934. Fats and Oil Studies No. 5, The American VegetableShortening Industry. Food Research Institute, Stanford University, Stanford, California, pp. 251–259. 73. Ho, C. T., Q. Chen, and R. Zhou, 1996. Flavor compounds in fats and oils. In Bailey’s Industrial Oil and Fat Products, 5th edition, Vol. 1. Hui, Y. H., ed. John Wiley & Sons, New York, pp. 83–104. 74. Fuller, G., G. O. Kohler, and T. H. Applewhite, 1996. High-oleic acid safﬂower oil: A new stable oil. J. Am. Oil Chem. Soc., 43:477–478. 75. Smith, J. R., 1996. Safﬂower. AOCS Press, Champaign, Illinois. 76. Kharchenko, L. I. and K. I. Soldatov, 1976. Accumulation of fatty acids in lipids from seeds of a high-oleic sunﬂower mutant during ripening. (Translated from Russian). Fiziologiia I Biologiia Kulturnykh Rastenil, 5:808–813. 77. O’Keefe, S. F., V. A. Wiley, and D. A. Knauft, 1993. Comparison of oxidative stability of highand normal-oleic peanut oils. J. Am. Oil Chem. Soc., 70:489–492. 78. Warner, K. and S. Knowlton, 1997. Frying quality and oxidative stability of high-oleic corn oils. J. Am. Oil Chem. Soc., 74:1317–1322. 79. Petukhov, I., L. J. Malcolmson, R. Przybylski, and L. Armstrong, 1999. Frying performance of genetically modiﬁed canola oils. J. Am. Oil Chem. Soc., 76:627–632. 80. Petukhov, I., L. J. Malcolmson, R. Przybylski, and L. Armstrong, 1999. Storage stability of potato chips fried in genetically modiﬁed canola oils. J. Am. Oil Chem. Soc., 76:889–896. 81. Xu, X-Q., V. H. Tran, M. Palmer, K. White, and P. Salisbury, 1999. Chemical and physical analyses and sensory evaluation of six deep-frying oils. J. Am. Oil Chem. Soc., 76:1091– 1099. 82. Warner, K., P. Orr, L. Parrott, and M. Glynn, 1994. Effects of frying oil composition on potato chip stability. J. Am. Oil Chem. Soc., 71:1117–1121. 83. Evans, C. D., K. Warner, G. R. List, and J. C. Cowan, 1972. Room evaluation of oils and cooking fats. J. Am. Oil Chem. Soc., 49:578–582. 84. Mounts, T. L., K. Warner, and G. R. List, 1994. Performance evaluation of hexane-extracted oils from genetically-modiﬁed soybeans J. Am. Oil Chem. Soc., 71:156–161. 85. Moulton, K. J., R. E. Beal, K. Warner, and B. K. Boundy, 1975. J. Am. Oil Chem. Soc., 52:469–472. 86. Tompkins, C. and E. G. Perkins, 2000. Frying performance of low-linolenic acid soybean oil. J. Am. Oil Chem. Soc., 77:223–229. 87. Akoh, C. C., 1998. Reduced-calorie fats and fat replacers. In Emerging Technologies, Current Practices, Quality Control, Technology Transfer and Environmental Issues. Vol. 1. S. S. Koseoglu, K. C. Rhee and R. F. Wilson, eds. AOCS Press, Champaign, Illinois, pp. 223–234. 88. Akoh, C. C., 1994. Oxidative stability of fat substitutes and vegetable oils by the Oxidative Stability Index method. J. Am. Oil Chem. Soc., 71:211–216.

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89. Romero, A., F. J. Canchez-Muniz, C. Tulasne, and C. Cuesta, 1995. High performance sizeexclusion chromatographic studies on a high-oleic acid sunﬂower oil during potato frying. J. Am. Oil Chem. Soc., 72:1513–1517. 90. Romero, A., C. Cuesta, and F. J. Sanchez–Muniz, 1999. Does frequent replenishment with fresh monoenoic oils permit the frying of potatoes indeﬁnitely? J. Agr. Food Chem., 47:1168– 1173. 91. Omura, K., 1995. Antioxidant synergism between butylated hydroxyanisole and butylated hydroxy toluene. J. Am. Oil Chem. Soc., 72:1565–1570. 92. Jaswir, I., Y. B. Che Man, and D. D. Kitts, 2000. Synergistic effects of rosemary, sage and citric acid on fatty acid retention of palm olein in deep fat frying. J. Am. Oil Chem. Soc., 77:527–533. 93. Alaiz, M., R. Zamora, and F. J. Hidalgo, 1995. Natural antioxidants produced in oxidized lipid/amino acid browning reactions. J. Am. Oil Chem. Soc., 72:1571–1575.

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CHAPTER 7

Hot Air Dryers

ROBERT SUNDERLAND

1. INTRODUCTION

D

is one of the oldest unit operations in the food processing industry, with origins dating back to antiquity. It was considered an art for centuries, and did not become understood as a science until the 20th century. Globally, dry foods are very large industries. Also, drying often occurs as part of larger food processes with different names. For example, baking biscuits is largely a drying operation. Many shelf-stable snack foods, including pretzels, baked corn chips, and some crisp potato snacks, are dried substantially during baking. Even frying can sometimes be considered a form of drying in hot oil, especially in the case of fried snacks like potato chips because large amounts of water are evaporated during processing. This chapter reviews the drying process and factors that affect its outcome. Due to better understanding of the process and associated changes in the resulting products, the science of drying has become increasingly complex in recent years. A food engineer designing a drying process now has newer concepts and options that were not available until several years ago. One must have an understanding of the basic principles and relationships associated with drying to properly use these options. Modern drying systems require signiﬁcant outlays of capital and, once in place, often have production life spans longer than 20 years. Choosing an inappropriate piece of equipment, because of a lack of understanding drying systems, can negatively impact production capabilities and proﬁts for many years. Drying has traditionally been deﬁned as the unit operation that converts a liquid, solid, or semisolid material into a solid product with signiﬁcantly lower moisture content. The terms “drying” and “dehydration” are often used RYING

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WATER HOLDING CAPACITY OF AIR TEMPERATURE (Deg. C)

MOISTURE IN AIR (kg H2O / kg dry air)

25

0.020

30

0.028

40

0.049

50

0.087

60

0.150

Air heated to 134°C has 70X water holding capacity of 20°C air.

Figure 7.1 Water-holding capacity of air.

interchangeably; however, the words are not synonymous. The U.S. Department of Agriculture lists dehydrated foods as containing no more than 2.5% water, while dried foods have been exposed to a water removal process and contain more than 2.5% water. In most food drying systems, heated air is passed through a bed of moist food product. The addition of thermal energy causes the air to increase in temperature and hold signiﬁcantly more water than cool air (Figure 7.1). The circulating heated air is also the vehicle for transporting evaporated water away from the drying product. In addition to affecting moisture content, the drying process may also cause other physical and chemical changes, some of which are desirable and others not. Many types of dryers are available to the food industry. They differ chieﬂy in how the food product is conveyed and in the way heat is transferred into the product. Some of these dryers are batch type, and others operate in continuous mode. They may also be categorized by operating pressures, being either vacuum or near-atmospheric. Dryers are generally classiﬁed into four broad categories: r Convection drying relies on heating the product by contact with hot air. Convection-style dryers may well comprise over 90% of food product dryers currently operating. A few of the various convective dryer styles available to industry are the ﬂash dryer, spray dryer, rotary dryer, ﬂuid bed dryer, and conveyor dryer. Because of its ability to process a wide range of products, the continuous conveyor dryer is the most commonly used in today’s food processing plants. r Conduction drying relies on heating the product by direct contact with a drying pan or ﬂame. Griddles or tortilla ovens are examples of conduction-type dryers. r Radiative-type dryers lend themselves best to specialized applications, such as toasting and ﬂavor development in the snack food industry. Direct-ﬁred

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infrared heat is a good example of radiative dryers. Although independent dielectric heating has found limited use to date in the snack food industry, combining several methods of heat transfer such as convection and microwave may dry snack foods more economically and provide unique properties. r Volumetric drying typically uses radio frequency waves (induction heating and microwaves) to heat the product from within. Energy costs are high for these methods alone, and they have found limited use to date in the snack food industry. Combinations with other heat transfer methods, for example, ﬁrst removing the bulk of the moisture by convection drying followed by microwave ﬁnish drying, may dry snack foods more economically and produce unique properties.

2. FUNDAMENTALS OF DRYING The convection-type dryer has two major characteristics: gentle handling of products and use of heated air passing through, over, or impinging on a bed of product. Applications of several terms, common to industry, are discussed in food plant operations.

2.1. BLACK BOX APPROACH Commercial drying requires a compromise between conﬂicting parameters of many types of equipment. Conveyor-type convection dryers use convection heating to evaporate moisture. It is useful to think of a dryer as a sort of black box (Figure 7.2). Heated air enters the bottom and exits at the top. As the product passes through the box, its moisture content decreases. At the same time, the air that passes through the product increases in moisture content. In this simpliﬁed model, what happens inside the box is not considered, only net changes to the product and air streams. "BLACK BOX" APPROACH TO DRYING

PRODUCT

AIR

Figure 7.2 Black box approach to drying.

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Although the moisture content of the food product decreases as it passes through the box, the temperatures of the product at different points may increase, decrease, or remain the same. The moisture content of air increases as it passes through the black box, and air temperature decreases. As the wet-bulb temperature of the air approaches the dry-bulb temperature, the drying potential of the air also decreases. Assuming an upward airﬂow, from a practical standpoint, this means that the lowest layer of product, which is ﬁrst exposed to the drying air, becomes drier than the upper layers. This problem may be alleviated somewhat by alternating the direction of airﬂow within the dryer (Figure 7.3), or by using multiple conveyors. Most modern food dryers incorporate some form of multiple conveyor system, either in a staged or a multipass conﬁguration. A staged dryer is one where the product is transported from one dryer to another dryer (Figure 7.4). The multipass conﬁguration retains the product within the same dryer framework, with separate independently speed-controlled conveyors assembled directly one above the other and moving the product in opposite directions in successive passes (Figure 7.5). Drying is one of several unit operations that include changing materials from one phase to another. This phase transfer is complicated because heat and mass must be transferred simultaneously, but in opposite directions. The liquid portion must ﬁrst be vaporized before it can be transferred to the air. It is important to note that this transfer is affected by the presence of solid material, which interferes with heat, vapor and liquid movements.

2.2. DRYING CURVES The science and mechanics of drying are relatively well-understood phenomena. Data relating moisture content to time can be gathered when a product, like a snack food, is collected and dried experimentally. Plotting the data graphically produces a drying curve (Figure 7.6). If moisture content is plotted against time, the curve can be divided into three major sections. In the ﬁrst portion (A–B), internal heat is still causing evaporation at the surface, which continues to cool the product. This portion of the curve ends when the surface temperature of the pellets reaches the wet-bulb temperature of the drying air. The second portion (B–C) is the constant-rate period. Drying proceeds by diffusion of water vapor from the saturated surface of the pellets through a stagnant ﬁlm into the moving air stream. Moisture movement within the solid is rapid enough to maintain a moisture-saturated condition at the surface. The rate of drying is controlled by the rate of heat transfer from the air to the drying surface. Since the rates of heat and mass transfer must remain balanced, the temperature of the saturated surface remains constant. Also, since these dryers are operated with forced convection air, the product temperature approaches the saturation, or wet-bulb, temperature of the air. The vast majority of the moisture

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Figure 7.3 Different air ﬂow patterns in three-pass dryer.

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Figure 7.4 Staged dryer.

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Figure 7.5 Three-pass dryer.

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MOISTURE CONTENT VS. TIME

MOISTURE CONTENT (DRY BASIS)

A

B

C

D

0 0

TIME

Figure 7.6 Drying curve, moisture content vs. time.

evaporated from foods occurs during this constant-rate period. The drying rate is dependent on raw materials, processing conditions, the food product’s cell structure and the product’s surface area:volume ratio (Figure 7.7). The third portion (C–D) is the falling-rate period. The evaporating surface can no longer be kept saturated by moisture movement within the pellet through this period. The evaporation location moves from the perimeter into the pellet’s core, and the drying rate decreases. It is now governed by internal moisture migration. The falling-rate period most often determines the overall drying time required. As the pellet is continually exposed to heated air within the dryer, its surface temperature increases until it eventually equals the dry-bulb temperature of the air.

DRYING RATE VS. TIME B

C

A DRYING RATE

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TIME

Figure 7.7 Drying rate vs. time curve.

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The critical moisture content is the point at which the constant-rate period ends and the falling-rate period begins. If the ﬁnal moisture content is above the critical moisture content, the entire drying process will occur under constant-rate conditions. If, on the other hand, the initial moisture content is below the critical moisture content, the entire drying process will occur in the falling-rate period. Critical moisture contents are difﬁcult to predict, and values published in the literature are only approximate. Actual drying tests should be conducted if accurate values are required. Once the test work has been completed, it is no longer necessary to predict drying curves, and the data obtained can be used in designing a drying process. Food dryer manufacturers have long understood how these theories relate to drying foodstuffs. The challenge has been in implementing them into commercially sound designs that are energy-efﬁcient and economically viable.

2.3. MOISTURE-EVAPORATION CALCULATIONS The chief objectives in drying snack products include reducing the moisture content and developing desired textures and ﬂavors. The moisture content of product entering the dryer is one of the most important variables and can be determined by a gravimetric method. Assuming that only water leaves the sample, the moisture content can be determined by drying a preweighed sample to a constant weight. This moisture content has traditionally been expressed in two forms, either “as is” or “dry basis.” These two terms are not interchangeable and, at times, create confusion. r Moisture content, wet basis or “as is” (MCWB), may be deﬁned as: % kg moisture per kg wet solids =

(mass of water) × 100 (mass of water + mass of solids)

r Moisture content, dry basis (MCDB), is normally deﬁned as:

% kg moisture per kg dry solids =

(mass of water) × 100 (mass of solids)

The relationship between moisture content, wet basis (MCWB), and moisture content, dry basis (MCDB), is: (MCDB) =

(MCWB) (1 − MCWB)

Moisture content, wet basis (MCWB), is the form familiar to most. However, the reader should be alerted to the existence of moisture content, dry basis (MCDB), which sometimes is used by dryer engineers. Conceptually, if a dried product contains 20% moisture, MCWB, it also contains (100% − 20%) = 80%

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TABLE 7.1.

Effects of Moisture Content on Dryer Load. Incoming Material Supplied to Dryer at Constant Rate, but with Differences in Moisture Content; Moisture Content of the Product Exiting Dryer is Kept Constant. Moisture Content

3,000 kg/hr Wet Product Supplied A B C D E F

Moisture in product Solids in product Amount of saleable product at 6.5% moisture Amount of water left in saleable product Amount of water to dry Load increase or decrease

Calculations

25%

28%

3,000 kg × % MCWB 3,000 − A B/(1.00 − 0.65) = B/0.935

750 kg 2,250 kg

840 kg 2,160 kg

2,406 kg

2,310 kg

C--B A--D 690 kg/594 kg = 1.161

156 kg 594 kg ---

150 kg 690 kg +16.1%

solids. The same product would have ([20%] × 100)/80% = 25% MCDB; or each unit weight of product dry solids is accompanied by an additional 25% of its weight as moisture. The amount of water to be removed by a dryer is highly inﬂuenced by the incoming rate of partially processed product, as well as its moisture content and that desired in the ﬁnished product. For example, given an incoming weight of 3,000 kg/hr of multigrain snack material from the extrusion system with a moisture content of 25% (wet basis), the dryer must evaporate 594 kg water for product to exit the system at 6.5% moisture content. Next, a change is made to the extrusion system, which results in the dryer receiving the same weight of material at a higher moisture content of 28%, with no changes in moisture content of the exiting product. Calculations in Table 7.1 show that 690 kg/hr of moisture must now be removed instead of the previous 594 kg/hr. The rather inconspicuous increase of 3% moisture coming into the drying system has placed slightly more than a 16% additional load capacity on the dryer, which may exceed its design capacity. In a second example, the dryer load becomes even greater if the extrusion system continues to process the same weight of premix, and produces wet product at 28% moisture content instead of the former 25%. Assuming that the moisture content of the premix entering the feeder is 10%, the amount of dry matter processed in one hour would be 2,250 kg = (1.00 − 0.10)X ; X = 2,500 kg. Table 7.2 shows that the load increase on the dryer would then be +21%.

3. PSYCHOMETRIC CHARTS Absolute humidity is the weight of moisture contained per unit weight of air in an air-water vapor mixture. The term “relative humidity” will not be used in this presentation because it has no meaning at the temperature used in these

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TABLE 7.2.

Effects of Moisture Content on Dryer Load. Incoming Material Supplied to Extruder Feeder at Constant Rate. Differences Are Developed in the Amount and Moisture Content of Extruded Product. The moisture Content of Product Exiting the Dryer Is Kept Constant.

2,500 kg/hr of 10% Moisture Content Premix Processed A B C D E F G

kg/hr extruded product Moisture in product Solids in product Amount of saleable product at 6.5% moisture Amount of water left in saleable product Amount of water to dry Load increase or decrease

Moisture Content Calculations 2,250 = ([100%− %MC]/100)X ; X = A × %MCWB A−B C/(1.00 − 0.65) = C/0.935 D−C B−E 719 kg/594 kg = 1.210

25%

28%

3,000 kg 750 kg 2,250 kg

3,125 kg 875 kg 2,250 kg

2,406 kg

2,406 kg

156 kg 594 kg ---

156 kg 719 kg +21.0 %

dryers. Saturation is the maximum quantity of water vapor that air can hold at a speciﬁc temperature. percent saturation (weight of moisture in unit weight of air) = × 100 (maximum weight of moisture that could be held in the same unit weight of air at that speciﬁc temperature) The concept of percent saturation is extremely important in designing and operating drying systems. For a given quantity of air, the amount of moisture that can be held increases as the air is heated. The reverse occurs as the air is cooled. When air holds the maximum amount of moisture possible at its respective temperature, it is said to be 100% saturated. Cooling the saturated air results in some of the moisture precipitating until the saturation level is reestablished at the new temperature. Heating saturated air increases its water-holding capacity. Various types of instruments can measure percent saturation. Electronic devices rely on changes of current ﬂow in an exposed chemical surface as changes in humidity occur. Some mechanical devices rely on changes in length of hair or plastic strip length with changes in humidity. Comparison of dry-bulb and wet-bulb temperatures is often used because of its conceptual simplicity. Drybulb temperature is simply the temperature of the air. Wet-bulb temperature is a measurement of the same air, using a thermometer whose stem is surrounded by a fabric sleeve that is kept wet. The wet-bulb reading will be lower than the dry-bulb reading by an amount indicative of how rapidly moisture evaporates from the fabric sleeve. The operator determines the percent saturation in the air stream by comparing both readings on a psychometric chart. One hundred percent saturation corresponds to the point where dry- and wet-bulb

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D

C

B

A

75% 30% 10% 100% 50% 20%

W A T 0.15 W E A R T E P R E R 0.10 C O K N G T E D N R 0.05 T Y A I R 10° 0.00 10

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ADIA BAT IC S ATU RAT ION

35° 30° D

30

B

40

50

60

70

80

90

LINE S

B E F O R E P A R O D U C T

100 110 120 130 140 150 160

DRY BULB TEMPERATURE, °C

Figure 7.8 Psychometric chart.

temperatures are the same. The wet-bulb temperature is also referred to as the “saturation temperature.” Psychometric charts can also provide additional current status information, such as the amount of moisture in the air as weight of water vapor per unit weight of air, energy content, and air densities, and so on. Psychometric charts can become so crowded with information that they are difﬁcult to read except by more experienced operators/engineers. “Adiabatic” is a term that means constant heat content. In the case of air, this means that as the air is cooled by evaporating water, the total heat content of the air-water vapor mixture remains constant. Drying, as conducted in a drying system, can be demonstrated on a psychometric chart using the example in Figure 7.8. The drying unit operation can be divided into several sequences: r A. Heating of the drying air. The air is heated from 70◦ C to 150◦ C, dry

bulb; this appears as a horizontal line on the psychometric chart because no moisture is added to the air at this point in the dryer. As a result, this increases the saturation temperature from 47◦ C to 55◦ C. r B. Adiabatic cooling as the heated air is passed through the moist product. The hot air is next transported through the moist bed of product. The product releases a portion of its moisture into the air, increasing its moisture content from .07 to .10 kg water per kg dry air and simultaneously reducing the process air temperature from 150◦ C to 90◦ C (dry bulb). This step follows the 56◦ C adiabatic saturation line.

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FRESH AMBIENT AIR

A

C EXHAUST AIR B

B

Figure 7.9 Airﬂow related to psychometric chart in dryer cross-section.

r C. Mixing stage as the humid air is partially exhausted and replaced with

ambient air. Next, the moisture-laden air is further cooled as fresh ambient air is introduced into the drying system to replace a portion of air that is normally exhausted from the drying system. The dry-bulb temperature decreases from 90◦ C to 70◦ C, and the water content decreases from 0.07 to 0.10 kg water per kg dry air. The mixed air is at point A, ready for reheating. The three-part series represents a simpliﬁed full drying cycle on the psychometric chart. The cross-section of a typical two-pass conveyor dryer, illustrated in Figure 7.9, shows where the key psychometric chart points occur on the machine. Point A coincides with the 150◦ C heated air forced by the circulating fans to the product beds. Point B coincides with the heated air after passing through the product layer. Process air temperature is reduced via adiabatic cooling from 150◦ C to 90◦ C as the water is evaporated from the product layer. A portion of this moisture-laden cool air is next removed from the drying system as exhaust air, and an equal portion of fresh ambient air is added to the system as “makeup” for the lost exhaust air. A great portion, generally more than 80%, of the air is recirculated within the dryer. The recirculated and fresh airs are combined at point C. Process air (dry-bulb) temperature and saturation temperature are processing variables that may be changed. Operating a dryer at lower-process temperatures and higher air saturation levels tends to dry products more uniformly with lower

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utility costs, but requires use of a larger dryer. Operating the same unit at a highprocess temperature and lower air saturation generally results in higher utility costs per unit throughput, but allows use of a smaller dryer. Often, the characteristics of the product being dried deﬁne the range of process temperatures available to the operator. Speciﬁc components of a recipe may be heat-sensitive and may not tolerate excessive temperatures. Desired product ﬂavor, texture, or organoleptic qualities may dictate minimum or maximum temperatures for the formulation. Generally, if a dryer is operated at high process temperatures and high process humidities, evaporative cooling is reduced causing high product surface temperatures. Operating at low process temperatures and high humidities may lead to moisture condensation within the dryer, causing corrosive damage; in extreme cases, water droplets may be seen falling onto the product bed and microbiological growth is risked.

4. SIZING A DRYING SYSTEM After the basic requirements of drying the foodstuff are understood, the next step is sizing the application. The equation in Figure 7.10 deﬁnes the basic relationship. Note that any system of units is acceptable as long as they are compatible. Product ﬂow rate may be either initial or ﬁnal, “as is” or “dry basis,” but product density and bed depths must be calculated at the same point and on the same basis as the ﬂow rate. The equation may be solved for any variable. However, for sizing a dryer, often the bed area is the unknown. To solve for the bed area, either the remaining variables must be known, or values must be assumed. Normally, the process under consideration determines the mass ﬂow rate and the material’s bulk density.

BASIC DRYER SIZING EQUATION 3 BULK DENSITY (kg/m )

BED DEPTH (m) MASS FLOW RATE (kg/hr) RETENTION TIME (hr)

BED AREA =

(MASS FLOW RATE) X (TIME) (BULK DENSITY) X (BED DEPTH)

Figure 7.10 Basic dryer sizing equation.

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4.1. BED DEPTH The product’s bed depth normally is not known and not easily predicted. Obviously, increasing the process bed depth will reduce the overall size of the dryer, and therefore capital cost of the project. On the other hand, deeper bed depths have other negative effects that must be considered. If airﬂow is through the product bed, deeper depths create more air restriction and thus reduce process air velocity. If the airﬂow is across the bed or impinging upon it, a lower percentage of the product is exposed to the process air. Both of these scenarios will reduce the drying rate, and therefore increase the overall drying time required. Deeper beds also increase the ratio of product mass:air mass. This both reduces the amount of heat available and increases moisture content of the air, again resulting in an increase in the required drying time. Since increasing the bed depth also increases the required drying time, a compromise must be made when determining the optimum bed depth. This is usually done experimentally for new products. Samples are dried at various bed depths and the drying times are measured. The above equation may then be used to determine which bed depth results in the lowest overall dryer size. The bed depth also is affected by other product characteristics. If the material to be dried is fragile or soft, the bed depth may be limited by the point at which unacceptable product degradation occurs. Sometimes, wet products are sticky or too wet and tend to form solid mats if the bed depth is excessive.

4.2. EFFECTS OF PRODUCT ON DRYING TIME Many factors can affect drying time. The ﬁrst is bulk density. Typically, drying time is directly proportional to product density. A second is particle size. Large particles require longer times to dry than smaller particles because the moisture must travel further to get to the product’s surface. Third is product texture, including surface roughness and porosity. The surface area:volume ratio is a good indicator of these factors. The greater the ratio, the quicker the product drying. Product packing is fourth, and is affected by particle size and shape. Particles packed too tightly have the same effect on drying as large particle size.

4.3. EFFECTS OF PROCESS AIR ON DRYING TIME Both velocity and temperature affect the performance of process air within the dryer. Heat and mass transfer must occur through a stagnant-air ﬁlm between the particle surface and the moving air. Increasing air velocity decreases the thickness of this ﬁlm and increases the drying rate. In addition, increasing the process air velocity increases the ratio of air to product. This makes more heat

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available and reduces partial pressure of the water vapor, both of which increase drying rate. Air velocity is normally limited by how much the product bed can tolerate without disturbance. In some cases, air velocity may be limited by mechanical considerations like the capacities of the fans and heat sources. Normally, air velocity should be at the maximum rate that can be handled by the product and the mechanical equipment. Temperature also is an important air characteristic. In most cases, increasing the process temperature decreases the required drying time. Product degradation is the major limit on process temperature. All food products have a limit, which, if exceeded, will result in destruction or damage of the product. Many food products exhibit a characteristic known as “case hardening,” whereby the product forms a dry outside layer that is impervious to moisture migration if a certain temperature is exceeded. Energy efﬁciency is another limit. Normally, increasing process air temperatures also increases energy consumption and results in lower efﬁciencies. The optimum solution is to balance the decrease in dryer size with the increase in required energy consumption that results from operating at higher process temperatures. The moisture content of the process air is yet another characteristic. Although this is sometimes expressed as “relative” or “absolute” humidity, percent saturation is more useful because the drying rate may be expressed as a function of the difference between the dry-bulb and wet-bulb temperatures. Obviously, the greater percent saturation, the less capacity that air has to hold additional moisture, thus requiring additional drying time. Speciﬁc products such as pastas and third-generation snacks require precise control of humidity within the drying air. This family of products may occasionally need added humidity within the dryer in the form of steam. If dried under low-humidity conditions, these dense products will produce inferior ﬁnished goods. Operating a dryer under these conditions tends to seal the outside layers before enough moisture migrates from the interior to the perimeter of snack pellets. This can lead to cracking, checking and surface blistering in extreme cases. Non-uniform drying of these products may not become evident until it is later found that they expand unevenly in hot oil or hot air. Accurate humidity sensors are essential when drying third-generation snacks.

5. SELECTING A DRYER Baker [1] outlined ﬁve basic steps in dryer selection, including: (1) State the application(s) as accurately and thoroughly as possible. (2) Collect all available data pertinent to the application. (3) Determine the critical parameters.

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Figure 7.11 Dryer planning worksheet.

(4) Narrow the choices to three or four drying systems based on the above variables. (5) Evaluate all the critical information, including ﬁnal product and cost considerations, when making the ﬁnal decision. In many cases it can be said that deciding on the most appropriate choice in dryer selection is still an art. But this art has been aided by inputs of experience,

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Figure 7.12 Industrial food dryer/cooler. (Wenger Manufacturing Company, Sabetha, Kansas.)

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product knowledge and science. Often, a right or wrong choice may not exist because more than one solution may be technically and economically viable. A careful evaluation of the various styles of equipment may help narrow the ﬁeld of possible choices. Often, dryer vendors are helpful in identifying viable design concepts and estimating energy requirements and capital outlay. Reputable vendors offer in-house trials to more precisely determine project requirements. Specifying the needed ancillary equipment like product bed distribution devices, continuous ﬁnes removal, instrumentation and control requirements also is important. General dryer worksheets (Figure 7.11) are useful in identifying the critical parameters and ensuring that valuable information is not excluded or overlooked as non-essential. Dryer manufacturers are knowledgeable about the time required and typical costs associated with installation of their equipment (Figure 7.12). With cost data for different alternatives in hand, it should be easier to select one of the candidates as a clear favorite. But before making the ﬁnal decision, the following questions also should be considered. (1) Are the accuracy and reliability of the competing quotations comparable? If not, might a cost advantage exhibited by one vendor turn out to be limited? (2) Does the hardware conﬁgured meet sanitation requirements with adequate accessibility, complete or partial stainless steel construction, and having no non-essential horizontal surfaces? (3) Does the hardware conﬁgured meet applicable safety and environmental requirements? (4) Does the most probable equipment supplier have the technical competence, experience, and backup support to design, build, install and commission the dryer? (5) Are there major differences in energy utilization between the different dryer types? (6) Have any hidden costs, for example, the resulting need for added boiler capacity, increased production ﬂoor space, or commissioning fees, been taken into account? (7) Is the dryer vendor willing to guarantee production throughputs and uniformity of processed goods?

6. REFERENCE 1. Baker, C. G. J., 1997. Dryer selection. In Industrial Drying of Foods. C. Blake, ed. Blackie Academic and Professional, London. pp. 255–266–268.

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SECTION III

SNACK FOODS PREPARATION AND DEDICATED EQUIPMENT

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CHAPTER 8

Potatoes and Potato Chips

WILBUR A. GOULD

1. POTATO PRODUCTION

1.1. HISTORY OF THE POTATO

T

white potato is a native of South America and has long been a food staple of inhabitants of Chile, Columbia, Peru, Ecuador and Bolivia. The ﬁrst recorded contact of the white man with the potato was by Gonzal Jiminez De Quesada in 1537 at the village of Sorocota about 7 degree latitude N. The white or Irish potato is one of the world’s most important food plants. It follows after wheat, rice and corn as a major food crop. Since its introduction to Europe from South America in the 16th century, its adaptability and capability to yield good crops have made it a food staple in nearly every civilized country. The annual world production of potatoes is about 300 million metric tons. The United States is far outranked by Russia, Poland and China in production of potatoes. These three countries grow over 50% of total world production, whereas the United States produces about 7%. The potato is one of the lowestcost foods in the world, and is widely accepted because it has a mild compatible ﬂavor. Today, about two-thirds of the harvested U.S. crop is processed into frozen french fries, potato chips, dried potato products, and canned potatoes. About 125 domestic potato chip factories process nearly 50,000,000 hundred weight (cwt) of potatoes per year. Per capita potato chip consumption is about 17 lbs. HE

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1.2. POTATO PRODUCTION Potatoes grow best on lighter soils in comparatively cool and moist climates. As a result, they are raised extensively in Northern Europe, Ireland, Northern United States and Canada. The ﬁrst domestic U.S. production is reported to have occurred in Londonderry, New Hampshire, in 1719 from stock brought from Ireland. Potatoes are grown in nearly every state in the United States, with concentrations in Maine, New York, Michigan, Wisconsin, Minnesota, North Dakota, Idaho, Washington, Oregon and California. About 15% of the U.S. crop is produced in the southern states, particularly Florida. Potatoes are grown on approximately 1,400,000 acres (566,802 hectares) in the United States. Yields vary upwards to 1,000 cwt per acre, but average around 350 cwt/acre.

1.3. ANATOMY OF THE POTATO The potato is an annual plant, which generally is propagated asexually from cut pieces of tubers. At the time of ﬂowering, tuber formation is usually initiated by enlargement of the tip of the rhizome. The rhizomes arise from the underground portion of the stem. Many factors may affect the formation and number of tubers, including: soil temperature, moisture supply, length of light period and formation of carbohydrates in the plant. The tuber, which is the edible portion of the plant, consists of a thickened, underground stem (Figure 8.1.). Tubers may be dug before they are fully mature to meet user demands. Usually, the immature potato has a skin or periderm that is ﬂuffy with curled fragments. Immature tubers should not be stored as they may break down quickly if not used promptly.

1.4. TUBER MATURITY “Mature tubers” are those tubers that come from ﬁelds where the vines have died or have been killed with the tubers left in the ground for upwards of two weeks before digging. Maturity is measured by determining the sucrose content in the tuber. The sucrose or chemical maturity monitoring (CMM) assay should

Figure 8.1 Longitudinal diagram of a potato slice.

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Figure 8.2 Typical changes in sucrose concentration of potatoes during growth, harvest and storage.

be 1% or less if the tubers are to be stored for the chip market. As shown in Figure 8.2, sucrose should be monitored during growth and storage. Harvesting should take place when the sucrose content is below 1.5%. It should remain at this level or lower during the storage life of the potatoes. They must be used when the sucrose level starts rising in storage, or dark chips will result. In most cases, sucrose will be too high for any amount of reconditioning to lower the glucose level to 0.15%. Without doubt, bruising is the second most serious factor when working with potatoes for the chip market. Bruises developed during harvesting, handling and storage of tubers create large losses of raw product. To prevent shatter bruise and black spot development, tubers should never be handled when the temperature is below 45◦ F (7.2◦ C). Preferably, tubers should only be handled when the temperature is above 55◦ F (12.7◦ C). The types of defects are classiﬁed in Table 8.1.

1.5. HARVESTING, HANDLING AND STORAGE OF POTATOES Freshly dug potatoes must be properly cured or suberized (healed from digger and/or other mechanical damage) before low-temperature storage. The humidity should be high, that is, 95–99% in a well-ventilated area to allow suberin formation. A layer of suberin or periderm can develop in less than 48 hours, with three layers in six to seven days. Formation of the periderm is essential to prevent rot or microorganism penetration. Temperatures during the suberization

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TABLE 8.1.

Common Types of Defects in Potatoes. Physiological Disorders Black heart Brown center Enlarged lenticels Growth cracks Hollow heart Internal brown spot/heat necrosis Internal sprouts Stem end browning Sunburn/greening Fungal Diseases Black scurf Early blight Fusarium dry rot Late blight Sclerotinum Silver scurf Vascular discoloration Bacterial Diseases Black leg Ring rot Scab, surface or pitted Silver scurf Soft rot Virus Diseases Net necrosis Entomological Problems Flea beetle Nematodes Tuber moth Variegated cutworm White grubs Wire worms Mechanical Damage/Injuries Blackspot Skinning/Feathering Shatter bruise Pressure bruise

process should be maintained at 60◦ F (15.6◦ C). After the wounds are healed, the temperature may be gradually lowered to the desired storage temperature. This is determined by tuber variety and expected length of the storage period. To prevent weight loss and excessive peel loss at the time of use, the storage temperature should be low enough to allow the tuber to go into its rest stage. Tubers can be stored for up to 10 months if storage conditions are appropriately controlled, including regulation and maintenance of temperature and humidity up to 99% throughout the storage pile by airﬂow that provides thorough air distribution and proper ventilation.

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2. POTATO ANALYSIS AND COMPOSITION

2.1. TUBER COMPOSITION Composition and amounts of nutrients stored in tubers are affected by: (1) the growing season—including temperature and moisture; (2) the soil type and nutrient elements in the soil; and (3) the genetic characteristics of the speciﬁc cultivar or variety. Composition is of particular importance and concern to the chip manufacturer. Approximate analyses of white potatoes are shown in Table 8.2. The wide range of nutrients indicate that many variables may affect composition and, in part, explain why tubers differ widely. Without question the variety or cultivar is the number one cause of composition difference.

2.2. POTATO VARIETY/CULTIVAR A chip-type potato must have two basic characteristics. First, it must be a variety that can be grown proﬁtably in the environment and cultural conditions of the speciﬁc region. This implies it must have: (1) high yields of marketable size and grade quality tubers; (2) disease resistance; (3) maturity to ﬁt the growing season of a given area; and (4) tubers that store well without rotting or sprouting and maintain their chip quality. Second, a chipping variety must meet the speciﬁcations of the chipper. This implies the variety must produce potatoes that: (1) chip to acceptable color (low in reducing sugars); (2) produce acceptable chip volume or have high dry matter content (speciﬁc gravity) and low percent of peeling waste; (3) are free from blemishes, including defects, mechanical injury and physiological disorders; and (4) have good texture and ﬂavor in the ﬁnished products. Well over 100 different cultivars are used in today’s potato industry. However, only a few are of interest to the chipper. Some are shown in Table 8.3. Many new numbered cultivars are in the testing stage and include some new “cold chippers,” that is, potatoes that can be stored at or near 40◦ F (4.4◦ C). All in all, better potatoes for the market are obtained by storing at colder temperatures. TABLE 8.2.

Proximate Analysis of White Potato. Percent

Constituent Water Total Solids Protein Fat Carbohydrates Ash (minerals)

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Minimum

Maximum

63.0 13.0 0.7 0.02 13.0 0.44

87.0 37.0 4.6 0.96 30.5 1.99

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TABLE 8.3.

Some Potato Varieties/Cultivars for Chip Use.

Variety/ Cultivar

Speciﬁc Gravity

Atlantic Chipeta Gemchip Kanona Kennebec NorValley Pike Snowden

Storage ◦ F

Shape

1.089 1.078 1.080 1.077 1.080 1.080 1.094 1.085

Oval-Rd. Oval-Rd. Round Round Oblong Rd-Oval Round Round

50 50 50 50 55 42 45 45

Advantages include: (1) less prevalence of diseases; (2) less loss of moisture or shrinkage in weight; and (3) little or no sprouting, with no need for sprout inhibitors.

2.3. SPECIFIC GRAVITY Besides the previously mentioned ﬁeld characteristics of varieties, total solids content (speciﬁc gravity) is by far the ﬁrst criterion the chipper uses. Potatoes with high solids content produce more chips per pound, as shown in Table 8.4. Also, other factors being constant, the chips will have lower oil content and better ﬂavor. Speciﬁc gravity or total solids varies with varieties, growing areas and maturity, but remains fairly constant during the normal life of the potato if the relative humidity remains high (>95%). Total solids can be measured by determining the loss of moisture by drying the potato. Generally, this is too timeconsuming and costly for everyday use. Presently, three methods are used to TABLE 8.4.

Inﬂuence of Speciﬁc Gravity on Chip Yield and Chip Oil Content. Calculated Using Linear Regression Equations. Speciﬁc Gravity

Yield of Chips (%)

Oil Content of Chips (%)

1.060 1.065 1.070 1.075 1.080 1.085 1.090 1.095 1.000 1.105 1.110

28.44 29.22 30.00 30.78 31.56 32.33 33.11 33.89 34.67 35.45 36.23

47.04 45.71 44.38 43.05 41.72 40.39 39.06 37.73 36.40 35.07 33.74

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determine the speciﬁc gravity of potatoes: (1) the brine method; (2) weight in air vs. weight in water; and (3) the Snack Food Association’s potato hydrometer method. The brine method is determined by ﬂoating potatoes in brine solutions of known salt concentration. Its advantage is that individual tubers can be separated without destruction. However, the method requires time and the use of standardized solutions. The weight in air methods is somewhat simpler in that only a balance and a container of water are needed. The tuber(s) are weighed in air and then weighed in water and the speciﬁc gravity calculated using the following formula: speciﬁc gravity =

(weight of tuber in air) (weight of tuber in air) − (weight of tuber in water)

Larger sample sizes improve accuracy of the method. The potato hydrometer method requires a standard potato hydrometer; wire basket to hold 8 lb of potatoes; calibration rod (272 g); 30-gallon container; and a scale to weigh the 8 pounds of tubers. The hydrometer, rod and basket are available from the Snack Food Association. A plastic 30-gallon garbage container is satisfactory. Eight pounds of potatoes are weighed in air, placed in the basket, and this is suspended in water with the calibrated hydrometer attached. The reading is taken directly from the hydrometer indicating the potato solids or the speciﬁc gravity (Table 8.5). For every 0.005 increase in speciﬁc gravity, TABLE 8.5.

a

Conversion of Speciﬁc Gravity of Potatoes to Water, Dry Matter and Starch in Percent.a

Speciﬁc Gravity

% Water

% Dry Matter

% Starch

1.050 1.055 1.060 1.065

86.12 85.06 84.01 82.95

13.88 14.94 15.99 17.05

7.85 8.85 9.84 10.84

1.070 1.075 1.080 1.085

81.90 80.85 79.79 78.73

81.10 19.16 20.21 21.27

11.83 12.83 13.82 14.82

1.090 1.095 1.100 1.105 1.110

77.67 76.62 75.56 74.41 73.45

22.33 23.38 24.44 25.49 26.55

15.81 16.81 17.80 18.80 19.79

Calculated from Von Scheele equations: % Starch = 17.564 + 199.07 (Sp. Gr. − 1.0988) % Dry matter = 24.182 + 211.04 (Sp. Gr. − 1.0988) % Water by difference; or 100 − % dry matter

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Figure 8.3 Relationship of total solids to speciﬁc gravity in potatoes.

an additional pound of chips can be obtained per 100 pounds of raw potatoes. The relationship of speciﬁc gravity to total solids is shown in Figure 8.3.

2.4. SAMPLING With any of the methods, care must be taken to ensure the potatoes are clean and disease-free. The tubers should be selected at random and be representative of the entire lot. The sample should be a representative part or a single item from a larger whole or group presented for inspection or shown as evidence of quality. The sampler should select three representative samples at random from the load by scooping up the tubers rather than hand selecting them. This author recommends that grade and quality evaluation follow the diagram shown in Figure 8.4.

2.5. PULP TEMPERATURE AND OTHER CHARACTERISTICS Pulp temperature is one of the ﬁrst characteristics to check in determining how a load of potatoes has been handled. The pulp temperature should be near 68◦ F (20◦ C). If the pulp temperature is below 50◦ F (10◦ C), the load may have to be reconditioned (warmed up to lower the reducing sugar content to less than 0.15%) for a few days before use. Size and shape are of great signiﬁcance in determining the yield and peel loss of the tubers as shown in Table 8.6.

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Load of Potatoes

Select three 25 lb representative samples at random from each load of potatoes and blend. Divide sample.

A. 1/2 of Sample 1. Determine Pulp Temperature

B. 1/2 of Sample Fry for Chip Quality Evaluate for Color

2. Wash and Determine % External Defects and indicate types. 3. Weigh out three 8 lb samples, determine specific gravity of each lot and average the values.

Evaluate for Freedom from Defects: A. % Blisters B. % Minor Defects C. % Major Defects

4. Count the number of tubers in each

Evaluate for Flavor

8 lb lot and average. Moisture 5. Size grade a 25 lb sample into Large (> 3 inches in diameter), Medium (2 to 3 inches in diameter), and B size (less than 1 3/4 inch in diameter and calculate % of each.

Texture

Oil Content

6. Peel and determine % peel loss. 7. Cut the Large tubers and determine % Internal Defects and indicate Types 8. Randomly select 25 tubers, plug them using a 1/2 inch borer and determine both Glucose and Sucrose values using the YSI (Yellow Springs Instrument) or similar method.

Figure 8.4 Quality and grade evaluation of potatoes for chip use.

The raw potato is the most important material in manufacturing potato chips. Speciﬁcations in Table 8.7 detail signiﬁcant characteristics when procuring potatoes for chip manufacture.

3. POTATO CHIP MANUFACTURE The unit operations in manufacturing potato chips are shown in Figure 8.5. Each is a separate and important step, and has speciﬁc parameters with which the operator must be familiar to produce high-quality and uniform chips.

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TABLE 8.6.

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Relationship of Tuber Size to Various Physical Constants for Tubers of Different Diameters. Sphere Diameter of Potatoes in Inches

Physical Constants

1.5

2.0

2.5

3.0

3.5

4.0

Surface area in sq. inches 7.06 12.6 20.4 28.1 39.2 50.0 Volume in cubic inches 1.76 4.19 9.16 14.13 23.82 33.51 Ratio of area to volume 4.00 3.00 2.50 2.00 1.75 1.50 Approximate no. tubers/lb 11 8.0 5.03 2.60 1.80 1.00 Approximate no. slices/lb 264 256 201 125 101 64 Approximate no. of tubers/8 lb 88 64 40 21 14 8 1/16 peel removal (% volume loss) 21 17.0 14.50 12.0 10.5 9.0

3.1. RECEIVING AND GRADING When potatoes are delivered at the chip plant, the receiving clerk should examine the truck or rail car for the condition of the vehicle and the overall condition of the load. Acceptability of the potatoes should be ascertained by: (1) determining the pulp temperature; (2) examining the condition of the load TABLE 8.7.

Cultivars Maturity Sugars: Reducing Sucrose Size Uniformity of size Shape Eye depth Peel Dirt External defects

Internal defects

Flesh color Specific gravity Total solids Chip color Flavor

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Speciﬁcations of Potatoes for the Chip Market. Atlantic, Gemchip, Snowden, or equivalent No feathering; firm; skin set Less than 0.15%, but 0.00 preferred Less than 1.5%, but 0.00 preferred Minimum of 2 inches diameter; maximum of 3-1/2 inches Maximum variation of 3/4 inch Round Shallow Light in color; less than 1/8 inch thick None, clean Maximum of 4% bruises, preferably 0% No soft rot No greening No sprouts No wire worm No insect damage No hollow heart No discoloration No rot No internal sprouts White to light yellow or gold Greater than 1.080 Greater than 20.2% SFA 3 or lower; Agtron (E30) (90/90) >45 Typical and no off-flavors

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Figure 8.5 Flow sheet of potato chip processing.

for freezing injury, off-odors, cleanliness of the potatoes including freedom from soil, sprouts, and the soundness, appearance and general ﬁrmness of the tubers; (3) noting if the vehicle is clean and sound; and (4) sampling the load for quality evaluation by selecting, at random, three or more 10 to 25 lb samples. The samples then should be evaluated for speciﬁc gravity and graded for size and absence of external and internal defects. A subsample should be fried, in the plant on the conventional fry line or in the laboratory, for chip color. A reducing sugar evaluation should be made if the potatoes do not fry satisfactorily. If the tubers are destined for storage at the chip plant, a sucrose evaluation must be made to determine if they are acceptable for storage. The reducing sugar level should be below 0.15%, preferably at 0%, and the sucrose value should be less than 1.50%. If all is satisfactory, the load can be weighed in as an acceptable load either for immediate use or for storage. A Delivery Data Form should be completed (Figure 8.6).

3.2. DESTONING Potatoes are destoned to remove any stones that may be in the load. Stones cause serious damage to the equipment and problems in the slicing operation,

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Figure 8.6 Potato receiving and test form.

and typically are removed by ﬂoating the potatoes in water, wherein the stones sink to the bottom and the tubers ﬂoat. This may be done with vertical screws or in rifﬂe-type washers. Some growing areas are notorious for stones, particular by virgin ﬁelds. In addition to stones, metal, wood, plastic, metal cans, and so on, must be removed. Usually, this is accomplished by visual inspection of the tubers on conveyor belts prior to the next unit operation.

3.3. PEELING Tubers may be peeled in batch machines or in continuous machines. They generally are peeled using carborundum rolls or with brushes depending on the age of the tuber. As tubers in storage age, the peel or periderm increases to several cells thick and should be removed. However, freshly dug tubers, and in particular immature tubers, need only a light brushing to remove peels. Peel losses can exceed 20% of the tuber weight depending on size of tubers, their age, dwell time in the peeler, use of caustic (alkali) and type and style of peeler. Peelers are designed for a speciﬁc throughput, and it behooves the operator to run the peeler at the right capacity for efﬁciency in peeling. Excessive peel removal means lower chip yield and increased waste to be disposed.

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3.4. WASHING, SORTING AND TRIMMING These unit operations are important for producing clean potatoes free from defects before slicing. A 1/2-inch deep defective area represents eight or nine slices that may be defective. It is much easier and more efﬁcient to remove the defective area ahead of the slicer and, of course, ahead of the fryer. Some manufacturers now use electronic sorters ahead of the slicer to remove offquality potatoes. By removing defective slices ahead of the fryer, energy and oil are saved and cooking efﬁciency is improved.

3.5. SLICING Without doubt, this is the most important operation in a potato chip plant. Efﬁcient slicing produces clean slices with no feathered edges or torn pieces. Good slices adsorb less oil and do not leave potato pieces in the oil, which hastens its breakdown. Urschel Laboratories, Valparaiso, Indiana, developed the Model CC Slicer for the chip trade (Figure 8.7). The potato is forced against the inner surface of the slicing head assembly by centrifugal action. The slicing head consists of 8 separate slicing head shoes and knives. A slice is produced as the product passes each knife in a smooth and uninterrupted manner (Figure 8.8). The trailing edge of each slicing casting has a hardened stainless steel insert

Figure 8.7 Model CC slicer. (Courtesy of Urschel Laboratories, Valparaiso, Indiana.)

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Figure 8.8 Centrifugal potato slicing action, model CC slicer. (Courtesy of Urschel Laboratories, Valparaiso, Indiana.)

strip that is ﬂuted to permit small bits of foreign matter to drop out ahead of the next knife. When slicing at 0.060 in. (1.5 mm) thickness, the top capacity is 15,000 pounds per hour. However, to operate at peak efﬁciency in terms of slice uniformity, the slicer should not be used for more than 8,000 pounds per hour. The manufacturer states that when making ﬂat slices, 80% will not vary by more than 0.004 in. (0.10 mm). By changing the blades, the cuts may be made smooth, wavy or crinkle (“V”) cut (Figure 8.9). Regardless of the cut style, the disposable knives must be changed as often as needed to produce a good clean cut, hourly or sooner if the cut is not clean. High speciﬁc gravity and/or dirty potatoes may be problems for the knives, and the operator must test the slices regularly for the uniformity of slice thickness and the type cut being made. Poor operation of the slicer will lead to many problems in the ﬁnished chip including high oil content, faster breakdown of the oil, ﬁlter problems and others.

3.6. WASHING POTATO SLICES There are two schools of thought with regard to washing following slicing. Some say there should be no washing of the slices, while others pay great attention to this operation. This author’s experience indicates that the slices should be free of loose starch before entering the fryer to prevent oil breakdown and dark specks on the chips. Washing by agitation and by counterﬂow of the water so that clean water is the last water on the slices is recommended. The temperature of the water may be elevated if sugar is present in the slices. By taking the wash water temperature up to 180◦ F (82◦ C), with a dwell time of 30 seconds, chip color can be improved by 1 point on a 5-point color scale. However, the chip will taste more like a cooked potato and have a ﬁrmer texture. Some prefer the ﬂavor and texture of the hot water-treated slices to straight cold water wash. Other processors experience difﬁculties in washing because the water is too soft, resulting in chip slices lacking in texture. The water should

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Figure 8.9 Types of ﬂat, wavy and crinkled cuts available for potato chips, model CC slicer. (Courtesy of Urschel Laboratories, Valparaiso, Indiana.)

be hard, that is, 250–350 ppm hardness, and it should be at or near the pH of the tuber slices (6.2) for greatest efﬁciency. The slices may be blown dry or nearly dry with air knives to remove excess water prior to entering the fryer. The “knives” may be above and below the slices for maximum water removal before cooking. Alternatively, the slices may be shaken or vibrated to remove as much moisture as possible before entering the fryer. Some manufacturers partially dry the slices before frying.

3.7. DRYING AND/OR FRYING This unit operation is in evolution because the oil content of the ﬁnished chip is a signiﬁcant concern to some customers. The market share of low-fat to no-fat chips is increasing, and is up to 11%. This author prefers that potato chips be fried in oil for best ﬂavor. However, drying by itself or partial drying prior to frying is being used. Drying takes much more time and the resultant product is very mealy with little or no ﬂavor other than dried potato ﬂavor. It has never been conducive to high potato consumption and, having lived on dried potatoes

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while in the military, this author does not want to go back to dried potatoes. Regardless, some in the industry believe this is the way to make potato “chips.” This method does not conform to the Saratoga-style chip that the industry built its reputation on. Nevertheless, the oil content of chips should be, and perhaps will have to be, much better controlled if this industry is to survive. Other ways to control the oil content of potato chips exist and should be exploited as many in the industry are doing. Generally, chip manufacturers control the oil content of their chips by: (1) carefully selecting varieties/cultivars that are high in total solids content; (2) slicing thick with less potato surface area for oil adsorption; and (3) using higher temperature and shorter dwell time in the fryer. Oil content can vary from 0 up to more than 40%. In this author’s opinion, oil content should be between 26 and 30% for ideal chips. Data in Table 8.8 show fry time in seconds for tubers of various speciﬁc gravities at three-slice thicknesses and at four fryer inlet temperatures for ﬂat-style chips. Turnover of the oil is an important factor to keep in mind when frying potato chips. Turnover simply means the amount of oil that is used during a given run. Ideally, one should hope to turn over the oil each 8-hr shift. Assuming a fryer with 1,000 pound oil capacity, and 33% oil content in the ﬁnished chip, the oil would be totally replaced for every 3,000 pounds of chips produced. Obviously, in practice oil is gradually replaced during a run. By constantly turning the oil over, it should always be fresh and properly ﬂavor the chips. TABLE 8.8. Frying Time in Seconds to 1.50% Moisture Content for Flat-Style Potato Chips for Selected Speciﬁc Gravities at Three-Slice Thicknesses and at Four Frying Inlet Temperatures.

Oil Inlet Frying Temperatures Speciﬁc Gravity 1.065

1.075

1.085

1.095

1.105

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◦

Slice Thickness

375 F 190◦ C

350◦ F 177◦ C

325◦ F 162◦ C

300◦ F 149◦ C

0.070 0.060 0.050 0.070 0.060 0.050 0.070 0.060 0.050 0.070 0.060 0.050 0.070 0.060 0.050

154 101 53 150 96 49 145 96 51 143 91 45 141 86 40

209 146 111 200 141 104 196 137 100 187 131 96 178 128 93

261 212 165 257 212 160 252 207 156 245 198 153 230 194 149

316 300 233 308 292 228 300 285 225 296 277 220 285 270 218

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More is said about the types of frying oils used in a separate chapter dedicated to this subject. Each type of oil imparts different ﬂavors to the chips, and some manufacturers specify the oil species because the market they have developed demands that type of oil ﬂavor. Some manufacturers always use blends to keep the ﬂavor more neutral and be more ﬂexible when purchasing oils in the commodity market. Dried potato chips are dried in conventional or impingement ovens with no oil. The drying process takes much longer, but may enable easier control of the color and moisture content of the chips. Although the thinner slices dry faster, most dried chips should be sliced thicker than fried chips. Dried chips develop off-ﬂavors more quickly than fried chips unless they are blanched before drying. A hot water blanch just before drying is acceptable. As learned during World War II, oxygen scavengers should be used in packing dried potatoes to better control development of off-ﬂavors.

3.8. INSPECTION Chips are inspected following the frying/drying operation to remove discolored, burned, or defective chips. This was done by “chip pickers” in the past—people on the line who picked out the bad chips. Now, electronic equipment is available to “kick out” the defects—the off-colored or unsuitable chips. The advantage of electronic inspection is that equipment works all the time without tiring, and is as effective as management wants it to be by appropriate adjustments. It should be noted that any pickout, kickout, or throwout is costly at this point in a chip plant. The chip may be worth 25 cents per ounce after frying, whereas the raw potatoes were worth only 3–4 cents per pound. One need only compare and see the quick loss of proﬁt by improper operation of this unit operation. Defective chips are not desirable, and it behooves individual plants as well as the industry to present clean, acceptable chips to customers.

3.9. SALTING AND SEASONING The most important characteristic of any snack food is the taste of the ﬁnished product. The objective is to give customers the consistent product they expect every time. Most snacks, including potato chips, are salted. Salt is the least costly of all the ingredients and is used to enhance the ﬂavor of the chips. Generally, chips are salted directly from the fryer to take advantage of the hot oil for binding the salt crystals to the chip. The Snack Food Association has recommended a salt level of 1.75% plus or minus 0.25%. Potato chips may be seasoned with BBQ, vinegar and onion, cheese and other ﬂavors. At the present time, about 25% of the potato chips are ﬂavored with one or another type of seasoning. Generally, the seasoning is applied topically in rotary drums or sprinkled on top like salt is applied. Many chips are consumed

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with given dips and salsas. Usually dip chips, such as the wavy-style chips, are cut thicker. In very large operations, the ﬂow of chips may be split into two or more lines, each with a packaging and casing machine, to produce different-ﬂavored potato chips simultaneously.

3.10. PACKAGING AND CASING Most snacks are packaged on form, ﬁll and seal machines using speciﬁc multilaminated bags for given regions of the world. Metallized foil is a prominent type of package. Selection of the packaging material should be based on the contemplated shelf life of the product. Long shelf life (over 10 weeks) requires low-moisture/vapor proof ﬁlms. All packages should be properly ﬁlled, sealed and coded. The bag should be full and may be gassed packed using an inert gas (nitrogen) to prolong the keeping quality of the chips while in marketing channels. All packaged snacks should be properly coded with the pull date (or last date of sale) included. The code is to protect the manufacturer as well as the customer and detailed information may prove very helpful. The last check in the operation is at the case packer to ascertain that the bag is properly sealed and packaged. Chips are cased to improve and facilitate handling practices. Nevertheless, they should be handled with tender, loving care to prevent breakage and retain product quality.

3.11. WAREHOUSING Packaged chips are placed in warehouses to await shipment to distribution centers or stores. Warehoused chips should be handled with care, and ﬁrst-inﬁrst-out (FIFO) practice should be followed. Warehouses for holding the chips should be operated at or below room temperatures to prevent shortening their shelf life.

3.12. QUALITY CONTROL OF POTATO CHIPS The quality of potato chips is dependent on the speciﬁc gravity of the raw potato, the quality (peroxide value and free fatty acid content) of the oil used in frying, proper salt and seasoning, and the MVTR (moisture vapor transmission rate) of the package. Auditing the ﬁnished product for moisture content, oil content, salt content, color, texture and ﬂavor is a basic requirement. Evaluation of the seal integrity and gas content of the package also is required. Good-quality manufactured potato chips have a shelf life of 10 weeks plus or minus 2 weeks depending on storage temperatures, packaging materials and/or exposure to

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direct light. Store-shelf sampling in the market place is a must to ensure the quality of the product that reaches the customer. Customers must be given what they expect under any given label all the time.

4. SUGGESTED READING 1. Brown, C. R., 1993. Origin and history of the potato. American Potato J., 70:363–375. 2. Cunningham, C. E., H. J. Murphy, M. J. Goven, and R. V. Akeley, 1959. Yields, speciﬁc gravity and maturity of potatoes. Maine Agr. Exp. Station Bulletin, 379, February. University of Maine, Orono, Maine. 3. Gould, W. A., 1979. Evaluation of potato cultivars before and after storage regimes for chipping. American Potato J., 56:133–144. 4. Gould, W. A., 1985. Changes and trends in the snack food industry. Cereal Foods World, 30(3):219–220. 5. Gould, W. A., 1994. Snack Food Manufacture and Quality Assurance Manual. Snack Food Association, Alexandria, Virginia, April. 6. Gould, W. A., 1999. Potato Production, Processing and Technology. CTI Publications, Inc., Timonium, Maryland. 7. Gould, W. A. and G. Clark, 1963. Potato chip research plant. Farm and Home Research, 48(6):88–89. 8. Gould, W. A. and J. Deppen, 1969. Handling potatoes for chipping. Ohio Report, 54(4): 25–28. 9. Gould, W. A. and S. Plimpton, 1985. Quality Evaluation of potato cultivars for processing. North Central Regional Research Bull, 305, August. 10. Habib, A. T. and H. D. Brown, 1956. Factors inﬂuencing the color of potato chips. Food Technol, 10(7):332–336. 11. Hasagawa, S., R. M. Johnson, and W. A. Gould, 1996. Effect of cold storage on chlorogenic acid content of potatoes. Agricultural and Food Chemistry, 14(2):165–169. 12. Hill, M. K. and W. A. Gould, 1970. Effect of storage conditions on chip quality of potatoes. J. Food Sci., 42(4):927–930. 13. Lulai, E. C. and P. H. Orr, 1979. Inﬂuence of potato speciﬁc gravity on yield and oil content of chips. American Potato J., 56:379–390. 14. Keng Chock, Ng., H. D. Brown, R. H. Blackmore, and J. Bushnell, 1957. The relation of the calcium content of potato tubers to the quality of potato chips. Food Technol., 11(2): 118–122. 15. O’Keef, R. B. 1979. New potato varieties. Chipper/Snacker, February, 24. 16. Ratcliffe, J. D., 1975. A practical analysis of the in-plant peeling losses on potatoes. Food Trade Review, October:36–38. 17. Rose, D. H. and H. T. Cook, 1949. Handling, storage, transportation, and utilization of potatoes. U.S.D.A Bibliographical Bull., No. 11, December, 23 pp. 18. Sawyer, R. L., 1979. The future role of the potato in the world. New Zealand Potato Bulletin, June:18–21. 19. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, Alexandria, Virginia.

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20. Sijbring, P. H. And J. Van der Velde, 1969. Principles of vacuum frying and the results of vacuum frying of chips in practice. Food Trade Review, 39(6):39–42. 21. Sowokinos, J. R., 1980. Three applications of sucrose-rating to minimize sugar accumulations in stressed potatoes. Chipper/Snacker, September, 29–30. 22. Willard, M. J., 1993. Potato processing: Past, present and future. American Potato J., 70(5): 405–418.

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CHAPTER 9

Use of Dried Potatoes in Snack Foods

VELDON M. HIX

1. INTRODUCTION

S

Chef George Crum ﬁrst served “Saratoga Chips” to Commodore Vanderbilt, potato chips have been the most popular snack food in the American diet [1]. From their almost accidental beginning in 1853, they have grown into the major snack food throughout most of the developed countries of the world. Sales of potato chips in the United States alone reached $5.2 billion in 1997 and increased by more than 6% over 1996 [2]. A small, but signiﬁcant portion of total potato chip sales consists of socalled “fabricated” snacks—those made from dried potato products. In 1997, fabricated potato snacks accounted for about 15% of total potato chip sales, or nearly $800 million [2]. Generally, fabricated potato snacks may be deﬁned as having been made from dried potatoes as opposed to being processed directly from fresh potatoes like regular potato chips. The most common dried potato products used in snack foods are: potato starch, potato ﬂakes, potato granules, potato ﬂour and dried, ground potatoes. This chapter describes how these ingredients are manufactured and used to produce a variety of snack foods. INCE

2. HISTORY OF FABRICATED POTATO SNACKS One of the earliest fabricated potato snacks, called NibbitsTM , was developed by Gerkens in 1964 [3]. In this process, potato ﬂour was mixed with water and salt to form a loose, friable dough, which was extruded under high pressure into

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strands having an elastic or rubbery consistency. The strands were cut to length and dried to about 14% moisture to form a pellet or half product. The pellets were subsequently fried in hot oil, whereupon they expanded to four to ﬁve times their original size. The fried pieces had a crispy, but somewhat spongy, texture and a bland, slightly oily ﬂavor. A number of similar products were developed in the 1960s and 1970s including those described by Fast at Nabisco, Inc. [4] and Popel [5]. The process described by Fast et al. included extruding a potato dough into round pellets, which then were sheeted to form ﬂat chip-like pieces. The chips were dried and subsequently fried in hot oil to form a highly expanded, crispy snack chip. The Popel process involved extruding a cooked potato mixture into a thick, ﬂat ribbon, which was partially dried, then cut into smaller squares that were further dried to form a half product, which subsequently was fried. In an alternate process, the cooked potato mixture was extruded into a round “rope,” which was partially dried then sliced into thin, round pieces that were dried further and later fried. These puffed products are still manufactured throughout the world, although the processes have been considerably improved. Most manufacturers now use a one-step cooker-extruder process where the dried potato mix and water are added separately to the extruder. By varying the moisture and extrusion conditions, a ﬁnished, puffed snack can be made, or a half product (pellet) can be produced, which is dried and subsequently puffed by frying in oil or heating with hot air. A wide variety of shapes and sizes can be made by changing the dies used with the extruder. Since these puffed potato-based snacks are quite bland, they usually are highly seasoned with a wide range of ﬂavors. They have become popular in many countries in Europe and Asia, but have not been widely accepted in the United States. Another early fabricated potato chip was described by Hilton at the Frito-Lay Company [6]. In this process, fresh potatoes were washed, peeled and trimmed, then ground to form a mixture of ﬁne solid particles in liquid. This mixture was heated to gelatinize a major portion of the starch present and thereby increase the viscosity. After cooling, the mixture was formed into chip shapes by extruding and cutting. The chips were dried to increase the solids content and fried in hot oil. The resulting product had a friable texture with excellent ﬂavor. Advantages of these processes were twofold: (1) lower-quality potatoes than are required for making chips cut and fried directly from raw potatoes could be used; and (2) the products could be made from potatoes having reducing sugar contents higher than is acceptable for conventional potato chips. In a later modiﬁcation of this process, Wisdom and Hilton fermented the ground potato mixture using yeast to lower reducing sugar levels and prevent excessive browning during frying [7]. A product using these processes has been marketed for many years by the Frito-Lay Company under the brand name MunchosTM .

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The most successful fabricated potato snack is PringlesTM , produced and marketed by the Procter & Gamble Company. This product has been sold since the early 1970s and has become especially popular in the past few years in Europe and Asia. The process, described by Liepa, includes the steps of making a dough from dried potatoes and other ingredients, sheeting and cutting the dough into chip shapes, and frying the cut pieces in an indexed fryer such that all the fried pieces have the same shape and curvature [8,9]. This latter step is very important because the product always has been sold in a cylindrical canister where the saddle-shaped chips are neatly and compactly stacked. This unique package provides protection from breakage and a small compact size in contrast with the large, bulky packages normally used for potato chips. In addition to the unique design of the frying equipment, controlling the level of free starch in the dried potato ingredient and the lipid content of the dough were said to be key steps in the process. A formula was presented that deﬁned the relationship between these two factors and was used to calculate the acceptable ranges of free starch and lipid content. In 1997, PringlesTM captured nearly 12% of the total U.S. potato chip market, ringing up sales of slightly over $600 million. During the early and mid 1970s, other manufacturers produced and marketed products similar to PringlesTM in a variety of shapes and sizes and equally creative packages. One of these was described by Weiss et al. of General Mills [10]. It was made by preparing a dough from potato ﬂakes, potato granules and water, and sheeting and cutting the dough into continuous chip-shaped ribbons, which then were fried in hot oil and broken into individual chips for packaging. None of the other fabricated potato snacks was commercially successful in the United States. However, some of the equipment for these products found its way to Europe. Several formed fabricated potato snacks are still being manufactured in Germany and marketed there and in surrounding countries under brand names such as ChipposTM , ChipslettenTM , and StapelchipsTM . Another unique potato snack of the 1960s was developed by Willard [11]. This process consisted of drying diced potato pieces to about 20–40% moisture, equilibrating for about two hours in a closed container and frying in hot oil. In an alternate process, dried diced potatoes were rehydrated to about 20–40% moisture, equilibrated and fried. These processes resulted in crispy, crunchy snack pieces with excellent toasted potato ﬂavor. However, the product was high in fat content, and the color was difﬁcult to control because of varying reducing sugar levels in the diced potatoes. As a result, this snack never became commercially successful. However, Willard went on to develop a number of successful fabricated potato snacks, many of which are still being marketed in many countries around the world. The most successful of these products is an extruded potato ring, ﬁrst introduced in England in 1973 under the brand name Hula HoopsTM . The process,

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as described by Willard, involves blending dehydrated potato ingredients, such as potato ﬂakes and potato starch, with salt and water to form a loose, friable dough, extruding the dough through an oriﬁce by means of a piston extruder and cutting the pieces to a desired length directly into hot oil for frying [12,13]. The cut pieces were said to expand to about twice their original thickness during frying. This expansion produced a porous structure in the fried product, which gave a very satisfying, crunchy texture to the product. The product quickly became the best-selling salty snack (exclusive of regular potato chips) in England and remains so today. It is especially popular with children, who take small packets of the product to school in their lunch boxes and enjoy eating the crunchy potato rings off their ﬁngers. The product was introduced in many countries around the world, including the United States, and is still popular in Canada, Europe, Japan and a number of Paciﬁc Rim countries. During the 1980- to- 1995 period, the Miles Willard Company of Idaho Falls, Idaho, developed a number of fabricated potato snacks, which were licensed to, and marketed by, the Keebler Company in the United States. The ﬁrst of these was called Krunch-TwistsTM . It was made from dried potato ingredients, which were mixed with water to form a dough and extruded with a unique die, which twisted two strands of dough together. The twisted strands were cut to length and fried to form a braid-shaped snack [14]. Another popular potato snack, ﬁrst marketed by Keebler, was called Tato SkinsTM . It was designed to resemble a common restaurant product, wherein a wedge of baked potato, with skin on and with a layer of potato meat attached thereto, is seasoned with cheese, onion, and so on, and served as an appetizer. The snack version was made from a dried potato dough and sheeted in two layers: one dark, to resemble the potato skin, the other light, to represent the potato meat. The sheeted product was cut into potato wedge shapes and fried in hot oil to form a crisp, crunchy potato snack having a strong potato ﬂavor. The potato ﬂavor and appearance were enhanced by addition of “real” potato peel material to the dark dough. The process for manufacturing this product contained some unique steps, which served to prevent bubbling of the chips during frying, and to give the pieces a natural-appearing curved shape. These steps are described in detail in several U.S. patents issued to Miles Willard Company [15–17]. The most successful of the fabricated potato snacks developed for the Keebler Company was called O’BoisiesTM . They also were sheeted from a potato dough, cut into potato shaped pieces and fried in hot oil. However, the cut pieces were given a brief heat treatment in a continuous hot-air oven before frying [18,19]. The effect of this heat treatment was to form numerous small bubbles on the surface of the chips during frying, which resulted in a very light, crisp texture in the ﬁnished product. A product similar to O’BoisiesTM , but with a rippled surface also was developed by Miles Willard Company and marketed by Keebler as RipplinsTM . The development of this product involved a unique design for corrugated sheeting

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rolls to make a rippled surface [20]. With this unique design, potato dough was fed directly into the rippled sheeting rolls to form a thin, rippled sheet, which was cut into chip shapes and immediately fried in hot oil. The product had a light, crisp texture with a pleasant fried potato ﬂavor. Some of these potato snacks ﬁrst introduced by the Keebler Company have since been licensed to other companies and are being produced and marketed in several countries around the world, most notably in Japan and the United Kingdom. With recent interest of consumers in low- or reduced-fat foods, some companies have produced fabricated baked potato crisps. These are similar to the sheeted, fried products except they are baked instead of fried. The best known of these products is Baked LaysTM , marketed by Frito-Lay. Although these products enjoyed a good measure of initial success, repeat sales have been disappointing. The main problem appears to be lack of ﬂavor and dry mouth feel compared with higher-fat products. A recent development by the Proctor & Gamble Company, called “Olestra,” may alleviate this problem. Olestra is reported to be a sucrose polyester product that mimics the effect of fat in snacks, but is not absorbed by the body. Although there has been some controversy regarding adverse effects on the digestive system by this product, initial sales of snacks fried in Olestra have been very encouraging. Figure 9.1 shows a sampling of the fabricated potato snacks that have been sold in the United States and around the world over the past 30 years.

Figure 9.1 Fabricated snacks made from dried potatoes.

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3. DRIED POTATO INGREDIENTS FOR FABRICATED POTATO SNACKS The principal dried potato products that have been used in fabricated potato snacks are: (1) potato ﬂakes; (2) potato granules; (3) crushed potato pieces; (4) potato starch; and (5) potato ﬂour. Talburt and Smith have covered the manufacturing processes for these products quite thoroughly in Potato Processing, and they are only brieﬂy summarized here [21]. Signiﬁcant differences exist in the characteristics of these products when used in making fabricated potato snacks. The objective of this section is to outline the differences and explain why they are critical to the development of successful snack products from dried potatoes.

3.1. POTATO FLAKES Although drum-dried potato ﬂakes have been made for nearly 100 years, it has only been since the early 1960s that they have become a recognized and popular alternative to fresh potatoes. In the typical ﬂake process, potatoes are washed, peeled, cut into thick slices and then precooked, cooled, cooked, mashed and drum dried [22]. Various additives such as citric acid, sodium acid pyrophosphate, sodium bisulﬁte and antioxidants may be mixed with the cooked potato before drying to preserve color and ﬂavor. Monoglyceride emulsiﬁers are added to facilitate release of the dried potato sheet from the drum and to complex the free starch. The resulting potato ﬂake, when rehydrated with hot water, produces mashed potatoes for consumption not unlike those made from scratch by cooking and mashing fresh potatoes. The ﬂake process was designed to produce mashed potatoes with a dry, mealy texture like that of fresh-cooked, mashed potatoes. For this reason, potato ﬂakes have become the product of choice for home preparation and make up virtually all of the products sold for instant mashed potatoes at retail. Early developers of fabricated snacks found these potato ﬂakes difﬁcult to use. Because they were manufactured with a low level of free starch to produce a dry, mealy consistency upon rehydration, it was difﬁcult to make a cohesive, formable dough when they were used in snack products. Some attempts were made to modify the characteristics of the ﬂakes by grinding to ﬁner particle size and by reducing the emulsiﬁer level. Both of these efforts increased the level of free starch in the ﬂakes and resulted in a more cohesive snack dough. Potato ﬂakes produced in this way came to be known as “snack ﬂakes.” Although these snack ﬂakes partially overcame the lack of cohesiveness problem in snack doughs, they did not contribute enough potato ﬂavor to snack products. Many of the compounds that give the characteristic ﬂavor of potatoes are volatile and are lost during the precooking, cooling, cooking and drum-drying steps of the ﬂake making process. In addition, many of the ﬂavor

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components are leached out of the potatoes during precooking and cooling by the large volumes of water used. During the early development of PringlesTM , Procter & Gamble developed a modiﬁed potato ﬂake process where the amount of peeling was reduced and the precook and cool steps were bypassed. The dried ﬂakes also were ﬁnely ground, normally so 70–80% would pass through a U.S. 40 mesh (420 micron) screen. The resulting product came to be known as “Low Peel/Low Leach” (LP/LL) potato ﬂakes and quickly became the standard ingredient for fabricated potato snacks. The reduced level of peeling, coupled with reduced leaching achieved by elimination of the precook and cool steps, preserves more of the natural potato ﬂavor. In addition, elimination of the precook and cool steps resulted in more broken or damaged potato cells and increased the levels of free starch. This resulted in a signiﬁcant increase in the water-absorbing and water-holding capacity of the potato ﬂakes. When mixed with water, these ﬂakes create a cohesive, but non-sticky dough that can be easily formed and handled through the snack process. Their ability to absorb and hold water improves uniform expansion of the snack during baking or frying and results in the desired crisp, crunchy texture. Unfortunately, not all ﬂakes are created equal. There are often signiﬁcant differences in the water-absorption and water-holding capacity among ﬂakes produced by different suppliers. Quite often, there are differences in ﬂakes produced by a single supplier depending on the time of year and condition of potatoes used. Another signiﬁcant problem with LP/LL potato ﬂakes is caused by high levels of reducing sugars. During baking, frying or other heat treatment, reducing sugars react with amino acids to produce browning in the snack product. If reducing sugar levels are too high, excessive browning can occur and the snack color will be unacceptably dark. Generally, ﬂakes with reducing sugar levels above 3% are unacceptable for use in fabricated potato snacks. However, some processes, like those used for baked products, require reducing sugar levels as low as 1% or less. Because of less leaching, reducing sugars levels are higher in LP/LL ﬂakes when the process bypasses the precook and cool steps. It is well known in the industry that potatoes in storage undergo a constant interconversion of starch and sugar depending on temperature. The common practice in the potato chip industry is to precondition the potatoes for a period of time at a temperature signiﬁcantly higher than the storage temperature to lower the level of reducing sugars and prevent excess browning. Generally, this conditioning is not done in the potato ﬂake industry because the potatoes for processing normally are sorted from those destined for the fresh market and must be processed within a short time after washing and sorting. Preconditioning in this case would reduce the storage life of the fresh market potatoes and make them more susceptible to bruise and rot.

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Since the sugar levels in potatoes normally increase over time in storage, the best option for snack producers is to purchase their potato ﬂake supplies early in the processing season. Another helpful practice to minimize variations in snack quality is to blend ﬂakes from several suppliers. This helps even out variations in ﬂake characteristics and provide a more consistent product to the snack process.

3.2. POTATO GRANULES Potato granules are a dried product consisting of single potato cells or small aggregates of cells. The granule process is similar to that for ﬂakes, up to and including the cooking steps. Potatoes are washed, peeled, cut into slabs, precooked, cooled and cooked. After cooking, dried material from a secondary drying step is added to the cooked potatoes in a continuous mixer. The dried material absorbs water from the cooked potatoes and provides an abrasive surface to break the cooked potato into individual cells and aggregates of cells. The mixture then is conditioned to equalize the moisture between the dry material and the cooked potatoes. The potato mix next passes through a series of drying and screening steps, after which the bulk of the material is added back to the initial mixer with cooked potatoes and the remainder, 10–12% of the total, passes through the ﬁnal dryer. Additives, such as mono- and diglycerides, are added to complex free starch to improve the texture of the rehydrated product. Sodium acid pyrophosphate, sodium bisulﬁte, citric acid and antioxidants may also be added during processing to preserve color and ﬂavor [23]. The resulting product is a ﬁne powder, substantially all of which will pass through a U.S. 80 mesh (178 micron) screen. Because of the drying and conditioning processes involved in their manufacture, the potato cells in granules are case-hardened and quite resistant to breakdown and release of free starch during rehydration and mixing. This is in contrast to the cells of potato ﬂakes, which are more fragile, easily broken if overmixed during rehydration and produce a heavy, sticky texture. Because of their high density and resistance to breakdown during rehydration, potato granules have become the product of choice for food service operations where mashed potatoes are served. They are easier to prepare in large quantities and less susceptible to operator errors. However, the same characteristics that make granules a favorite for mashed potatoes are a detriment for fabricated snacks. Because potato granules are low in free starch and absorb water slowly, they will not form a cohesive dough that can be sheeted or extruded by conventional means. For this reason, potato granules are not used as the major ingredient in most fabricated snacks. However, they are often used at fairly low levels in

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combination with potato ﬂakes and starch to help control expansion, as pufﬁng or bubbling, and provide increased crispness or crunch in fried or baked snacks. Some snack manufacturers use a modiﬁed potato granule product called “snack granules.” It is made by eliminating the precook and cool steps in the process, as is done in production of LP/LL potato ﬂakes described previously. This product has more free starch and better water-absorbing properties than regular granules, which in most cases still is not enough of an improvement to be used as the major potato ingredient. The product also tends to have higher levels of reducing sugars, which may lessen its usefulness as a snack ingredient. There is one exception to the above. In a number of areas, such as the United Kingdom, Europe and parts of Asia where puffed or pellet-type snacks are popular, potato granules have become the preferred ingredient for potato-based products. These processes use a cooker extruder, where the high heat and pressure quickly break down the cell structure of potato granules and release starch, which combines with the available water to rapidly gelatinize. Depending on how the process is controlled, the product may be puffed as it exits the extruder or may be extruded as a dense, gelatinous mass, which is dried and later puffed by means of frying or hot air treatment.

3.3. POTATO STARCH Potato starch is made by a relatively simple process involving grinding or milling raw potatoes to disintegrate the cells and release the starch, screening and washing to remove impurities, and drying. Most processes also involve centrifugation, settling and vacuum ﬁltration to separate the starch solids from the water, which contains dissolved materials from other solid components of the potato such as ﬁber and proteins [24]. The ﬁnal dried starch product is a very ﬁne, white powder containing about 18% moisture. Since it has been processed without heat, there has been no swelling or gelatinization of the starch granules and the product is essentially inert in its dried form. When heated to a temperature above about 155◦ F (68◦ C) in the presence of water, the starch granules swell rapidly to form a thick, gelatinous mass. It is this rapid swelling of the starch granules that makes potato starch a preferred ingredient in potato snacks. Normally, the potato starch is mixed with other dry ingredients and water is added to form a dough. Since the potato starch has not been heated, it absorbs very little water and contributes no viscosity or cohesiveness to the dough. However, when the snack dough pieces are heated during frying or baking, the starch granules absorb water and swell, creating expansion within the dough piece. As heating continues, the water is turned to steam and escapes from the piece, leaving numerous tiny air spaces within the structure. These air spaces contribute greatly to the crispy, crunchy texture of

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the fried or baked snack. Thus, the texture of the snack product can be partially controlled by varying the level of potato starch used in the formula. Generally, potato starch levels in excess of about 35% of ingredient dry weight result in too much expansion, often cause bubbling or pufﬁng, and produce a spongy texture. Pregelatinized potato starches, which absorb water and impart viscosity and cohesiveness to a dough without heating, also are available. These starches gelatinize further and promote expansion in the snack dough pieces during frying or baking. Typically, pregelatinized starches cause more expansion than raw potato starch and must be used at a lower level in the formula. In recent years, a variety of modiﬁed potato starches have become available and have proven useful in speciﬁc applications. These products have not been used extensively in fabricated potato snacks, but have proven more useful in baked goods or frozen foods. Normally, modiﬁed starches are signiﬁcantly higher in price than regular potato starch, which precludes their use in many applications.

3.4. GROUND OR CRUSHED DEHYDRATED POTATO DICE AND SLICE PIECES Dehydrated potato dice and slices for later rehydration and consumption have been produced since before World War II. Potatoes are washed, peeled, cut into slices, normally 1/8 inch thick, or diced into various-sized pieces ranging from 1/4 inch cubes to chunks as large as 3/4 inch by 1 inch by 3/8 inch. The cut pieces are blanched to inactivate enzymes, which cause darkening and off-ﬂavors, and then dried by some type of hot-air dryer to a moisture content of about 6–8% [25]. Initially, crushed or ground dried potatoes were made as a by-product of the dried slice and dice processes. Dried slice or dice pieces, having minor defects such as dark spots or scorched areas, were sorted out of the product stream electronically and ground through a hammer mill or similar equipment. This product became commonly known as “crushed dice” and was sold to manufacturers of potato products such as potato pancake mix or corned beef hash. Depending on the end use, the crushed dice was ground to meet certain screen speciﬁcations. A typical coarse-grind speciﬁcation would allow 20–30% to pass through a U.S. 20 mesh (840 micron) screen. A typical ﬁne-grind speciﬁcation would allow 20–30% to pass through a U.S. 40 mesh (420 micron) screen. In recent years, use of crushed dice has increased signiﬁcantly due to increased demand by snack manufacturers, and the supply available as a byproduct of slice and dice processing can no longer meet the demand. To meet the need for this product, potato processors are forced to produce it from top-grade slice and dice rather than from pickouts. This results in a signiﬁcant increase

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in the price charged for the product and has caused some snack manufacturers to look for less expensive alternatives. The earliest use of crushed dice products in fabricated potato snacks was as the base ingredient in extruded, puffed or pellet-type snacks such as the NibbitTM product described previously. The crushed dice is well suited for highly expanded products, since grinding the potato pieces results in a high proportion of ruptured cells and high levels of free starch. However, in recent times, many manufacturers have switched to potato granules and ﬂakes, which are less expensive than crushed dice. More recently, it has been discovered that crushed dice can be useful in sheeted potato snacks for contributing a more crunchy texture and preventing or limiting pufﬁng or bubbling during frying or baking. Willard describes a means of controlling bubbling in fried snacks through the use of various types of particulate ingredients including crushed dice [26]. A formula is presented whereby bubbles greater than a certain size can be prevented by adding speciﬁc quantities of particles of speciﬁc sizes.

3.5. POTATO FLOUR Potato ﬂour is a drum-dried product similar to potato ﬂakes, but with a few signiﬁcant differences [27]. Historically, potato ﬂour has been made from lower grades of potatoes than potato ﬂakes. In the potato ﬂour process, potatoes are: (1) cooked, but not precooked or cooled; (2) dried without additives; and (3) ground to a very ﬁne particle size. Typically, there are two granulations of potato ﬂour: “granular,” which is ground to pass through a U.S. 40 mesh (420 micron) screen, and “ﬁne,” which passes through a U.S. 80 mesh (178 micron) screen. Potato ﬂour is probably the oldest commercial dehydrated potato product, having been produced for sale in the United States as early as 1917. Primary uses for potato ﬂour have been as a thickener in soups and gravies, as a breading meal and as an additive in baked goods. Potato ﬂour promotes fermentation of yeast and provides excellent antistaling properties. It also contributes a pleasant “potato” ﬂavor. In recent years, as technology has advanced and new starches, emulsiﬁers and dough conditioners have been developed, the use of potato ﬂour in food products has decreased dramatically. In the early years of fabricated potato snack production, potato ﬂour was a commonly used ingredient. The potato ﬂour process results in a dried product with a high level of broken and damaged cells, and thus a high free starch content. For this reason, potato ﬂour has excellent water-absorbing and waterholding characteristics. When mixed with water, potato ﬂour forms a cohesive, elastic dough that can be readily shaped and handled. Unfortunately, these same characteristics may cause excess expansion and bubbling or pufﬁng during frying or baking if the level of potato ﬂour in the

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formula is too high. For this reason, potato ﬂour was typically used only as a minor ingredient in fabricated snacks, added mostly to improve the cohesiveness of the dough and to add potato ﬂavor. Since the development of the LP/LL potato ﬂake product, which is similar to potato ﬂour except for its emulsiﬁer content, the use of potato ﬂour in fabricated snacks has all but stopped.

4. OTHER POTATO SNACK INGREDIENTS Obviously, many other ingredients can be and are used in making fabricated potato snacks. Generally, these include oils and emulsiﬁers, starches of various kinds, corn ﬂour and meal, and ﬂavorings. These ingredients normally are added as processing aids, to facilitate handling of the dough, or to incorporate certain ﬂavor, texture, or appearance characteristics in the product. Their possibilities are limited only by the imagination of the food scientist.

5. FUTURE OF FABRICATED POTATO SNACKS To anyone who follows the marketing ﬁgures of snack foods, it is obvious that fabricated potato snacks have not made signiﬁcant inroads into domestic sales of standard potato chips cut from fresh potatoes. However, sales of fabricated snacks are growing, especially in the developing countries of the world. There are various reasons why this growth can be expected to continue: (1) The various processes used for production of fabricated potato snacks provide unlimited opportunities for incorporation of ﬂavors, colors and other unique ingredients, and for creation of new shapes and sizes, a continuing ﬂow of new and distinctive potato snack products are expected for years to come. (2) As health issues become more important, people will demand more healthy snack foods. Reduced calories and fat content will continue to be important for many people, but reduced salt and fortiﬁed products are also becoming important. Changes in formulas, and addition of nutrients, can be much more easily accomplished with fabricated snack processes than with the traditional potato chip process. (3) As the economies of underdeveloped countries grow and income levels increase, people will have more ﬂexibility in how they spend their income. As this happens, snack foods will become one of their more important choices. (4) Many of the developing countries of the world have very little land suitable for growing potatoes. Dried potato ingredients can be imported in these areas for production of snack products. Many of these countries already

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import signiﬁcant quantities of potato snack products made elsewhere and these imports can be expected to increase. (5) Potatoes continue to be a relatively inexpensive source of food energy and nutrition. As the world population continues to grow, the demand for products made form potatoes will continue to increase.

6. REFERENCES 1. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association. Alexandria, Virginia, January 8, p. 10. 2. SFA, 1998. State of the snack food industry. Snack World, 55(6):Sw-8. 3. Gerkens, D., 1964. Method of producing a crispy expanded formed foodstuff. U.S. Patent No. 3, 131,063. April 28. 4. Fast, R. B., G. Rock, and C. E. Spotts, 1969. Process for making a puffable chip-type snack food product. U.S. Patent No. 3,451,822. June 24. 5. Popel, G. T., 1974. Preparation of a puffed starch containing food product. U.S. Patent No. 3,800,050. March 26. 6. Hilton, B. W., 1966. Potato chip products and process for making same. U.S. Patent No. 3,230,094. January 18. 7. Wisdom, L. W. and B. W. Hilton, 1974. Process for producing potato chips. U.S. Patent No. 3,835,222. September 10. 8. Liepa, A. L., 1971. Preparation of chip-type products. U.S. Patent No. 3,576,647. April 27. 9. Liepa, A. L., 1976. Potato chip products and process for making same. U.S. Patent No. 3,998,975. December 21. 10. Weiss, V. E., G. M. Campbell, and G. L. Wilson, 1977. Fried formed chip. U.S. Patent No. 4,032,664. June 28. 11. Willard, M. J., 1972. Preparing a patato snack product. U.S. Patent No. 3,634,095. January 11. 12. Willard, M. J., 1975. Expanded fried potato snack product. U.S. Patent No. 3,886,291. May 27. 13. Willard, M. J., 1976. Method for making expanded potato based snack products. U.S. Patent No. 3,997,684. December 14. 14. Willard, M. J., J. J. Arnold, and V. M. Hix, 1989. Method for preventing distortion in the shape of fried strand-like expanded snackes. U.S. Patent No. 4,879,126. November 7. 15. Willard, M. J., K. E. Dayley, V. M. Hix, and D. A. Holm, 1989. Float-frying and dockering methods for controlling the shape and preventing distortion of single and multi-layer snack products. U.S. Patent No. 4,650,687. March 17. 16. Willard, M. J., K. E. Dayley, V. M. Hix, and D. A. Holm, 1989. Method for controlling pufﬁng of a snack food product. U.S. Patent No. 4,889,733. December 26. 17. Willard, M. J., K. E. Dayley, V. M. Hix, and D. A. Holm, 1989. Fried snack product having dockering holes therein. U.S. Patent No. 4,889,737. December 26. 18. Holm, D. A., V. M. Hix, and M. J. Willard, 1990. Method for controlling the surface bubbling of fabricated snack products. U.S. Patent No. 4,931,303. June 5. 19. Holm, D. A., V. M. Hix, and M. J. Willard, 1991. Controlled surface bubbling fabricated snack products. U.S. Patent No. 4,994,295. February 19.

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20. Hunt, D. R., K. E. Dayley, M. J. Willard, and D. W. Brister, 1990. Process for producing rippled snack chips and product thereof. U.S. Patent No. 4,973,481. November 27. 21. Talburt, W. F. and O. Smith, eds., 1987. Potato Processing, 4th edition, Van Nostrand Reinhold, New York. 22. Willard, M. J., V. M. Hix, and G. Kluge, 1987. Dehydrated mashed potatoes-potato ﬂakes. In Potato Processing, 4th edition, W. F. Talburt and O. Smith, eds. Van Nostrand Reinhold Co., New York, pp. 557–612. 23. Talburt, W. F., F. P. Boyle, and C. E. Hendel, 1987. Dehydrated mashed potatoes-potato granules. In Potato Processing, 4th edition, W. F. Talburt and O. Smith, eds. Van Nostrand Reinhold, New York, pp. 535–555. 24. Treadway, R. H., 1987. Potato starch. In Potato processing, 4th edition, W. F. Talburt and O.Smith, eds. Van Nostrand Reinhold, New York, pp. 647–663. 25. Talburt, W. F., and R. W. Kueneman, 1987. Dehydrated diced potatoes. In Potato Processing, 4th edition, W. F. Talburt and O. Smith, eds. Van Nostrand Reinhold, New York, pp. 613–646. 26. Willard, M. J., and K. E. Dayley, 1989. Prevention of pufﬁng during frying of expanded snack products. U.S. Patent No. 4,861,609. August 29. 27. Willard, M. J. and V. M. Hix 1987. Potato ﬂour. In potato Processing, 4th edition, W. F. Talburt and O. Smith, eds. Van Nostrand Reinhold, New York, pp. 665–681.

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CHAPTER 10

Tortilla Chip Processing

SURENDRA P. MEHTA

1. INTRODUCTION

T

chips are a very important part of the U.S. snack foods market and are becoming popular in Europe, Australia, Asia and Southeast Asia. They are made from ground masa, produced from alkaline cooked whole kernel corn or alternatively from dry masa ﬂour. The masa is sheeted into thin layers that are cut into small pieces—typically triangular or round. The pieces then are partially baked in an oven, cooled and subsequently fried into crunchy chips. Tortilla chips are eaten as snacks, with or without salsa, as nachos (tortilla chips covered with melted cheese sauce), or as part of a main meal. Their consumption has increased greatly in recent years. As we know them today in the United States, tortilla chips probably originated in the Los Angeles, California, area in the early 1960s. Corn tortillas then were made from whole-kernel corn. Raw corn was cooked in alkali, soaked, washed and ground to produce masa paste, which then was formed into thin tortillas, 5–6 inches in diameter. The tortillas were consumed fresh and would stale rapidly. One day, the owner of a company cut his leftover stale tortillas into small pieces, and fried them until they were crisp. The tortilla chips were originally sold at the tortilla factory itself, and later to local restaurants. This was the beginning of what now is more than a 4-billion dollar industry. Indians, in what is now Mexico, produced a product called “totopos,” which basically was a 10- to 12-inch diameter dried or baked tortilla that was consumed with beans, napales (cactus) and cheese, just like tostadas. This product is still available in its authentic form in Mexico, although it is not easy to ﬁnd. In some parts of Mexico, fried pieces of tortillas are now called “Totopos.” ORTILLA

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Sheeters and cutting heads were developed later to increase the production capacity of tortilla and tortilla chip lines. The process was further simpliﬁed by producing triangular-shaped dough pieces at the sheeter head itself. This gave birth to modern commercial production of tortilla chips. A few additional process steps, such as equilibration of baked tortilla chips, were added to improve on-line production. Outputs of earlier tortilla chip processing lines were 300–400 lbs/hr, compared to 3,000 lbs/hr capacities of current single lines. However, 500–1,200 lbs/hr lines are common for startup companies. Originally, tortilla chips were fried in lard on a stove top or in small batch fryers. Later, continuous direct-ﬁred fryers were used. The next advancement was indirect-heated fryers, using heat exchangers that came from the potato chip industry where they already were used successfully. Heat and Control, Inc., pioneered in developing the continuous indirect-ﬁred fryer for corn and tortilla chips.

2. PROCESSING STEPS The basic principles of tortilla chip production have remained unchanged for centuries, and are described in Chapter 4. Current methods and equipment used for industrial production of tortilla chips are discussed in this chapter. Many signiﬁcant advances in processing equipment have reduced production costs, while improving product quality. The major steps in tortilla chip production are: cooking and soaking corn, washing and draining, grinding, feeding and/or presheeting masa, sheeting and cutting, baking and toasting, equilibrating, frying, cooling, seasoning and packaging. Two basic methods of preparing masa are used. The original and most common is to cook corn in lime (nixtamalization) and then wash and stone grind it into fresh masa. Dry masa ﬂour (Chapter 4) can also be mixed with water to prepare wet masa for shaping into tortilla chips and related products. The use of dry masa ﬂour is growing signiﬁcantly and has increased the overall production of tortilla chips because of its convenience, reduction of processing wastes and reduced capital outlays for production facilities.

3. CORN COOKING AND SOAKING Corn cooking and soaking equipment that provides a consistent quantity of uniformly cooked corn from batch to batch within preset process parameter limits is required. Three different major types of corn cooking and soaking equipment are used.

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3.1. DIRECT-FIRED COOKING/SOAKING TANKS Different-size and -shape tanks are used to cook the corn. The tanks are ﬁlled with 500 to 1,000 pounds of dry corn, plus water and lime. This mixture is then heated by gas burners mounted underneath the tanks. In this method, corn is cooked until the boiling point is reached, then soaked in the same tanks for 8–14 hours. Some manufacturers cook the corn at 170◦ F (77◦ C), and then soak for 18 hours or more. Up to an hour may be required to cook one batch of corn. This is the oldest method of cooking corn. Frequent manual agitation of the mixture is required to achieve consistent cooking. The method is popular with small producers because of its lower equipment cost and ﬂexibility. It is good for initial startup of processing plants. However, it is labor-intensive, fuel efﬁciency is low, and the corn is often cooked inconsistently within a batch and among different batches.

3.2. STEAM-INJECTION COOKING/SOAKING TANKS This method uses vertical round tanks with conical bases, equipped with spargers through which steam is injected into the corn, water and lime mixture. Also, a pump is used to recirculate water from the bottom of the tank to the top. Water, heated with injected steam, is dumped on a stationary cap, which spreads it uniformly over the entire surface of the tank. The steam is shut off when the mixture reaches the desired temperature, which can be as high as 190◦ F (88◦ C). Circulation of water at this stage cools the corn and reduces hot spots that may have developed. The water is circulated until a desired lower temperature, typically 150◦ F (66◦ C), is reached. The corn then is soaked in the same tank. These tanks are designed to cook 4,000–5,000 pounds of dry corn per batch. The total cooking and cooling cycle may take up to three hours, and soak time may be as long as 12 hours. Advantages of this method include large quantities of corn cooked at one time; besides, cooking and soaking are done in the same tank. Problems encountered in this method include: r The corn may not be cooked uniformly because of the large mass of heated

corn.

r Water and lime cannot be cooled quickly and uniformly enough to prevent

hot spots from developing.

r The process requires a signiﬁcantly long time to rise to cooking temperature. r Segregation may result when corn with different cooking properties is ﬁlled

into the tank, resulting in overcooking in some regions.

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3.3. STEAM-JACKETED COOKING KETTLES WITH DOUBLE AGITATORS This method results in the most uniform cooking of corn. The equipment consists of a steam-jacketed kettle with double counterrotating agitators. The mixture of corn, water and lime is heated by steam in the jacket of the cooking kettle. The corn does not come in contact with the steam. The outer agitator, equipped with a scraper, continuously moves the corn away from the walls of the kettle and towards the center. At the same time, the inner agitator moves the corn in the counter-direction. Thus, the corn is cooked evenly throughout the batch. In this process, the mixture is heated to a predetermined temperature, ranging from 180◦ F (82◦ C) to near the boiling point, and is cooked at that temperature from as little as 1–2 minutes to as long as 30 minutes. The mixture can then be cooled in the same kettle by adding cold water and taking advantage of the agitation system at the same time. Temperature “rise time” is the time from start of the cooking cycle until the desired cook temperature is reached. It has an effect on the ﬁnal texture of the product. By varying the steam pressure on the kettle wall, heat input is adjusted and rise time can be precisely controlled. Rise time and the other cooking parameters are monitored through PLC or relay logic controls to ensure repeatability and consistency. Kettles of various sizes are available for cooking from 250 to 2,900 pounds of dry corn per batch. When a steam-jacketed kettle is used for cooking corn, soaking (steeping) is done in separate soak tanks (Figure 10.1). The cooked mixture is transferred from the kettle to the soak tank by pump. Sometimes, to reduce process cycle time, the cooked mixture is dumped into a quench tank for cooling and pumped from there to the soak tanks. Some tanks are equipped with air agitation to stir the corn and eliminate hot spots. This allows uniform soaking of the corn throughout the batch. Steep times vary from 6 to 14 hrs or longer, and allow moisture to equilibrate throughout the kernels while the lime continues to act on the cell walls and other components. Because of the counter-rotating agitator system, this method ensures uniform cooking within each batch because time and temperature are precisely controlled. Likewise, cooling and changes during soaking are controlled and uniform. The major disadvantages are the higher initial investment in cooking and soaking equipment and the need to pump corn more than in other cooking-soaking methods.

4. WASHING AND DRAINING At the end of the soak period, the corn is washed to remove the pericarp (hull, skin, husk), water and lime. The quality and quantity of hull removal, i.e., how clean the corn becomes, depend on corn cooking parameters and design and the operating process parameters of the washing equipment. In the

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Figure 10.1 Typical corn cooking and steeping layout using steam-jacketed kettles and soak tanks. Product ﬂow: dry corn hopper, cooker, steep tanks. (Heat and Control, Inc., Hayward, California.)

traditional process, corn is only rinsed, leaving most of the husk on. However, other processes call for removing almost all of the hull. Corn with hardly any hull is referred to as “squeaky” clean. Washing equipment must: (1) separate and drain the soak water from the corn; (2) uniformly remove pericarp from the cooked, soaked corn kernels; and (3) drain excess surface moisture from the corn after washing. After soaking, the mixture of corn and soak water is pumped to the washing and draining equipment (Figure 10.2). The pump and impeller design selected must minimize corn damage. The prime function of this transfer equipment is to completely drain the soak water and transfer the corn into the barrel of the corn washer. The less soak water going to the washer, the smaller the amount of water required for cleaning. Moving belts or tapered hoppers with augers and perforated bottoms are used to drain soak water. Draining belts minimize damage to the corn and are preferred. Drum-type washers are most commonly used in making tortilla chips. The perforated stainless steel drum typically has internal spirals along its entire length and water spray nozzles strategically located along the length of the drum. In most installations, a booster pump is used to increase the pressure of city water to improve pericarp removal.

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Figure 10.2 Corn washing, draining and grinding equipment ready for operation. Product ﬂow: corn-water separator, auger feeder, corn washer, drain conveyor, corn mill feeder, corn mill, masa hog. (Heat and Control, Inc., Hayward, California.)

A belt-type conveyor, generally 10–15 feet long, is used to drain excess water from the washed corn. The corn is then transferred into the metering hopper of the grinder (Figure 10.2). A modular design, where draining belts, corn washer, and grinder are stacked one over the other, is preferred to minimize space requirements.

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5. GRINDING EQUIPMENT Corn is brought to the grinder (mill) by the drain conveyor (Figure 10.2) and is metered into the stones with an auger located in the hopper above the grinder. It is ground between a stationary stone and another that is moving. The stationary stone is adjusted to create a gap between the stones to control the particle size of the masa. The production rate of the grinder depends on the diameter of the stones and the rotation speed. Too high a speed, too narrow a gap, improperly dressed stones, and overcooked nixtamal produce hot, sticky masa if lava or aluminum oxide stones are used. The sharpness of the cutting edges and the conﬁgurations of grooves in the stones are major limiting factors. Also, the geometry of the stones is very important. The stones must be mounted perfectly parallel and be properly secured to the mounting plates to ensure consistent grind. Grinders using steel plates (Figure 10.3) can run at much higher speeds and produce masas with lower temperature and reduced stickiness. A masa temperature close to 100◦ F (38◦ C) is desired. These grinders can process up to 6,000 pounds of masa per hour, compared with 4,000 pounds per hour maximum of corn mills with aluminum oxide stones. Few large tortilla chip manufacturers use lava (natural) stones. Based on two shifts per day, lava stones may need redressing every 3–4 weeks or more often.

Figure 10.3 Stainless steel plate grinder for producing masa at high capacity. Product ﬂow: cooked corn hopper, corn feeder, distribution disk, rotating and stationary mill plates. (Courtesy of Cantrell International, Division of A. C. Horn & Co., Dallas, TX.)

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As these stones wear, they produce ﬁner and stickier masa even when the same gap setting is used. Operators of grinders with lava stones require signiﬁcantly more experience to adjust the grinder and produce consistent masa compared to mills with aluminum oxide stones. For the same two-shift operation, aluminum oxide stones may last 4–6 months, while steel plates may last 9–12 months. The type of grinder affects masa properties signiﬁcantly, and care is required in selecting the proper grinder for the desired end product. Corn grinding equipment should have the following capabilities: r Maintain a constant gap between the stones or metal plates, while keeping both stones or plates parallel.

r Be designed to prevent the stones or plates from touching. r Use long-lasting stones. r Be able to grind different kinds of nixtamal to produce masa with speciﬁc

properties for different uses. Equipment suppliers can provide information on characteristics of different grinders and guidance in selection. Homogeneity in masa refers to its distribution of particles, very small in size to very large, depending on the type of tortilla chips desired. It is determined during grinding, with a signiﬁcant amount of starch gelatinization also taking place in the process. Generally, the ﬁner the particle size, the greater the gelatinization. Lava stones in the traditional process produced a wide variety of particle sizes and more gelatinization compared to aluminum oxide stones or metal plates, which were developed later. Also, lava stones are much harder to maintain and do not grind as consistent a masa as other grinding surfaces. The end gelatinization of masa can be closely controlled by changing cooking and soaking conditions, and adjusting grinding parameters. However, grinding can compensate for poorly cooked nixtamal to only a limited extent. Consequently, proper cooking is critical in obtaining masa appropriate for subsequent operations.

6. RECONSTITUTION OF DRY MASA FLOUR Alternatively, masa can be produced by adding water to dry masa ﬂour and mixing for a certain period, generally less than 10 minutes. The mixing time, type of mixer, and water temperature and quantity, signiﬁcantly affect masa properties. Water temperature can be adjusted to increase the rate of rehydration and to compensate to some extent for variations in masa hydration rates. Rehydration of dry masa with high-speed mixers is a major mistake since starch granules are damaged and sticky masa results. Masa ﬂour and water can be mixed using batch-type or continuous mixers. Continuous mixers eliminate the labor required for transferring masa from

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the mixer to the masa feeder or to other devices feeding the sheeter. Batchtype mixers are most commonly used due to ﬂexibility of mixing time and reduced cost of equipment. Many process improvements take advantage of the ﬂexibility of the batch mixers, requiring little or no labor for transferring masa from the mixer to devices feeding the sheeter (Figure 10.4). Batch mixers allow

Figure 10.4 A commercial mixing-sheeting installation. Product ﬂow: masa mixer, presheeter, sheeter, takeout belt, oven. (Heat and Control, Inc., Hayward, California.)

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incorporation of additional ingredients more easily and are available from more suppliers. A broad range of masa ﬂours are available from many suppliers. Tortilla chip producers often blend several masa ﬂours to produce unique chips for their customers. Advantages and disadvantages exist in using raw corn or masa ﬂours as starting materials (see Chapter 4). Masa ﬂours have been improved to the point where some customers demand only masa ﬂour products, other markets insist on products made from raw corn, and still others blend cooled fresh nixtamal masa with that made from rehydrated dry masa ﬂour.

7. MASA FEEDING/PUMPING/PRESHEETING The next step involves preparing masa from the ground nixtamal particles, and moving it from the grinder to the sheeter. A mixer is used to produce the cohesive masa in some installations. Methods for transferring masa to the masa feeder or presheeter include: r Carts ﬁlled with masa from under the grinder or mixer are elevated above

the masa feeder or masa presheeter. The masa is dumped into the hopper and is fed into the rolls of the sheeter (Figure 10.4). r The masa may be pumped from the mixer or grinder directly to the sheeter (Figure 10.5). In this case, the masa is transferred from the grinder or mixer into a masa hog, which pushes it into the inlet of a pump that delivers it to the sheeter. In another variation, the masa is formed into 4–6 inch diameter,

Figure 10.5 Masa transfer system. Product ﬂow: grinder, pump, sheeter. (Heat and Control, Inc., Hayward, California.)

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4–10 inch long logs that are carried into the hopper of the masa feeder or presheeter by two rubber belts. One of the functions of the masa feeder is to knead ground nixtamal from the grinder into a cohesive, homogeneous masa that is extruded through a nozzle into a 1-inch thick ribbon that goes into the sheeter. When masa is fed to the sheeter directly from the grinder, the thin layer coming out of the sheeter often has holes that cause defective chips. This problem is reduced when dry masa ﬂour is used to produce masa, because the reconstituted masa is more cohesive than freshly ground product. The other function of the feeder is to automate feeding of masa, which allows the operator to concentrate on the quality of the product coming out of the sheeter. The operator typically spends much time adjusting the ﬂow of the masa to the sheeter. For this reason, pumping masa is preferred over using a masa feeder. Pumping systems work well if the moisture content of masa is above 48%. Pumps generally are used for cooked corn and can also be used for transferring masa made from masa ﬂours. r Masa presheeters work the best for feeding the sheeter. They knead the masa into a cohesive, homogeneous mass and form it into a thin sheet. Some producers of presheeters provide considerable automation and relieve the sheeter operator for other functions, thus reducing labor costs.

8. SHEETING/CUTTING The sheeting process is the same, regardless of whether the masa is processed using cooked corn or masa ﬂour. In this process, the masa ﬂows into the sheeter and passes through two counter-rotating rolls, which reduce it to a thin sheet—the thickness depending upon the gap between the two rolls (Figure 10.6). Sheeters are designed so the sheet of masa tracks on the front roll of the sheeter, leaving the back roll clean. Transfer of the masa sheet to the front roll is accomplished in two ways. r The most common method until a few years ago used a wire across the back roll close to the pinch point of the rollers. As masa passed through the gap between the two rolls, the wire, held tight against the back roll, scraped the masa off the back roll and allowed it to go with the front roll. r The most common current method takes advantage of the differential speeds of the two rolls. As the masa passes through the gap between the rolls, it leaves the roll that is turning more slowly and sticks to the faster roll. The sheet of masa is then cut into small pieces by a cutter that rotates snugly against the front roll. At this point, the raw tortilla pieces are scraped from the front roll, land on the sheeter takeout belt and move into the oven. The scrap masa is recycled (Figure 10.6).

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Figure 10.6 A 4-ft wide sheeter in operation producing restaurant-style tortilla chips. (Heat and Control, Inc., Hayward, California.)

9. BAKING Tortilla chips traditionally were baked in three-tier (triple-pass) ovens. A new trend is to use single-pass ovens, which have easier maintenance, much longer belt life and other advantages.

9.1. THREE-PASS OVENS Three-pass ovens are still most commonly used for baking tortilla chips. Three belts are stacked, one over the other (Figure 10.7). Design is an important factor in selecting an oven because it affects the tracking of the belts. Belt tracking for three-pass ovens is much harder to maintain because the length-towidth ratio is much smaller compared to single-pass ovens. The type of burners used determines temperature variation across the width of the belt in the oven and should be minimized. Some equipment manufacturers use lateral heat-distribution burners to balance the temperature across the belt. The burners should be easy to replace and repair. Generally, ribbon burners are used under each pass of the oven. In addition, the top tier of the oven also has infrared burners above it. These help bake the

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Figure 10.7 Triple-pass oven for baking/toasting tortilla chips. (Heat and Control, Inc., Hayward, California.)

top side of the product, which facilitates product transfer from the top tier to the middle tier without product sticking to the transfer chute. CB5 and open weave are the two most common types of wire mesh belts used for tortilla chips. Each type imparts slightly different baking and blistering characteristics to tortilla chips. In order to produce good-quality products, it is important that the product temperature on each belt be measured and modulated within close tolerance of the set point. Lately, manufacturers have been designing ovens with separate drives for each belt. This helps ﬁne-tune the quality of the product. PLC-based controls are becoming popular for controlling the functions mentioned above. These controls store different settings in their program memories to reduce change over time when changing products. Tortilla chips typically are baked for 15–25 seconds. Typical temperature ranges for top, middle and bottom belts are 600–750◦ F, 400–550◦ F and 250–350◦ F, respectively.

9.2. SINGLE-PASS OVENS Recently, more processors have begun using single-pass ovens for making tortilla chips (Figure 10.8). Single-pass ovens require signiﬁcantly more space lengthwise than three-pass ovens, but this disadvantage can be reduced by locating the equilibrator underneath the oven. Single-pass ovens generally are more expensive, but lower maintenance and reduced downtime offset the initial higher cost. They cost more because they have more sophisticated burner systems, improved belt tracking control and larger diameter drive rolls, which reduce fatigue and increase the belt life by 2–3 times that of three-pass ovens.

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Figure 10.8 A single-pass oven in operation producing tortilla chips. (Heat and Control, Inc., Hayward, California.)

This sophistication signiﬁcantly contributes to improving the consistency and quality of tortilla chips. In the next 5–10 years, single-pass ovens will likely become the industry norm for baking tortilla chips. Belt tracking is much easier to control for single-pass ovens because the length-to-width ratio is much bigger. Maintaining the desired temperature across the width of the belt is also easier, because there is only one set of burners under the belt, compared to three sets in three-pass ovens. Generally, cast iron ribbon burners are used under the belt. Burners above the belt may be cast iron, similar to those under the belt, or infrared. The typical temperature range for the belt is 550–700◦ F. Tortillas are baked for 15–30 seconds. Baking equipment should have the following characteristics: r r r r r r r

Good tracking mechanisms for the belt(s). Ability to maintain temperatures within close tolerances. Minimum product temperature variation across the width of the belt(s). Easy access to the burners for repair or replacement. Sufﬁcient heat output for the rated oven capacity. A reliable pilot system for lighting and proving the burner ﬂame. Sufﬁcient dwell time for the products to be made.

10. CONDITIONING/EQUILIBRATION As baked tortilla chips come out of the oven, they are dry on the outside and moist on the inside because baking traps the water by sealing the outside surfaces. If the chips are fried immediately, water inside the chips turn into

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Figure 10.9 Equilibration of tortilla chips after baking. Product ﬂow: belt from oven, equilibrator, fryer. (Heat and Control, Inc., Hayward, California.)

steam and they puff up like balloons. To avoid this, the chips are held on a multitier conveyor to provide time for moisture equilibration. Generally, equilibration time depends on size of the masa particles, degree of gelatinization, and moisture content of the baked chips. Equilibration time can be reduced by adjusting these parameters. In fact, some manufacturers now use a very short, 15-feet long, single-tier conveyor, with 2–3 chips piled on each other. Other manufacturers use 5-tier equilibrators, with dwell time commonly 2–10 minutes. The equipment needs to provide the necessary dwell time, since equilibration of moisture throughout the chip directly affects texture, appearance and oil content (Figure 10.9).

11. FRYING After equilibration, the chips are fried in oil (Figure 10.10). Depending on the manufacturer, the oil temperature at the inlet of the fryer may range from 340◦ F to 385◦ F; 360–375◦ F is the most common frying temperature. Lower oil temperature results in higher oil uptake by the products. The frying time may range from 40 seconds to 120 seconds, depending on the moisture content of

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Figure 10.10 An indirect-ﬁred fryer producing tortilla chips. Oil ﬂow: heat exchanger, fryer, oil ﬁlter, return to heat exchanger. Product ﬂow: fryer, ambient air cooler, conveyor to seasoning drum, seasoning coating drum. (Heat and Control, Inc., Hayward, California.)

the baked chips, range and distribution of masa particle sizes, thickness of the chips, temperature of the oven belt and dwell time in the oven. All of these variables, along with frying time, affect the texture, appearance and ﬂavor of the chips. The frying process removes the moisture and replaces it with oil. The ﬁnal moisture content in the fried chips ranges from 1 to 2%; moisture contents higher than 2% result in tough, chewy texture and reduce shelf life. Factors to watch in the frying process include: r Maintaining an even ﬂow of raw chips into the fryer to make a product with

consistent quality, including oil and moisture content. The fryer production rate should always be maintained close to the designed capacity. This ensures good oil turnover rate, reduced free fatty acid (FFA) content, and longer shelf life for the product. Adjustment of the oil level and velocity, along with speed of the submersion paddles, help clear the product at the inlet of the fryer. Proper clearing reduces clustering of chips, enhances uniformity and reduces defects. r Feeding too much baked product into the fryer. This results in improper clearing of the product and causes excessive boiling at the feed end. It also

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increases oil absorption. Oil volume in the fryer should be as low as possible and uniformly maintained. This causes faster oil turnover, which generally ensures lower FFA development and longer shelf life. Properly designed and operated fryers produce consistent quality, and excellent products. Frying equipment should have the following capabilities: r r r r r r r r r

Ability to maintain the desired oil temperature within close tolerances. Ability to provide necessary product clearing at the infeed end of the fryer. Ability to controll product ﬂow throughout frying. Ability to completely submerge chips under the oil and turn them over several times. Proper ﬁltration. Low system oil volume for faster oil turnover. Oil level control. Higher fuel efﬁciency. Ease of cleaning.

11.1. DIRECT-FIRED FRYERS Direct-ﬁred fryers have a direct source of heat, consisting of burners that heat a pan, which in turn transfers the heat to the oil. Alternatively, the burners are inside tubes immersed in the oil. The burners heat the tubes, which in turn heat the oil. Different arrangements of tubes are available. Some of the most common are single U-tubes, multiple longitudinal tubes parallel to the ﬂow of the product, and multiple tubes at 90 degrees to the ﬂow of the product. Direct-ﬁred fryers have lower initial costs and are typically used in small startup operations. The reduced capital costs are offset by higher operating costs due to lower combustion efﬁciencies. The slower oil turnover rate affects product shelf life and quality. Other disadvantages include: more oil degradation due to higher oil ﬁlm temperatures, limited clearing of product at the infeed end of the fryer, difﬁculties in cleaning because ﬁnes build up in hard-to-reach areas, less efﬁcient removal of ﬁnes from the oil and reduced reliability and durability because the pan becomes extremely hot and warps.

11.2. INDIRECT-FIRED FRYERS Indirect-ﬁred fryers generally use heat exchangers. The oil is heated in the heat exchanger and pumped through tubes to the fryer pan for frying the tortilla chips. The oil is circulated in tubes in the heat exchangers, with the heat source outside the tubes. Heat sources include natural gas, diesel fuel and high-pressure steam.

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Advantages of indirect-ﬁred fryers include: r Lower operating cost due to much higher combustion efﬁciencies of

80–85%.

r Faster oil turnover rate contributing to longer fryer life and product shelf

life. Less oil degradation due to lower oil ﬁlm temperature. Good clearing of product at the infeed end. Easy cleaning by a clean-in-place (CIP) system. Efﬁcient ﬁnes removal due to high oil circulation in the fryer (the ﬁnes are kept in suspension and removed by the ﬁltration media). r More reliable and durable equipment because the heat source is away from the pan. r r r r

The major disadvantage is the signiﬁcantly higher initial cost.

12. PROCESS FLOWCHART The ﬂow diagram (Figure 10.11) shows how the processing steps and equipment are integrated into a production line for raw corn and dry masa ﬂours.

13. RAW MATERIALS The ingredients for tortilla chips have been discussed in Chapters 3 and 4. This section presents an industrial perspective on the relative importance of raw ingredients. The basic raw materials for producing tortilla chips are corn or dry masa ﬂour, lime, water, oil, salt and seasonings. Working with suppliers to secure a consistent supply of the ingredients is essential to producing a goodquality product.

13.1. CORN For consistent quality, corn kernels should be uniform in shape and size. Uniformity is the major concern since corn varies appreciably in cooking properties. Communication with the corn supplier is essential for avoiding problems and for anticipating changes in corn that always occur from year to year and even within the year. A good supplier has the proper equipment and procedures to dry, clean and store the corn, and should know which hybrids are similar in cooking properties. Raw corn should not contain more than 8% cracked or broken kernels, because they absorb water at a faster rate, enhancing gelatinization. Broken kernels also cause higher dry-matter losses, which reduce yields and increase sewer

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Figure 10.11 Sequential process diagram for tortilla chip production.

charges. They overcook and become mushy, causing high dry-matter losses and sticky masa that is difﬁcult to sheet and produces signiﬁcantly more defective chips. Corn kernels with softer endosperm have lower yields than kernels with harder endosperm. Corn that produces the required end product and yields should be selected. Moisture content of corn should be 13–14% to ensure it can be stored with good resistance to mold growth and absorbs water rapidly during cooking and

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soaking. Corn with 12% moisture or less is considered “dry” corn, and the kernels tend to crack each time the corn is transferred.

13.2. MASA FLOUR Using dry masa ﬂour instead of raw corn eliminates the need for local cooking, steeping and grinding processes, and related equipment. Close work with the supplier helps determine the best masa ﬂour or combination of masa ﬂours. Some manufacturers combine ﬂours from different suppliers to obtain desired chips and sometimes blend freshly ground masa with dry masa ﬂour. Oil and seasonings are discussed in Chapters 6 and 19, respectively. Oil quality is extremely important and must be maintained. The use of excess lime is necessary, but should be held to the lowest level possible since only a small quantity of lime is absorbed by the corn with the rest going down the drain. Unabsorbed lime increases sewer charges, and incomplete washing and higher absorption darken product color. Purity of the water sometimes affects snack product quality. Continuing increases in consumption of tortillas chip are expected as more consumers around the world become acquainted with them, and local or new textures and ﬂavors are developed.

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CHAPTER 11

Snack Foods from Formers and High-Shear Extruders OCTAVIAN BURTEA

1. INTRODUCTION

T

chapter focuses on the preparation of fried corn chips and puffed snacks made by high-shear extruders and ﬁnished by frying or baking. A brief history of corn-based snacks processing also is included. HIS

1.1. RELATIVE SIZE OF CORN SNACK INDUSTRY The history of potato chips can be traced back to 1853 (see Chapter 2), but the ﬁrst recorded sales of commercial corn chips in the United States occurred in 1932. Over the years, the use of corn as a raw snack food ingredient has grown steadily to where it is approaching twice that of potato products. In 1999, approximately 2.015 billion pounds of corn tortilla and tostada chips, corn snacks, and corn-based puffed products (primarily cheese-ﬂavored) were sold for $5.512 billion in the United States through retail outlets (supermarkets, convenience stores, mass merchandisers, warehouse clubs, vending machine, drugstores and other outlets). This compares to approximately 1.539 billion pounds of potato chips and snacks, worth approximately $4,688 [1]. These ﬁgures do not include retail outlet sales of popcorn (0.648 billion pounds, $1.731 billion sales), nor sales of fried/baked corn tortilla or tostada chips or other corn products sold in volume for restaurant use, nor popcorn sold by movie theaters and vendors at other events, nor the sale of specialty items like CornnutsTM . Brands leading the sales of potato- and corn-based snacks belong to large companies, which have recognized the advantages of offering a variety of both

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products in national distribution. Tortilla chip processing is reviewed in Chapter 10 and commercial popcorn processing in Chapter 14.

2. HISTORY OF CORN SNACKS PROCESSING EQUIPMENT The use of corn as a principal snack ingredient has risen rapidly, but its developmental history is not as well known as that of potato chips. Snack manufacturers have closely watched advances in processing potato and corn products, and quickly incorporated machines and technologies which improved operations of either product line. This includes materials handling equipment, fryer and oven designs, oils selection and use, seasonings and applicators, packaging materials and package forming-ﬁlling-closing machines. Dry potatoes and other starch-containing ingredients are easily used in corn extrusion equipment. Three broad categories of corn snacks exist: r Fried corn chips, introduced in the early 1930s; r Extruder-puffed fried and baked corn snacks, ﬁrst marketed extensively just

after World War II; and

r Tortilla chips, a modiﬁcation of earlier tostadas, introduced in the mid 1960s

and now the most popular corn snack product.

2.1. EARLY MILLING OF CORN To ensure understanding, readers are advised to ﬁrst determine what is meant by the word “corn” in the speciﬁc setting. Corn (Zea mays, maize), as we know it, is a New World crop unfamiliar to Europe and the Middle East before the voyages of Columbus in the 1490s AD. However, the term “corn” has been commonly applied to the local major cereal crop in various parts of the world, a practice that continues today. Man started grinding grains by beating barley, wheat and rye seed between stones, followed by manual winnowing to remove the chaff. Crude stone mortars and pestles (Figure 11.1) were developed in Asia Minor about 10,000 years ago, followed by the saddlestone (a device in which the grain was ground between a hand-held long stone and a concave bedstone) about 5,000 years ago, and the lever mill about 2,500 years ago. By Ancient Egyptian times, milling had evolved into a multistep process and included repeated winnowing/sieving and grinding [2]. The Romans are credited with developing the two-stone rotary mill about 2,300 years ago—the bottom stone remained stationery, while the grain entered the center of the turning top stone and worked its way to the edges. Hard Vesuvian lava stones, which were longer-wearing than previous stones, also were introduced. This design was quickly adapted to animal power. Small hand-powered rotary mills, known as “querns,” are still used in some parts of the world.

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Figure 11.1 Ancient manual grain grinding equipment: (a) mortar and pestle; (b) saddlestone; (c) lever mill; (d) rotary mill. (From: Bass, E.J., 1988. Wheat ﬂour milling. In Wheat: Chemistry and Technology, Vol. II, 3rd edition. Y. Pomeranz, ed. American Association of Cereal Chemists, Inc., St. Paul, Minnesota, pp. 1–68. With permission.

Animal power was partially replaced by water power about 2,000 years ago, and the dome-shaped stones evolved into ﬂatter, horizontal millstones (Figure 11.2). The ﬁrst wind-driven mills were built in Europe about 1,000 years ago [2]. Archeological evidence supports the use of corn (maize) as food in the Tehuacan valley of Mexico 6,500–7,000 years ago. However, the Indians had only progressed from crude stones to the metate (a saddlestone-type device), which early European settlers initially adopted for grinding. This device also was

Figure 11.2 Early millstones. (From: Bass, E.J., 1988. Wheat ﬂour milling. In Wheat: Chemistry and Technology, Vol. II, 3rd edition. Y. Pomeranz, ed. American Association of Cereal Chemists, Inc., St. Paul, Minnesota, pp. 1–68. With permission.

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effective for grinding wet corn steeped in wood ashes by the native nixtamalization process. The next level of corn grinding development was the hominy block, a wooden mortar and pounding pestle that could be made by hollowing tree stumps at the cabin site. It was replaced by purchased hand-operated family querns—small burred stone mills dating from Roman times [3]. Local wateror animal-powered mills eventually could be supported as population densities increased. Although principles learned during the evolution of barley, wheat and rye milling, and the later development of smooth and ribbed steel rolls, were readily adaptable to dry milling of corn ﬂour and grits, scaleup of wet grinding from the metate was developed by the mechanized tortilla and corn snacks production industries.

2.2. CORN CHIP EQUIPMENT DEVELOPMENT The ﬁrst use of equipment to produce corn chips as we know them occurred in San Antonio in 1932. Elmer Doolin, founder of the Frito Company, purchased a recipe, rights to 19 small retail accounts, and the equipment—an old, hand-held potato ricer—for $100. The seller was a Mexican who was homesick and wanted to return to his native land. Doolin and his mother set up initial operations in her kitchen, with a production rate of 10 lbs/hr. Sales, from the back of his Model T Ford, averaged $8–10/day, resulting in a $2 proﬁt. The business grew rapidly, and Doolin moved production from his garage in San Antonio to a manufacturing plant in Dallas within a year [4]. Isadore J. Filler, from Dallas and also inspired in San Antonio to produce a corn snack, was granted a trade mark for “Corn Chips” by the state of Texas in 1932 and applied to the U.S. Patent Ofﬁce for a similar trade mark in 1935. This may partially explain Doolin’s selection of the name FritosTM . Filler’s product was made by grinding, rolling and cutting masa into a rectangular shape. By 1959, when Doolin died of a heart attack at age 56, he had transformed the initial $100 loan from his mother into a company with sales of over $50 million/yr [4]. Initially, corn was cooked in lime water on a stove, drained and ground by hand. The dough, or “masa,” was hand pressed by a converted potato ricer into ribbons and cut to length. They were fried in vegetable oil, salted and packaged for sale. As sales grew, Doolin found that he had to develop his own manufacturing equipment. The ﬁrst change was replacement of the potato ricer with a hand press that extruded strips of corn dough [4]. Additional improvements to increase production and improve the quality of FritosTM followed quickly. A corn precooker was made from a 55-gallon drum by removing the top third and ﬁtting it with a perforated screen about 2 inches from the bottom. Corn, lime, and water were put in the drum and a burner lit under the bottom. The corn was agitated manually and quench water was added

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to the drum after cooking. The batch size was 50 lbs of corn; using a line of drums, the production rate was increased to about 200 lbs/hr [4]. The ﬁrst corn washers were developed in the late 1930s to early 1940s, consisting of a perforated 6-inch diameter drum driven by an electric motor and a water spray to remove the husk (pericarp) and steep liquor. These machines were hand fed from the cookers and emptied into catch tubs with a perforated bottom to allow water drainage [4]. As competitors started selling corn chips, they also contributed their skills to mechanizing the process. At the same time, a commercial tortilla-making industry, developing in California, also was wrestling with problems of masa preparation and handling. Where patents existed, processes and equipment designs became public domain upon their expiration, but often became obsolete earlier by alternative developments. Mexican tortilla mills with three horsepower motors and 6 in. diameter volcanic lava stones were used to wet grind cooked corn into masa. These mills had “ﬂoating” mill stones and the non-rotating stone was moved in and out to set the coarseness of grind. The design is still used by some very small manufacturers [4]. A mechanical screw press was developed by Elmer Doolin and the Lawson Brothers Machine Shop in Dallas, Texas, to extrude the masa into ribbons, which fell into the frying oil. The machine had a vertical design and consisted of an 8-in. diameter barrel, a die that screwed into the bottom, and a piston that was driven by an acme screw thread. When the piston was retracted and swung to the side, another loaf of masa could be loaded for extrusion. These machines were complicated and difﬁcult to manufacture, and also were easily damaged, especially by foreign objects [4]. The ﬁrst fryers, as we know them today, were designed in a U or horseshoe shape, so that a ﬂow of oil could be achieved since sanitary pumps, able to withstand the high temperatures of the cooking oil, were not available. Heating was done with a small natural gas burner that did not have a combustion air blower. One circulator wheel and one takeout conveyor maintained the ﬂow of chips through and out of the fryer, and a butterﬂy valve on the fume stack controlled the temperature. Production rates were in the range of 150 to 200 lbs/hr [4]. The 1950s brought many advancements in technology and equipment, some of which are still in use today. The 55-gallon drums used to precook the corn were replaced by the steam-jacketed round bottom kettle, with a counterrotating agitator and scraper developed by the Hamilton Kettle Company of Hamilton, Ohio. (The company has recently been purchased by the Allegheny Hancock Corporation and moved to Weirton, West Virginia.) Development of the cooker also brought a need for the ﬁrst soaking vats, which were formed from large sheets of stainless steel, rolled with a large radius in the bottom and ﬁtted with end panels [4]. Similar vats are still used today in lines up to

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800 lbs/hr. For larger capacities, soaking vats have been replaced by vented tanks with air agitation of the liquid. The mechanical screw press was replaced by a horizontal 8-inch diameter cylinder with the piston driven by compressed air. A 90-degree elbow, or turntube, was ﬁtted to the discharge end of the cylinder, and the 10-inch die was mounted by use of a stem assembly. The cutter bar was driven by a pneumatic die grinder motor ﬁtted with an air regulator to control speed. Another air regulator controlled the air pressure to the cylinder to control the rate of extrusion. Because of the compressibility of air, constant adjustment of the regulator was required during the extrusion stroke to control chip length. This increased production rates to over 400 lbs/hr [4]. Although the basic shape of the fryer remained the same, several changes were made to increase the output and overall quality of corn chips. The fryer became larger and was ﬁtted with paddle wheels and a submerging conveyor to better cover the chips with oil. Larger burner systems were developed with combustion air blowers to increase BTUs per hour to heat the oil more efﬁciently. Also, a gas modulator system, with a temperature controller and ﬂame safeguard equipment was added [4]. The popularity of fried corn snacks increased tremendously during the 1960s, causing the Frito-Lay Company to increase production, and other companies to join the industry. Larger precook kettles were put in use, as well as larger and improved corn washers, now equipped with drain conveyors [4]. Major advancements in corn grinding technology also occurred. A larger, more powerful, and extremely rigid, corn mill was developed by Frito-Lay engineers and built by Alamo Machine Works in Fort Worth, Texas. This mill was revolutionary in several ways. It was the ﬁrst to use a 30-horsepower motor and the ﬁrst to bolt one of the stones rigidly to the hopper and also to advance the rotating stone to set the gap. Its rigid design and extreme accuracy in stone alignment and gap adjustment greatly increased the quality of the masa [4]. Availability of volcanic lava stones from Mexico was unreliable at times. Development of a man-made millstone material began in the mid 1960s, requiring several years for completion. The new stone, using mid-eighteenth century European technology and constructed of aluminum-oxide, was available in unlimited supply at a ﬁxed cost. It was also considerably harder than the lava stone and had a longer life span and improved the consistency of the grind. The majority of larger corn masa snack producers worldwide use these stones today [4]. The pneumatic systems on the extruders were replaced by hydraulics, increasing output and achieving more consistency in chip length. Dies were increased from 10-inch diameter to 12-inch. In the early 1960s, the ﬁrst hydraulic extruder was designed and built for Frito-Lay by L. C. Miller Company, Long Beach, California, from World War II surplus parts. Using the same basic design, Frito-Lay engineers developed a more modern hydraulic corn chip extruder

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using updated hydraulic units and controls. Modernized versions of this extruder are in use today [4]. At the same time, Heat and Control, Incorporated, San Francisco, California, successfully adapted a remote heat exchanger to a corn chip fryer. This protected the oil from overheating, increased fuel efﬁciency and removed the dangers associated with large burners in a direct-ﬁred fryer. Because high-temperature sanitary pumps were used to circulate the oil, fryers could be designed in a straight-through design, simplifying equipment layout [4].

2.3. FRIED AND BAKED SNACKS DRY EXTRUDER DEVELOPMENT In the late 1920s, Clair B. Matthews, an agronomist in Beloit, Wisconsin, devised a machine that pulverized, macerated and partially cooked animal feed to increase its digestibility and reduce intestinal injuries. To perfect the method, Matthews joined with Harry W. Adams, an attorney in Beloit, Wisconsin, and an engineer, E. E. Berry, to form the Flakall Corporation in Beloit in 1932. A U.S. patent was issued for the process on June 7, 1938, and the ﬁrst commercial product, ﬂaked rabbit feed, was sold during the Depression and World War II [4]. One day, Flakall Corporation operator, Ed Wilson, noticed white sticks of puffed cooked corn exiting while he was cleaning the machine with cracked corn. Instead of throwing them away, Wilson took the sticks home where his wife deep fried and salted them for snacks. His neighbors liked the product, especially with cheese on it. That Wisconsin community had the ﬁrst taste of Korn KurlsTM , which would become a national and international snack favorite. A U.S. patent was applied for the machine and process in 1939 and granted in 1942 [4]. World War II delayed commercialization, but in 1946 Harry W. Adams and his two sons formed the Adams Corporation. They began producing the original frytype snacks commercially. Two additional plants were opened in Lambertville, New Jersey, and in Anaheim, California. The extruder then consisted of a 6-inch-diameter rotating head assembly (“rotor”), a 6-inch-diameter stationary head (“stator”) and a feed screw. By creating low shear, friction and heat, the moisturized corn meal was exploded to form rough, irregular-shaped collets of low bulk density suitable for frying. These were then coated with a cheeseoil-salt slurry solution in a tumble drum to make the fried cheese puff [4]. Also in 1946, with the assistance of an engineer, Cyrus H. Heigl, the corporation developed an extruder to produce a lighter, smoother collet suitable for baking. This machine had a short, high-shear auger and sleeve, and a die to form the gelatinized corn meal into various shapes, which were cut to length by a separate rotating knife. After baking (drying) in an oven, the collets were coated with a cheese slurry. The Adams Corporation dominated the extruded snack foods industry during the following years [4].

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In March 1961, the Adams Corporation was acquired by Beatrice Foods Company of Chicago, Illinois. This gave the Adams Corporation access to research and development tools for improving the extrusion process and snack products. Beatrice president, William G. Karnes, saw the opportunity to expand the snack business internationally, and Adams International, an entity separate from Adams Corporation, was organized as a new division of Beatrice Foods Company in August 1963. By 1974, Beatrice Foods had closed all of the Adams Corporation domestic plants. Adams International ﬂourished by maintaining its leasing-only policy for extruders until 1981, when the policy was changed to include equipment sales domestically and internationally [4]. Since the Adams Company would only lease and not sell extruders, after the Adams patents had expired, the Frito-Lay Company decided in the late 1960s to build their own extruders. Maddox Machine Shop, Dallas, Texas, founded in 1952, had long made spare parts and corn chip equipment for the Frito Company. This specialty business had expanded after the merger to form Frito-Lay. Sam L. Maddox, working with Frito-Lay’s engineers, developed a much larger and stronger extruder, which had a precision handwheel for head gap adjustment, an integral takeout conveyor and an enclosed extrusion area used with a dust collection system. New versatility was brought to the extruded snacks ﬁeld, and new shapes began to appear [4]. Maddox Metal Works purchased the assets and designs of Adams International in 1991. Large extruders, designed and built by Wenger Manufacturing Company, Sabetha, Kansas, originally for breakfast cereals, pet foods and other grain processing, appeared in the snack foods industry in the late 1970s. These are extremely versatile machines, consisting of a drive and segmented screw and barrel sections that can be arranged in different conﬁgurations and lengths as required for speciﬁc processes. Conﬁgured with a short L/D barrel, they can be operated as friction extruders to produce highly puffed pieces for seasoning and baking. Longer L/D barrels can include jacketed heating and cooling sections for making non-expanded “half product pellets” (collets), which are dried and can be puffed later by oil frying, rapid hot air heating, or microwave ovens. In the 1980s, Wenger Manufacturing Company began manufacturing twin-screw extruders, which had originated in Europe. The corotating, self-wiping screws act as highly efﬁcient pumps and give consistent product throughput, which enables better control of product dimensions, important in making intricately shaped pieces. The production of two-colored pieces, and center-ﬁlled pieces consisting of several different materials, also is possible.

2.4. TORTILLA CHIP DEVELOPMENT The Frito Company of Dallas, Texas, and the H. W. Lay Company of Atlanta, Georgia, merged in 1961, two years after the death of Frito founder Elmer

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Doolin. At that time, H. W. Lay Company was the national leader in potato chip sales and owned regional corn snack brands, while the Frito Company led in corn snacks and owned regional potato chip brands. Each company saw the advantages of completing distribution and advertising of their lead products nationally. Additional national sales expertise was added when Frito-Lay, Inc., merged with Pepsi-Cola in 1965 [4]. While visiting retail outlets in 1964, Arch West, marketing vice president for Frito-Lay, and George Ghesquiere, division vice president, noticed bags of locally made toasted tortillas in some stores. After verifying that tortilla chips could be produced by automated equipment with Alex Morales, whose company, Alex Foods, Anaheim, California, made taco shells for Frito-Lay’s Disneyland restaurant, West returned to Dallas to develop and present a plan to Frito-Lay executives. The name DoritosTM , meaning “little gold,” was selected for the new product [4]. With approval to proceed, West returned to Morales to prepare enough product for an in-store concept test. At that time, it was decided to make DoritosTM in triangular shape so no money would be wasted on die cutting. The concept test went well, and Frito-Lay loaned Morales the money to purchase new equipment for making market test quantities. The product was accepted in the West and Southwest so enthusiastically that Morales’ production facilities were soon exceeded, and Frito-Lay established a production line in Tulsa, Oklahoma. DoritosTM was rolled out nationally in 1966 as the ﬁrst new type of corn snack since 1946. Sales of the new triangular-shaped tortilla chip passed the traditional corn chip (FritosTM ) in the 1970s [4]. Much of the Tulsa, Oklahoma, line consisted of Frito-Lay’s existing corn chip equipment, including cookers, washers, grinders and fryers. A J. C. Ford Company sheeter and tortilla oven were used. Later, personnel from the J. C. Ford Company formed a new company named Electra Foods Machinery Company. With the growth in DoritosTM sales, and more experience in engineering and construction at Electra Foods Machinery Company, better sheeters and ovens were developed for the many companies introducing tortilla chips in various shapes. Also, toward the end of the 1960s, a system was developed to plasticize and pump the masa to the sheeters, eliminating human contact [4]. Upgrading of equipment for better product quality and greater production capacity dominated the 1970s. During these years, Casa Herrera Company, Los Angeles, California, became a major oven and allied equipment fabricator in the growing Mexican-style tortilla and tortilla chip industry [4]. During the 1980s, industry capacities began to level off and snack processors began seeking increased operating efﬁciency to remain proﬁtable. Equipment fabricators focused on elimination of wastes and increasing the efﬁciency of their equipment. Potato chip producers became increasingly interested in cornbased products. Spin-offs of the earlier dominant equipment fabricators (Casa Herrera, Electra Foods Machinery Company, Frito-Lay, Inc., Heat and Control,

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Inc. and Maddox Metal Works) became major factors in producing corn snacks equipment [4]. Today, totally computer-controlled corn cooking and soak systems are available. Sanitary pumps, capable of moving cooked corn with minimal damage, exist. Corn mills are better than ever and man-made millstones are commonplace. Masa pumping systems for tortilla chips, and continuous extruders for corn chips, eliminate human contact from raw corn to the ﬁnished product. Tortilla sheeters have been improved and toasting made more efﬁcient. More fryers are using high-pressure steam for heating oil and are achieving thermal efﬁciencies in the 80% range. Signiﬁcant advances have been made in seasoning applications equipment, including development of electrostatic salt, dry seasoning mix, oil spray and slurry-type applicators. Production rates of corn snack lines have gone from 10 lbs/hour by Elmer Doolin in the 1930s to more than 3,000 pounds per hour.

3. CORN CHIP PROCESSING Corn chips are made by steeping corn with alkali, soaking to absorb more water, washing, grinding the cooked corn into masa, extruding and cutting masa chips, frying, cooling, salting (seasoning if used), and packaging. In some parts of the world, “corn chips” means products made by sheeting masa and drying partially by baking, and frying—essentially similar to domestic preparation of fried tortilla chips. In this section, “corn chips” speciﬁcally means products made by forming and cutting masa into ribbons that fall directly into a fryer. Domestically, large snack food companies contract the growing of selected food grade corn hybrids, and receive and clean the corn before sending it to their snack processing plants. Some companies make dry masa for rehydrating and use in producing snacks. Smaller companies, which use fresh masa, mostly depend on specialized corn suppliers to collect and clean the corn, and check the aﬂatoxin content for them. Overseas, it may be necessary for snack processors to purchase corn locally and do the cleaning themselves. The sequence in making corn chips includes: r r r r r r r r r r

Cleaning corn (if purchased directly) Alkali cooking (simmering) Post-cook soaking Washing (and hull removal) Milling into masa Extruding, cutting, dropping into hot oil Frying Draining Salting (and application of additional optional ﬂavorings) Packaging

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The reader is referred to Chapter 3 (Food Quality of Corn);Chapter 4 (Alkaline-Cooked Corn Products);Chapter 6 (Oils and Industrial Frying); Chapter 10 (Tortilla Chip Processing); and Chapter 20 (Snack Seasonings Application) for related information.

3.1. CORN QUALITY Although corn chips can be made from prepared dried masa, for the most part the masa is made on site. Over 90% of the corn grown in the world is for feed and industrial use (starch, sweeteners and ethanol) and is not considered food grade. Historically, the Mexican tortilla has been made from white corn, and the original DoritosTM are reported to have been made from white corn. The majority of masa-based snacks (corn chips and tortilla chips) are made from approximately 60:40 mixtures of yellow and white dent corn, whereas extruder-puffed snacks are made mainly from degermed yellow corn meal. In recent years, domestic sales of white corn tortilla chips have grown rapidly because they are different from traditional products and have milder ﬂavor. Yellow corn varieties yield more grain per acre, cost less than white and have a stronger ﬂavor. The inclusion of white corn with yellow corn in corn chips has resulted in milder-ﬂavored products and has enabled raising the temperature of corn chip frying without production of burnt notes as when yellow corn is used alone. The goal of quality control is to make a consistent product, day in and day out, in spite of variations in raw materials. This is accomplished by constantly monitoring corn and product quality and ﬁne-tuning process conditions to compensate for minor changes that occur during the year. Obviously, the ﬁnished product can never be better than the raw material it is made from. Fewer ingredient variations lead to fewer process adjustments, more consistent quality and less waste. Quality control starts at the receiving dock of the processor or the corn supplier. Processors of masa snacks can minimize variations in corn quality by purchasing the same variety of corn throughout the year and having the supplier always deliver it at a constant moisture level. Our experience has shown that corn in the 11–12% moisture range damages easily in handling, and corn in the 14–15% range needs to be processed quickly or dried to guard against mold growth in storage. Higher percentages of cracked and broken kernels will lower ﬁnished product yield, but can still be processed if kept to less than 18–20%.

3.2. ALKALINE COOKING OF CORN Generally, snack foods plants are built with basically ﬂat, well-drained ﬂoors. Equipment may be put on cat walks to adjust for differences in height, and to take

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advantage of gravity ﬂow where possible. Some of the lighter-weight pieces, like formers, extruders, and seasoning drums, are put on casters to facilitate easy changeover of the processing line for making different products. Corn is a starchy grain, slightly acidic in pH and covered by a hull (skin) known as the “pericarp,” which protects the kernel from moisture penetration, growth of molds and aﬂatoxin development. The alkaline cooking process consists of: (1) heating corn, water and lime, typically in a steam-jacketed roundbottom kettle equipped with an agitator, to a temperature slightly below boiling; (2) holding corn at the cook temperature for a speciﬁed period; and (3) transferring the cooked corn by pump to soaking tanks where additional moisture penetrates the kernels. Cooking corn in pure water is not effective. Lime (which forms calcium hydroxide, Ca(OH)2 , in water) is used at 1% by weight of corn to chemically attack cell walls and other components of the kernel. Protein begins to cook and the starch begins to gel once the corn reaches 65◦ C (150◦ F). Cooking of the starches occurs when corn is held above 65◦ C. Dry, ﬂaky masa is a sign of undercooked corn, while hot, sticky masa normally is a sign of overcooked corn. The higher the temperature, the faster the cook. Before the advent of modern temperature controllers and steam systems, the batch would be brought to a boil and then held for a period of time. Lowering the cook temperature to slightly below the boiling point, to about 95–99◦ C (203–208◦ F), increases ﬁnished product yield dramatically by limiting overcooked kernels. Cooking corn at a vigorous boiling temperature causes significant over-cooking. Corn is cooked longer for making corn chips, compared with tortilla chips, to: r Loosen the pericarp so it can be separated completely. r Incorporate 40–43% moisture in the kernel at the end of the cooking cycle. r Gelatinize enough of the starch in the kernel to make the dough cohesive for

proper extrusion of the corn chip.

r Quickly bring the temperature below 61◦ C (142◦ F) to stop the cooking by

adding cold water which typically is added to the cooker at the end of the cooking time. This starts the “soak” or “steep” process. Moisture after cooking corn normally is 40–44% for corn chips and 35–36% for tortilla chips. The core temperature of the corn batch should be veriﬁed immediately after transfer to the soak tank. Typical soak times for cooked chip corn are 12–16 hours, and 8–12 hours for tortilla chip corn. Corn is saturated after 12 hours of soaking, but a longer steep is used for corn chips than for tortilla chips to further soften the kernels. The steep liquor should be drained and replaced with fresh water (and lime) if conditions occur that require corn to remain in the soak tank for more than 20 hours. Product has been produced successfully using corn soaked more than 30 hours by this technique. Typical moisture contents after soaking are 50–52% for corn chip corn and 44–45% for tortilla chip corn.

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3.3. CORN WASHING The purpose of washing is to remove most of the pericarp and excess alkali. The pericarp will be high in moisture from the alkaline cooking; failure to remove it will raise the pH of the masa above the target of 7.0. High masa pH will darken the product and can cause problems in the fryer, including development of high free fatty acid (FFA) levels in the oil and foaming. Typically, large volumes of water, at 15–21◦ C (60–70◦ F), are sprayed for 2 minutes, at high pressure, on the corn in a barrel or tumbler constructed of perforated metal. This is followed by approximately 6 minutes draining of the excess water on a drain conveyor. Corn typically is washed to “squeaky clean” for high-quality chips—a condition that experienced operators recognize by feel when a handful of washed corn is rubbed tightly. Hulls that are not removed will foul (“load up”) the millstones and raise the masa temperature. In addition to making the masa hot and sticky, hulls can hang up on tortilla sheeter wires and rip holes in the sheeted product. The black specks in the ﬁnished product once were considered a defect, but now are desired for corn chips and tortilla chips. They are from the hilum of the corn kernel and indicate that the products were made from whole ground kernels of nixtamal. For corn chips made from dry masa, black specks from corn dry milling fractions are sometimes added to give an “authentic” appearance to corn chips.

3.4. MILLING COOKED CORN Milling the masa is one of the most critical operations in the process. The granulation and extent of plasticizing that take place during the milling operation determine many properties of the ﬁnished product including texture, hardness and oil absorption. Basically, two types of wet milling processes are used for corn snacks, the old traditional mills with volcanic lava stones and the newer precision models with man-made stones of aluminum oxide. Development of the continuous rotary method of grain milling dates back to about 1000 BC. Today’s geometric designs for millstones closely resemble designs from the Roman Empire. The traditional lava stone from Mexico uses a Roman cut known as 4-Quarter Dress. Amazingly, only minor modiﬁcations in design were required to go from dry milling to the wet milling used today. For most practical purposes, lava stones have no place in a modern corn snack factory. No two lava stones are the same, and they generally are too soft for production of consistent masa. A set of dressed lava stones installed in the morning may be worn signiﬁcantly by the end of the day. As the stones wear, the grind changes, affecting the ﬁnished product. The continuous changes in lava stones made setting up processing lines that produce consistent product impossible and led to the old belief that producing

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high-quality corn chips was an art with the secret in the skill and feel of the operator. The most important invention in the last half century related to product consistency and quality is easily the aluminum oxide millstone. Work to develop a man-made stone that would withstand the abrasiveness of corn began in the 1960s and required several years. Aluminum oxide (Al2 O3 ) is a natural material, related to ruby and sapphire, and nearly as hard as diamond. With it, the grind can be held to exact speciﬁcations for days and weeks before the stones need changing. Photos of a modern corn masa mill and an aluminum oxide millstone are shown in Figure 11.3. Millstones are not designed to grind or pulverize corn, but rather to shear it. The feather grooves found on the outside perimeter of millstones do as much as 90% of the shearing and sizing of the corn. Because these grooves are cut off center, they do not meet in parallel but pass each other at an acute angle that moves continuously outward with a cutting effect that resembles the cutting edges of a pair of scissors. With proper millstone design and sharp feather grooves, the masa will not be overheated and sticky. The condition and wear of the feather grooves can usually be judged by the rise in temperature of the masa over time. The sharper the edges of the grooves, the more efﬁcient the cutting action and the better the masa. A set of aluminum oxide stones can mill approximately 4,000–6,000 tons of cooked corn before being sent to the manufacturer for resurfacing. Most of the lines we have seen operate with too ﬁne a grind. This is usually to compensate for problems elsewhere in the line and results in making the product too dense and hard. The millstones in a properly set up masa mill are parallel to each other (deviation less than 0.076 mm, 0.003 inch) and remain parallel throughout the production run. Millstones out of parallel do not make a consistent grind and usually require closer resetting of the stone gap for compensation. A close stone gap makes the grind ﬁner, increases density of the masa and the product and makes the product too hard. A proper corn chip is light and airy with a honeycomb effect inside. A proper granulation of the masa will contain some larger particles along with ﬁne particles. The larger particles give texture to the formed product and allow oil to penetrate and moisture to easily evaporate during the frying operation. Corn chips made from properly granulated masa expand about 10–15% during the frying operation, whereas little if any expansion occurs with a ﬁne grind masa except in extreme cases where the product explodes or pillows. The oil content is usually lower when the masa is ground too ﬁne because the density of the product inhibits oil penetration. A stone gap of 0.55–0.71 mm (0.022–0.028 in) is recommended for grinding corn chip masa. It is larger than for tortilla chips because the corn chip is thicker, and its dough is coarser to avoid blistering, pufﬁng and an oily appearance. Mill exit temperatures are approximately 43.5–48.5◦ C (110–120◦ F). Corn chip masa

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Figure 11.3 (A) Modern masa corn mill; (B) Aluminum oxide “synthetic” millstones. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

is often several percent higher in moisture content, more gelatinized and sticky, and goes directly from the former into the oil at 207–212◦ C (405–415◦ F). By comparison, tortilla chip masa contains approximately 51% moisture, and the raw tortilla chips are reduced to 30–36% moisture in the toaster oven before frying.

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3.5. MASA EXTRUSION The masa is extruded by a minimum-shear horizontal hydraulic piston former as shown in Figure 11.4. The masa passes through a 90◦ forming head and strands of cut chips fall into the fryer. When larger line capacities are desired, the former may be built with two pistons. The extruded strips are ∼0.5 in. wide and are cut into 1.0–1.5 in lengths (12.7 × 25.4–50.8 mm).

3.6. FRYING CORN CHIPS The moisture content of corn chips going into the fryer is considerably higher than that of tortilla chips and extruded fried puffed snacks; therefore, a large water removal capability is required. The choice of fryers depends on the capacity requirements of the speciﬁc plant and other snacks that may be made on the same line. However, it should be remembered that frying oils absorb ﬂavors and colors from the product, which limits the ﬂexibility of fryer use unless the oil is changed with an accompanying thorough cleanout between some products. Fryers with ﬁre tubes in the oil are still used in small installations that process low-moisture-content snacks, but most corn chips are processed in fryers with remote heat exchangers as shown in Figure 11.5. Oil is taken from the fryer by sanitary pump, heated as it passes through pipes in a gas-ﬁred heater, and is returned to the fryer co-current with the corn chips. Submerger belts ensure the product is covered with oil and control the duration of the frying process. Frying, frying oils and commercial fryers are reviewed in Chapter 6. Frying of corn chips for 80–100 seconds at 195–205◦ C (386–401◦ F) is recommended for most vegetable oils. Final moisture of the product should be 1.5–3.0%; the oil content is 35–38%. Domestic frying oils typically arrive at the chip plant at slightly less than 0.05% FFA. A properly designed corn chip fryer will have good oil turnover rates and will maintain oil FFA values in the 0.2–0.25% range. With oil being one of the most expensive commodities in the product, extra expenditures in purchasing a well-designed frying system are warranted to minimize product quality problems and to avoid discarding oil. A properly designed frying system has heating efﬁciencies of 75–80%, about a 5◦ C T (temperature differential between the oil and exiting product), oil turnover rates of less than 8 hours, and continuous ﬁltering. Life expectancy of fryers is in the 25-year range.

3.7. COOLING AND SEASONING Because of their high density, non-puffed corn snacks contain a large amount of latent heat that must be removed before seasoning and packaging. Two

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Figure 11.4 Hydraulic extruder for shaping and cutting masa ribbons in making fried corn chips. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

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Figure 11.5 Discharge (oil draining) end of indirect-ﬁred continuous corn products fryer. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

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methods are currently used to cool corn chips. The ﬁrst is a conveyor or series of conveyors designed to allow sufﬁcient time for the product to cool. With corn chips, up to 20 minutes may be required, and space requirements for this system are high. The second and more popular method uses an enclosed, slow-moving conveyor immediately after the fryer, equipped to force large amounts of plant air through the chips for cooling. Typically, these conveyors are the width of the fryer and about three meters long. Product temperature can be controlled by varying the speed of the conveyor (dwell time) and adjusting the airﬂow rate with a damper. Most seasonings will adhere to wet, oily spots when present, and the best salt and seasoning coverage occurs on a uniform chip surface. Cooling the corn chips before seasoning improves coverage because oil spots are eliminated. Problems can occur when dairy-based seasonings are applied to hot products, because heat from the oil melts the dairy product, causes its breakdown and shortens the snack’s shelf life. Packaging of hot products can also cause problems by expanding the air or nitrogen inside the bag as it is sealed. As the product cools, the bag may collapse and contract. Seasoning application systems are covered in detail in Chapter 20. Corn chips usually contain enough oil so that an additional oil spray is not necessary for powder adherence. Signiﬁcant advances have been made in the development of electrostatic seasoners. They work by applying a high voltage charge to the seasoning powder and grounding the product in the tumbler applicator. Like magnets, the oppositely charged seasoning and product have strong attraction to each other, so the majority of the seasoning will end up on the product and not in the plant. Electrostatics are used for applying salt and powdered seasonings; systems for applying oil sprays and cheese slurries have been developed. Longterm savings on seasonings are signiﬁcant; electrostatic seasoners can pay for themselves in a very short period of time on corn chip lines.

3.8. FRESH MASA CORN CHIP SUMMARY Recommended conditions for producing extruded fresh masa fried corn chips are summarized in Table 11.1.

3.9. SHEETED FRIED CORN CHIPS Some processors prefer to make a sheeted fried corn chip. They feel that extrusion through the former results in a chip that is too dense, while sheeting results in a lighter chip. A line that can produce 300 lb/hr of sheeted corn chips or 500 lb/hr tortilla chips is shown in Figure 11.6. It would not include the former shown in the drawing. Hydrated masa ﬂour or fresh masa can be used. When making corn chips, the rolls on the sheeter are changed, and the raw chips bypass the toaster oven and conditioning conveyor, going directly to the fryer.

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TABLE 11.1.

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Recommended Conditions for Producing Corn Chips.

Processing Step Corn cooking

Cooked corn cooling Corn soaking Corn washing Corn milling

Masa extruding Corn chip frying Corn chip cooling Seasoning

Conditions Minimum temperature rise time 13--18 min. Cook time 20--45 min. at 95--99◦ C (203--208◦ F) Water-to-corn ratio (by weight) = 1.5/1 Lime, Ca(OH)2 /corn ratio = 1/100 Cooked corn moisture = 40--42% Quickly, to below 61◦ C (142◦ F) 12--16 hours at 45--60◦ C (113--140◦ F) Soaked corn moisture = 50--52% 8 min. at 15--21◦ C (60--70◦ F ) Add water to 50--52.5% moisture Masa temperature = 43.5--48.5◦ C (110--120◦ F) Masa pH = 6.9--7.0 Stone gap = 0.55--0.71 mm (0.022--0.028 in.) Die opening = 1.32 mm (0.52 in.) Product length = 38.1--5.08 mm (1.5--2 in.) 80--100 seconds in oil at 209--213◦ C (405--415◦ F) Final moisture =<1.5%; oil content 35--38% 3 min to reduce temperature to 40◦ C (104◦ F) Salt 2--3%; Cheese, barbecue, salsa, etc., 6--9%

An advantage of a sheeting line is that it also can be used for making chips from dried potatoes and other fabricated snacks.

4. EXTRUDED BAKE-TYPE SNACKS Puffed snacks typically are made on friction extruders, or cooking extruders conﬁgured to operate like friction extruders. These machines sometimes are called “dry extruders” because very little, if any, moisture is added to the ingredients. After extrusion pufﬁng, the moisture content is reduced to 1.5–3% by drying in ovens before application of seasonings.

4.1. HIGH-SHEAR EXTRUDERS Most extruders in use today for snack foods are single-screw, short-barrel extruders with a length-over-diameter ratio (L/D) of 4 or less. Low-capacity extruders have a L/D ratio of about 2, while L/Ds for larger-capacity machines may be as high as 4. These machines are of the adiabatic (autogenous) type, meaning all the heat is developed by the conversion of mechanical energy to thermal energy in the extruder barrel and no heat is added or removed by other methods. This is accomplished by the compression and shear of the product. The only external heat required for these machines is for preheating the die

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Figure 11.6 Layout, combination 500 lb/hr tortilla chip or 300 lb/hr corn chip line. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

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at initial startup. By design, short-barrel, high-shear extruders are limited to low-moisture ingredients and to production of highly expanded products with low bulk densities. This is exactly what the snack food industry wants, and adiabatic machines by far are the most popular and widely used extruders for snacks that leave the plant in expanded state. The machines are easy to operate and maintain and are highly efﬁcient in terms of power requirements to output. They also are the least expensive design of extruder available for snacks and can be made in a wide range of outputs, from less than 150 lbs/hr to over 800 lbs/hr from a single machine.

4.2. BASICS OF OPERATION A helical screw, sometimes referred to as an Archimedes screw because it is capable of conveying ﬂuid materials, is commonly used as the material transport device. This design does not have positive displacement, and slippage occurs when resistance is met. Slippage is the cause of shear. A full screw in a smooth bore barrel does not develop much shear because of lack of resistance, and the product simply rotates with the screw. Straight grooves cut into the barrel wall increase shear on the product and generate more heat, but not enough for highly expanded snack products. Most snack food extruders today use barrels with helical grooves machined in them. A typical design is double-lead tapered grooves, opposite hand (in turn direction) to the ﬂights on the screw. By tapering the grooves, and making them more shallow, the volume of the barrel is reduced as product is moved forward with increasing compression. Machining the grooves in the opposite hand from the feed screw increases shear exponentially. The resistance (back pressure) is formed by various ﬂow plates and dies ﬁtted to the end of the barrel (also called a stator). Some manufacturers use the term “tooling” when referring to parts that contact and machine the product and are worn themselves in the process. In this section, they will simply be called barrels or stators, screws, rotors, plates, dies or knives. In the high-shear extrusion process, moistened, starchy, and/or proteinaceous materials, are compressed, sheared and heated to form a melt that is forced through a die opening to the atmosphere. Because the exit temperature can reach as high as 149◦ C (300◦ F), some cooking (gelatinization) of the starches occurs during the extrusion process in addition to shearing. By the time the material reaches the die opening, it has been heated and pressurized to over 102 atm. (1,500 psi), resulting in a semiliquid mass of gelatinized starch containing superheated water. The pressure instantly drops to zero when the product exits the die opening, and the superheated water drop ﬂashes to steam, causing the product to expand (puff) and cool. The faster and greater the pressure drop through the die, the greater the product expansion. The amount of pressure

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Figure 11.7 Barrel (stator) and screw (rotor) components of bake-type puffed snack high-shear extruder. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

drop can be controlled by the design of the ﬂow plates and dies, speed of the screw, condition of the barrel, clearance between the screw and the barrel and moisture of the material. Decreasing the moisture content increases internal shear, temperature and pressure and results in a more expanded product with a lower density. A drawing of the processing components of a high-shear extruder for making bake-type snacks is shown in Figure 11.7.

4.3. SCREW The screw, sometimes called the “feed screw” or “auger,” is the heart of the extruder. It is the means for transporting ingredients inside the extruder and the principal means for shearing the product. The screw conveys material by viscous drag against the barrel. This resistance to forward movement causes the transported material to slip against itself, thus transforming mechanical energy into heat. The large drive of the extruder is always connected to the screw because the rotation of the screw against the material consumes the mechanical energy of the machine. Feed screws can be designed with single lead (thread), double lead or sometimes quad-lead ﬂights. These ﬂights can be full radius or square cut. The highest production machines typically have screws with two to four leads and square grooves for maximum transport and shear properties. The diameter of the screw root is increased, and the ﬂights cut shallower, to compress

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the product as it travels towards the die. The greatest shear and compression take place at the exit end of the screw, and most wear occurs in this area. The end of the screw ﬂights should always be inspected for sharpness and wear when evaluating extruders.

4.4. BARREL OR STATOR The barrel of a high-shear extruder is responsible for most of the compression developed in the material as it is transported toward the die by the screw. The grooves also taper in depth, getting shallower toward the die end, and compress the product. As the barrel wears, the volumetric area near the die increases, thus lowering compression and development of heat. As wear increases further, the edges on the grooves smooth over to the point that shear also is decreased, further affecting the performance of the extruder. Most plants keep track of barrel performance and wear by tracking the number of hours the part has been in operation. Although easy to do, this is not an accurate method of evaluating performance. The preferred method is to track the amount of product processed by the component in either pounds or kilos. Processors sell product by the pound, not the number of hours required to make it. Costs of extruder components should be evaluated against product throughput and not hours of operation.

4.5. FLOW PLATES AND DIES Flow plates, sometimes called “breaker” or “pressure” plates, are located before the die and are an essential component of a single-screw high-shear extruder. They consist of a plate, or a series of plates, drilled with numerous holes in various sizes and patterns. Their purpose is to increase back pressure on the screw, minimize product surging and ensure uniformity of pressure behind the die, and stop any hard or uncooked pieces from entering and plugging the die. Fewer and/or smaller holes increase pressure in the barrel, resulting in greater expansion of the product. Double- or multiple-ﬂow plates are sometimes used to increase the amount of shear on the material, reduce surging, and to further increase the expansion and lower the density. The die is the most interesting part of the machine, but also is one of the simplest. Single-oriﬁce dies are used for special shapes such as rings, tubes, or animals. Because the available die opening area is smaller with a single oriﬁce die, the production rate normally will drop when it is used. Multiple-oriﬁce dies are used for simple shapes such as curls, balls and sticks. The openings are placed in a circular pattern and typically cut with a rotating knife centered on the die. Most dies of this conﬁguration have provisions for plugging some of the openings to increase pressure in the machine. A typical Maddox/Adams corn curl die has 12 holes. Depending on the capacity of the extruder, between 0 and 6 holes could be plugged to achieve the desired back

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Figure 11.8 Photograph of MX-550/650 bake-type snack extruder. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

pressure with new barrels and screws. As these wear and compression is lost, more holes can be plugged to bring the pressure back to within speciﬁcation. A photo of a bake-type puffed snacks extruder is shown in Figure 11.8. Extruder manufacturers commonly offer more than 50 die designs. Machine shops that specialize in designing new dies also exist. Three-dimensional animal

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shapes have become a popular novelty in recent years. They are made using a four-bladed knife, with the two opposing blades shorter than the others. As the animal shape is extruded as a rod through the die, it is partially cut by one of the shorter knives. This creates the opening between the legs on the underside of the animal. Then, the longer knife cuts across the entire die face freeing the entire animal shape.

4.6. RAW MATERIALS Extruded snack foods typically are made from degermed corn because oil in the germ can reduce pufﬁng. Corn is easy to extrude, gives a nice texture and ﬂavor, and normally is accepted readily in the market. High percentages of ﬂour in corn meal cause problems with moistening the meal uniformly and is a prime cause of extrusion problems. The characteristics desired in coarse granulated meal from degermed yellow corn are shown in Table 11.2. Using corn as a base, potato granules, sorghum grits, defatted soya grits, green peas, quinoa seeds, dried vegetable ﬂours and kelp ﬂour can be added in various percentages to make products with unique ﬂavors and/or textures. Rice meal of the proper granulation, semolina (wheat) and milo (sorghum) can be run at up to 100% in these extruders. Sorghum expands similar to corn. White food types produce bland, light-colored extrudates with subtle ﬂavors useful in snacks (Chapter 3).

4.7. PROCESSING AND CONTROL A layout of a baked extruded snack line is shown in Figure 11.9. This line uses a single-pass dryer. Triple-pass dryers are available if space is limited, and the additional drying capacity is required. If the snack processor is certain that simple shapes (sphere, rod, crosses, small cross, doughnut, alphabet letters, etc.)

TABLE 11.2.

Coarse Granulated Corn Used for Snack Foods Extrusion.

Characteristic Analysis Moisture Fat Protein Granulation On U.S. 20 (841 microns) On U.S. 25 (706 microns) On U.S. 30 (594 microns) On U.S. 40 (420 microns) Through U.S. 40

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Typical

Range

13.00% 0.70% 7.00%

12.50--14.00% 0.50--1.00% 6.50--8.00%

8% 20% 35% 35% 2%

5.0--20.0% 15.0--35.0% 25.0--45.0% 20.0--40.0 0.0--3.0%

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Figure 11.9 Concept layout, line for bake-type extruded puffed snacks. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

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Weight Changes of 1,000 Lbs of 13% Moisture Corn Meal in Production of Bake-Type Extruded Snacks.

Procedure Starting corn Moisten to 16% to improve extrusion 3% average loss of fines in oven, conveyors, coating tumbler 8% average loss of moisture between extruder and drying oven 7% average loss of moisture at oven 40% increase by application of 1/3 cheese and 2/3 oil slurry

Weight Change (lbs)

Resulting Weight (lbs)

--+30 −30

1,000 1,030 1,000

−80

920

−64 +342

856 1,198

will be produced, a less expensive rotary (revolving barrel) oven may be used. However, belt ovens are needed when producing fragile products, like large simulated onion rings. The extrusion process is primarily controlled during operation by changing screw speed using the variable-speed drive provided. The desired extrusion temperature is 154–188◦ C (310–370◦ F). Additionally, the moisture content of the corn can be varied from the general target of 16%, and compensation made for temperature loss due to wear on the screw or barrel by partially plugging the multihole die plate. Ingredients can cause considerable problems. For example, old corn meal is difﬁcult to extrude, sometimes virtually impossible. Meals produced from hard varieties of corn, as grown in France and Italy, extrude well, but the wear rate on the screw, barrel, and die components increases dramatically and sometimes nearly doubles. Problem corn meal can be addressed by the addition of oil (if too ﬂoury), vinegar (for old corn) and emulsiﬁers (to produce lighter bulk density, ﬁner structure). The extruder manufacturer should be consulted before trying these additives. Extruded puffed corn collets contain approximately 6–8% moisture, and are dried to 1.0–1.5% moisture content in a rotary oven or belt dryer operating at 190◦ C (375◦ F). They should be allowed to cool to 70–91◦ C (175–195◦ F) before application of seasonings. A materials balance for typical production of baked corn snacks is shown in Table 11.3.

5. EXTRUDED FRY-TYPE SNACKS The fry-type snack extruder is a unique machine, that produces only one product by design. Its history has been reviewed in Section 2.3. Most of the fry-type extruders in operation today produce only between 250 and 300 lbs/hr

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of raw product, but recent developments by Maddox/Adams have increased the capacity for a machine of the same size to over 600 lbs/hr.

5.1. BASICS OF OPERATION Technically, this extruder falls into the medium-shear category. Like the direct expansion extruder, it uses a screw and a stator to create shear and heat (Figure 11.10), but differs in that it does not extrude the product through a die. Instead, it uses a rotating plate called a “rotor” and a stationary plate, part of the stator, to shape and expel the product. The screws of these machines are highly polished and ﬁt closely inside the bore of the stator. The stator consists of two parts, the barrel and the faceplate. The barrel portion is machined with straight grooves and provides a mild shearing of the material against the screw. The faceplate (Number 4) typically is constructed of brass or bronze and machined with angular slots to ease product transition from the barrel. The rotor spins at a relatively high speed and is in close proximity to the stator. The rotor is ﬁtted with a second brass or bronze faceplate (Number 8) and three internal cutters, sometimes called “ﬁngers.” In operation, moisturized corn meal is introduced to the screw and transported into the barrel section of the stator. Here, pressure and shear heat the corn meal to approximately 121◦ C (250◦ F) and the material changes into a homogeneous plasticized mass. At 121◦ C, the starches are cooked and the water becomes

Figure 11.10 Barrel and screw components of fry-type puffed snack extruder. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

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superheated, as in the baked-type snack extruders. The three internal cutters in the rotor cut streams out of this mass, which are then extruded radially between the two plates. The machine is designed so that the necessary heat and pressure are created progressively and controlled by a combination of the screw speed and the space between the plates. Additional heating of the material takes place as it is extruded between the plates from friction created by the high rotational speed of the rotor. As the material exits from between the plates, the pressure drops from 48 atm (1,000 psi) to atmospheric and the superheated water ﬂashes to steam, expanding the product. As in the baked extruders, the higher the pressure drop, the greater the expansion. However, because the pressure is inherently lower in this type of extruder, the expansion is considerably less and the product density higher. The unique forming action that takes place between the plates produces an irregular, rough-shaped product of varying lengths. With its higher density and lower expansion, this product is more suited to frying than the high-shear expanded products, which would absorb oil like sponges.

5.2. SCREW The screw, or auger, is critical to the operation of the fry-type extruder. As mentioned earlier, this screw is highly polished and all machining marks are removed. The screw must be allowed to slip in the product easily to generate sufﬁcient shear to heat the material for extrusion. Non-polished screws and ﬂights with machining marks will grip the material too tightly and not create enough shear. When this happens, the extruder tends to ﬂake out because the temperature of the material is not high enough to heat the moisture to the required superheated stage. Power requirements for the screw are much lower than on a direct expansion extruder, and typically are about 25% of the power required for the entire machine.

5.3. STATOR The stator is manufactured in two parts, the base and the faceplate to be described in a separate section. The base is machined from alloy steel and heat-treated for wear resistance. Over time, it will wear through and require replacing. The bore is short, typically about 3 inches and, when combined with a 3-inch diameter screw, has a barrel L/D ratio of only 1. With the extremely short L/D ratio, only shallow straight grooves are machined into the bore for shearing purposes. Anything more aggressive would inhibit the performance of the machine and change product characteristics.

5.4. ROTOR The rotor consists of six parts, the steel base, faceplate, center plug, and three internal cutters. The steel base is not heat treated, and is only used as a

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base to mount and hold the product-contacting components. Over the years, many different conﬁgurations have been used for the center plug. The original plug, described in the 1939 patent, was a simple smooth dome. Later, this was replaced by a plug with two distinct twirls for reasons unknown. In the 1970s, a three-twirl plug was developed to match better with the three internal cutters. The latest models have reverted back to the original smooth design center plug for producing lower product densities and higher outputs. The three internal cutters, or ﬁngers, do the brunt of the work and are the ﬁrst components to wear out. These devices normally are machined from tool steel and are heat treated, although some manufacturers use stainless steel, which does not hold up as well. The function of the ﬁngers is to cut streams from the plasticized mass and extrude them between the plates. Technically, they cut inside the machine and are called “internal cutters.” Usually a set of heads will require replacement of the ﬁngers at least once before the plates wear out.

5.5. FACEPLATES Steel and cast iron plates were used in earlier machines, but almost all the extruders today use bronze alloy plates. Steel and cast iron plates require preheating and do not maintain as constant a temperature as the bronze plates, making them more temperamental in operation. Two types of bronze are used, SAE 62 and SAE 63. Both are copper-based alloys with about 10% tin content. SAE 63 differs from the 62 alloy by the addition of 0.5% lead. This material sometimes is referred to as “leaded gun bronze.” The addition of lead during the manufacturing of steel and other alloys softens the material and makes it easier to machine. The soft leaded bronze in the extrusion application makes the heads easier to start and minimizes the breakin period. The downside is that the wear rate of the heads is faster because of their softness, and they will not last as long as the nonleaded heads. The concern of some food processors about the material containing lead is unfounded. The extremely small amount of lead is added as an alloying agent during casting and is impossible to extract from the ﬁnished material. Maddox/Adams sells about equal numbers of leaded and nonleaded heads. The stator faceplate is machined with grooves and ribs to ease material transition from the barrel to between the plates. Over time, these ribs wear and smooth over. Another problem with the stator brass is the ﬂat surface. Hours of operation will cause the surface to become concave, impeding the ﬂow of material across it and reducing the output of the extruder. A simple check of the surface with a straight edge should be done weekly to ensure it is still ﬂat. The rotor faceplate sometimes has three pockets or swirls machined into it to blend with the ﬁngers. Maddox/Adams has tested rotor faceplates with large pockets, small pockets, and without pockets, and has not noticed signiﬁcant performance differences. The rotors without pockets machined into them appear to make a lighter-density product than the others, but not by much. A photograph

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Figure 11.11 Photograph of FCP-600 fried cheese puff extruder. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

of an Adams/Maddox fry-type puffed snack extruder is shown in Figure 11.11. A two-tank coating cheese slurry and heating system is shown in Figure 11.12.

5.6. RAW MATERIALS Corn normally is the ingredient of choice, although rice ﬂour and potato granules can be added to a corn base. Typically, a coarser granulation corn can be used for fry-type extruders than for bake-type extruders, and corn grits sometimes can be run. The ﬂour content should be less than 2% for ease of moisturizing and reliable operation of the extruder.

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Figure 11.12 Cheese slurry heating and preparation system. (Courtesy of Maddox Metal Works, Inc., Dallas, Texas.)

5.7. PROCESSING AND CONTROL The main means of controlling this extruder is by adjusting the gap between the rotors with the handwheel. Because of the speciﬁc design, only one shape can be obtained—irregular-shape corn curls. The width and length of the curl can be changed by changing the distance between faceplates and knife speed. Because these extruders are autogenous in design but operate at lower rates of shear and temperature, the temperature of the raw material is more critical than for high-shear extruders. Generally, corn meal under 21◦ C (70◦ F) does not operate reliably in a fry-type extruder. Corn meal under 15◦ C (60◦ F) does not run at all. For this reason, the corn meal should be stored in a heated warehouse to ensure the temperature can reach at least 21◦ C before use. As with the bake

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Weight Changes of 1,000 lbs of 13% Moisture Corn Meal in Production of Fry-Type Extruded Snacks.

Procedure Starting corn Moisten to 16% to improve extrusion 3% average loss of fines between fryer, chaff tumbler and conveyors 8% average loss of moisture between extruder and fryer 7% average loss of moisture through fryer 25% average weight increase by absorption of oil 20% average weight increase by application of 1/3 cheese and 2/3 oil slurry

Weight Change (lbs)

Resulting Weight (lbs)

--+30 −30

1,000 1,030 1,000

−80

920

−64 +214

856 1,070

+214

1,198

extruders, problem corn meals can be addressed in the ﬁeld by additions of oil, emulsiﬁers and/or vinegar, but the extruder manufacturer should be consulted ﬁrst. A materials balance for typical production of fry-type corn snacks is shown in Table 11.4.

6. REFERENCES 1. Authors unknown. 2000. State of the industry report 2000. Snack Food & Wholesale Bakery, 89:(6, June), SI-1-SI-74. 2. Bass, E. J. 1988. Wheat ﬂour milling. In Wheat: Chemistry and Technology, Vol. II, 3rd edition. Y. Pomeranz, ed. American Association of Cereal Chemists, Inc., St. Paul, Minnesota, pp. 1–68. 3. Alexander, R. J. 1987. Corn dry milling: Processes, products, and applications. In Corn: Chemistry and Technology. American Association of Cereal Chemists, St. Paul, Minnesota. pp. 351–376. 4. SFA. 1987. 50 Years: A Foundation for the Future. Snack Food Association. (Current address) Alexandria, Virginia.

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CHAPTER 12

Snack Foods from Cooking Extruders

GORDON HUBER

1. INTRODUCTION

S

NACK food extrusion includes subjecting properly selected grains to a variety

of complex physical processes to yield a variety of snacks. Extrusion offers many basic design advantages that minimize time, energy and cost inputs while adding versatility and ﬂexibility to the manufacturing process. In extruding snack foods, grain and other ingredients are mixed and cooked under pressure, shear and high temperature in a tube (barrel). The resulting mass is forced through a die, after which it is cut into individual pieces and assumes the many shapes that consumers have come to expect in the snack food aisles of markets. Novel ingredients, cutting-edge extrusion technology and innovative processing methods are combined to yield new snack products with ever-widening appeal to health-conscious consumers, to shoppers seeking a crispier pork rind, or to gastronomes who favor shrimp-ﬂavored snacks. Because of the complexity of the snack food extrusion process, it is best to approach it systematically by considering four areas of processing: formula, hardware, software and ﬁnal product. The formula, of course, consists of various ingredients. The hardware includes the physical components of the extrusion system. The software controls the conditions under which the hardware processes the formula; and the ﬁnal product is the outcome of the optimized combination of formula, hardware, and software. Results of research conducted by Wenger Manufacturing Company are included in this chapter.

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2. FORMULA A snack food formula can consist of many different ingredients, from plant, animal and chemical sources. Typically, a formula is comprised primarily of carbohydrates, with smaller amounts of proteins, lipids and other ingredients, such as seasonings and processing aids. Corn is described in Chapters 3 and 4, starches in Chapter 5 and dry potatoes in Chapter 9.

2.1. CARBOHYDRATES IN EXTRUSION PROCESSING Carbohydrates are the most abundant class of biosynthetized organic compounds. They constitute about 75% of the plant world and are widely distributed as important physiological components. Plant carbohydrates in one form or another supply the human race with more than 70% of its energy requirements [1]. Many sources and types of carbohydrates are available for formulating new and different products. Carbohydrates give these products functionality and organoleptic properties, such as texture, appearance and ﬂavor. Careful consideration must be given to the effects that each source or type of carbohydrate, natural or modiﬁed, has on extrusion processing and the functionality of the ﬁnal product. Carbohydrates are a main food constituent, generally present in food products at a 70% level or greater. They work in extruded products as binding agents, viscosity builders, suspending agents and emulsiﬁers. Also, they inﬂuence the texture and esthetic characteristics of foods including expansion, bulk density, mouth feel, gelation, clarity and ﬂavor. Carbohydrates may be grouped into four general categories: starches, ﬁbers, gums, and sugars.

2.1.1. Starch A wide variety of endosperm fractions and isolated starches are available for use in extruded snack food formulas. Sources include sorghum (Chapter 3), barley, corn, oats, potato, rice, tapioca and wheat. Each has its own properties; potato starch consists of granules that are large and irregular in size and shape (Chapter 9); rice starch has small, regular granules, making it a good binder and expander; wheat starch granules tend to be disk-shaped; corn and sorghum starches are of moderate size and are spherical in nature (Chapter 3). Each starch also exhibits different swelling characteristics in the extrusion process. For example, wheat starch swells in a two- dimensionalal X-Y direction and corn starch swells in a three-dimensionalal X-Y-Z direction. Starches consist of glucose chains. The smaller chains are linked together to other chains, either straight or branched. The straight chains are called amylose, and the branched chains amylopectin. The amylose and amylopectin portions

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of the starch behave differently during extrusion, resulting in speciﬁc characteristics. Research has shown that starches with a 50% blend of amylose and amylopectin give the best expansion characteristics. However, as amylose content was decreased, the bulk density also decreased, indicating increase in overall expansion. Amylose in starch forms complexes with lipids during extrusion, which reduce the water solubility and digestibility of cooked starches. As starch in the presence of lipids is exposed to increasing amounts of heat and pressure, the amount of amylose-lipid complexing increases. Unmodiﬁed pregelatinized starches normally fall into one of four distinct categories: r Starch that has lost birefringence (the crystalline structure inherent in raw starch that refracts light) but has not been swollen.

r Starch that has lost birefringence and has been swollen or enlarged. r Starch that has lost birefringence and has been exposed to enough heat and

shearing action to cause the amylose portion of the starch to leach out into an aqueous solution. r Starch that has lost birefringence and has been exposed to enough heat and shear to degrade the amylopectin and amylose into shorter or lower molecular weight chains. Gelatinization (Chapter 5), or cooking, of starches during the extrusion process requires moisture, heat and retention time in the extruder barrel. Chemical modiﬁcation may also affect the gelatinization of starches. The point of initial gelatinization, and the range over which it occurs, is governed by starch concentration, method of observation, granule type and heterogeneities within the granule population under observation. Irreversible changes occurring within starch granules involve the collapse of molecules, simultaneously with swelling, crystallite melting, loss of birefringence, viscosity development and starch solubilization.

2.1.2. Fiber Fiber sources most commonly used in foods include: beet pulp, cellulose (wood), corn, fruit, oat, pea, rice, soy and wheat. Fiber is used as a bulking agent, to provide nutritional attributes and to modify the texture of many extruded products. Fiber usage is often limited by its effect on product expansion. Beet pulp, fruit, pea and soy ﬁbers are considered to reduce expansion the least and may be added to starch-based formulas at levels from 5 to 10%. The addition of oat and rice ﬁber normally reduces expansion characteristics considerably. The purity of the ﬁbers has a direct inﬂuence on their expansion characteristics. Protein and lipid contents solubility and particle size also inﬂuence the amount of expansion that can be expected when ﬁber is added to a formulation.

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In many cereal grains, it is hard to separate protein and the lipid fractions from the remaining grain constituents. Fibers with the lowest protein and lipid contents, and smallest particle size, allow the highest degree of expansion. Oat bran and rice bran typically are high in protein and lipid content and tend to reduce expansion when added to formulas of extruded foods. A reduction in radial expansion and increase in axial expansion occur as ﬁber is increased from 10% to 20% in a formulation. However, total expansion may be only slightly reduced. High ﬁber formulations may be expected to increase only slightly in soluble dietary ﬁber content, by approximately 3%, during the extrusion process. Carbohydrate analysis results shift upward by approximately 4 to 5%, indicating hydrolysis of small amounts of the hemicellulose fraction to yielding shorter chains of sugars.

2.1.3. Gums or Hydrocolloids Gums are commonly referred to as viscosity builders capable of forming colloidal gels. In many cases, hydration and extrusion of gel-forming gums alter their gelling characteristics, resulting in formation of weak gels. As a result of their hydrophilic nature, gums effectively inﬂuence extrusion processing conditions and extruded products. They reduce evaporation rates, alter freezing rates, enhance textural properties and act as stabilizers. The most commonly used gums or hydrocolloids include: gum Arabic, pectins, agar, carrageenin, alginates, guar, locust bean and psyllium. When choosing hydrocolloids (gums) for speciﬁc applications, the required viscosity, gel and emulsiﬁcation characteristics, rate of hydration, dispersion problems, effects on processing conditions, effects of particle size, availability and effects on product mouth feel should be carefully considered.

2.1.4. Sugars Sugars provide ﬂavor, sweetness, energy and nutrition, texture, stabilization, water activity control and color control. in extrusion processing. Commonly used sugars include: sucrose, dextrose, fructose, corn syrups, honey, fruit juices, xylose and sugar alcohols. Low-molecular-weight starches and dextrins, sugars and salts at low percentages have a viscosity-thinning effect within the extruder. Additives that lower viscosity within the extruder barrel result in increased expansion at the die. These effects are shown in Table 12.1. Sugars tend to tie up water needed for gelatinization of starches. Therefore, the time and temperature required to gelatinize starches in extruded food products are increased. As sugars are added at higher levels, extruder screw conﬁgurations may need to be altered to generate more shear or pressure, or to convert more mechanical energy heat to properly cook or expand the desired product.

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TABLE 12.1.

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Effect of Low-Molecular-Weight Carbohydrates on Bulk Density [2].

Ingredient Soy fiber product Corn flour Maltodextrin (5 DE) Bulk density

Formula #1

Formula #2

85% 15% --308 g/L

85% 10% 5% 190 g/L

Sugars complex with proteins result in browning reactions. Temperatures normally are low enough, and moistures high enough, so that these browning reactions are not a problem during extrusion, but browning may need to be controlled in post-extrusion drying or toasting operations. Sugars may also be used to control the water activity in extruded products because of their hydrophilic nature and are commonly used as coatings for many extruded products. For coating applications, granular sugars may be melted with heat and small amounts of water, or blends of sugar and honey may be utilized.

2.1.5. Proteins Protein typically is the second major constituent of snacks and foods. Although protein content has never been a main concern in the snack food industry, a growing public awareness of proper nutrition and nutraceuticals is causing this to change. Proteins are made up of amino acids, some of which are dietary essentials for proper health and nutrition for humans. Molecular weights of proteins vary between a few thousand to several million daltons. Proteins are of either vegetable or animal origin and can be classiﬁed into various groups. Fibrous proteins are most commonly derived from animal sources; globular proteins commonly come from vegetable sources. Although proteins from animal sources are more expensive, their amino acid proﬁles more closely match human requirements than vegetable proteins. Vegetable protein sources are usually lacking in one or more of the essential amino acids and require supplementation to balance nutritional requirements. Proteins may also be classiﬁed by solubility. For example, proteins concentrated in the aleurone, germ and pericarp fractions of cereal grains include albumins, which are water-soluble and coagulate with heat, and globulins, which are soluble in dilute salt solutions. Prolamins are concentrated in the starch endosperm fractions of cereal grains and are alcohol soluble (70% ethanol), and glutelins are soluble in dilute acids or dilute alkali. Globular proteins in soluble state may be thought of as long chains of amino acids, which are interconnected, or cross-linked, to form a somewhat spherical mass. These so-called globules begin to unravel when exposed to moisture and heat. During additional heating in the presence of moisture, these proteins

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begin to denature or become insoluble. Denatured proteins, incorporated in a snack food formula, are considered to be less functional and contribute little or nothing to the expansion process that occurs during extrusion. Not all cereal proteins behave in similar fashion. Wheat protein (gluten), for example, behaves very differently than corn protein (zein). This may be observed by mixing water with wheat ﬂour to form a dough, compared to mixing water with corn ﬂour. The dough from the wheat ﬂour is cohesive and elastic and may be stretched into a thin sheet if mixed properly. The dough from corn ﬂour is non-elastic and has no stretching capabilities. These differences have a strong impact on the textural and ﬂavor properties of extruded snack products. During the extrusion process, proteins become denatured and change from soluble to insoluble forms. This happens at 60–70◦ C (140–160◦ F). On the other hand, starch gelatinizes or changes to more soluble forms at 51–78◦ C (124– 172◦ F).

2.1.6. Lipids Grains may be the main ingredients in snack food recipes, but it is the lipids or fats that provide many of the appealing qualities characteristic of snack foods. Lipids are classiﬁed as polar or non-polar. Lipids, derived from vegetable sources and most commonly used in snack foods extrusion, are non-polar and unsaturated. Many snack foods are either fried in hot vegetable oil or coated with vegetable oil to adhere ﬂavors and seasonings to the product. Lipids also may be considered an extrusion aid, and provide a means of controlling the surface and internal textural properties of snack foods. The role of lipids will become more evident throughout the remainder of the chapter.

2.1.7. Other Ingredients As mentioned previously, many other additives or processing aids may be included in formulas to modify the operating window of the extrusion system, or to impart changes in textural properties of snacks. The following examples help us understand the inﬂuence of additives. r Salt is a critical ﬂavor-enhancing ingredient for savory snack. It also assists

equilibration of moisture in snack pellets (third-generation snack foods, half products). Salt is hygroscopic and limits the availability of water for gelatinization of starches if used at high levels. r Baking soda (sodium bicarbonate) may be used for creating nucleating sites for steam in both direct expanded products and in snack pellets. An increased number of smaller cells results, and the ﬁner cell structure in the product is usually more desirable to the consumer. However usage levels higher than 1% impart distinct ﬂavors associated with sodium bicarbonate.

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Proper combinations of ingredients yield products with pleasing textures and ﬂavors. Speciﬁc combinations of ﬂours affect ﬂavor development. For example, barley blended with wheat gives a sweet, pleasant taste, whereas a barley and corn mixture may have a bitter aftertaste. Potato-corn blends give better meat ﬂavor attributes than potato-rye mixtures.

3. HARDWARE Two types of cooking extruders, single-screw and twin-screw, are commonly used for producing snacks foods. Single-screw extruders are the more widely utilized of the two extruder types, producing many common snack foods such as corn-based fried or baked collets (corn curls). However, half products may require the more sophisticated twin-screw extruders. With its improved pumping action, the co-rotating twin-screw extruder ensures precise process control and ﬁnal product consistency. Introduction of the twin-screw extruder has required snack food manufacturers to develop a sound understanding of the mechanisms of both the singleand twin-screw extruders for each to be used for the processes it performs most efﬁciently. No one individual extruder conﬁguration or type, whether single or twin-screw, is compatible with all snack processes and raw materials. Since success, failure, or product life cycle in the market place, depend on the quality of the product, snack food manufacturers must be able to determine product quality and understand which extrusion-processing parameters and ingredient interactions inﬂuence that quality. The ability to control extrusion-processing parameters determines how reproducibly and consistently product quality can be maintained.

3.1. OVERVIEW The simplest extrusion mechanism is a piston contained within a cylinder, which is capped with a shaping oriﬁce, or die. Material is loaded into the cylinder, the piston moves forward creating pressure at the die, and the material emerges in its shaped form from the die and cut to the desired length. This type of extrusion process is batch in nature because the piston must be retracted periodically to permit reﬁlling of the chamber. Furthermore, the heat buildup in the extrudate is usually limited to the viscous energy dissipation in the die [3]. The extrusion process can be made continuous by replacing the piston with a helical screw. Material is fed continuously into an inlet hopper and transported forward by the rotation of the screw. As it reaches the die, the pressure increases to the level required to propel or force the extrudate through the die oriﬁce. The rotating screw moves material from inlet to discharge. As a result of the material slipping on the screw surface, friction between the two results in heating the material. These extruders can be either single-screw or multiscrew in design.

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In the mid- to late 1940s, the ﬁrst extrusion-cooked, expanded food products (corn snacks) were commercially produced using single-screw extruders. Corn is heated sufﬁciently within the extruder to completely gelatinize the starch and disrupt the protein matrix. Because of the temperature and moisture conditions that exist during processing, an exothermic post-die expansion of the product takes place, resulting in a light-density, crisp product. The 1960s brought the ﬁrst commercial continuous production of dry expanded ready-to-eat snacks and cereals using the single-screw cooking extruder. Traditional breakfast cereal production methods have fought hard to compete in limiting the use of extrusion cooking in this product area. Steady improvement in process control, equipment design, including introduction of twin-screw technology, better scientiﬁc understanding of the extrusion process and raw material behaviors have kept extrusion cooking technology at the forefront of research, allowing greater penetration of the snack food and cereal industries.

3.2. ADVANTAGES OF EXTRUSION Extrusion cooking offers several advantages over the processes it replaces. The most signiﬁcant advantage is that the process is continuous. Dry powders can be preblended and fed continuously, in a uniform manner, into an extrusion cooker. This results in less material involved in the process at any given time. Furthermore, the ability to control quality is maximized because poor-quality product is recognized immediately. Corrective action is easily taken, and the process is brought back into control with minimal waste. Several processing steps are combined in the extrusion cooker. For example, water and other liquids, steam and solids can be continuously and uniformly combined, eliminating the need for additional pieces of complex equipment and resulting in more compact installations. Overall, utilities consumption for extrusion is lower than that of alternative processes, because lower moisture levels are used for cooking and shaping a ﬁnal product and because less heat is lost to the surroundings. Manpower requirements are usually lower when using cooking extruders compared to other processes. Large commercial extruders require little attention during operation. Modern process controls further reduce manpower requirements in production operations. In addition, extrusion is versatile. It provides precise hardware and process controls, which permit the use of a wider range of raw materials to make a speciﬁc product. As a result, formulations can be altered to lower-cost materials and ﬁnal products are often improved.

3.3. PHYSICAL COMPONENTS The food extruder must complete a number of operations in a short time under controlled, continuous and steady-state conditions. The operations may

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include heating, cooling, conveying, feeding, compressing, reacting, mixing, melting, cooking, texturizing and shaping. Energy sources to provide heat for cooking, texturing, or melting may include: r Conversion. Mechanical energy is dissipated into the product in the form of

heat caused by shearing, or by friction generated by pumping or conveying inefﬁciencies. For high-shear extruders, essentially 100% of the heat may be generated through shear. This type of machine is called an “adiabatic extruder.” r Conduction. Heat, from a thermal ﬂuid or other external jacketed source, is transferred through the barrel into the product. r Convection. Heat is transferred into the product directly, as by direct steam injection into the extrudate. Each energy source has its advantages and disadvantages. Typically, a combination of the three is most practical. Several basic components have speciﬁc functions common to all extrusion equipment (Figure 12.1): r A feeding system, which usually consists of a live bottom-holding bin and a

variable-speed metering device to feed raw dry-mixed ingredients uniformly and in uninterrupted manner at the desired ﬂow rate. r A preconditioner in which liquids, and/or steam or other vapors, may be uniformly combined with the premetered dry formula mix. r An extruder assembly, whose barrel segments, screws and shearlocks conﬁguration has been preselected to properly feed, knead and cook the dry or premoistened feedstock. r A ﬁnal die to restrict the extruder discharge and shape the product, and a device to cut the extruded proﬁle to the desired length.

3.3.1. Feeding System Premix holding bins, designed to prevent bridging of raw materials and normally of circular design, are mounted on load cells for accurate control of uniform feeding rates into the extrusion system. Feeding systems can be volumetrically or gravimetrically controlled. Gravimetric systems typically deliver raw materials to within 0.5–1% of the desired mass ﬂow rate, but volumetric systems have much lower accuracy due to density changes that occur during ﬁlling and unloading the holding bins. Since most food extrusion systems, both single- and twin-screw, are starve fed—that is, the screw is fed at less than the maximum volume it can convey—the throughput of the system is determined by the dry formula feeder.

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Figure 12.1 Extrusion system overview. Product ﬂow: live bottom-holding bin, feeder, preconditioner, extruder assembly, knife, pneumatic pickup. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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3.3.2. Preconditioning Cylinder A preconditioning step is not required for all extrusion processes, but basically two types of preconditioners are available for snack foods extrusion. Pressured preconditioners operate at elevated pressure and temperature, but have been shown to be nutritionally detrimental and are more expensive to purchase and operate. Atmospheric preconditioners are the more common. These operate at atmospheric pressure and thereby are limited to a maximum temperature of 100◦ C (212◦ F). Preconditioning cylinders are available in a variety of designs. They may have one or two shafts. The most modern design has two shafts of different diameters operating at different speeds (rpms); it provides better mixing and longer controlled retention time. The cylinders may be equipped with a single agitator, dual agitators, or dual agitators with differential speed/differential diameter. Single-agitator mixing cylinders are used in extrusion applications of low to moderate capacity where steam and water are mixed and continuously blended with the dry raw feedstock. Dual-shaft preconditioners are required when total hydration of raw materials is necessary for complete gelatinization of starches (Figure 12.2).

3.3.3. Extruder The extruder is the heart of the extrusion system. Although various singleand twin-screw machines have been placed in the general category of food extruders, this ignores the fact that each type has distinct operating principles and works best for speciﬁc functions and processing applications. Cooking extruders can be classiﬁed thermodynamically, by pressure development, or by shear intensity. From a theoretical thermodynamic point of view, extruders are: r Autogenous (nearly adiabatic), generating their own heat by conversion of

mechanical energy in the ﬂow process.

r Isothermal or constant temperature. r Polytrophic, operating between the autogenous and the polytrophic, with

part of the energy derived from mechanical dissipation and part from heat transfer. These classiﬁcations become important only when modeling the behavior of the cooking extruder, which can be complex because nearly all cooking extruders operate polytrophically. In addition, single-screw extruders may be divided into four subcategories based on shear or mechanical energy requirements: r Low-shear forming. r Low-shear cooking.

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Figure 12.2 Dual-shaft, differential speed/diameter preconditioner. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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r Medium-shear cooking. r High-shear cooking.

Twin-screw extruders can be further subdivided into several classiﬁcations based on mechanical design: r r r r r

Co-rotating intermeshing. Co-rotating non-intermeshing. Counter-rotating intermeshing. Counter-rotating non-intermeshing. Conical intermeshing.

Also, food extruders can be classiﬁed by their method of pressure development, either as positive displacement or viscous drag. Single-screw, co-rotating twin-screw, and non-intermeshing cooking extruders are viscous drag extruders. They depend on friction between the screw and barrel surfaces and the extrudate for product conveying and pressure development. The intensity with which the extrudate is sheared is another way to classify cooking extruders. This permits identiﬁcation and cross-reference of products to process the variables and physical parameters of the extruder. Numerous subclassiﬁcations also exist. The extruder proper consists of the drive and bearing assembly, the extruder barrel and screws, and the extruder die (Figure 12.3).

3.3.3.1. Drive and Bearing Assembly The drive and bearing assembly are designed to supply power to the rotating extruder shafts and screws. The drive system may be either ﬁxed or variablespeed. Twin-screw applications are nearly always variable-speed, while singlescrew applications may be either. Variable-speed single-screw extruders are becoming more common in the snack food extrusion market. Two or three bearings in the bearing housing, which typically is oil lubricated, support the extruder shaft(s). One bearing must support both the thrust load of the extruder shaft and the radial load. The other supports only the radial load. In the single-screw extruder, the physical size of the bearing is limitless, while in the twin-screw extruder, the interrelationship between the two parallel shafts establishes a size limitation, resulting in stacking of multiple bearings to handle the thrust loads. Bearing assemblies for twin-screw extruders are more complicated because more components, such as drive and torque dividing gears, are required (Figure 12.4). The lubricant used in the bearing housing should be of high quality and approved for use in food processing. It should contain additives to prevent breakdown of its lubricating ability if contaminated with small amounts of water.

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BEARING & GEARBOX ASSEMBLY

BARREL ASSEMBLY

Figure 12.3 Extruder bearing, gearbox and barrel assemblies. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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END VIEW

TOP VIEW

MAIN GEARBOX

THRUST BEARING ASSEMBLY

Figure 12.4 Twin-screw extruder gearbox and thrust bearing housings. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

Power can be input to the extruder shaft either by a gear train or from V-belts. Both methods of power transmission provide adequate speed reduction from the motor speed to the rotation speed required for the extruder screws. If the power is input through a gear drive, adequate torque overload protection must be provided to prevent damage to the gears and motor in the event of an overload. V-belts are self-protecting and slip if they become overloaded. The bearing housing, drive motor and extruder barrel must all be on a frame of adequate strength to support all external loads applied to it.

3.3.3.2. Extruder Barrel. The extruder barrel consists of heads (non-rotating parts), screws (rotating parts) and the die assembly (Figure 12.5). Barrels of modern single- and twinscrew extruders are usually segmented and jacketed for temperature control. Although segmented extruders are more expensive to manufacture and purchase, their long-term costs are lower because only the most worn extruder sections need to be replaced instead of the entire extruder barrel. Extruders for second-generation (direct-expanded) snack products are normally short (less than 10:1 L/D ratio). It is important that the extruder conﬁguration, consisting

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Figure 12.5 Single-screw extruder barrel. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

of screws, steamlocks and barrel segments be properly selected to feed, mix and cook/melt the process material as it passes through the extruder.

3.3.3.3. Extruder Screws: Single Process stability. This is a top issue for extruder users. Discounting raw material variations, and assuming the cooking extruder is fed a consistent supply of raw material, changes in ﬁnal product can be directly related to the uniformity of ﬂow within the barrel and to variations in pressure just inboard of the die. To facilitate movement of the food mass, the barrel wall of the single-screw extruder may be smooth, or constructed with longitudinal or helical grooves (Figure 12.6). The grooves force the extrudate to slip on the screw ﬂight surface and thus be moved from the inlet to the die. Longitudinal grooves increase the

Figure 12.6 Smooth, straight- and spiral-ribbed head (barrel) sections of single-screw extruders. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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leakage of extrudate from one screw ﬂight to the next, thus decreasing conveying efﬁciency and increasing the residence time. Spiral grooves assist in pressure buildup by increasing the pumping action of the rotating screw. Screw design. In single-screw cooking extruders screw design is varied. The helix of the screw can be of constant pitch and depth from inlet to discharge. Both the screw pitch and ﬂight depth usually decrease from inlet to discharge. This is done in an effort to achieve complete barrel ﬁll at the varying extrudate densities that are encountered in moving material from the inlet hopper to the die. Most feedstocks have a bulk density of about 500 g/L in their powdery form as they enter the hopper of the extruder barrel. As the extrudate melts and ﬂows together during the cooking and mixing process within the barrel, its density increases to as high as 1,800 g/L just inboard of the die. Therefore, it is necessary to reduce the displacement volume of the barrel to achieve a continuous ﬂow. If interruption occurs in the ﬂow mass within the barrel, surging or uneven ﬂow will be observed at the die. The angle of the screw ﬂight relative to the centerline axis of the screw also must change. In the feeding zone, at and immediately after the inlet hopper, the screw ﬂight must be at nearly a right angle relative to the screw centerline (Figure 12.7). This promotes conveying of relatively low bulk density material. As the extrudate density increases, the face angle of the screw ﬂight ﬂattens out to increase mixing and decrease conveying efﬁciency. Reducing the bore diameter of the ﬁnal portion of the extruder barrel, referred to as coning or adding a conical section, has been found advantageous. It aids in building up pressure and in reducing the shear rate. Reduction of shear rate is extremely important when overshearing of fragile extrudate must be prevented (Figure 12.8).

FEEDING SCREW

KNEADING SCREW

COOKING SCREW

SCREW FLIGHTING TYPES FOR SINGLE SCREW EXTRUDERS Figure 12.7 Screw ﬂight proﬁles, single-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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Figure 12.8 Single-screw extruder conical section. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

Single-ﬂight screws are most often used in the feeding zone for maximum free volume. Two-ﬂight or double-ﬂight screws typically are used in the kneading or mixing section, whereas either double- or triple- (three) ﬂight screws are used in the ﬁnal cooking/melting zone. Increasing the number of screw ﬂights increases the screw surface-to-volume ratio, thus increasing the conversion of mechanical energy into heat by friction.

3.3.3.4. Extruder Screws: Twin Process stability. The co-rotating twin-screw cooking extruder reduces the ﬂuctuation of die pressure because of the more positive transport provided by the two intermeshing screws. In contrast to the single-screw extruder, it relies on the interaction of one screw ﬂight within the ﬂow channel of the adjacent screw, as well as friction, to transport material forward. This reduces the total dependence on frictional forces for transport, and thus results in the process operating with a uniform in-barrel ﬂow, leading to a more uniform die pressure despite changes in extrudate viscosity. In the co-rotating twin-screw extruder with fully intermeshing screws, one screw ﬂight interacts with the ﬂow channel in the adjoining screw. Therefore, it is not necessary to provide antirotational mechanisms in the barrel walls. If material sticks to the screw surface, the adjacent screw crest will wipe it from the companion screw ﬂank as the two screws intermesh, thus transporting the extrudate forward. This distinctive screw-to-screw interrelationship results in a speciﬁc geometric screw ﬂank proﬁle that must be maintained to minimize the buildup of residual material on the screw surfaces (Figure 12.9).

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Figure 12.9 Twin-screw extruder barrel assembly. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

Screw design. The positive pumping characteristic of the twin-screw extruder limits its ability to effectively convert mechanical energy into heat through friction. This problem is overcome by the use of reverse ﬂight screw elements and/or by the addition of lobe-shaped shear/kneading elements to the extruder screw conﬁguration (Figure 12.10). Both of these elements can reduce the

KNEADING ELEMENTS FORWARD PITCHED POSITION.

KNEADING ELEMENTS REVERSED PITCHED POSITION.

KNEADING ELEMENTS NEUTRAL PITCHED POSITION.

KNEADING ELEMENT ORIENATATION

Figure 12.10 Kneading screw elements and orientations, twin-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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TABLE 12.2.

Screw Design Parameters for Fully Intermeshing Self-Wiping Extruders.

Design Parameters Model Parameters r Screw diameter r Shaft center distance Screw Parameters r Screw pitch r Number of flights

Screw Characteristics Root diameter Flight depth Free volume Flight profile

positive conveying features of the twin-screw extruder, thus forcing the extruder barrel to ﬁll. This allows compression, heating and shearing of the extrudate as required. The lobe-shaped shear/kneading (shearlock) elements can be assembled either in a neutral manner (90◦ increments) or to assist or resist forward transport of the extrudate. Shearlock elements conﬁgured in a neutral manner mix and knead the extrudate while relying on the upstream screw element for transport of material through the group of shearlocks. Those conﬁgured to assist forward transport provide more mixing and kneading than do screw elements, but somewhat less forward transport. When conﬁgured to resist forward transport, the lobed elements provide kneading and mixing while tending to pump more extrudate toward the inlet than toward the die. Therefore, the extruder screw immediately upstream of a conﬁguration like this must force the extrudate through the shearlock set. The reverse ﬂight screw elements have three negative consequences: high pressures at undesirable points in the extruder barrel, excessive screw and barrel wear, and inability of the barrel to empty itself. Design variability. The design options for a co-rotating twin-screw extruder screws are limited because of the geometric interdependence of one screw relative to the other (Table 12.2). The screw pitch can be changed without limit in a twin-screw extruder. However, practical limits exist. The number of ﬂights can be varied, but most typically it is set at one, two, or three. Cut ﬂight screws can be used at any position in the barrel. For each twin-screw extruder, the shaft-to-shaft center distance and screw diameter are ﬁxed. Thus, the screw root diameter is ﬁxed, resulting in a ﬁxed ﬂight depth. (Flight depth will vary depending on the manufacturer.) Once the number of screw ﬂights and the screw pitch have been ﬁxed, a deﬁnite relationship must be maintained to generate the ﬂight proﬁle of the self-wiping, fully intermeshing screw. This geometric interdependence limits the variations that can be made to the screw proﬁle in the fully intermeshing twin-screw extruder. Because of the

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TWIN ISOLATED CHAMBERS

FINAL CONICAL BARREL SECTION

Figure 12.11 Final conical barrel section, twin-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

ﬁxed center distance, it is not possible to use screws of varying ﬂight depths to enhance feeding and create compression. Thus, other mechanisms must be used to enable the fully intermeshing twin-screw extruders to convey, compress, shear and cook the extrudate. Conical elements. Conical ﬁnal screw elements, added to the discharge end of the co-rotating, fully intermeshing twin-screw cooking extruder, eliminate the need for complicated die adapters (Figure 12.11). These conical elements, which normally are about 1.5 diameters in length, greatly improve performance. Laboratory testing and production history have demonstrated the value these conical ﬁnal screw elements contribute to the operation of the extruder. The ﬁnal conical elements are fully intermeshing at their inlet end. Because of the cone angle relative to the extruder shaft axis, the two complementing conical screws gradually lose intermeshing while maintaining a constant ﬂight depth and uniform ﬂight proﬁle. Thus, the conical elements are not intermeshing at the discharge end. Likewise, the bore of the ﬁnal head element is conﬁgured with two conical bores to match the screws. The conical bores in the head reach a point where they are non-communicating with each other. Several interesting and rewarding phenomena result from this geometric form. First, the circumferential pressure gradient decreases from a maximum at the inlet end of the conical element to zero near the point where the screws lose radial communication with each other. There is no circumferential pressure gradient from this point to the end of the screw. Therefore, die adapters

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are simpliﬁed or even eliminated. Because of the conical conﬁguration of the ﬁnal section, the volume from its inlet to the discharge is signiﬁcantly reduced. This results in a rapid compression of the extrudate, a rapid increase in barrel pressure and resistance for the upstream portion of the barrel to push against. The ﬁnal conical elements also force a maximum pressure and extrudate density just inboard of the ﬁnal die. The ability to maintain this high density and the associated pressure in the ﬁnal section is responsible for the high degree of extruder stability and control. Extruder barrel and screw wear has been reduced in co-rotating twin-screw extruders equipped with conical ﬁnal screws. By forcing circumferential pressure symmetry in the highest pressure region of the barrel, extreme screw separating forces that exist in more conventional twin-screw extruders are minimized. Therefore, contact of the screw with the barrel is reduced, eliminating the typical non-symmetrical wear. The value added to the raw material by a process improvement must be sufﬁcient to cover the added initial equipment investment and operating costs. Twinscrew extruders typically cost 60 to 100% more than single-screw extruders of equivalent production capacities. Production experience indicates that electrical energy costs for operating twin-screw extruders tend to be 20–50% higher than for comparable single-screw machines. Wear costs using twin-screw extruders may vary from slightly less than to as much as double that of single-screw extruders, depending on the application.

3.3.3.5. Die and Knife The extruder barrel is capped with a die that contains one or more openings through which the extrudate must ﬂow. These openings shape the ﬁnal product and provide a resistance against which the screw must pump the extrudate. Either a knife mounted to run against the die face or a remote cutting device establishes the ﬁnal product length. The speed of the rotating knife assembly can be used to regulate the length of the ﬁnal product, or alternative post-die devices can be used to establish ﬁnal product length and shape. Single, double and even triple die plates may be used to alter or change the ﬁnal product texture and mouthfeel (Figure 12.12).

3.4. CONVEYING EQUIPMENT Many types of conveying equipment are available. Pneumatic conveying has several advantages for collecting product directly off the extruder (Figure 12.13). The high airﬂow across the extruder die, while the extrudate is being cut, minimizes the possibility of product sticking together either during

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SINGLE DIE

DOUBLE DIE

TRIPLE DIE

SINGLE DIE WITH SPACER

MULTIPLE DIES FOR SNACK EXTRUSION

Figure 12.12 Multiple dies for extruding snack foods. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

Figure 12.13 Pneumatic takeaway hood for cut extrudates. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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Figure 12.14 Convection belt dryer. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

the cutting process or while being conveyed. Moisture loss of 2–3% may occur during conveying. Removal of this surface moisture is an advantage when conveying certain types of snack products.

3.5. DRYING SYSTEMS Most snack products must be dried after extrusion. Reducing the moisture content helps to control texture, appearance and shelf life of the product. Of the many available, the most common type of dryer in the snack food industry is the belt dryer (Figure 12.14). Belt dryers are usually termed multiple-pass or multiple-stage, meaning that a dryer contains two or more belt conveyors. The conveyors are perforated to allow airﬂow. Product is fed into the dryer, creating a uniform layer on the dryer belt conveyor. Several types of leveling devices are available, including oscillating spout, oscillating belt conveyor, biased slot-vibrating conveyor, leveling rake, or leveling auger. The oscillating spout or conveyor and the biased slot-vibrating conveyor are the most commonly used. Dryers typically are either gas ﬁred or use steam coils as sources of heat. Steam heating is preferred if humidity must be controlled in the dryer and temperatures will be less than 175◦ C (347◦ F). Direct gas ﬁring requires considerable air exchange to maintain an environment that supports a ﬂame. If speciﬁc humidity levels are not important, and required temperatures are greater than 150◦ C (302◦ F), direct gas ﬁring is recommended. In limited cases, indirect heating options are available but increase the cost of the dryer. It is important that dryers be insulated and have well-balanced airﬂows to achieve uniform moisture levels throughout the bed depth and across the bed width of the belt dryer conveyors. Careful consideration should be given to the construction and functionality of a dryer. Sanitation, maintenance and structural

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durability are among the most critical issues. These needs can be addressed with access doors for easy cleanout; sloped ﬂoors and internal surfaces to avoid ﬁnes accumulation; bearings that are easily and safely accessed; structural provisions for thermal expansion; and high tensile-strength components. Product cooling is an integral part of drying. This may be done in the dryer itself, or in a separate unit. If product is packaged prior to cooling, moisture can condense on the packaging material, providing an environment for mold growth and therefore reducing shelf life of the product.

3.6. APPLICATOR/DRYER An applicator/dryer has become an integral component in snack food processing lines in recent years. Originally designed for sugar coating and frosting breakfast cereal, this system has gained signiﬁcant usefulness in the snack food industry as a superior method of coating snack products with colors and ﬂavors (Figure 12.15). The applicator/dryer is commonly included as an equipment component of lines producing low-fat snacks. The applicator dryer, when used in conjunction with fat-free gums as the application (tacking) agent, greatly reduces total caloric fat content in ﬁnished products. For example, snack manufacturers producing third-generation snacks, often microwave or hot-air puff rather than fry the product. Because surface oil is absent, other means must be used to adhere seasoning mixes to the product. Many sweet or savory snacks may be produced with no added fat with the assistance of the applicator dryer and fat-free gums. Basically, the applicator/dryer consists of a large perforated drum inside a gas-ﬁred dryer section. Heated air is introduced in the drying zone through slots in the drum to reduce the moisture of the applied ﬂavoring. The design and direction of the perforations on the reel direct the heated airﬂow in the direction opposite to the drum’s rotation. Within the reel, multiple drying areas allow coating and drying in successive steps that result in a very even multilayered coating effect. Coating/drying is repeated 2–3 times during the process to ensure consistent coating of the product and a moisture level suitable for packaging, storage, or downstream processing. Efﬁciencies of applicator/dryers are calculated on a base product moisture of 3%, a ﬁnished product moisture of 3% and a syrup with 80% solids (20% water). These capacities are based on a calculated operational efﬁciency of 84% due to required shutdown for cleaning. Available syrup or oil/ﬂavor systems include one kettle batch, two-batch kettles continuous, two-batch kettles with a heat exchanger and a continuous system with a sugar dissolver or continuous mixer. Syrups that have sticky

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Figure 12.15 Applicator/dryer for snacks and other foods. (Wenger Manufacturing, Inc. Sabetha, Kansas.)

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sugars such as honey, molasses and corn syrups severely decrease efﬁciency due to more frequent cleanups being required.

4. SOFTWARE (CONDITIONS)

4.1. INDEPENDENT AND DEPENDENT VARIABLES AND CRITICAL PARAMETERS The conditions, or software, under which extrusion systems process a formula, include both independent and dependent variables. Independent variables are those parameters that the extruder operator can directly control. Dependent variables are parameters that change as a result of changing independent variables. Independent variables include: r Dry recipe mix r Dry recipe feed rate r Water injected to preconditioner r Steam injected to preconditioner r Preconditioner speed r Preconditioner conﬁguration r Water injected to extruder r Steam injected to extruder r Extruder conﬁguration r Extruder speed r Extruder barrel temperature r Die conﬁguration Dependent variables include: r r r r r r r r

Retention time in preconditioner Temperature in preconditioner Moisture in preconditioner Retention time in extruder Temperature in extruder Moisture in extruder Pressure in extruder Mechanical energy input

The interactions of these independent and dependent variables and how they affect a ﬁnal product are complex and difﬁcult to understand without a thorough understanding of extrusion, the science of raw materials and sensory analysis. It would take a complete book to describe and discuss these interactions.

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However, extensive research indicates that all of these complex interactions result in changes of four basic extrusion parameters, which have been named “critical parameters”. These critical parameters affect the ﬁnal product quality and sensory attributes of extruded products. Product responses include: r Moisture—Shelf life, stability. r Expansion—Bulk density, size, shape. r Solubility—Stickiness, adhesiveness. r Absorption—Water, fat, milk. r Texture—Mouth feel, cell structure. r Color—Light, dark. r Flavor—Strong, mild, rancid. Product responses are measures of ﬁnal product quality that result from changes made to independent or dependent variables.

INDEPENDENT AND DEPENDENT VARIABLES

RAW MATERIALS

CRITICAL PARAMETERS

PRODUCT CHARACTERISTICS

Product characteristics are a result of speciﬁc critical parameters induced on raw materials. We interact with these critical parameters through changes in the independent variables. Critical parameters include: r Moisture—the actual moisture in the product or extrudate. r Thermal energy input—heat from thermal ﬂuids, steam or electricity that is transferred to the heads of the extruder, or direct injection of steam or any other type of liquid additive. r Mechanical energy input—heat dissipated into the extrudate caused by the shearing and pumping action in the extruder barrel. r Retention time—total time the product is in any speciﬁc region of the extrusion process.

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CRITICAL PARAMETER Moisture

DESCRIPTION Actual moisture in the process

Mechanical energy input GME = gross mechanical energy

GME =

Power Mass flow rate

SME =

(PowerLoaded )−(PowerEmpty ) Mass flow rate

SME = specific mechanical energy Thermal energy input Expressed in same energy units as mechanical energy units = kj/kg or kwh/kg

Retention time t¯ = Average retention time m = Amount of extrudate in the process ˙ = Mass flow rate m

=

kWh kg

=

KWh kg

For heating the extruder barrel: Thermal fluids Steam heat Electrical heat For direct heating of the extrudate: Direct steam injection Other liquid or vapor injection Total time in each part of the process t¯ =

m ˙ m

The interaction among these variables, the critical parameters and the hardware components illustrates the way science and engineering have shaped the extrusion ﬁeld. Table 12.3 shows several typical extrusion processing conditions for a directexpanded cornmeal-based snack product: r Feed rate is an independent variable that inﬂuences many of the others. In

some control systems, all the remaining inputs are slaved or controlled from the dry feed rate. r Screw speed also is an independent variable that inﬂuences variables like in-barrel pressure, retention time and extrudate temperature. The twin-screw extruder is more responsive to changes in screw speed than if cooking is conducted in a single-screw extruder. This is due to its material transfer characteristics. By varying the speed of the screw in a twin-screw extruder, TABLE 12.3.

Processing Conditions for a Cornmeal-Based Extruded Snack.

Dry corn meal feed rate Extruder screw speed (rpm) Extruder barrel temperature Extruder barrel pressure Moisture added into the extruder Moisture of extruded product Bulk density of extruded product

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450 kg/hr 300--600 120--160◦ C, 248--320◦ F 70--150 atmospheres 1,020--2,2050 psig 13 kg/hr 8--10% MCWB (moisture content, wet basis) 36--64 g/l

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it is possible to maintain more precise limits on product quality over the wear life of the barrel components. Furthermore, varying the screw speed can compensate for certain variations in raw material characteristics. Because screw speed is such an inﬂuential variable in twin-screw extrusion, the twin-screw machine is usually better for those plants making a wide variety of products at relatively low volume. Screw speed and die conﬁguration changes can be made along with a formulation or recipe adjustment to change the ﬁnal product. Extruder-screw conﬁguration changes are required less frequently in these applications when using twin-screw cooking extruders than when using single-screw machines. r Barrel temperature is actually a function of extrudate temperature and the thermal ﬂuid or heating element temperature used for heating or cooling the extruder barrel. The actual extrudate temperature is difﬁcult to measure accurately because of this interaction. r Barrel pressure development within the extruder barrel is a response to: feed rate, characteristics of the raw material, extruder screw speed, moisture in the extruder barrel, temperature of the extrudate, geometry of the die and the amount of open area. In general, it is desirable for the barrel pressure to increase from atmospheric at the inlet to a maximum just inboard of the die. Detrimental characteristics are often observed in ﬁnal products if the extruder conﬁguration forces excessive pressure and shear too far upstream from the die. Reverse-ﬂight screw elements can induce excessive pressure and shear. The pressure is always higher on the upstream side of a reverse-ﬂight screw element, decreasing along its length. This excessive pressure may cause excess power demands on the extruder drive and alter expansion characteristics (and thus texture and mouth feel) of the ﬁnal product. Optimum extruder performance, in making direct-expanded products from starchy and/or proteinaceous ingredients, is achieved when the maximum barrel pressure is at the discharge end of the extruder screw. The pressure around the inside circumference of each screw in the co-rotating twin-screw extruder is not uniform. At any axial position from the extruder inlet, each barrel bore has a low pressure point near where the screw rotates away from the apex formed by the two intersecting barrel bores. The pressure increases, moving circumferentially around the inside of the individual barrel bore until a maximum pressure is reached at the point near where the screw rotates toward the apex formed by the two barrel bores (Figure 12.16). This circumferential pressure proﬁle forces screw separation, causing the screws to contact the barrel wall. The result is high screw wear and high barrel wear in a local area on each extruder bore. When a die is located adjacent to an extruder barrel with this varying circumferential pressure ﬁeld, non-uniform die ﬂows result. This yields products of varying length after cutting. Varying product characteristics also may result.

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HIGH PRESSURE POINT

HIGH PRESSURE POINT

Figure 12.16 Kneading lobes, co-rotating twin-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

Non-uniform die ﬂow can be overcome by using long and/or complicated die spacers. These can cause major quality problems in the ﬁnished product because without proper streamlining, extrudate can stagnate in the die spacer, burn and later break free to contaminate the product. r Moisture is a critical catalyst in twin-screw and single-screw cooking processes. Moisture in the form of steam, injected both into a preconditioning device and into the extruder barrel, brings additional energy for cooking. This increases extruder capacity and reduces the requirement for large drive motors. Moisture is necessary for starch gelatinization and protein denaturation. As moisture is increased (within limits), the mechanical energy required for processing decreases. Moisture, both steam and water, added to a preconditioning device softens the particles of cereal grain, thus reducing their glass and melt transition temperatures, which also reduces abrasiveness. This reduces extruder component wear and in turn operating costs. Twin-screw extruders reduce, or even eliminate, the need for adding water or steam to the dry formula during extrusion cooking. Operating experience demonstrates that both twin-screw and single-screw cooking extruders can process foods under low moisture conditions. Processing nutritional food products at barrel moisture levels below 20% has been proven to be uneconomical and nutritionally undesirable. Low-moisture extrusion results in production of certain undesirable dextrins as a result of increased shear energy inputs. Losses of vitamins and reduced amino acid availability are greatly accelerated as extrusion moistures are decreased. For this reason, vitamins and heat-sensitive nutrients are added topically post extrusion when processing at low moisture conditions.

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4.2. EXTRUDER CONFIGURATION Proper extruder conﬁguration is the key to using a variety of raw materials to yield a wide range of ﬁnished products. Conﬁgurations of the preconditioning chamber, the screw and barrel of the extruder, and the die, must be considered. A closer review of the extrusion process follows.

4.2.1. Preconditioning Chamber Conﬁguration Prepping the feedstock by preconditioning is an important part of the extrusion process. Mixing, hydration, cooking, pH modiﬁcations and addition of vapors, ﬂavors, lipids, color and meat slurries may all take place in a properly designed preconditioning process. The most important single aspect of preconditioning is the added mixing and retention time, which are imperative for all reactions, chemical or physical. In addition, preconditioning improves the development of certain ﬂavor components within the ﬁnal product. During extrusion processing with high mechanical energy inputs, which result when no preconditioning is used, starch and protein matrixes melt and ﬂavor components are encapsulated so they cannot be released in the mouth. By preconditioning, the starch and protein matrixes become more pliable and more easily deformed, which makes them less susceptible to damage and melting in the shear environment of the extrusion process. This improves availability of ﬂavor components for quick release during chewing. In the past, extrusioncooked cereal grain products were thought not to maintain the same cooked grain ﬂavor as in longer cooking time processes. However, preconditioning has changed this perception and is now used to enhance the ﬂavor of cereal grain products during the extrusion process. Experience has shown that consumers prefer the taste of cereal grains that are cooked slowly and with high moisture. This ﬂavor development during the cooking process is attributed to the many complex reactions that occur. One example is the Maillard reaction, which results from amino acids, proteins and peptides reacting with reducing carbohydrates during cooking. Low-molecularweight carbonyl compounds produce Maillard reactions by condensing with amino acids and other amino derivatives to form heterocyclic products such as dihydropyridenes. A second factor contributing to ﬂavor development is the steam stripping or distillation of volatile ﬂavor components. One example is the bitter ﬂavor associated with raw oat products. During the cooking process, these volatile ﬂavors are stripped and vented to the atmosphere. In many cases, ﬂavor components also may react to give secondary ﬂavor attributes. A preconditioning step may not be required for all extrusion processes. In general, preconditioning should be considered any time the in-barrel moisture content is expected to be above 15% or when raw material particles are

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particularly difﬁcult to hydrate. The preconditioner provides sufﬁcient retention time: to hydrate the raw material particles; to heat the raw material particles prior to being introduced into the extruder barrel; and to mix raw materials added in separate streams. Modern preconditioning technology provides for retention times up to 3 minutes, and in some cases even longer depending on the capacity of the system. The method of water addition is also an important part of preconditioning a product formulation. The residence time of the raw material in the conditioning cylinder after injection of water with steam permits the moisture to penetrate the grain particles uniformly throughout each particle. This equilibration provides a more uniformly cooked and textured ﬁnal product. Pressurized conditioning chambers normally provide approximately 1 to 3 minutes residence time at temperatures up to 115◦ C. Research indicates that pressurized preconditioners have a detrimental effect on the nutritional quality of food and feed products [4]. In addition, their design and operation are more complex. Atmospheric conditioning chambers provide from 20 to 240 seconds retention, during which time the product premix is preheated and moisture is allowed to penetrate the individual particles.

4.2.2. Screw and Barrel Conﬁguration A number of different screw segments and locks can be assembled on an extruder shaft, with their effects on the ﬁnal product ranging from minor to profound. As noted in the Hardware section, each segment is designed for a speciﬁc purpose. Functionally, some segments convey raw or preconditioned material into the extruder barrel, while other segments compress and degas the feedstock. Others must promote backﬂow (reduced conveying efﬁciency), shear and numerous other tasks. Where kneading is required, kneading screws may have one or multiple ﬂights (Figure 12.17). Some kneading screws may be “cut ﬂight” (have interrupted ﬂights) to improve dispersive mixing, increase backﬂow, or increase mechanical energy dissipation into the extrudate. The cut ﬂight screw elements reduce conveying efﬁciency and thus add residence time to the product being conveyed through the barrel of the extruder. The screws may also have various pitches (Figure 12.18) to increase residence time within the extruder processing chamber without changing the free volume of the screw. The ﬁnal cooking screws segments may be conical. These conical elements cause a rapid pressure increase, a uniform pressure distribution around the screw periphery and dampening of any pulsations that may be present in the ﬁnal section of the extruder. The process stability and feed uniformity gained by the twin screw is not particularly important when producing a chunk-type ﬁnal product, but it is extremely important when producing an intricately shaped ﬁnal product. Color of the ﬁnal product may be more uniform, and production of burnt or overcooked

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SINGLE FLIGHT

DOUBLE FLIGHT

FULLY INTERMESHING COROTATING SCREWS.

Figure 12.17 Fully intermeshing, single- and double-ﬂight co-rotating screws for twin-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

product will be reduced. Product density is generally more consistent. Thus, package ﬁll is more uniform. Heads, or the barrel segments that surround the screws, also affect shear energy input and mechanical energy dissipation within the barrel of the extruder. The barrel segments may be ribbed to increase the function of each speciﬁc extruder segment. For example, ribbing may be used to increase the volume in the inlet of the extruder barrel for feeding higher capacities. Special attention should be given to the advantages of using a conical section at the discharge of an extruder barrel. This has been fully discussed in the previous Hardware section of this chapter. SCREW PITCH

PITCH = 0.5

PITCH = 0.75

PITCH = 1.0

Figure 12.18 Screw segments with different pitches for co-rotating twin-screw extruder. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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All cooking extruders generally have three processing zones: feeding, kneading and ﬁnal cooking (Figure 12.19). In the feeding zone, low-density discrete particles of raw material are introduced into the extruder barrel inlet. This often preconditioned material is then transported into the interior of the extrusion processing chamber. The ﬂow channel of the screw is typically ﬁlled with low-density material. The density is low because of the air trapped in the incoming material and due to its granular nature. The incoming material is compressed slightly, expelling the air. Water is typically injected into the extruder barrel in the feeding zone to facilitate development of texture and viscosity, and to enhance conductive heat transfer. The compression started in the feeding zone continues into the kneading zone, and the ﬂow channels of the extruder are ﬁlled to a higher degree. Within this zone, the extrudate begins to lose some of its granular deﬁnition, density increases, and pressure builds. The mechanism of shear begins to play a dominant role because a ﬁlled barrel condition exists. Barrel pressure is modest in the early part of the kneading zone and, when desired, permits the injection of steam at pressures of between 5 and 9 atmosphere (73.5–132 psig). The steam carries thermal energy and moisture into the extrudate. The discrete particles of material begin to agglomerate because of increasing temperature resulting from conduction, direct steam injection and dissipation of viscous energy resulting from friction. Steam brings additional energy into the extrudate, thus increasing capacity and reducing energy costs. Steam is typically injected at 7–9 bar (103– 132 psig), and water at 2 bar (30 psig). The extrudate begins to form a more integral ﬂowing dough mass, moves past its glass transition temperature, and typically reaches its maximum compaction as it moves through the kneading zone. The shear in this area of the extruder barrel is moderate and the extrudate temperature continues to increase. The ﬁnal cooking zone of the extruder barrel is the area where transformation into a homogeneous plasticized mass and texturizing occur. Temperature and pressure typically increase most rapidly in this region, and shear rates are at their highest because of the extruder screw conﬁguration and maximum compression of the extrudate. The pressure, temperature and resulting ﬂuid viscosity are such that the extrudate, now above its melt transition temperature, is expelled from the extruder die to yield the desired ﬁnal product texture, density, color and functional properties. The single-screw extruder has some deﬁnite process limitations in the food processing industry. The most obvious limitation centers around its ability to transport sticky and/or gummy raw materials. The single-screw cooking extruder is further limited in its ability to process materials that become extremely sticky or gummy during heating and compression, or that react adversely to the shear environment of the cooking extruder. Process instability on the single-screw extruder generally manifests itself in product surging—that is, non-steady-state ﬂow at the extruder die.

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Figure 12.19 Processing zones, single- and twin-screw extruders. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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4.2.2.1. Energy Conversion Transformation of mechanical energy into heat necessary for cooking becomes increasingly difﬁcult as lipid levels in formulas exceed 7% because fat acts as a lubricant. Twin-screw extruders can process formulas with more than 25% internal lipid content while maintaining high levels of mechanical energy conversion. This is made possible by speciﬁc screw conﬁgurations that are not feasible in single-screw extruders. Steam injection into the extruder barrel is also a contributing factor to cooking formulas high in fat content. Although steam is injected into the barrel of single-screw extruders, and fat can be added to a total formulation in excess of 17%, twin-screw extruders are able to process higher fat content formulas more consistently. Use of a twin-screw extruder may also result in better lipid binding, thus less exuding of fat from the product during handling and storage. This may only have application if producing a high caloric density snack.

4.2.2.2. Costs Extruder operating costs increase exponentially as in-barrel processing moisture is decreased below 27%, and levels off above this level. The major factors contributing to increased operating costs are electrical energy cost for the main drive motor and cost of barrel replacement components. Total operating costs of the extrusion cooker, both single-screw and twin-screw, increase by about 2.7 times as process moisture is decreased from 27% to 15%, with electrical costs increasing about 4.7 times and wear costs increasing 4.8 times. When producing direct-expanded snack foods, higher-moisture-level extrusion is not an option. It is important to note the exponential nature of the increase in electrical and wear costs, compared to merely a linear decrease in water, steam and drying cost as the processing moisture is decreased from 27% to 15%. The nature and magnitude of these two inverse-cost relationships permit rapid capital recovery of the investment cost of the drying equipment required when processing at moisture levels of 22–29%. The point to be understood here is that reducing moisture during extrusion to reduce drying cost may not result in an actual overall cost reduction but may increase it.

4.2.3. Die Conﬁguration Many times, the effects of die designs on the functional properties and quality of ﬁnal products are overlooked. Die shear rates may be altered dramatically by changing from a single die with one opening to a triple or quadruple die with multiple openings and ﬂow channels. When changing from a single-die

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conﬁguration to a multiple-die conﬁguration, the degree of barrel ﬁll is also increased. In general, dies with high shear rates cause starch-bearing products to have increased stickiness, increased water absorption and increased solubility.

5. EXTRUDED PRODUCTS Many processes may be performed on a properly conﬁgured extrusion system. Several different types of snack foods and the uniqueness of each are described in the following. Second-generation (direct-expanded) snacks, such as corn curls, third-generation snacks (half products or pellets), co-extruded products, masa-based snacks, and crispbreads require somewhat different processing. Diverse grains, formulated in countless ways and subjected to varying process conditions, can be used to make a wide spectrum of extruded snack foods.

5.1. DIRECT-EXPANDED OR SECOND-GENERATION SNACKS Direct expanded, or second-generation, snacks make up the majority of extruded snacks on the market. Expanded snacks, with a variety of attributes, including high-ﬁber, low-calorie, and high-protein contents, can be produced. They are usually “light,” meaning they have low bulk density, and are seasoned with an array of ﬂavors, oils and salt (Figure 12.20). These snacks can be ﬁnished by frying (for example, corn or cheese puffs) or baked (for example, corn curls or chips). The basic process for making these snacks is the same: Properly selected corn meal is fed into an extruder at a constant rate. The meal is exposed to moisture, heat and pressure as it is transported through the extruder into the extruder die. As the material exits the extruder die, it expands due to pressure release and is cut to the proper length with a rotating knife, leaving the cylinder-shaped collet. At this point, the collets can be fried or baked (dried) to yield the desired snack.

Direct Expanded Snacks (2nd generation)

Figure 12.20 Second-generation direct-expanded snack foods. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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Typical Corn Meal Speciﬁcations for Fried Collets.

Property

Typical Analysis

Minimum

Maximum

12.0 7.0 0.7 0.5 0.4 79.4

11.0 6.0 0.5 0.4 0.3

13.0 8.0 1.0 0.6 0.5

0 0.3 8.7 43.0 45.0 2.0 1.0

0 0 4.0 30.0 35.0 0 0

0.1 2.0 18.0 50.0 55.0 8.0 2.0

% Moisture % Protein % Oil % Fiber % Ash % Nitrogen-Free Extract % Granulation, U.S. Sieve On 16 On 20 On 25 On 30 On 40 On 50 Through 50

5.1.1. Fried Expanded Collets The original snack food produced using an extruder, still familiar today, is the fried collet made from corn meal or grits (Table 12.4) and coated with cheese powders and ﬂavors. The extruded collets sifted to removed ﬁnes, fried in vegetable oil and seasoned (Table 12.5). The manufacture of corn puffs requires several major pieces of equipment, described as follows: r A blender, normally of a vertical design, moisturizes corn meal while a

vertical auger moves the meal from the bottom to the top of the mixing tank, and water is added in measured amounts. r Bucket elevators or similar conveying systems transfer moisturized cornmeal from the blender to the holding hopper of the extruder. r The cornmeal passes through the extruder, where it is compressed. The work performed on the cornmeal during extrusion is transformed into heat. The pressure and heat cause the cornmeal to form a partial visco-amorphic TABLE 12.5.

Typical Cheese Coating Recipe.

Ingredient Extruded corn product Coconut oil Cheddar cheese powder Acid whey powder Cheese flavor Salt Total

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Formula A

Formula B

57.8% 28.0% 7.0% 3.5% 3.5% 0.2% 100.0%

66.0% 24.0% 9.3% --0.7% --100.0%

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mass. As this material passes through the heads, the superheated moisture instantly vaporizes, causing pufﬁng of the cornmeal. A perforated tumbler removes most small pieces and unpopped meal from the good collets before frying. The fryers are designed to remove moisture and introduce oil into the collets. Both direct-ﬁred and heat exchanger-type fryers work well. Because of the short residence time the product is in the fryer, proper sizing is critical to achieve correct oil turnover rates. The coating tumbler is designed for a uniform and positive ﬂow of product down the length of the unit. Longitudinal ﬂights turn the bed of collets over while liquid cheese slurry is dispensed inside the tumbler. The cheese mist system includes controlled temperature, hot water-jacketed kettles equipped with mixers and recirculating pumps where cheese, oil and salt are homogeneously mixed together. The temperature of the cheese/oil mix is held at 49–55◦ C, 120–130◦ F.

5.1.2. Baked (Dried) Expanded Collets or Shapes An example of a second popular expanded, extruded snack is the baked collet, or corn curl. Spinoffs of the expanded snack use other cereal grain ﬂours, tuber ﬂours, ﬁbers and proteins. Dried potato is commonly added to corn or rice for making potato-ﬂavored snacks. Snacks containing high levels of potato ﬂour or granules (greater than 65%) are better suited for the twin-screw extruder because of the sensitivity of potatoes to heat. The bland ﬂavor of rice makes it desirable for preserving more expensive ﬂavor attributes (Figure 12.21). Fiber, cellulose, bran and fruit-derived pectins may be blended with cereal grain or protein blends to make healthful snacks. Fiber and proteins may each be added at 20% levels to expanded snack formulations. Higher levels may be added when more soluble ﬁbers and proteins are used. Low levels of lowmolecular-weight starches also counter the effects of ﬁber and protein additions. Extrusion-reacted ﬁber or bran yields softer-textured snacks when high levels of ﬁber are desired. The moisture content of the extruded product is normally between 8 and 10% on a wet basis and requires additional drying to produce the desired product crispness. Temperatures of 150◦ C (300◦ F) and retention times of 4 to 6 minutes are used to lower the moisture content of these products to 1–2%. Product ﬁnes (particulate matter separated from the ﬁnal product shape due to handling) that have been produced during conveying and drying must be separated before coating the extruded products with ﬂavors. The ﬁnes tend to absorb ﬂavor and oil coatings and agglomerate into undesirable forms. The most popular ﬂavoring for extruded corn-based snack products is cheddar cheese. Two methods of application are most common. When using the dry-ﬂavor application method, the extruded product is ﬁrst sprayed with

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DIRECT EXPANDED SNACK FLOW DIAGRAM Figure 12.21 Flow diagram for direct-expanded snacks. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

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vegetable oil and then dusted with a variety of dry ﬂavors or seasonings. Alternatively, the oils, ﬂavors and spices may be mixed together in a tank and the slurry applied to the extruded snack as it is tumbled in a ﬂavor-application reel (Table 12.5). The particle size of corn meal or the cereal grains used may inﬂuence the texture and mouth feel of the ﬁnal snack. The degermed cornmeal most commonly used in extrusion systems today has the same particle-size analysis and speciﬁcations as listed in the previous section (Table 12.4). Many other grades or granulations of degermed corn meal are available. If a ﬁner texture or cell structure, or softer bite, is desired, the snack producer may decide to use raw materials having smaller particle size. On the other hand, crunchier snacks, with larger cell structure, also appeal to consumers. A coarser granulation of degermed corn grit is used for this texture. Premoistening or preconditioning of coarse granulation ingredients may be required to eliminate the grittiness in the ﬁnal product. A large amount of ﬂour or ﬁnes in coarse meals is undesirable for extrusion, especially when using a single-screw extruder. Flour tends to segregate in the feeding system and in the inlet portion of the extruder barrel. When water is added in the extruder barrel, the ﬂour absorbs the water quickly, leaving less moisture available for the coarser particles, and may disrupt the product and cause ﬂuctuations in its quality. Typical processing conditions for second-generation snack products were listed in the software section of this chapter.

5.2. THIRD-GENERATION SNACKS OR PELLETS Third-generation snack products (3G) or “pellets” are sometimes referred to as “semi-” or “half products.” Following extrusion cooking and forming into dense pellets, the pellets are dried to a stable moisture content to assure stability during storage. Then, they are distributed to processors, where they are puffed or expanded by immersion in hot oil or hot air pufﬁng. They are also sold for frying or pufﬁng by the consumer at home, or in restaurants for immediate consumption. After the ﬁnal pufﬁng step, the products can be salted or ﬂavored externally. Some products contain ﬂavoring within the pellet itself. Stability during storage and the high bulk density of the packaged, non-expanded thirdgeneration snacks enhance their marketing potential. Newer variants of the original third-generation snacks now can be expanded or puffed by infrared or microwave heating. Raw materials used for 3G snack products are mostly starch-based. Speciﬁcations for these ingredients are dependent on the method or equipment chosen for extrusion of the pellets. Production of pellets may be divided into two processing classiﬁcations: cold forming extrusion or cooking extrusion. If cold-forming extrusion is used, ingredients other than potato ﬂour must be pregelatinized for optimal expansion of the ﬁnal product.

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Pregelatinized ingredients are usually costly. Thus, the increased cost of cooking extruders is often recovered within the ﬁrst or second year of manufacturing of a snack pellet. After the dry ingredients have been uniformly blended, it is suggested that liquid ingredients such as shortenings, ﬂavors, or water be applied as sprays in the batch mixer or injected into the preconditioner or mixing cylinder of the extruder. It is important that the raw materials be completely cooked in the extrusion process unless the formulation contains pregelled starches. A “good cook” is deﬁned as the combination of temperature, residence time, and moisture content during extrusion to fully gelatinize the starchy components in the formulation. The temperature proﬁle in the extruder (which is dependent on ingredient characteristics, extruder conﬁguration and processing conditions) is substantially above the gelatinization temperature of the starches found in the formulation unless they have been precooked. Typical extrusion-cooking processing conditions include 100–150◦ C (212– 302◦ F), barrel temperatures, 25–30% moisture content, and 30–45 seconds residence time. The speciﬁc mechanical energy input is usually low as the main portion of energy required for gelatinization of the starch is supplied from thermal energy. Thermal energy sources can include steam, hot water or other thermal ﬂuids circulated through the jacketed barrel to provide external heat, and hot water injected directly into the product in the mixing cylinder or extruder barrel. The segmented barrel of the cooking extruder increases product versatility. Various heads, screws and steamlock designs can be incorporated into the conﬁguration to produce the desired cooking conditions. The most common setups are conﬁgured to provide a moderate-to-low shear input during the extrusion cooking step. Following the cooking step, the material is passed into a forming extrusion zone, which cools and densiﬁes the cooked, plasticized mass. The forming step may be accomplished in a separate extruder or in a secondary zone of the cooking extruder. This portion of the process has a low-shear conﬁguration containing a minimum of restrictions except for the ﬁnal die. The forming zone usually is characterized by positive forward transport conﬁgurations complemented by maximum cooling to reduce product temperature to about 70–95◦ C (158–203◦ F). The cooled, visco-elastic product is shaped by the ﬁnal forming die, which contains a sufﬁcient open area to prevent expansion of the cooked dough. Various shapes of third-generation snacks before and after frying are found in Figure 12.22. The cooked, densiﬁed, shaped products extruded through the forming die contain 20–25% moisture after a slight ﬂashoff during the small decompression step. Proper drying reduces the moisture content of the pellets to approximately 12%. The drying step is very critical in the production of good-quality thirdgeneration snacks. Drying temperatures of 70–80◦ C, 158–176◦ F, and retention times of 1–3 hours are employed in this important production step.

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Third Generation Snacks (3G, pellets)

Figure 12.22 3G snack products in pellet and expanded forms. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

If the drying time is rushed using normal drying conditions, some of the moisture in the extruded pellet is distributed close to the periphery of the product, but most is located in the center of the pellet. Experience has shown that third-generation snack pellets dried in this manner fry up or expand better following a holding period of approximately one day during which the moisture equilibrates by migration. This equilibration process may be accelerated by proper temperature and humidity control during drying. One option is to slightly overdry the outer portion to allow products to achieve a lower internal moisture content, then increase the humidity conditions in the dryer to increase the moisture of the exterior to match the interior moisture, thus reducing total equilibration time required. Prior to consumption, third-generation snacks are expanded in hot oil or air. The frying procedure involves complete immersion of the pellet in 150–200◦ C (302–392◦ F) oil for 15–30 seconds. The expansion of pellets in hot air is gaining popularity because of the low caloric content of the ﬁnal product. The frying process can be divided into three phases. During the ﬁrst phase, some moisture moves from the periphery of the snack pellet into the oil. The snack pellet becomes warmer and more plastic in texture. Heat penetrates to the center of the pellet, and moisture throughout the pellet turns to steam. If the product is thoroughly cooked and properly formed, it will have gas-retaining

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Typical Formulas for Third-Generation Snacks

Hard, Crunchy Texture 92.0% Ground corn 5.0% Cornstarch 0.5% Monoglyceride 2.5% Liquid shortening

Soft, Frothy Texture 55.0% Cornstarch 30.0% Wheat starch 14.0% Tapioca starch 1.0% Deoiled lecithin

properties, which are critical to successfully producing the expanded product. Moisture in the product will turn into steam due to the high temperature of the oil and expand inside the product where it is trapped to form an expanded product with desirable cell structure and mouth feel. The temperature of the product immediately prior to frying has a noticeable impact on the texture of the ﬁnal product. This is most noticeable if equilibration of the moisture within the pellet is not complete. Extrusion systems for production of Third-Generation snacks are efﬁcient, economical to run, and make products with built-in marketing ﬂexibility due to long shelf life and high bulk density prior to frying or hot air expansion. Example recipes are shown in Table 12.6. Inclusion of monoglycerides, which are commonly used to reduce the stickiness of extruded products, reduces expansion during pufﬁng. On the other hand, tuber starches, such as tapioca or cassava, increase expansion during pufﬁng. This is due to the longer amylose chains (ﬁve times the length), which have better ﬁlm-forming properties. Meat (such as shrimp, crab, chicken, etc.), vegetable powders, yogurt or other ﬂavor-or nutrient-containing ingredients sometimes are added at levels up to approximately 30% while maintaining desirable ﬁnal product textures. Many third-generation snack pellets are made by extruding the cooked dough into the form of a sheet, passing the extruded sheet through embossing rolls to add texture to the surface, and then passing the sheet through a rotary die-cutting device, which cuts the sheeted product into individual pieces. Embossing is important for controlling curvature of the product during and after frying and minimizing the surface contact area to avoid pieces sticking together (Figure 12.23). Three-dimensional pillow-like shapes may be made using the same method by overlaying one sheet onto another prior to passing them through the ﬁnal rotary die cutting rolls. Fillings may be applied between the sheets to make ﬁlled products.

5.3. CO-EXTRUDED SNACKS Co-extrusion has been practiced for many years. Co-extruded snacks typically have an extrusion-cooked outer shell with a pumpable, but not freeﬂowing ﬁlling. Many variations of this concept may be made with dies and

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Figure 12.23 Rotary die cutter used in making various 3G product shapes. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

post-extrusion equipment such as rollers, stampers and belt-type cutters. Examples include exotic shapes, pinched ends to entrap the ﬁlling, multiple shells and ﬁllings and sandwich shapes (Figure 12.24). Few truly co-extruded snacks have found success in the consumer marketplace. In many cases, the shelf lives of the products have been short due to migration of moisture and/or lipids from the ﬁlling to the outer shell. However, technological advances in this area are providing ways to increase the compatibility of ﬁllings, with a wide range of different moisture and lipid contents, with outer shells. r Equipment. Choices of extruder type and conﬁguration are largely

dependent on the desired ﬁnal product characteristics. The process-control advantage of the twin-screw extruder makes it the best choice for this type of products. If a light-density cereal-based snack with a light-density cereal-based ﬁlling is the chosen product, two extruders conﬁgured for light-density snacks, sharing one common die, would be used. r Die Design. Co-extrusion dies may have several different design concepts. It is extremely important to fully understand the range of possible design

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Coextruded Products

Figure 12.24 Examples of coextruded (center-ﬁlled) products. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

considerations and their limitations. Normally, simple snack extrusion equipment may be ﬁtted for dies or sandwiching techniques (Figure 12.25). The extruder-cooked portion of the snack ﬂows directly through the die parallel to the direction of ﬂow through the extruder barrel. The ﬁlling is ﬁrst pumped into the die, perpendicular to the ﬂow of the outer shell extrudate and into the center of the extrudate ﬂow region, where it turns 90◦ to ﬂow with the shell extrudate. The amount of ﬁlling (within a limited range) pumped into the outer shell controls the outer product dimensions and the ﬁlling-to-shell ratio of the ﬁnal product. Pulling or stretching the extrudate also may be used to control the wall thickness of the outer shell, thereby affecting the ﬁlling-to-shell ratio. Careful consideration should be given to ﬁllings that are heat-sensitive or contain high lipid content. Temperatures may reach 140--150◦ C (284--302◦ F) when extruding highly expanded outer shells. Fillings injected through the die at these temperatures may experience a temperature rise of 30◦ 50◦ C (54–90◦ F) unless special insulating materials are used. The temperature rise does not come from the die alone, but also from the heat being transferred from the extrudate into the ﬁlling.

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FILLING PASTRY TUBE

PRODUCT ENTRANCE

FILLING

PRODUCT ENTRANCE

FILLING PASTRY TUBE FILLING

Figure 12.25 Example of coextrusion die for making center-ﬁlled snack foods. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

5.4. MASA-BASED SNACKS, INCLUDING TORTILLA CHIPS The demand for precooked masa ﬂours in the United States has increased in recent years as many of the ethnic foods initially consumed in the Southwest gain popularity. In response to the demand, manufacturers have sought more efﬁcient and cost-effective ways of producing precooked masa ﬂours. The traditional alkali corn-cooking procedures for preparing masa are being replaced by more efﬁcient, large-scale operations where the corn is cooked and ground immediately with little or no steeping. Several steps are involved in preparing masa in a cooking extruder and ﬁnal products when using bulk corn: r r r r r r r r r r

Bulk corn storage Grinding Mixing with water Extruding Drying Grinding Mixing with water and ﬂavors Cold extrusion Frying Packaging

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r Corn Preparation. Corn from bulk storage is ground through a 1.5 mm

screen and transferred to a batch or continuous blending or mixing system.

r Mixing. The ground corn is kneaded with water and 0.5–1% calcium

hydroxide, Ca(OH)2 , to a moisture content of 20–25%. Normally, a 15-minute mix time allows sufﬁcient moisture penetration. The exact moisture and calcium hydroxide levels depend on the variety of corn and the type of calcium hydroxide used. r Extruding. The extrusion process consists of several steps: —Bin and feeder: The feeder controls the rate of product ﬂowing through the extrusion process. This is very important for stability and a uniform ﬁnal product quality. —Preconditioning cylinder: Live steam is injected into the mixing cylinder to temper the corn prior to extrusion to ensure that all particles have been fully penetrated by moisture. Temperatures of 70–75◦ C (158–167◦ F) are desirable. —Extruder cooking: The preconditioned corn is extruded through a 6–9 mm die oriﬁce (the number of holes is dependent on the capacity of the equipment) with a minimal amount of mechanical shear energy input. Generally, the temperature of the extruder barrel is approximately 120–150◦ C (249–302◦ F) and pressures between 10–15 atmospheres (147–223 psig). —Cutting: As the extrudate exits the die oriﬁces, it is cut to lengths by a rotating knife and conveyed mechanically or pneumatically to a dryer. —Drying: The cooked, moist extrudate must be dried to approximately 10–12% moisture. The drying is done rapidly to produce a non-sticky premium-quality precooked masa. Temperatures of 150◦ C (302◦ F) for 15 minutes residence time are commonly used. —Grinding: After drying, the processed corn is ground through a 40- or 60-mesh screen and stored for packaging. r Cold Forming. The ground instant masa is hydrated and formed into shapes for frying. More recently, processes have been developed to streamline production of masa and minimize production of wastewater steams or efﬂuents. This is accomplished by adding dry-milled corn fractions in the proper proportions to mimic the composition of the original masa (including alkali), fully hydrating the masa to greater than 35% moisture and ﬂash-drying the hydrated masa to reduce the moisture content and cook the corn particles to match the characteristic of the original masa process. These newer methods of producing corn chips, tortilla chips and other masabased snacks produce products that are quite different from traditional masa production. See Chapter 4 for details on masa production, especially dry masa

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ﬂours. The precooked masa ﬂour may simply be tempered with water and formed into a shape using a forming extruder. The formed snacks are then fried, ﬂavored and packaged for sale to the consumer.

5.5. FLAT BREAD, CRISPBREAD AND CRACKERS Of European origin, crispbread has become an international product. Similar to toasted bread, it has become popular in the expanding health food market. Traditional methods of producing crispbread involved rolling and sheeting a dough followed by baking. Introduction of the extrusion process, using either twin-screw or single-screw extruders, has complemented and often replaced the traditional methods of production. Extruded ﬂatbreads, or crispbread, can be produced economically in a greater variety of forms and ﬂavors to suit local tastes than traditional crispbread. The extruded crispbread can be processed to almost any texture, toasted and even sandwiched with various ﬁllings to broaden the product possibilities. Due to process ﬂexibility, crispbreads vary from one manufacturer to another in size, shape, degree of toasting, color, texture and ingredients used. By virtue of their low density and light texture, crispbreads can be designed as low-calorie products that appeal to weight watchers. Although crispbread can resemble biscuits in many ways, it is generally a direct-expanded extrudate. Manufacturers of crispbread, with the support of ﬂavorists, nutritionists and food scientists, are improving the market potential. The current market favors the savory end of the ﬂavor spectrum, but sweetened varieties of crispbread are marketed. These sweetened products may range from simple chocolate-enrobed crispbreads to those sandwiched with a cheese or jam layer. Although various shapes have been introduced, the most common is a ﬂat, rectangular-shaped portion. Large crispbread sections may possess creases, which allow portions to be snapped off and consumed as a ﬁnger food with savory dips. Crispbreads may also be enriched with proteins and dietary ﬁber sources to enhance the products and to appeal to the health-minded consumers.

5.5.1. Process Description Contrary to traditional processing methods, extruders cook, cool, shear, mix, knead, shape and form the product in one operation. The raw materials, including ﬂours and powder-like ingredients, whole grains and/or meals, are preblended and metered into the extruder. The most common extruder utilized is the co-rotating twin-screw cooking extruder. Although blends of ﬂour, milk powder, vegetable oil, sugar and salt are metered as a dry mix into the extruder, liquids such as syrups or oils may also be injected into the extruder barrel to vary the formulation. The mix is cooked and formed in the extruder under low moisture (10–15%) and high temperature

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(120–175◦ C, 248–347◦ F) to yield a light, crispy product. Mechanical energy inputs are generally high, and output capacities range from 90–15,500 lbs/h. The extruder discharge usually is equipped with a single- or multislotted die with plastic or teﬂon guides on the outboard side. The strands of extruded product are conveyed to a cutting unit and then dried or toasted to 4% ﬁnal moisture content. Occasionally, the strands are continuously extruded into a traveling band oven, at temperatures up to 750◦ F. This baking or toasting step is very short (5–15 seconds), achieving the desired color development and moisture content (4–6%). A device at the end of the toaster cuts the crispbread into the required lengths, which are then transferred by conveyors to packaging equipment. The speciﬁc density of the crispbread is very light. The product usually is stacked in the retail package to avoid breakage and allow portion selection.

5.5.2. Formulation To improve the nutritional appeal of crispbread, various sources of bran or ﬁber are added to base formulations. In Europe, different types of crispbread are produced with dietary ﬁber levels of about 12%. A recipe for crispbread may include the following ingredients for increasing dietary ﬁber content: r 60% cereal ﬂour or starch r 30% wheat bran r 10% wheat gluten A more typical crispbread formulation is: r r r r r r

68% wheat ﬂour 20% rice ﬂour 5% sugar 4% dried milk 1% salt 2% vegetable oil

Increasing the protein, fat, or ﬁber levels tends to decrease expansion and yields a harder bite and texture. Conversely, increasing the starch level increases expansion and yields a softer bite.

6. NEW DEVELOPMENTS: FUTURE OF SNACK FOODS EXTRUSION

6.1. SUPERCRITICAL CARBON DIOXIDE PUFFING Food scientists are always seeking new and different product textures. In the past, extruded products were limited to cell structures expanded by water

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Normal Steam Expansion

CO2 Expansion

Figure 12.26 Micro-cellular structures of steam and supercritical carbon dioxide-puffed corn snacks. (Wenger Manufacturing, Inc., Sabetha, Kansas.)

vapor. By using supercritical carbon dioxide as the driving force for expansion, products with extremely ﬁne cell structure can be produced (Figure 12.26). Altering product cell structure is only one of many applications for this technology. For example, because of the harsh conditions associated with extrusion, heat-sensitive dairy products traditionally have not been used as ingredients in extrusion processing. However, development of this new process, supercritical ﬂuid extrusion (SCFX), “exploits the thermosetting properties of whey proteins to generate and control unique morphological microstructures within extruded products, such as cereals and other snack food” [5]. Researchers have used supercritical carbon dioxide under high pressure to expand cereal products. Cereals that are expanded by supercritical carbon dioxide puff at lower temperatures than if expanded by steam, thus preserving the heat-sensitive whey proteins. Flavors or nutraceuticals may be solubilized, carried with the supercritical carbon dioxide used for expansion and deposited into

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the extrudate as the pressure is released to subsupercritical conditions prior to exiting the die. Dairy solids contents in cereals have been increased to about 4.0% by weight. The extruded product showed 23% water absorption in a 100% relative humidity atmosphere, compared to 36% for the control produced by conventional extrusion techniques. This difference is due to a smooth product surface with a porous interior that has a non-communicating cell structure. It is conceivable that these products will maintain crispness and crunchiness in more adverse environment conditions. It is possible to use heat-sensitive ingredients and minimize breakdown of milk proteins and starches with low-shear, high-moisture techniques, but the high moisture tends to collapse the extruded product, and the expanding carbon dioxide often ruptures weak cells. On the other hand, thermosetting ingredients such as whey proteins can strengthen cells. The structure can then be set by post-extrusion drying.

6.2. CONCLUSION This chapter has only touched the surface of the vast potential for development of many new and innovative snack food products using extrusion technologies. The important point to remember is that extrusion is a compact, ﬂexible and economical tool that may be used to design and shape the products of the future. Its rapid acceptance in food and snacks processing during the past several decades portends a growing role in the future.

7. REFERENCES 1. Thomas, D. J. and W. A. Atwell, 1999. Starches. Eagan Press, St. Paul, Minnesota. 2. Rogols, S. and R. J. Anderson, 1987. Effect of Maltodextrins on the Extrudability of Soy Fiber. 72nd Annual Meeting, November. American Association of Cereal Chemists, St. Paul, Minnesota. 3. Hauck, B. W. and G. R. Huber, 1989. Single vs twin screw extrusion. Cereal Foods World, 34(11):930–939. 4. de Muelenaere, H. J. H. and J. L. Buzzard, 1969. Cooker extruders in service of world feeding. Food Technology, 23:345–351. 5. Kuntz, L. A., 2000. Breakfast cereals grow up. Food Product Design, 10(5):85–120.

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CHAPTER 13

Perfect Pretzel Production

E. TERRY GROFF

1. THE PRETZEL: A SNACK FOOD WITH 800 YEARS OF HISTORY

T

pretzel is one of the world’s oldest snack foods. The word pretzel stems from the Latin, pretiola, or little reward. According to popular legend, it was invented by a monk in the twelfth century to be given to children as a reward to those who said their prayers correctly. Legend also has it that the crossed center of the pretzel form represents the crossed arms of prayer, the early Christian sign of the cross, which predates the folded hands we are familiar with today. The pretzel appears on the coat of arms of the bakers of Vienna, ﬁrst awarded in 1529 [1]. Pretzel bakers, up early to bake their wares for the day, heard the Turks tunneling under the city walls and gave the alarm that saved the city. A grateful prince awarded a coat of arms to the bakers (Figure 13.1), thus establishing the pretzel as the symbol of bakers throughout Europe. Today, all over Europe, but especially in Germany, Switzerland, and Austria, the sign of the pretzel signiﬁes a bakery—which may or may not make the pretzels displayed on its sign. The pretzel has taken many forms during its 800 years of evolution and is manufactured and sold in six of the world’s seven continents. It is the third largest selling salty snack in the United States, with sales totaling $1.3 billion in 1998 [2]. HE

2. TYPES OF PRETZELS Pretzels are divided into two broad categories: soft and hard. Soft pretzels, the largest of all pretzel types, are traditionally shaped and consumed as fresh

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Figure 13.1 Pretzel maker’s and baker’s coat of arms. First awarded in Vienna in 1529; currently used throughout Europe.

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TABLE 13.1.

Item

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Characteristics of Selected Pretzel Types. Size 4 × 5

Standard soft Stadium soft 8 × 8 Regular twist 3 × 3 × 3.75 Mini 1.5 × 1.5 × .187 Bavarian 3 × 3 × .5 Hanover hard 3 × 3 × .6 Sticks 3 × 4 Nuggets 1 × 1.5 Logs 2.75 Rods 7 Specialty shapes ---

Unit Weight Count per Pound Moisture (%) 3 oz 6 oz 2.5 g 1.5 g 15 g 16 g 1.0 g 2.8 g 2.6 g 14 g ---

5.3 2.7 120 303 30 26 454 162 162 32 200--300

18--23 18--23 2.5 2.5 2.7 2.7 2.0 2.5 2.5 2.5 2.5

bread-like snacks. They are often baked at the point of sale, served fresh, and have a shelf life measured in hours. Hard pretzels are smaller, crispy and consumed like breadstick snacks. Hard pretzels have a shelf life of six months in good packaging. Some of the important characteristics of pretzel types are listed in Table 13.1. The size and shape of a pretzel are signiﬁcant and are at the core of why certain shapes are valued by individual consumers. Unlike other snack foods, the pretzel has the combination of alkaline exterior and acidic interior. The two radically different pH levels give pretzels their unique and characteristic ﬂavor. It is the unique combination of shape and composite pH that attracts pretzel eaters.

3. FORMULATION The pretzel is a simple and basic food. The most basic formula consists of only ﬂour, yeast, salt and water. Malt is often added for both color and sweetness. Hydrogenated soybean oil is commonly added as a fat to soften the texture.

3.1. SOFT PRETZELS Soft pretzels are similar to fresh bread, and bread ﬂour is the most common ﬂour used in their manufacture. Like bread, soft pretzels require a gluten structure to capture the carbon dioxide from yeast fermentation and sufﬁcient protein to resist staling. Hard spring wheat ﬂour, with a protein content of 11–14.5%, commonly makes up 100% of the ﬂour component of soft pretzel formulas. Some manufacturers, in pursuit of lowering total manufacturing cost, blend in lower-priced, lower-protein winter wheat ﬂour (protein content 8.5–9.5%) and may further add soft winter wheat ﬂour with protein as low as 7.5% to the mix.

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TABLE 13.2.

A Typical Soft Pretzel Formula.

Ingredient Flour (14--14.5% protein) Nondiastatic malt Compressed yeast Water

Quantity (lb)

Baker’s Percent

200 4.0 3.0 90

100 2 1.5 45

Low-protein components reduce shear in the makeup equipment and make the dough more extrudable, but shorten the shelf life of the baked product because higher ratios of water to gluten tend to stale more quickly. Some soft pretzels are manufactured in a central location, par-baked and frozen, and ﬁnish-baked at the point of sale and served to the consumer right from the oven. In this case, the use of a portion of lower-protein ﬂour reduces cost to the manufacturer but does not create a perceptible difference to the consumer. Where shelf life is more critical, bakers obtain better results with formulas that use a single, high-protein type of ﬂour. A typical soft pretzel formula is shown in Table 13.2.

3.2. HARD PRETZELS Soft red winter wheat with a low protein content is the best ﬂour for hard pretzels because most are extruded through dies to create their unique shapes, and consumers want crispy textures. The use of ﬂour with stronger protein, while adding strength to the ﬁnished piece, also creates more shear in the extrusion equipment, which may damage the extrudate, create unsightly marks in the ﬁnished product and also slow production. Nondiastatic malt is a traditional choice of pretzel bakers for adding ﬂavor and color to the dough. It is a humectant and extends the shelf life of the ﬁnished product. When active yeast is used as a leavening agent, diastatic malt is often selected for its enzyme diastase which promotes yeast activity by modifying the starch in the ﬂour. Corn syrup is almost colorless when added to the dough and is useful in markets where brown-colored baked products are perceived as burned. Corn syrup is less expensive than malt, is sweeter and also acts as a humectant. Adding malt to the formula darkens both the interior and the exterior of the pretzel. Corn syrup is not as effective in bringing out ﬂavors in baking as malt, but is widely accepted in bakeries because it is easy to handle. As in all baked goods, fats have an enormous inﬂuence in pretzels. Added to the dough, fats impart tenderness, moisten mouth feel, improve structure and strength, provide lubricity, incorporate air and aid in the transfer of heat [3]. Generally, it is not necessary to add more than several percent fat to substantially change the product. Pretzels are one of the few snack foods that can be made without the addition of any fat and have among the lowest fat contents among snack foods.

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TABLE 13.3.

A Typical Hard Pretzel Formula.

Ingredient Flour (soft winter wheat; protein 7--9%) Hydrogenated soybean oil Diastatic malt Active dry yeast Baking soda Water

Quantity (lb) 200 8 4 2 .125 54

Baker’s Percent 100 2 2 1 .0625 37

Active yeast is the most commonly used leavening agent in pretzels. Instant active dry yeast is most popular in batch mixing processes, often added directly to ﬂour before hydration. In modern continuous mixing applications, yeast slurries are created by mixing either active dry yeast or compressed (crumbled form) yeast with water, which is then metered into the continuous mixer in correct proportion with other ingredients. Chemical leavening systems can also be used in pretzels although they do not create the glycerol, organic acids, aldehydes, fusel oil or alcohol ﬂavor precursors associated with yeast activity [4]. Ammonium bicarbonate is used by some bakers. Decomposition at room temperature is insigniﬁcant, but above 140◦ F (60◦ C) it decomposes into ammonia, carbon dioxide and water. When ammonium bicarbonate is used to leaven cookies and crackers, the cell structure porosity of these products allows full escape of the ammonia during baking [5]. In pretzels, however, bathing the pretzel in a mild solution of sodium hydroxide and water prior to baking creates a shell that can trap some of the ammonia. The trapped gas can create blisters, which later dry and break, resulting in an unsightly product. If the shell fails to break, the trapped ammonia also creates an off-ﬂavor. In general, the use of ammonium bicarbonate is not recommended in pretzel manufacture. A typical hard pretzel formula is shown in Table 13.3.

4. PROCESSING

4.1. MIXING Integrated machinery is available for fully automated production that produces consistent pretzels (Figure 13.2). Pretzel dough is a low absorption dough (35 to 45%) and is very stiff, requiring a great deal of energy to mix. Batch mixers have been designed speciﬁcally to handle pretzel dough [Figure 13.2(a)]. Processors typically increase the horsepower of their mixers when specifying pretzel mixing service. Batch mixers have the advantage of being very ﬂexible and able to handle a wide array of formulations and products. However,

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Figure 13.2 Schematic of automated pretzel-making line.

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they have the disadvantage of producing batches that must be mated to what is otherwise continuous production. One of the chief problems with batch mixing in pretzel manufacture is the change in dough viscosity that occurs during the time interval between batches. The change creates variations in the extruded weight of the product. As a result, underweight product may burn in the oven while overweight product will be underbaked, resulting in higher moisture content. In addition to batch mixers, continuous mix systems are available and very efﬁcient when long runs of one type of pretzel product are made. A typical continuous mix system consists of a gravimetric dry ingredient feeder for the ﬂour and mass ﬂow liquid metering for the water, fat, sugar and yeast slurry. Continuous mixers consist of a single shaft with a multiplicity of impellers and mixing blades mounted to achieve the desired actions of shear, stretching and pressure. At the completion of the mixing cycle, the dough emerges from the discharge oriﬁce, is cut to predetermined chunks and is ready for transfer to the extruder.

4.2. DOUGH-HANDLING SYSTEMS Fully automated dough-handling systems are capable of depositing dough into hoppers of many extruders without underﬁlling or overﬁlling. This greatly improves scaling weights and helps ensure accurate, continuous production. When integrated with batch mixers, the dough-handling system includes a loaf-making machine that receives the entire batch of dough and gently guides it by two slow-turning feed rolls through an oriﬁce, cutting the dough into the predetermined loaves ready for transfer to the extruder. From this point on, transfer of the dough is similar for batch or continuous mixing systems. The dough is deposited on a lift conveyor that consists of three belts, two of which operate vertically, trapping the loaves between them and delivering them to the shuttle. Because the loaves always are uniform in size, the lift conveyor is extremely reliable in lifting the dough piece to the shuttle. The shuttle is a self-contained transporter built on a frame that moves rapidly on rails over the hoppers of the dough-forming machinery, normally extruders. After receiving the dough, the shuttle moves away from its home station and carries the loaf to the speciﬁc hopper compartment or zone requiring dough, where it is discharged by a pneumatically operated clam-shell door, similar to the bomb bay doors found on military aircraft. The required dough level is determined by level control switches mounted in the shuttle support frame. An onboard programmable logic computer keeps track of requests for dough and sends the shuttle to the various hoppers on a ﬁrst-call, ﬁrst-served basis to each extruder hopper.

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Figure 13.3 Schematic of pretzel-forming extruder and cutter.

4.3. EXTRUSION The development of extruders [Figures 13.2(b) and 13.3] for forming pretzels marked a major breakthrough in high-volume production. The function of the extruder is to force the dough through an array of dies to produce rows of pretzels simultaneously. A nearly limitless array of die patterns are easily interchangeable on an extruder, giving it ﬂexibility to make all pretzel shapes with a single machine. Pairs of screws are driven through heavy-duty gear boxes by variable-speed motors. There may be as many as six pairs of screws per extruder, each pair fed by its own dough hopper. The screws transport the dough to be extruded into a primary compression barrel, then into a pressure equalization chamber and ﬁnally into the die that shapes the pretzel, cutting it with a high-speed cutter band stretched across the face of all the pretzel dies. The reciprocating knife is capable of making from 20 to 265 cuts per minute. Where shapes are small, it is sometimes possible to arrange the dies so that a single knife stroke cuts two pretzels at a time, thus doubling the output of the machine. A guillotine cutter [Figure 13.2(d)] is used to cut nuggets, sticks and rods. As with the dough-conveying system, the extruder is designed to transport and form the extruded dough without changing the properties of the dough. The short-barrel, low-pressure design reduces friction and thereby reduces stress on

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the dough (Figure 13.3). Augers are machined from a high-density, food-grade plastic for non-stick performance and minimum friction, and are lightweight, readily removed and easily cleaned. Production rates can range from 200 to 2,000 lb (90 to 900 kg) per hour, depending on the dough and the size of the pretzel being extruded.

4.4. PROOFING From the extruder, the cut pretzel drops onto a prooﬁng conveyor [Figures 13.2(c) and 13.4], which is designed to provide a holding period between the extruder and cooking—the next automatic process. The length of prooﬁng time of pretzel products depends on dough formulation. Traditional hard, thin, pretzels require approximately 5 minutes on the prooﬁng conveyor, while thick, Bavarian pretzels often require up to 20 minutes to properly proof. When higher levels of yeast are used for production of soft pretzels, prooﬁng times may be as long as 25 minutes. Because the prooﬁng conveyor is ﬁxed in length, the design is almost always a compromise. When a wide variety of pretzel products is to be produced on the same line, the prooﬁng conveyor must be long enough to handle the product requiring the longest proof. Prooﬁng conveyors are often operated under ambient conditions in the oven room, meaning there is no cover over the conveyor. Products requiring proofing temperatures in the 100◦ F (38◦ C) range usually need an enclosed prooﬁng conveyor conﬁgured with controlled heat and moisture. On the proofer, the extruded dough piece develops an outer sealing skin that later becomes important in creating the rich, lustrous appearance of the ﬁnished product. The rest period also allows time for the yeast action to round out the cut piece and increase its volume before entering the caustic cooker [Figure 13.2(e)].

4.5. COOKING Of all the operations in the production of pretzels, cooking is the most important and, in some ways, the most interesting. Proper application of cooking solutions to raw pretzels is the most taste-critical step in their processing. Time, temperature and alkalinity (pH) are the key factors in developing the taste in pretzels. In the cooker [Figure 13.2(e)], the formed pretzels remain in their production rows and are transferred through an automatically fed pool solution of hot water and sodium hydroxide. Here, the surface pH of the dough becomes alkaline. The contrast of the alkalinity of the surface and the acidity in the interior makes the taste of pretzels unique. During the 10 to 15 seconds that the product is exposed to the 200◦ F (93◦ C), 1.0–1.5% sodium hydroxide solution: r Surface alkalinity is changed. r The surface starches are gelatinized.

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Figure 13.4 Formed pretzel dough leaving extruder-cutter on prooﬁng conveyor.

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r Sugars in the surface are caramelized, creating the basis for the characteristic

lustrous brown appearance of the product when later exposed to oven heat during the baking cycle. Automatic cookers,with adjustable level controls that allow the immersion pool to be lengthened or shortened by the operator, are available. Although adjustable while in operation, the system maintains a liquid level within a tolerance of 0.01 in. (0.254 mm). Also, the concentration of sodium hydroxide solution does not vary more than plus or minus 1%, and immersion time does not vary more than plus or minus 10%. In many cookers, a hydrometer is used to control the concentration of sodium hydroxide. Each time the water control system calls for more solution, the ﬂow of water through a venturi draws a metered amount of 50% alkali solution and combines it with the entering water stream. Different concentrations of sodium hydroxide can be obtained by changing the size of the oriﬁce in the venturi tube. Cooker heat is provided by ﬁring gas through a totally enclosed immersion tube designed to transfer the maximum BTUs directly into the surrounding solution. The belt and rack system can be raised out of the tank of the automatic cooker at the touch of a control button. In the lifted position, operators have clear and virtually instant access to the immersion tube and the sloped tank bottom. The cooker has a fully enclosed design that keeps steam vapor and dust out of critical components as a sanitation feature. The full hood may be raised or lowered automatically. Soft pretzel products with higher yeast content tend to ﬂoat in the alkaline solution of the cooker. In those cases, the formed pretzels are conveyed either beneath a waterfall-type curtain of sodium hydroxide solution, or through the tank under a holddown top belt.

4.6. SURFACE SALTING After cooking, the wet, steamy pretzels are conveyed under a steady curtain of salt [Figure 13.2(f)] delivered by a specially designed roll. Excess salt falling through the wire-mesh conveyor belt is automatically cleaned of large particles and dust and recirculated to the dispensing device. The salting process is bypassed in making salt-free products. Typically, large pretzels are salted with large grains of salt and smaller pretzels with a smaller size.

4.7. BAKING After the very short salting process, the product proceeds to the baking chamber. The pretzel oven operates at maximum efﬁciency by close integration of chamber headroom, moisture exhausting and temperature control. The efﬁciency arises from the conﬁguration of two separate chambers, one above the

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TABLE 13.4.

Item Regular thins Mini pretzels Soft pretzels Bavarians Rods

Oven Conditions Required for Manufacturing Various Pretzels. Temperature (3-zone oven) 550/500/500◦ F 550/500/500◦ F 600/575/500◦ F 350/350/325◦ F 325/350/325◦ F

288/260/260◦ C 288/260/260◦ C 315/302/260◦ C 177/177/163◦ C 163/177/163◦ C

Time (minutes) 2.8 2.5 4.5 8 10

other—the oven above the dry kiln—each equipped with a traveling wire-mesh belt and each operating independently in the opposing direction. The oven/drying kiln is constructed in modular sections coupled together to achieve speciﬁc length requirements. Oven bands are available from 39 in. (1 m) to 80 in. (2 m) wide. A wide variety of bake times and temperatures are used in pretzel baking. The breadth of oven performance required for pretzel manufacture is shown in Table 13.4. Temperature control is essential. For example, if the dough temperature increases too rapidly, the surface of the product will dry before the internal moisture is driven off, resulting in formation of blisters on the surface. Each pretzel product has a heat process proﬁle peculiar to its particular shape and/or formula. For optimal results, the oven must have the capability of matching its heat proﬁle with the requirements of the respective pretzel type. In the past, many bakers used direct-ﬁred ribbon burners installed above and below the oven band. Although generally inefﬁcient, well-designed, direct gas-ﬁred (DGF) ovens have broad capabilities for matching product proﬁles because of the multiplicity of burners and ability to operate each one at a different setting. However, DGF ovens are difﬁcult to adjust from product to product and have the further downside of variability in zone temperature. Today, the most popular ovens used in making pretzels are hybrid designs that combine radiant and convective energy control in the ﬁrst zone and forced convection in succeeding zones and in the dry kiln. The ability to change the proportion of radiation and convection in the ﬁrst zone enables pretzel bakers to easily adjust their oven proﬁle to the requirements of almost any product. Since the heat input to these ovens is computer controlled, there is little problem with repetition of setup as the baker moves from one product to another.

4.8. DRYING After the pretzel emerges from the oven, it is lustrous brown in color. However, the moisture content has been reduced to only 8 to 10%, and further drying, not baking, is required. The pretzels are allowed to follow the band over the main drive pulley where a knife frees them from the band, after which they

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gently cascade down onto the dry kiln wire-mesh band below. The kiln band travels in a direction opposite to that of the baking band where it enters the completely separate thermal structure of the drying kiln [Figure 13.2(h)]. At this point the product no longer remains in rows,but is allowed to form a bed on the dryer band. Drying time varies between 6 and 45 minutes, at temperatures between 240–270◦ F (115–132◦ C).

4.9. FINISHED PRODUCT CONVEYING As the product ﬁnally emerges, it is discharged to the side of the oven/dry kiln onto ﬁnished product conveyors [Figure 13.2(i)] leading to packaging machines. The moisture content at this point is 2–4%. Finished product moisture is critical. Pretzels too low in moisture tend to break easily during packaging and transport, while pretzels too high in moisture content easily become stale resulting in reduced shelf life. Color monitoring and computer control of the complete process from mixing through packaging is the latest addition to full automation. After the operator selects the products to be made, the system automatically sets temperatures, speeds, levels and pressures accordingly, and the computer monitors and regulates all process variables. The software can be modiﬁed to allow the operator to change all or some process set points and can also be designed to limit the range of the change allowed. Essentially, this means the oven can be controlled manually or automatically. Automation, safety, operation control and variety of products made are integrated requirements in the production system affecting the pretzel’s fragility and unique ﬂavor characteristics. All transfer points must be gentle and smooth; products must be kept at uniform shape and weight and proceed in even production rows to expose each piece to the same prooﬁng, alkali bath, cooking, salting and drying to achieve the same lustrous browning.

4.10. PACKAGING/COOLING Pretzels exiting the dry kiln process are quickly cooled to less than 200◦ F (93◦ C) by natural convection currents. Pretzels are resilient to breakage while two to three times (◦ F) warmer than room temperature. Breakage at the end of the kiln typically is less than 1/2 of 1% of total output. As the pretzel cools to room temperature, it becomes more fragile and must be handled with greater care. Finished pretzels are normally handled by an inclined belt conveyor from the dryer exit to a point overhead where they are gently transferred to an oscillatingmotion conveying system. These conveying systems consist of vibratory pan conveyors (long, sturdy sheet-metal trays that are lifted and thrust in a speciﬁc reciprocal pattern, which causes material in the tray to gently move forward). They have the advantages of being easy to clean and convey large quantities of

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product with virtually no physical damage. In the case of pretzels, too much agitation in the conveying system is certain to cause salt loss. On reaching the packaging area, the majority of pretzels move through multiple-head scales, which capture a tiny portion of the desired total package weight in a circular arrangement of weighing bins. A computer weighs each bin and rapidly calculates the combination of bins to be dumped that best equals the desired net weight of product. Scales of this type are very accurate, producing errors no greater than 1–2 grams at speeds of up to 150 bags per minute. Typically, a form, ﬁll and seal bagmaker receives the output of the scales. The bagmaker makes packages from roll stock consisting of several laminations of coextruded, preprinted material that is automatically fed into the machine. The ﬁnished product is placed into cartons either by hand or by machine.

5. PROBLEMS IN PRETZEL MANUFACTURE The problems encountered in the manufacture of pretzels are very similar to those associated with the production of bread, but with two very signiﬁcant exceptions:crystallization of the dough during extrusion and problems associated with the cooking bath.

5.1. CRYSTALLIZATION Crystallization occurs as a direct result of extrusion. Dough exiting the extruder has visibly changed color, taking on a slightly grayish cast. The dough forms into an extruded pretzel, but when picked up by hand, it exhibits complete lack of elasticity and cohesiveness, often simply falling apart. The product does not rise in the oven and develops a dense, glassy texture. When cooled, the pretzel is extremely brittle, often breaking into tiny pieces when placed under the slightest stress. Product breakage rates after packaging can easily exceed 50%. At this writing, no proven scientiﬁc explanation of crystallization in pretzels exists. However, logic requires us to examine the condition of starch within the dough before and after crystallization. Wheat starch is composed of two types of polymers: amylose and amylopectin [6]. Under the electron microscope, amylopectin is very much tree-like, having a complex set of branches in all directions [7]. When put under sufﬁcient pressure, or when damage or weakening of the amylopectin chains exists, the starch chains fracture and lose their normal ability to swell up in water and create the starch paste normally associated with gelatinization of starch. The resulting inability to paste and gelatinize normally is hypothesized to be responsible for the lack of product rise and lack of cohesiveness of the extrudate.

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When faced with crystallization, most bakers have learned they must somehow reduce the extrusion pressure. They may employ one or more of the following strategies designed to reduce pressure or reduce enzymatic damage to the dough: r Increase the proportion of water in the mix r Slightly increase ﬁnal dough temperature r Reduce production line throughput r Reduce the amount of yeast in the mix r Reduce ﬂoor time or hold time of the dough r Check to ensure that the dough is mixed to the peak of gluten development In severe cases of crystallization, it may be necessary to try changing the ﬂour if the baker is encountering sprout-damaged wheat.

5.2. PROBLEMS WITH COOKING (NaOH APPLICATION) The use of sodium hydroxide (NaOH) as a processing aid is unique to pretzels when viewed in the context of all baked goods. Indeed, the characteristic ﬂavor that makes a pretzel a pretzel instead of a cracker or breadstick is derived from the application of a mild solution of hot water and sodium hydroxide, which changes the surface pH of the acidic dough piece to alkaline and prepares the pretzel for the browning reaction in the oven. The effect of bathing the pretzel in an alkaline solution is not unlike brushing a loaf of bread with an alkali such as egg white to create a deep, brown crust. But, unlike the bread process, the cooker bath is heated to temperature of 190–205◦ F (88–96◦ C), which creates both thermal and chemical gelatinization of the surface starches in the pretzel. In addition, the heated solution caramelizes surface sugars that participate during gelatinization to create the unique glossy surface characteristic of pretzels. The rapid increase in dough temperature causes a concomitant increase in enzymatic activity as well as initial swelling of the starch granules in the dough. Because so much happens in the pretzel cooker, a lot can go wrong as well. Failure to maintain a constant proportion of NaOH to water alters the ratio of surface alkalinity to interior acidity and dramatically affects the taste of the ﬁnal product. Typical ranges for cooker solution concentrations are 0.5–2.5% NaOH, with a tolerance of plus or minus 0.1%. Immersion time, though less critical than alkali concentration, affects gelatinization and caramelization, and affects temperature rise in the pretzel during its trip through the bath. Changes in internal temperature of the pretzel change enzymatic activity and the extent of initial starch swelling of the product. During the cooking process, dextrins are stripped from starch and dissolve in the hot water solution. Other ingredients meet a similar fate, combining to form an ever-increasing concentration of unwanted compounds. These contaminants cloud the otherwise clear cooker solution and cause the ﬁnished product to lose its characteristic shine. Modern

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cookers employ pumps and ﬁlters to remove contaminants and extend the life of the solution.

6. REFERENCES 1. Emert, P., 1984. The Pretzel Book. Woodsong Graphics Inc. New Hope, Pennsylvania, p. 13. 2. Not identiﬁed, 1999. The right stuff: State of the industry. Snack Food & Wholesale Bakery, June, pp. SI 1–85. 3. Stauffer, C. S., 1994. Fat and oil functions. Baking and Snack Magazine, January, 15. 4. Sanderson, G., G. Reed, B. Bruinsma, and E. J. Walker, 1983. Yeast fermentation in bread making. American Institute of Baking Technical Bulletin, 5(12):1–7. 5. Dubois, D. K., 1981. Chemical leavening. American Institute of Baking Technical Bulletin, 3(9):1. 6. Faridi, H. and J. Faubion, 1990. Dough Rheology and Baked Product Texture. Van NostrandReinhold, New York, p. 112. 7. Dubois, D. K., 1980. Enzymes in Baking. American Institute of Baking Technical Bulletin, 3(10):2.

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CHAPTER 14

Popcorn Products

CHARLES CRETORS

1. INTRODUCTION

P

OPCORN is probably the oldest snack food in the world. Although nearly every

one in the United States has popped corn at home in a pot or wire basket, the average person knows very little about why popcorn pops and what affects the process other than heat. After a brief orientation to the industry and its history, this chapter describes why popcorn pops, the different kinds of corn available and the machinery used to make various products. The important factors and basic processes common to all popcorn production are discussed. From there, the three major areas of popcorn use: in-home preparation, commercial (movie theatre, concession and loose popcorn sales) and industrial (packaged products) are described.

1.1. SCOPE OF THE INDUSTRY In calendar 1998, popcorn was the third most popular domestic snack after tortilla and corn chips and potato chips. Grocery and convenience outlet sales totaled $1.686 billion, including microwaveable popcorn, $1.136 billion; readyto-eat popcorn, $0.465 billion; and unpopped popcorn, $0.085 billion [1]. These ﬁgures do not include sales of freshly popped popcorn, estimated to be about $1.0 billion at theatres alone and $0.250 billion at various public concessions, which brought total domestic sales of popcorn products up to approximately $2.936 billion. Popcorn, a New World crop, initially was grown exclusively in the United States. Currently, approximately 30% of the world’s crop is grown in other

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countries, including Argentina, Australia, South Africa, Ukraine and many European countries, for domestic use and export. Popcorn may be grown wherever other hybrids of corn are grown. One of the largest contributors to popcorn quality is the handling of raw corn after it has been picked. Corn processors in the United States usually have more experience in these techniques than those in other parts of the world.

1.2. HISTORY OF POPCORN AND POPPING EQUIPMENT Corn has been a basic food in South and North America for over 5,000 years. No one knows when primitive man ﬁrst discovered that certain varieties of corn exploded when exposed to intense heat, but it must have been a signiﬁcant advancement to a people with only teeth and crude grinding tools. All the native Americans ate popcorn to some degree. The ancient Inca and Peruvian civilizations used the colorful popcorn for both food and ceremonial decorations. The oldest identiﬁed corn poppers have been found along the Northeast coast of Peru and date from about 300 AD. The oldest written record is from a Spaniard in 1650, who said that the Indians called the popped product “pisancalla.” Early American settlers cultivated (ﬂint-type) popcorn, which was used as a snack and breakfast cereal; dent corn was used for corn ﬂour and corn bread. Many families owned corn poppers consisting of wire baskets, with long wire handles tipped with wood, for holding and shaking popcorn over ﬂames in ﬁreplaces. As cities grew, street vendors started selling popcorn. A hot-air process, with wire baskets shaken over a ﬂame, was used (Figure 14.1). In 1885, Charles Cretors left Decatur, Illinois, for Chicago to become a street vendor and develop a better peanut roaster. A gasoline-fueled wet (oil) popping machine, which also had a small compartment for roasting peanuts, was patented in 1983 and shown at the Columbian Exposition that year. The exposition was held to celebrate Chicago’s rebuilding from the Great Fire of 1871 and the 400th year of Columbus’ discovery of the New World. Passersby stopped to watch corn popping and purchase bags of fresh product for a nickel. These colorful machines were readily accepted by street vendors, circuses and carnivals, and used for many years (Figure 14.2). They were the forerunners of corn poppers that eventually would become ﬁxtures in shopping malls and movie theatres throughout the nation. Another milestone in popcorn history at the 1893 exposition was the introduction of Cracker JackTM caramel-coated popcorn, the ﬁrst commercially successful snack based on popcorn [2]. This product line, with the traditional small prize in the package, was purchased in 1999 by the nation’s largest snack foods producer, Frito-Lay Company of Dallas, Texas.

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Figure 14.1 Street vendor popping corn over a ﬂame, mid-1800s.

Over the years, C. Cretors & Company continued to innovate popcorn handling equipment. Developments included: r r r r

1916—First electric oil popper used commercially in movie theatres 1936—First electric kettle with a thermostat 1963—Automatic wet popper 1965—Cretors Automatic Cooker and MixerTM for cooking high-temperature candy and low-temperature savory ﬂavors and coating popcorn, now called the Cretors Caramelizer r 1970—Flo-ThruTM hot-air popper, the ﬁrst high-volume industrial popcorn popping machine [2]. A corn metering system, oil measuring system, microprocessor controls and bag-in-box oil pumps were developed later. As the popcorn processing industry grew, other innovators contributed their design skills and a number of equipment manufacturers exist currently. C. Cretors & Company also sold popcorn supplies from 1900 to the late 1930s, but suspended industrial sales to focus on popcorn processing equipment sold under the Flo-ThruTM line name.

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Figure 14.2 1893 mobile gasoline-fueled corn popper and peanut roaster. (C. Cretors & Company, Chicago, IL.)

2. RAW POPCORN SELECTION AND PREPARATION

2.1. WHY POPCORN POPS To meet the objective of presenting a pleasing product to the consumer, it is important to understand why corn pops before variety selection, harvesting, cleaning or processing can begin. Unlike most commercial snack foods, the pufﬁng process occurs naturally in popcorn. A popcorn kernel contains naturally all hard starch, about 14% moisture, and has a very tough pericarp (hull) and outer layers of the kernel that are capable of withstanding an internal pressure of 135 psi (gauge) or (9.1 atmospheres). When heated, temperature and pressure in the kernel rise, the internal moisture is turned into superheated steam, the starch gelatinizes and the endosperm becomes pliable and rubbery-like. At about 135 psi internal pressure, the kernel ruptures and the superheated steam expands the starch and proteins to form a foam. As the steam is vented, the internal temperature drops. At the lower temperature, the starch/protein polymers retrograde into glassy-like polymers in foam form, which make popcorn crispy (Figure 14.3). Optimum popping requires a delicate balance of heating and moisture content. If the kernel is heated too quickly, the starch at the center is not gelatinized or softened. Although starch at the outer edge reaches the required temperature

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Figure 14.3 Effects of temperature on expansion of popcorn: (A) appearance of kernels popped at 460◦ F and 420◦ F; (B) cellular structure, popped at 460◦ F; (C) cellular structure, popped at 420◦ F.

and pressure, causing the pericarp to rupture, the uncooked starch at the core of the kernel does not expand. If the heating process is too slow, the buildup of internal pressure cannot keep up with loss of moisture as steam vents from the tip of the kernel. Although the pericarp of the kernel is hard, non-porous, and can contain the increasing pressure, the tip, where the kernel was attached to the cob, is not pressure-tight and will gradually equalize the internal pressure with its surroundings. The optimum balance is to heat the kernel at a rate slow enough to cook the starch to its core before internal pressure ruptures the pericarp, but not so slow that the available moisture leaks out before the kernel reaches the popping temperature and pressure [Figure 14.3(C)]. The correct moisture for popcorn

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is in the range of 13.5–14.5%; it is not a constant and will vary from hybrid to hybrid and with the physical condition of the corn. With too little moisture, the kernels will not pop. With too much moisture, corn may develop a musty, stored ﬂavor. Optimum popping produces a 40-fold expansion as shown in Figure 14.4(D).

2.2. METRIC WEIGHT VOLUME AND BULK DENSITY EXPANSION TESTS Since popcorn quality is generally deﬁned by how large the kernels will pop or expand, a way is needed for determining whether decisions in breeding popcorns, selecting planting seed, drying corn after harvest, and adjusting corn processing machinery, are headed in the right direction. In practice, these are based on actual expansion tests. Two factors are important in making popcorn—the expansion of the kernel and the percentage of kernels that pop. Expansion is the increase in volume during the popping process. In general, the more the corn expands, the better the product. From a consumer’s view, highly expanded corn is more tender and contains fewer partially popped kernels that are hard to chew. From a manufacturer’s view, expansion directly affects the proﬁtability of the operation. In concession stands in movie theaters and at sporting events, the operator buys popcorn by weight and sells it by volume (a full bag or box). High expansion translates directly into increased proﬁtability. Each percentage point of increased expansion is a reduction in raw material cost. The ﬁnancial reason to favor high expansion is not as pronounced in snack food plants where the end product is packaged and sold by weight. However, it does exist. Customers equate highly expanded corn with high quality. For the manufacturer, high expansion creates a physically larger bag for the same weight and may be considered a better buy by the customer. Highly expanded corn usually also indicates a low percentage of unpopped kernels or scrap. In this case, corn is purchased by weight and sold by weight, and lower scrap reduces raw material costs. Two problems are created if expansion of corn supplied to a snack food manufacturer is not consistent. First, when customers do not ﬁnd a consistent product, they will not search for that speciﬁc brand. Second, when the expansion is low, a preprinted bag ﬁlled to the correct weight does not appear full to the consumer. Commercial raw popcorn processors and large popcorn buyers use the Metric Weight Volume TesterTM —MWVT (manufactured by C. Cretors & Co., Chicago, IL)—to determine the potential expansion of a batch of popcorn [Figure 14.5(A)]. The MWVT is the ofﬁcial measuring instrument of the Popcorn Institute, an organization that represents a large percentage of the popcorn processors in the world.

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Figure 14.4 (A) dent corn (l.) and four types of popcorn; (B) environmental scanning electron microscope (ESEM) micrograph of popcorn hard endosperm, SG = starch granule; (C) ball (l.) and ﬂake (r.) type popcorns; (D) popcorn expanded 40-fold by popping.

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Figure 14.5 (A) Metric Weight Volume Tester—MWVT (C. Cretors & Co., Chicago, IL); (B) polystyrene foam box used to measure expansion volume and bulk density.

The MWVT consists of a batch-type oil popper with a cylinder into which the popped corn falls. The cylinder is calibrated to deﬁne the expansion of the corn in cubic centimeters of popped corn per gram of raw popcorn input. The MWVT is equipped with instruments for accurately measuring the temperature and energy consumption of the popper and expansion of the popped corn. This makes it possible to duplicate results from one machine to another and provides a means of comparing different batches and hybrids of corn. The MWVT was originally developed for use by popcorn suppliers in their plants. Before hybrid grains became common, moisture and growing conditions were the primary factors affecting expansion of popcorn. The popcorn supplier would take a small sample from a large bin of freshly harvested corn, test it with the MWVT and record the result. The processor would then begin to dry small samples of the corn, testing the expansion as the process continued. As the normal harvest moisture decreased, the expansion increased. When the tests indicated the expansion was beginning to decrease, the processor knew at what moisture content the entire batch of popcorn should be dried to get maximum expansion.

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The MWVT is used primarily as a guide to predict the future performance of popcorn when it is popped. But once corn is popped, another method of measurement is needed. The most useful is bulk density. While the MWVT deﬁnes the volume of popcorn produced as a function of the amount of raw corn that was popped, bulk density of the ﬁnal product gives an indication of the effectiveness of the popping process itself. The measuring tube of the MWVT is 4.5 in. (11.4 cm) in diameter and 40 in. (101 cm) long. This provides good resolution and sensitivity for the laboratory. In the typical snack food plant, a quick method is needed for determining the effectiveness of adjustments made to the popcorn machine and the efﬁciency of the operation. When operating a popcorn machine, the bulk density of the popcorn can be measured with a large open box. The corn that is to be measured should be taken from the system after the sifter and before the coating or ﬂavoring is applied. (This is not possible in the case of oil-popped corn.) The box should be approximately 12 in. (0.3 m) on a side for a total volume of 1 cubic foot (0.027 m3 ) [Figure 14.5(B)]. The normal weight range of popped corn needed to ﬁll the box is 1.32–1.60 lb/ft3 (600–725 g), or 21–25g/L for ﬂake corn used to make salted and savory products. When making caramel corn, the weight is higher and the density is approximately 1.75–2.00 lb/ft3 (800 to 900 g), or 28–32 g/L.

2.3. VARIETIES, HYBRIDS AND TYPES Popcorn (Zea mays everta) is a form of ﬂint corn and differs from dent and other soft commercial corns in two ways [Figure 14.4(A)]. The ﬁrst is that it contains almost entirely hard starch [Figure 14.4(B)]. The second is that it has a very hard pericarp and outer layers of endosperm, which permit the internal pressure and temperature to rise high enough to pop. Also, see Chapter 3 on Food Quality of Corn. The original Indian corn is mainly grown as a curiosity and for decorative purposes, and the early popcorn varieties have essentially given way to highly improved hybrids. These are obtained by crossing different strains of popcorn to emphasize speciﬁc physical characteristics, popping expansion, taste and texture. The characteristics include kernel size, shape and texture. Two groups of popcorn are commercially available, yellow and white. White popcorn is a small white grain that appears similar to a grain of rice. Some speciﬁc hybrids use names like: baby rice, Japanese hulless or white hulless. The pericarp on this grain is thinner than on other hybrids, and after popping is not as noticeable when eaten. The popped kernels of these hybrids are very white, small in size and very tender. These hybrids are almost exclusively used in the home because they are very tender and fragile; breakage typically is excessive when used in commercial applications.

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Yellow popcorn [Figure 14.4(A)] is most commonly used in commercial operations. The kernels are rounded in shape and have a medium-yellow color. Several options within this group are available to the raw popcorn buyer. Various kernel sizes, deﬁned as small, medium, and large, are available. The popped kernels also differ in shape. Most corn takes on an irregular shape when it pops and is referred to as ﬂake or butterﬂy popcorn [Figure 14.4(C)]. Some hybrids take on a more rounded shape and are referred to as ball or mushroom corn. When ball-type corn is popped, the kernels expand from a small spherical shape to a much larger size. The slightly brownish color spots on the surface are the remaining areas that previously contacted the underside of the pericarp. The round ball shape should not be confused with heat balls that result from popping corn too rapidly. When a ﬂake-type kernel pops, it turns inside out, and pieces of the trapped hull can often be found inside. Popped ﬂake-shaped kernels are usually more tender and crisp, and are ﬂavored with salt and cheese in relatively gentle tumble drums. The ball/mushroomshaped kernels have fewer small protrusions to break off and are used in more vigorous ﬂavor application systems such as the caramel-coating process.

2.4. POST-HARVEST HANDLING AND PREPARATION Essentially all popcorn is grown under contract, in some cases by thirdgeneration farmers supplying the same corn processor or industrial user. Hybrid selection, production, harvesting, storage and handling are carefully controlled. Popcorn quality starts in the ﬁeld. Although popcorn grows on a stalk like other corns and can be harvested by the same processes, several precautions must be taken to get a top-quality product. The popcorn plants and ears are not as large as those of the more commonly grown ﬁeld corn. Adjustments and modiﬁcations must be made to the machinery to ensure the popcorn kernels are not damaged in the picking and shelling processes. Damage, in the form of scratches or cracks in the pericarp, reduces expansion of the kernels during popping. In the past, to avoid this problem some growers/suppliers would pick and husk the corn, and keep it on the ear until shelled at a central plant with the equipment adjusted to handle the smaller ears. This resulted in higher costs, but the corn was promoted as very high quality. After air and gravity separators, and precision sizers, most popcorn processors also use computerized color sorters. Virtually every kernel is inspected by an optical system that identiﬁes discolored kernels, weed seeds, stones and foreign matter, and removes them with a jet of air. After the corn is cleaned, sorted, and inspected, it is slowly dried to the optimum moisture content for maximum expansion during popping. Dried corn may be stored almost indeﬁnitely as long as the moisture level is not allowed to change. Kernels of popcorn over 4,000 years old, found in caves in New Mexico, have been successfully popped.

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2.5. PACKAGING FOR HOME, COMMERCIAL AND INDUSTRIAL POPPING 2.5.1. Home-Use Popcorn Popcorn purchased in grocery stores has the greatest variation in quality and packaging methods. Raw popcorn is often sold in ﬂexible laminated packaging. The primary requirement of this packaging is that it contain a barrier to eliminate the possible loss of moisture, which is critical to successful popping. High-proﬁle brands, such as Orville ReddenbackerTM , are packaged in screwtop plastic or glass jars. Reddenbacker had a major inﬂuence in improving the quality of popcorn for home use. He developed very tender ﬂavorful hybrids that were adapted to popping in the home and packaged them in glass jars, which kept the moisture at the correct level. Before Reddenbacker, popcorn was usually packed in inexpensive ﬂexible ﬁlms and had a tendency to dry out on the grocery store shelf. Orville Redenbacher made “theatre popcorn” quality available to the average person popping corn at home. Today, microwave popcorn is the most common form of packaging found in grocery stores. The packages are the result of much research, and many patents have been issued to manufacturers of these products. The typical microwave package contains popcorn, popping oil and salt for ﬂavor. When the package is placed in a microwave and cooked, the corn pops and the package expands to become a serving bag. Although these products are fast and easy to prepare, they are somewhat different from traditional oil-popped products.

2.5.2. Vendor-Use Popcorn Commercial processors, such as concession stands and movie theaters, buy their raw popcorn packed in two ways. The most common is a 50 lb (22.68 kg) plastic-lined paper bag. This package will keep corn fresh for at least six months if not exposed to excessive heat. Additionally, popcorn is sold in a 50-lb case of four 12 1/2 lb (5.67 kg) polypropylene bags. These small bags are useful in small concession stands where an open 50-lb bag would not be consumed for a long time.

2.5.3. Industrial-Use Popcorn Industrial processors start off where the commercial end; 50-lb bags are commonly used. However, automatic popcorn machines capable of consuming one bag a minute require larger units of measure for their raw corn supply. Bulk totes, with a capacity of 2,500 lb (1,134 kg) are available to the large industrial user. The totes are expensive and are recycled between the corn

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supplier and processor. They are usually used in conjunction with a long-term contract. Bulk shipping of popcorn is possible for processors using large volumes and equipped with a high level of automation. In this system, corn is loaded in bulk into a tank truck, and the plant that receives the popcorn is equipped with a large metal bulk tank to hold it. A typical load might be 40,000 lb (18,144 kg). When the truck arrives, it is emptied into a receiving pit or collector and pneumatically transferred to the storage tank. Corn is then fed from these tanks directly to the popper. Gentle handling of corn to avoid breakage is critically important.

3. POPPING METHODS

3.1. OIL POPPING 3.1.1. Popping Process The oil or wet popping process, patented by Charles Cretors in 1893, is most commonly used in point-of-purchase concession stands and was the most common in homes before the advent of the microwave. Corn and oil are placed in a container in a ratio of three parts corn and one part oil by volume. The corn begins to pop when the corn and oil reach the proper temperature. Enough heat (450◦ F, 232◦ C) needs to be applied to the bottom of the pan for a normal popping cycle of 2.5–3.0 minutes. At that time, the corn expands to its greatest volume. The time cycle may be adjusted by either changing the heating rate or, if the rate is ﬁxed, by changing the amount of raw material put in the cooking pan. The corn and oil must be agitated during the process to obtain even transfer of heat. In commercial machinery, a motor turns an agitator on the bottom of the popper kettle. In the home, the pot in which the corn is being popped is shaken over a burner on a stove. Popping corn in oil is probably the simplest snack-production process available and permits making the end product at the point of purchase. The aroma, animation, and the obvious freshness of the product, make the process ideal for concession stands where the consuming public can see and smell the product being made.

3.1.2. Oils Used Oil serves two purposes. The ﬁrst is the transfer of heat from the bottom of the popping pan or kettle to the popcorn kernels. The second is to add ﬂavor to the ﬁnished product. Generally, any shelf-stable oil that will tolerate the high temperature of the popping process can be used; see Chapter 6, Oils and Industrial Frying. Several

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factors should be considered when choosing popping oil. The ﬁrst is melting point. If the melting point is above body temperature, the ﬁnished product can leave a waxy coating inside the consumer’s mouth. Popcorn is often eaten in conjunction with cold drinks, which can accentuate the waxy sensation and make the product undesirable. Popular popping oils in the United States are coconut, corn, peanut, sunﬂower, canola, soybean and commercial blends. All have melting points below body temperature, and some are liquid at most room temperatures. The primary differences are their ﬂavors and how they perform in the popping kettle. The temperature in a popping kettle usually exceeds 450◦ F, a temperature that will carbonize and burn the residual oil left in the kettle. Some oils are more inclined to create a carbon buildup in the kettles, and a direct relationship to the amount of unsaturated fatty acids in the oil exists. For many years, coconut oil was the most popular popping oil. Initially, it was relatively inexpensive. It melts at 76◦ F, is very stable and has a good ﬂavor. This oil is also desirable from the manufacturing point of view because it creates a minimum of carbon in the popping kettle. The only negative is that it is highly saturated and is considered by some consumers to be unhealthy.

3.2. DRY POPPING This process is found in home, commercial and industrial applications. The ﬁrst hot-air poppers were wire baskets, holding a small amount of popcorn, that were held over a ﬁre. The baskets were shaken rapidly to agitate the corn and keep it from burning. Today, commercial versions of this process use a motorized rotating wire drum over an open ﬂame or electric heat elements. This type of corn popper was used in retail locations in the United States for many years before development of the oil pop method.

3.3. MICROWAVE POPPING The same process that warms a cup of coffee will pop corn. Microwave ovens can rapidly heat the water and starch throughout a corn kernel to the temperature of popping. Due to high energy costs of operation, this method of popping corn is found almost exclusively in the home, where microwave ovens are common.

3.4. INCOMPLETE POPPING Not every kernel in a popper charged with raw corn will pop. Additionally, some kernels will not pop completely, resulting in heat balls and hard or tough pieces. Being more dense than fully popped corn, these kernels normally settle

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to the bottom of the bowl or bag as consumers help themselves to the fresh product. However, they are undesirable in industrially made popcorn, especially in products like caramel corn where they may be stuck to fully puffed kernels by the coating and create dental pain and damage during mastication. Typically, screens are used to remove the smaller unpuffed kernels when making puffed corn products. These are further described under Sifting and Scrap in the next major section of this chapter.

4. HOME PREPARATION OF POPCORN AND EQUIPMENT

4.1. OIL POPPING Traditional salted popcorn is made by putting corn in a pot with oil and salt, and heating and shaking until popping is completed. Some experimentation is necessary to be successful. The level of heat applied to the pot must be controlled so that the popping process takes about 2.5 minutes from a cold start with oil and corn. If the oil is preheated, as some operators prefer, the popping time will be only about 1.5 minutes. Extreme caution must be exercised when preheating the oil. If the process is left unattended, the oil may become overheated and begin to burn.

4.2. DRY POPPING Hot-air poppers are popular in homes where consumers are concerned about fats and oils in their diet. Also, many people like them because they require little cleanup. Small hot-air home poppers operate on the principle of forcing heated air up through a bed of popcorn to heat it until it pops. The popped corn may then be seasoned with salt, butter or other ﬂavors as desired.

4.3. MICROWAVE POPPING Microwaving is probably the easiest way to prepare popcorn, requires the least cleanup, but is the most expensive in cost per serving. Raw popcorn and oil are packed in a specially designed package that is placed in a microwave oven and heated. Directions are printed on microwave popcorn packages. The packages are disposable serving containers for the ﬁnished product.

4.4. FLAVORINGS Salt is the most popular ﬂavoring for popcorn in the United States. When the corn is oil-popped, salt is added to the popping kettle with the raw corn and oil.

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The best type of salt to use is the ﬁnest size grade available. This is often called popcorn salt or ﬂour salt and is more like a powder than a ﬁne grain. Cheese and other ﬂavors can be added easily in powder form by shaking onto the corn after it is popped. Caramel corn is often made at home. Sugar, water and glucose (corn syrup) are brought to a boil and cooked to hard-crack temperature, about 300◦ F (149◦ C). After the sugar is cooked, a small amount of baking soda may be added to the mixture to cause it to foam. This foaming action increases the volume by four to ﬁve times. It is important that the kettle in which the sugar is cooked be large enough to contain the expanded volume. Popped corn is then mixed into the foaming caramel. While the popcorn is still warm, it may be formed into shapes such as balls or bars. If loose caramel corn is desired, a mixture of liquid lecithin and vegetable oil is sprayed on the caramel corn as it is worked on a ﬂat surface while cooling.

5. COMMERCIAL PROCESSES FOR FRESH POPCORN

5.1. OIL POPPING Popcorn machines for concession stands are available in a broad range of sizes. Small countertop machines, 14 in. (35 cm) deep by 20 in. (51 cm) wide, have a processing capacity of 7 lb (3 kg) of popped corn per hour. Large machines, 6 ft (1.8 m) long and nearly 7 ft (2.1 m) tall, are capable of producing 100 lb (45 kg) per hour of popped corn and are often found in movie theaters (Figure 14.6). The most prominent feature of these machines is the popper pan. This is a steel or aluminum pan with heating elements on the underside and a thermostat to control the temperature. In addition to heating elements, the pans are equipped with a motorized stirring mechanism to keep the corn from burning during the popping process. The larger machines are equipped with a pump and timer to pump the correct amount of popping oil into the kettle at the beginning of each cycle. The cabinets of larger machines may have many features. Enclosed models have exhaust fans and grease ﬁlters to trap any smoke or oil vapor produced in the popping process. The lower part of the cabinet usually has a perforated screen with circulating hot air to keep the popped corn warm and crisp. This perforated screen also has a section with a sieve to separate the unpopped and undersized kernels from the rest of the corn. The basic process is to add corn, oil and salt to the kettle and turn on the heat and agitator. When starting with a cold kettle, the ﬁrst cycle can take 6–8 minutes. The following cycles should take no more than 2.5–3.5 minutes. In most of these machines, the oil is supplied by a pump equipped with a timer to provide the correct amount to the kettle.

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Figure 14.6 Oil popper for large concession stands and movie theaters, 100 lb/hr (45 kg) capacity. (C. Cretors & Company, Chicago, IL.)

5.1.1. Salted Popcorn Salt can be added to the corn oil mixture at the beginning of the process. Salt is normally used in North America; sugar is more common in much of Europe.

5.1.2. Sugar Popcorn The sugar corn process is slightly different than that for salted corn and requires more attention from the operator. The basic problem is that popcorn pops at temperatures over 400◦ F (200◦ C), and sugar begins to carbonize badly above 310◦ F (155◦ C). This requires that thermostats on the popcorn kettle be set slightly lower than when popping salted corn, and the operators must be more attentive and empty the popping kettle as soon as the popping process

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is complete. The popping kettles also require more cleaning to remove carbon buildup from the residual sugar or from savory ﬂavors if used. While there are different recipes, typically the corn-to-oil ratio is reduced from 3:1 to 4:1, and the overall volume by 20 to 30%. The reduced volume is replaced with white granulated sugar. The sugar-to-corn ratio is usually 0.7–1.0 sugar to 1 of corn. The sugar is usually added to the kettle with the corn and oil, but some operators prefer to add the sugar just as the corn begins to pop. Adding the sugar later produces a whiter popcorn because sugar added at the beginning of the cycle has a greater tendency to burn and add a slight brown color to the corn.

5.2. DRY POPPING Batch-type dry poppers are rotating wire drums that are suspended over a ﬂame or electric heater. Corn is placed in the popper and the heat is turned on. As the corn pops, a screen made from coarse wire scoops the popped corn out of the rotating drum. This type of popper is often found in shops that specialize in caramel and other ﬂavored corns. Automatic dry poppers operate on the same principle as home poppers in that hot air is blown up through a bed of corn to heat it to popping temperature. With this machine, there is an option of producing dry corn for sale or letting the corn fall onto a pan with an agitator that stirs it while oil is added. After the corn is dry popped and screened, it may be ﬂavored with many different toppings. Popcorn has a pleasant neutral ﬂavor and just about any other ﬂavor can be added. The most common are oil and salt, cheddar cheese, sugar and caramel with nuts.

6. INDUSTRIAL PROCESSES FOR PACKAGED POPCORN

6.1. OIL POPPING Industrial oil popcorn production lines consist of one or more banks of the largest oil poppers set up over a conveyor belt (Figure 14.7). Typically, six poppers are set side by side and one operator adds corn, oil and salt to the machines. Operating on a typical 3-min cycle, the operators will dump, empty and reﬁll a popper every 30 seconds. Corn is usually fed by hand using sized measuring cups. Oil may be added to the kettle in several ways. In one option, oil is circulated from a large central oil storage tank to volumetric measuring points above each popper. When it is time to recharge a popper, the dry ingredients are added to the kettle and the oil measure is emptied into the kettle. Another approach is to have a timed metering pump at each popper. The dedicated pump may draw

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Figure 14.7 (A) industrial 200 lb/hr oil popper. (B) industrial oil-popping line consisting of smaller units mounted above takeaway conveyor and sifter to remove unpopped corn. (C. Cretors & Company, Chicago, IL.)

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oil from a manifold that circulates from a central tank, or from individual 50-lb (22.68 kg) pails. In an additional option, the pumps are immersed in the pails themselves and are equipped with thermostatically controlled heating elements to melt frying shortening or oils that are solid at room temperature.

6.2. DRY POPPING Currently, hot-air popping of corn is used mainly in industrial applications. The commercial hot-air corn popper is essentially a continuously fed, ﬂuidizedbed oven. While it is primarily a popcorn machine, it is also used to puff thirdgeneration snacks and roast peanuts and will process any type of snack that requires precise temperature and time control and a continuous process. The extremely high air velocity can transfer heat almost as quickly as oil popping processes. Continuous dry poppers recirculate 90% of the air used in the process and require a short time to reach a stable atmosphere once popping begins. This is due to the fact that almost 10% of the weight of the corn is lost as moisture inside the cabinet during the popping process. Within ﬁve minutes, the atmosphere in the cabinet is stable and a very consistent product is produced.

6.2.1. Dry Popper Design The basic design of a Cretors Flo-ThruTM Dry Popper is used as an example. The machine consists of an horizontal auger with nine complete ﬂights wrapped around the shaft. The auger has a 16 in. diameter and is wrapped with a perforated steel sheet with 3/32 in. holes. About 33% of the steel is open holes and 67% is metal. The combined auger and perforated steel wrap is called a popping drum and revolves as one unit [Figure 14.8(A)]. The entire assembly is installed in an oven [Figure 14.8(B)], which is held at a temperature of 430◦ F (221◦ C). A fan at the bottom of the oven blows hot air up through the bottom of the perforated rotating drum. Raw popcorn or any product to be processed is introduced into one end of the cylinder, and heated air is forced up through the perforations in the cylinder with enough pressure to ﬂuidize the material lying on the bottom surface of the drum. The high velocity of the air agitates the corn and provides for very rapid and uniform heat transfer. As the drum revolves, the heated product is propelled toward the popping and discharge end of the machine. Adjustable controls built into the machine provide full control of the process. The feed rate is usually adjustable and appropriate for the size of machine. The variable-speed drum permits control of the residence time from 15 seconds to as long as 5 minutes. When popping corn, the residence time is about 80 seconds at 420–445◦ F (215–230◦ C). The recirculating atmosphere makes it possible to control the temperature to within 2◦ F (1◦ C) once the process is stable. The volume of airﬂow that ﬂuidizes the product is controlled by the rpm of the

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Figure 14.8 (A) popping drum; (B) hot-air popping oven for industrial popper. (C. Cretors & Company, Chicago,IL.)

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Figure 14.9 (A) reel-type sifter used to remove unpopped and partially popped kernels and fragments of hot-air-popped pop corn; (B) closeup of sifter screen; (C) effects of popping temperature on popcorn bulk density and scrap. (C. Cretors & Company, Chicago, IL.)

blower. For popcorn, the best airﬂow is that which just provides ﬂuidizatioin and agitation. Excess air usually damages the popped kernels. The popped corn next enters a sifter [Figure 14.9(A) and (B)] to remove unpopped kernels and then proceeds to a coating drum where ﬂavorings are applied.

6.2.2. Operating Adjustment Options Popcorn kernels are a raw grain. The only prior processing they have been exposed to is cleaning, sizing, and drying to the appropriate moisture level for maximum expansion. The variability of a natural product requires that the popcorn machine operator be able to adjust the machine to compensate for variation in kernel size, shape, hybrid type and moisture content.

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The temperature is critically important [Figure 14.9(C)]. The typical dry popper has four variables that can be used to control the output of the machine. These variables are: feed rate, residence time, temperature and air circulation rate. Before a popper can be adjusted successfully, it is important to start from a neutral point. r Feed Rate. When tuning up a machine, the ﬁrst step is to check the feed rate of raw popcorn to determine if it is within the capabilities of the machine. A 200 lb/hr machine has a maximum feed rate of 200 lb/hr. If there is a question, it is best to check this out with the manufacturer. All Cretors’ machines use the model number as a designation of the maximum feed rate. This is the amount of raw corn fed into the machine, and not the output of the machine. Once the size of the machine has been determined, the calibration of the feeder must be checked to determine if the input is within the normal operating range of the machine. If difﬁculties in successfully controlling the output of the machine have been experienced, it is best to start at a feed rate of about 80% of the recommended maximum. r Residence Time. Once the feed rate is determined, the residence time of the corn in the popper must be checked. The ideal starting point is a residence time of 75–80 seconds. It is controlled by the rotational speed of the popping drum, which should turn at about 7 rpm to obtain the desired time. r Temperature. Temperature of the ﬁnal product is the most prominent variable and is dependent on the residence time (drum speed), size and hybrid of individual corn kernels, and moisture content of the corn. A good starting temperature for the popper is 435◦ F (224◦ C). r Air Circulation. Air circulation is controlled by the speed of the fan. The rpm required depends on many factors. The design of the particular machine and the internal clearances will affect the rpm needed for correct operation. It is best to check the manual supplied with the machine to determine the correct rpm. Adjustment of the blower rpm is extremely important for correct operation of the machine. It is important to understand the theory and function of air circulation in order to properly adjust the blower. A layer of corn lies on the bottom of a perforated drum in a continuous ﬂuidized bed popcorn machine. Heated air is forced up through the perforations with enough force to agitate the corn and cause it to act like a ﬂuid mass. The agitation and high velocity of air achieve a high rate of heat transfer between air and the corn. When the air pressure is too low, the air will not pass through the layer of corn and will not circulate within the cabinet. If the pressure is too high, the corn can be damaged by the violence of the airﬂow. The feed rate can be adjusted to provide the amount of corn required for any given process. It should be remembered that the quality of popcorn produced may deteriorate as the maximum rating of the machine is approached or

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exceeded. An increase in feed rate will increase the thickness of the corn bed on the bottom of the popping drum and may also require an increase in blower rpm. If the feed rate is already near maximum, the temperature also may need to be increased. Once the desired feed rate has been established by adjustment, the remaining three variables are used to control the character of the corn that is produced. It is important to adjust poppers in small increments: temperature, 2◦ F (1◦ C); drum speed, 0.1 RPM; and blower speed, 50 RPM and wait long enough for the change to take effect. If the drum speed is set to produce a residence time of 75 seconds, the results of any change to blower or drum speed require at least 75–80 seconds before the effects are seen. In the case of a temperature change, the time required for the cabinet to adjust to the new setting must be added to the residence time. When popped corn ﬁlls the drum above the center line, the drum’s rotation does not move all of it forward. Some spills over the center into the preceding space in the auger and moves backwards in the drum, eventually plugging the drum. Periodic plugging and clearing is called surging, and usually is caused by too high a feed rate. Surging can also be caused by too high a temperature, which causes the corn to pop in the ﬁrst half of the drum. A popper usually is considered to be operating correctly if the corn is heard to be popping at the discharge end of the popping drum. If the corn is popping in the sifter after it leaves the machine, the temperature is too low or some other variable is not correct.

6.2.3. Adjusting for Variability in Popcorn Referring to the two types of popcorn described earlier, ﬂake type (high volume, low density) and ball type (low volume, high density), the following adjustments may further optimize the popping operation: r Flake type —Characteristics: —Kernels are irregular —Kernels are fragile and crispy —Scrap rate is higher —Machine adjustments: —Lower the popping temperature —Slow the drum speed for longer residence time —Lower the feed rate r Ball type —Characteristics: —Kernels are more spherical

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—Kernels are stronger and tougher —Scrap rate is lower —Machine adjustments: —Raise the popping temperature —Increase the drum speed for shorter residence time —Increase the feed rate A wet (oil) popper heats the corn at anywhere from 420◦ F to 500◦ F (215– 260◦ F) in 0–180 seconds during the popping cycle. In contrast, a dry popper heats the corn at 430◦ F for 80 seconds and has a very narrow range of operating conditions. It requires a very uniform corn. Major variations in raw popcorn are moisture, kernel size, high-expansion corn, hybrid uniformity and changes in corn stored in the user’s warehouse or bins.

6.2.3.1. Moisture High-moisture corn pops at a low-temperature; low-moisture corn pops at a high temperature. If two bags of popcorn, one at 14% and one at 13%, are mixed completely and the moisture is checked, the assay will be 13.5% moisture. If put in a dry popper, with the temperature set to pop the high-moisture corn, most of the low-moisture corn will leave the machine unpopped and be discarded as scrap. If the temperature is increased to properly pop the low-moisture corn, the high-moisture corn will begin to pop early when the core starch has not yet been gelatinized, and small, tough, hard heat balls will be created and become even tougher in the hot-air popper. All the corn kernels must be equilibrated to the same moisture content.

6.2.3.2. Kernel Size Large kernels heat more slowly than small kernels. With a blend of large and small kernels, it is impossible to optimize hot-air popper conditions. The machine can only pop one size kernel satisfactorily.

6.2.3.3. High-Expansion Corn High-expansion corn is usually more desirable because it takes less weight to ﬁll a given bag than low-expansion corn. However, expansion of the corn affects the operation of the popper because the popping drum cannot be ﬁlled more than half way with popped corn. Often, the operator erroneously thinks the feed rate is too high. Prior popping of new corn samples helps to prewarn the operator. When a consistently high expansion corn is encountered, as with a newly introduced hybrid, reducing the dry popper feed rate reduces raw materials costs and does not reduce popped corn production. This is a distinct

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operating beneﬁt, provided the high-expansion corn still ﬁts into packaging materials with preprinted weights.

6.2.3.4. Hybrid Uniformity High-quality popcorn hybrids provide uniform grain with excellent potential for expansion and taste. However, environmental conditions signiﬁcantly affect popping quality. Popcorn suppliers have their corn grown in carefully selected environments that are consistently stable and provide good consistent corn quality for popping.

6.2.3.5. Corn Changes in Storage Reputable raw corn suppliers control their grain carefully to minimize variations in popping properties from shipment to shipment. However, changes occur in grain stored in the user’s warehouse or tanks. Repetitive major changes may require review of current packaging or operation of storage facilities. Accumulated adjustments that have been made while using the same shipment of corn over a long period may make the new shipment appear like an entirely different corn and therefore require major resetting of the hot-air popping equipment.

6.3. SIFTING AND SCRAP After the corn is popped, it must be cleaned to remove unpopped and undersized kernels. It is best to do this immediately after the corn has left the popper while the corn is still ﬂexible before cooling and drying. If the sifting process is delayed, popped corn becomes increasingly crisp, brittle and fragile, and unnecessary breakage occurs. The sifter is a stainless steel wire mesh drum that rotates on a horizontal axis. Unpopped, undersized and broken kernels pass through the 7/16 in. (1.1 cm) square opening between the wires and are separated from the rest of the corn (Figure 14.9). When small-grain, white popcorn is used, it is advisable to reduce the screen size to avoid discarding too much good corn.

6.4. POPPED CORN YIELD Popcorn is a natural product, and variations in the grain affect yield, even with sophisticated processing. For example, not all kernels will pop to the volume needed for commercial distribution, some kernels won’t pop at all and should never be packaged and sold. It is necessary to clean the popped corn with a rotary sifter before it is coated with ﬂavors or sold. A typical materials

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balance is: 100. kg −12. kg −8. kg 80. kg

Load of raw popcorn containing approximately 14% moisture Moisture and corn oil vapor loss during the popping process 88. kg Sifted out as unpopped or partially popped corn Popped corn yield produced from 100 kg raw popcorn, using a 7/16 in. (1.1 cm) wire-mesh sifting screen.

7. COMMERCIAL AND INDUSTRIAL FLAVORINGS AND APPLICATORS One or more ﬂavoring and color agents, like oil, salt, cheese or sugar, typically are added to corn after popping. Coating processes for popcorn are similar to those of other expanded snacks. They can be divided into two basic systems, batch and continuous.

7.1. BATCH APPLICATORS Batch coaters for salt and savory popcorn typically are coating pans that turn on an axis, inclined 30 degrees from horizontal [Figure 14.10(A)]. The popcorn to be coated is placed in the pan, and the oil coating and ﬂavor are introduced as the pan turns. The coating is either poured from a measuring pan or pumped in by a pump with a timer control. The pan is allowed to turn until the coatings are evenly distributed on the surface of the corn. At this point, the coating pan is stopped, emptied and reﬁlled for another batch.

Figure 14.10 (A) batch coating pan; (B) continuous horizontal coating drum. (C. Cretors & Company, Chicago, IL.)

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7.2. CONTINUOUS APPLICATORS Continuous coaters typically are horizontal stainless steel drums, 24–36 in. (60–90 cm) in. diameter, that turn on their axis [Figure 14.10(B)]. The coater may be depressed or inclined slightly to promote or retard product ﬂow. In principle, the popcorn and coating are introduced at one end of the rotating drum, and the coating is evenly distributed over the popcorn by the time the product exits from the other end of the drum. The continuous coater is usually equipped with a variable-speed drum drive to control residence time, a variablespeed pump so that the coating ratio may be varied and a dry applicator to apply salt or other dry seasonings.

7.3. SALT AND CHEESE FLAVORS Salt and cheese ﬂavors are usually applied with oil, which acts as a vehicle to carry the ﬂavor to the corn and help it stick. In the case of salted corn, the oil is sprayed on the corn with almost any type of spray nozzle at concentrations from 20 to 30% of the ﬁnished weight of the product. Color or ﬂavorings may be added to the oil to produce different products. Salt is blown or metered into the coater at a steady rate to produce the desired ﬂavor. To begin a cheese coating process, a slurry is prepared by mixing coconut oil or another shelf-stable oil with powdered cheese. Cheese content is usually 30%–50% by weight. This mixture is then heated to 120◦ F–130◦ F (49◦ –54◦ C) to melt the cheese. Melting the cheese is important because the coating sprays much more easily and is less likely to plug the pump, oil lines or spray nozzle. Additionally, the liquid cheese is better absorbed by the popcorn and is less likely to come off in the bag or on the customer’s hands. Care must be taken to not heat the oil and cheese mix too rapidly. If the surface temperature of the mixing kettle becomes too hot, the cheese will be darkened and the ﬂavor changed. Typically, cheese begins to break down above 130◦ F (54◦ C). An agitator must be in the tank to keep the oil and cheese blended. Cheese-ﬂavored popcorn can also be made by adding powdered cheese to either oil- or dry-popped popcorn. Although used in some plants, these products are not commonly seen because the powdery coating comes off on consumers’ hands, even though some manufacturers feel they have better ﬂavor. A typical continuous system for producing salty and savory popcorn is shown in Figure 14.11(A).

7.4. BATCH SYSTEM FOR SWEET/CARAMEL COATINGS The preparation of sweet-coated snacks is more complex than for salted and savory popcorn because the sugar coating must be mixed and cooked

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Figure 14.11 Systems for continuous production of: (A)savory ﬂavor-coated popcorn; (B) caramelcoated popcorn. (C. Cretors & Company, Chicago, IL.)

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Figure 14.12 Basic equipment for batch production of sweet caramel popcorn: (A) steam-jacketed kettle for preheating syrup; (B) copper kettle for cooking caramel; (C) mixing auger for coating popped corn; (D) working and cooling table for coated popcorn. (C. Cretors & Company, Chicago, IL.)

before application. The batch process for making sweet-coated popcorn begins by boiling a sugar solution in a stainless steel or copper kettle to make hard candy or caramel [(Figure 14.12(B)]. The boiling solution is then poured over the popped corn in a mixer, consisting of a drum rotating in a vertical axis with an internal vertical rotating auger along the side of the drum wall [Figure 12(C)]. The resulting action lifts and mixes the puffed product and sugar to distribute coating over the popcorn. Sugar or caramel is made in the batch system by adding sugar, water and glucose (dextrose) to the cooking kettle and heating to 300◦ F (149◦ C). This is called hard-crack candy. The recipe may include varying amounts of white sugar, brown sugar, butter and various other ﬂavorings or colorings as may be desired. If butter is used in the mix, it is added at the end of cooking so the

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ﬂavor won’t be lost. Just before the sugar mix is poured onto the product, a small amount of baking soda may be added to the mix to make it foam. Foaming doubles or triples the mix’s volume. The light frothy mixture does a better job of coating than the heavy sugar produced at the end of the cooking cycle. The amount of soda used must be watched very carefully. Too much causes a bitter taste in the ﬁnished product. It should be noted that copper catalyzes development of ﬂavor in the coating. Therefore, reformulation may be necessary if a copper cooking kettle is replaced with stainless steel or aluminum equipment. In larger systems, steam-jacketed cooking kettles [Figure 14.12(A)] are used to premix and preheat all the ingredients to 180◦ F (82◦ C) before they are added to the cooking kettle[Figure 14.12(B)]. This substantially speeds up the cooking process in the kettles. The maximum practical holding temperature for the premix is 180◦ F. If held above this temperature for more than approximately an hour, the premix color darkens and ﬂavors begin to change. As a result, caramel coating made from the same batch of premix will not be consistent from the beginning to the end. After the sugar and popcorn are well coated, a small amount of an oil/lecithin mixture is sprayed into the coating drum. The lecithin mix causes the product to separate into individual particles. The typical ratio is one part liquid lecithin to 10 parts oil. Hot caramel or candy-coated product from the coater is next placed on a cooling table [Figure 14.12(D)] and stirred with hand tools while it cools. Continuous agitation and lecithin are necessary to produce a free-ﬂowing product. If a large amount of product is to be made, a horizontal continuous cooling tumbler may be used. A cooling tumbler is a large drum about 4 ft (120 cm) in diameter and 8 ft (240 cm) long, made of perforated metal. The tumbling action provides the agitation necessary to separate the product, and the perforations allow air to circulate and cool the product to a temperature where it is no longer sticky. Air conditioning must be used with caution when cooling caramel corn. Popcorn and hot sugar are very hygroscopic and absorb moisture from the air quickly. Air-conditioning systems often produce cold air at very high moisture levels. It is important to temper the air to reduce its relative humidity.

7.5. AUTOMATED BATCH SYSTEMS FOR SWEET/CARAMEL COATINGS Automated batch sweet products coaters are different from the manual batch coaters in several ways: r The amount of sugar coating cooked is signiﬁcantly larger. r Cooking and mixing take place in the same piece of equipment.

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Figure 14.13 Cooker/coater for automated batch popcorn sweet coatings. (C. Cretors & Company, Chicago, IL.)

r Hydraulic or pneumatic power, rather than manual labor, is used to empty

the batch from the machine. Automated batch cooker/coaters generally have a batch size of 90 lb (40 kg) of sugar coating. All ingredients may be mixed and cooked in the kettle/coater [Figure 14.13]. The cycle time and the hourly production rate may be increased by premixing and heating the ingredients in a steam-jacketed kettle [Figure 14.12(A)]. Once the coating is fully cooked, the popcorn is added to the kettle and the internal mixing system is turned on to blend the products. When the corn is completely coated, a small amount of an oil/lecithin mixture is sprayed on the product to facilitate its separation into individual pieces as it cools. When the process is complete, the kettle/coater drum is dumped with the help of pneumatic or hydraulic cylinders. From the coater, the hot sugar-coated popcorn goes to a continuous cooler where it is cooled and agitated. This agitation, with help from the lecithin sprayed on earlier, causes the popcorn to separate into individual pieces. The popcorn is ready for packaging after it leaves the separating and cooling tumbler.

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7.6. AUTOMATIC CONTINUOUS SYSTEMS FOR SWEET/CARAMEL COATINGS The fully automatic continuous system [Figure 14.11(B)] uses premix kettles to hold all sugar ingredients at a high temperature. The premix is pumped to a thin ﬁlm concentrator, where the syrup is cooked to a hard-crack temperature (300◦ F, 148◦ C) in about ﬁve seconds. The caramel then ﬂows to a steam-heated, stainless steel trough with a steam-heated auger that blends the continuous ﬂow of popcorn and hot sugar into a ﬁnished product. At a point, about one third of the way through the coating process, a small amount of lecithin-oil mixture is sprayed into the coater to promote separation of the product into individual particles. From the coater, the hot sugar-coated snack goes to a continuous cooler where it is cooled and separated. After the caramel corn leaves the cooling and separating tumbler, it is ready for packaging.

7.7. FLAVORED POPCORN RECIPES The ﬂavor is very important to the ﬁnished popcorn product and often is the ﬁrst item in the snack name—cheese corn, caramel corn, or salt and vinegar. It is important that the amount of ﬂavor not be reduced in an effort to reduce costs, since usually it cheapens the product and makes it difﬁcult to sell. r Salted Popcorn

—Oil Pop Popcorn 3 volumes raw corn 1 volume popping oil Salt to taste (ﬂour or ﬁne salt) —Dry Pop Popcorn 80% popcorn (weight) 20 to 22% coating oil (weight) Salt to taste r Cheese-Flavor Popcorn 15–25 % cheese (weight) 28% oil (weight) 57% popcorn (weight) r Sweet Popcorn, Sugar Corn 3.0 volumes raw corn 0.75 volume popping oil 1.5–2.0 volume sugar depending on taste r Caramel Corn —Batch 70% light brown sugar 21% glucose

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9% water Flavorings as desired —Continuous 65% light brown sugar 25% glucose 10% water Flavorings as desired —Finished Product 70%–90% Sugar Coating 30%–10% Popcorn 100% 100% When working with artiﬁcial fruit color and ﬂavors, begin with white sugar, which does not add ﬂavor of its own.

8. POPCORN PACKAGING

8.1. RELATIVE HUMIDITY AND HYGROSCOPICITY Popcorn is the most hygroscopic of the crispy snacks. The following principles to keep popcorn fresh and crisp apply to all crispy snacks. Tough and chewy popcorn is most frequently caused by weather-related excessive humidity. In an oil-popping operation, the problem usually occurs during days when the relative humidity (RH) is over 50%. In the midst of the summer or a rainy season, 70–90% RH is a major challenge to handling popcorn. The desired moisture content for salted, cheese-ﬂavored, or other savory ﬂavors of snacks is 1.0–1.5% or less. A very crisp product at 1–2% moisture content turns into an increasingly chewy product at 4–5% moisture content. Some customers, especially fond of popcorn, object to moisture contents above 2.5%. The literature indicates that popcorn, initially at about 1.5% moisture, equilibrates to approximately 2.5% moisture at 20% RH in 15 minutes when completely exposed to the environment, 3.5% moisture at 30% RH, 4.5% moisture at 40% RH, 5.5% moisture at 50% RH, 6.5% moisture at 60% RH, and 7.5 % moisture at 70% RH [3]. Moisture absorption is slower in oil-popped corn. Nevertheless, minutes count when getting fresh popcorn into suitable packages, or at least into a protected temporary environment or tote.

8.2. SUGGESTIONS FOR KEEPING POPCORN CRISP r Burning natural gas and popping corn release large amounts of water into

the air. The popping room needs ample outside air intake and exhaust of

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steam and vapors directly from the poppers, whether oil or dry poppers. A hood is best for collecting the humid air. Air conditioning and humidity control usually are too costly for effective use in the popping room, and packaging is better done in a separate area. r Popcorn coming out of a dry popper is very hot and usually contains 3–4% moisture. The sifter and tumbler allow the corn to cool and dry to 1–2% moisture by exposure to the ambient air. If the corn is kept at least 20◦ F (11◦ C) above the room temperature, it will remain dry and crisp. r The best approach is to quickly package the product while it is more than 20◦ F (11◦ C) over the temperature of ambient room air. Popcorn should not be stored before packaging unless it has already dried and can be protected and kept dry by suitable enclosure. r Whenever the relative humidity is over 50%, the packaging area should have humidity control equipment. In the absence of environmental controls, maintaining the popcorn at 20◦ F (11◦ C) above room temperature keeps it dry and crisp. Popcorn and other snacks pick up moisture at over 50% relative humidity. The problem is critical at over 70% relative humidity. A 30%–45% relative humidity, which is normal in winter-heated areas, allows long-term storage of puffed snack products without packaging protection; 45% is borderline, while 20%–30% is safe over a long period of storage.

8.3. PACKAGING MATERIALS AND EQUIPMENT Protection of the packaged popcorn against gaining moisture must be continued to the sales outlet by appropriate packaging materials, and then for a reasonable time until the consumer opens the package. Seasoned products also need oxygen barriers to protect against oxidation of the oils. Internally enameled metal containers, sealed with appropriate tapes and containing small pouches of desiccant, offer excellent protection but are expensive. Their use is mainly limited to gifts or holiday parties. Where coloring agents are used in snack products, it is desirable to provide light-barrier protection, which can be accomplished by using metallized ﬁlm. Although not as effective as foil laminates, metallized polypropylene packaging ﬁlms are increasingly used because they are more economical. The pouches can be ﬂushed with nitrogen to remove oxygen, and sealed with a pillow headspace to help cushion fragile products against breakage. The reader is referred to Chapter 22 on packaging materials, and Chapter 23 on snack foods ﬁlling and packaging for further details.

9. RELATIVE NUTRITION Popcorn has not borne as much accusation of junk food as some of the other snacks. In fact, it is often considered a healthy snack. Dentists have

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endorsed salted popcorn as an alternative to a sweet snack. The American Dietetic Association permits popcorn as a bread exchange in weight control diets. In addition, the National Cancer Institute includes popcorn in its list of moderately high sources of ﬁber to help reduce the risk of colon cancer. Dry-popped corn has the same protein, fat, carbohydrate and mineral content per unit weight as natural whole popcorn, except in greater concentration because of moisture loss during popping. Air-popped corn contains about 30 calories per cup, oil-popped corn about 55 calories and lightly buttered popcorn about 90–120 calories. On a volume basis, popped popcorn is low in calories, and a high quality source of complex carbohydrates (ﬁber) compared to other snack foods [4].

10. MARKETING OF POPCORN While North America and most parts of Europe can be considered mature markets, many other parts of the world are only now discovering popcorn. Taste preferences vary from country to country, but caramel corn continues to be a strong seller in most areas. Caramel corn enjoys an image as a healthy food that satisﬁes the consumer’s craving for sweetness, is ﬁlling and is a fun product. With savory popcorns, a particular ﬂavor is often popular for a while, and consumers then change to a newer ﬂavor. Considerable potential exists for continued innovations in ﬂavor development and marketing. Starting in the 1980s, movie theaters in the United States began to divide their large auditoriums into several smaller rooms. This was done to give the moviegoer more choices in movies and to enable the concession stand to serve more customers. The average movie theater patron spends as much on snacks at the concession counter as at the ticket booth. Proﬁt dollars from the concession stand exceed those of ticket sales, with 80% of a movie theater’s proﬁt coming from cold drinks and popcorn, popcorn being the sales and proﬁt leader. Currently, movie theater attendance is at its highest in 40 years, and the growing number of megaplexes continue to provide fresh popcorn products to the public. Opportunities for selling new high-quality popcorn products through grocery and convenience stores have been demonstrated in recent years by introduction of products like white cheddar cheese popcorn, fat-free caramel popcorn, and gourmet caramel popcorn. Popcorn excels in the gift market relative to other snack foods. Some of the largest manufacturers of popcorn in the United States. ﬁll large decorated gift cans with divided sections of salted popcorn, cheese corn and caramel-coated popcorn. An innovative product example is (compressed) popcorn cakes, patterned after the earlier success of rice cakes as a low-fat snack food. Supermarket sales of popcorn cakes reached $200 million in the United States in 1997. These products offer the advantages of a ﬁxed number of calories per cake for

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consumers who count calories, and no shedding of ﬁnes as often occurs when handling popped corn. More recently, chocolate, caramel, savory and other ﬂavored corn cakes have been introduced, as well as mini-cakes speciﬁcally promoted as snacks. Improved ﬂavor systems, especially for no-fat or low-fat products, and improved packaging systems already shared with the rest of the snack food industry, indicate that increased sales of high-quality ready-to-eat popcorn products is limited only by individual abilities to innovate new products and creative marketing.

11. REFERENCES 1. SF&WB, (June) 1999. State of the industry. Snack Food & Wholesale Bakery, 88(6):SI-1-SI-82. 2. SFA, 1987. 50 Years: A Foundation for the Future. Snack Food Association, 1711 King St, Suite One, Alexandria, VA 22314. 3. Matz, S. A., 1993. Snack Food Technology, 3rd edition. AVI Van Nostrand, Reinhold, New York. 4. www.popcorn.org, June 22, 2000, Popcorn Board, Chicago, Illinium.

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CHAPTER 15

Snack Foods of Animal Origin

PETER J. BECHTEL

1. INTRODUCTION

F

OR the purpose of this chapter, a snack is a food product that is predominantly

consumed between meals. It is not clear when the practice of eating meals at prescribed times originated, but snacking between meals appears to have been institutionalized in recent times, resulting in a multibillion dollar domestic and international snack food industry. This chapter reviews snacks of animal origin including meat, ﬁsh, dairy and egg products. Meat snacks have their origin in meat- and ﬁsh-drying practices that were innovated to prevent rapid spoilage. Consumption of meat snack foods has received increased attention as the result of several popular diets that encourage consumption of increased amounts of protein and less carbohydrate. Raw meat consists of approximately 75% water,18% protein,varying amounts of fat (2–20%), less than 1% minerals and less than 1% carbohydrate. With a pH usually between 5.5–6.5, raw meat is an ideal substrate for microbial growth. In general, the place of meat in the human diet has been well established as an excellent nutritional source of high-quality protein, B vitamins including vitamin B12 , zinc, bioavailable iron and many micronutrients. A large variety of distinctive dried meat products exists, some of which are listed in Table 15.1. Most meat snacks ﬁt into the low-moisture category (water activity below 0.6) or intermediate-moisture category (water activity of 0.9–0.65) [1]. Lowmoisture meat-like snacks include jerky, dried ﬁsh and seafood products, which are stable at room temperature for long periods of time. Intermediate-moisture meat products usually are partially dehydrated to l5–50% moisture, and contain salt, sugar, or humectants added to further reduce water activity, and mold

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Intermediate- and Low-Moisture Meat Products.1

TABLE 15.1.

Name Beef jerky Biltong Bunderfleisch Carne de sol Charqui Dendeng giling Fermented sausages Khundi Pastirma Pemmican Prosciuto ham (raw) Sou song Spreck wurst Quanta 1

Region or Country North America South Africa Europe South America South America Indonesia Europe Africa Turkey North America Europe China Europe Africa

Partially taken from Reference [3].

inhibitors to prolong shelf life. These products are packaged to reduce development of oxidative rancidity and other ﬂavor problems. Generally, they can be stored at room temperature for long periods of time and are eaten without rehydration.

1.1. WATER ACTIVITY Knowledge of the percent moisture content in a meat product is useful for categorizing its potential for microbial and chemical degradation. However, water activity (A W ) measures availability of water for microbial growth and is a better predictive tool. Some water is bound very tightly to macromolecules in the food and is not available to support microbial growth. Typically, the additional water is loosely bound or free within the food and can be used by microorganisms. Free or loosely bound water vaporizes easily, whereas tightly bound water vaporizes with difﬁculty. Water activity is the ratio of the vapor pressure of the water in the food to that of water alone at the same temperature. Various instruments are available for measuring A W as the relative humidity in the air space of a small container in which a test sample has been allowed to equilibrate. The relationship between the moisture content of a food and water activity is described by a sorption isotherm as shown in Figure 15.1. Sorption isotherms for different foods often have common features; however, each food has a distinctive sorption isotherm for a given temperature. Temperature effects include changes in the physical properties of the product as well as in co-solubilities of the ingredients. Thus, the sorption isotherm for cooked beef is different from cooked beef

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Figure 15.1 Representation of sorption isotherm for cooked meat at 70◦ F (21◦ C).

containing salt [2]. It can be affected by many factors, including the product’s composition, process treatments, and by addition of salt, sugar or humectants [3]. Humectants bind to water very tightly and reduce its vaporization and availability to microorganisms for growth. In most meat and ﬁsh snack foods, the water content has been greatly reduced so microbial growth is not supported. However, removing moisture is expensive and leads to ﬂavor and texture changes. Therefore, it is usually desirable to remove the least amount of water possible while still inhibiting microbial growth. The creation of a shelf-stable meat snack requires the product to be free of bacterial, yeast and mold growth and to have minimal lipid oxidation, non-enzymatic browning and enzyme-catalyzed degradations. Water activity plays an important role in all these processes. The amount of moisture that must be removed from the product to obtain a desired A W can be determined from the appropriate sorption isotherm. Conversely, the water activity of a food product can be measured and used to predict potential problems that may be encountered [4]. Water activities of pure solutions can be estimated mathematically and are related to the percent mole weights of solvent (water) and solutes (dissociated ingredients) present in the mixture, rather than percent ingredient weights.

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Because of complete dissociation in solution, a mole of salt, with a molar weight of 58.44 g, theoretically provides twice the competition for water than a mole of glucose (180.16 g). Similarly, 3 carbon compounds (glycerin and propylene glycol) are more effective per unit weight in reducing A W than monose (6 carbon) sugars like glucose, which, in turn, is more effective than dioses like sucrose with 12 carbons. Prediction becomes more complex when macromolecules like protein in meat and cooked starch from cereal additives are encountered in foods [4]. Strategies for reducing water activity in a meat product include removal of water by dehydration and addition of compounds to bind water tightly in the meat product. The preparation of some meat products includes use of both strategies by adding salts and/or sugars and drying the meat product. Humectants such as glycerol and propylene glycol and other polyhydric alcohols have become common components in intermediate-moisture foods. These compounds reduce the water activity and often improve texture and other properties. Addition of large amounts of salt can create sensory problems, and addition of large amounts of humectants can introduce distinctive sweet ﬂavors. The water activity of fresh meat is above 0.99 [5]. Most intermediate-moisture meat products have water activities between 0.65 to 0.90 and contain less that 50% moisture. Low-moisture foods have water activities below 0.60, which corresponds to moisture contents below 15% for many meat products. Safety of intermediate-moisture meat products for human consumption requires that water activity be reduced below that necessary for growth of food-borne pathogens. In general, the water activity of intermediate foods should be reduced below 0.85 to inhibit most pathogenic bacteria, as shown in Table 15.2. However, many molds and yeasts continue to grow at an A W of 0.85 [6,7]. These can be further controlled by the addition of antimycotic compounds such as sorbic acid and potassium sorbate. The general topic of water activity and microbiology of meat drying has been well reviewed by Gailani and Fung [8].

TABLE 15.2.

Approximate Minimum Water Activity ( Aw ) for Microbial Growth.1

Organism Most bacteria Most yeasts Most molds Most halophilic bacteria2 Most xerophilic molds3 Extreme limit of osmophilic yeasts and xerophilic molds4 1

From References [1, 5, 8, and 21]. Halophilic means high salt tolerant. 3 Xerophilic means low moisture tolerant. 4 Osmophilic means high osmotic pressure tolerant. 2

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Factors that can alter the shelf life of meat snacks include: heating or cooking steps in the process, reduction of water activity, reduction of pH, addition of preservatives and reduction of the redox potential in the product [3]. Often the pH is lowered using organic acids or glucono-delta-lactone. A heating step can also be a low-temperature pasteurization process. Packaging can reduce the redox potential to inhibit the growth of bacilli and oxidation problems. The addition of nitrite (curing agent) to the product may have some positive effects including stabilization of color and ﬂavor components, and some inhibition of microbes. Mold growth can be reduced by smoke treatment of the product, dipping the product in a potassium sorbate solution and vacuum packaging [3].

2. JERKY PRODUCTS Preserving strips of meat by drying is one of the earliest food preservation methods and has survived for centuries because it preserves meat while maintaining its nutritional qualities, and desirable ﬂavor and texture properties. A publication of the Food and Agriculture Organization of the United Nations outlines some common meat preservation techniques [9]. Meat drying is often accompanied by other preservation methodologies like addition of salt and smoke treatment. Jerky includes a variety of products, ranging from intact strips of dried muscle to dried ground and comminuted products. It is expensive compared to other snack foods due to the high cost of meat before drying. Lean raw meat has a water content of approximately 70–75%, and the cost per pound of product increases dramatically as water content is reduced during drying. Meat with a high fat content is normally not used for jerky because rendering of fat interferes during the drying process, and also due to sensory and texture problems of the ﬁnished product. The USDA Food Standards and Labeling Policy Book [10] states that all jerky products must have a moisture-to-protein ratio (MPR) of 0.75:1 or less, and the meat species or kind must be in the product’s name. Jerky has a MPR lower than other common meat products such as pepperoni (1.6:1) or dry salami (1.9:1). Jerky products can be cured or uncured, smoked or non-smoked and dried using air or oven drying methods. Additional labeling possibilities exist. For example, a jerky produced from a large piece of beef may be called “natural-style beef jerky” provided an accompanying explanatory statement such as “made from solid pieces of beef” is used. A classic method for making beef jerky is to take 50 kg of beef and cut it along the direction of the grain in long strips that are 2–3 mm thick and 2.5 cm wide. Salt (4%), pepper (0.5%) and other minor ingredients such as soy sauce, garlic and lemon juice are mixed and used to coat the meat strips, which then are placed on wire racks. The meat strips are dried at 175◦ F (80◦ C) for about

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25 hours until brittle. The strips are then wrapped in a cloth and stored in a cool place for several days before transferring them to an airtight container at room temperature [11]. Other procedures include immersing cut strips of meat in a cold marinade containing salt, spices and cure agents for several hours. The marinated strips are then rinsed with water and dried in a smoke house at 131◦ F (55◦ C) or higher [12]. There are many variations on production of jerky from whole pieces of muscle. Most procedures cut the muscle with the grain and place the meat in a marinade prior to drying. Different spice mixes, cutting geometry, curing and smoking options, and packaging increase the variety of products made. The processing is simple enough that small meat processing plants can produce very distinctive products. Selling shredded jerky in a small round can, similar to that used for some tobacco products, is only one of the interesting packaging practices.

2.1. FORMED JERKY PRODUCTS Chunked and formed jerky products are made by mixing and massaging chunks of meat, spices and salt, and placing the mixture in a mold for heat treatment. The resulting solid piece of molded meat is then cut into strips and dried to the same 0.75:1 moisture-to-protein ratio. Jerky can be labeled “ground and formed” or “chopped and formed” when made from meat that has been ground or (bowl) chopped as shown in Figure 15.2. The ground or chopped meat is mixed with spices and salt and placed in molds that are heated. After ﬁrming, the meat is removed from the mold, cut to the desired shape and dried to the same MPR. Another product, labeled as “jerky

Figure 15.2 Flow sheet-ground and formed jerky processing.

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sausage,” can be made by mixing ground or chopped meat with spices and salt and stufﬁng it into small-diameter casings. The same MPR of 0.75:1 is required; however, the product may be dried at any stage in the process [10]. Another procedure used to make ground or chopped jerky products involves mixing ground or ﬂaked meat with curing agents, spices, salt and phosphates, and placing the mixture in casings that are tempered to 28.5 to 23◦ F (−2 to −5◦ C). Then, the ﬁrmed product is sliced, spread on racks and dried at 55◦ C or higher to the desired MPR [12].

2.2. JERKY INGREDIENTS AND SAFETY CONCERNS Ingredients used for formed and sausage jerky products include different species and kinds of meats, salt, spices, curing agents and sometimes binders. If the level of binder (e.g., soy protein concentrate) used is less that 3.5%, the label must list the binder in a qualifying statement. If levels of binder exceed 3.5%, the binder must be reﬂected in the product’s name. Regulations limit amounts of nitrite and other additives that can be used. Types of meat used to make jerky have included skeletal muscle from domestic and wild animals. A recent study found that jerky made from beef top round had more desirable sensory properties than jerky made from beef hearts or beef tongue [13]. In another study of highly spiced jerky-like products made from beef top round, turkey breast or emu cuts, the naturally lean emu product came out well in comparison [14]. Dried meat products, such as jerky, owe their existence in large part to the fact that, due to low A W , they do not support growth of most microorganisms. However, products can be contaminated with pathogenic microorganisms, introduced by ingredients or during processing, that multiply during the drying process. Although a speciﬁed heat treatment is not required in the production of jerky [10], it is recommended that the meat be heated above 160◦ F (71◦ C) prior to drying at 131◦ F (55◦ C). Many of the safety concerns for jerky products came from home manufacture, where problems may occur in monitoring and maintaining the temperature during drying [15]. Microbiological safety of shelf-stable meat products has been the topic of many reviews [8, 16]. Faith et al. [17] evaluated drying time, temperature and fat content on viability of E. coli 0157:H7 in ground and formed turkey jerky. They identiﬁed conditions that would result in a 5-log cycle reduction. Holly [18] inoculated product with Staphylococcus aureus, Clostridium perfringens, Bacillus subtilis and Salmonella strains, and reported that drying at 131–140◦ F (55–60◦ C) provided a margin of safety against the initial low numbers of pathogens naturally occurring on meat slices. Microbial problems with dried meat products are often the result of organism growth during the drying process. Usually, rod-shaped bacteria are more sensitive to dehydration than cocci, and endospores are largely unaffected.

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3. SHELF-STABLE SAUSAGE STICK SNACKS Many sausage or imitation-sausage stick products are marketed using proprietary names. The name sausage implies that the meat has been chopped. Long shelf lives of these products are obtained by strategies that can include reducing water activity, lowering pH, adding chemical preservatives and using mild heat steps. Dry-sausage stick products must have MPRs of 1.9:1 or less. The common non-refrigerated, semidry shelf-stable stick products must have MPRs of 3.1:1 or less and pH of 5.0 or less [10]. Other rules apply to other products in this diverse classiﬁcation of non-refrigerated, semidry shelf-stable sausages [10]. Dry or semidry stick products that do not meet USDA-FSIS definitions for sausages must include ingredient listings on the label. Formulation of a beef stick snack sausage product could include 100 kg beef (lean beef, beef trimmings, ﬂank), 2.5 kg salt, 1.25 kg dextrose, commercial spice blend, nitrite, sodium erythorbate and a commercial lactic acid starter culture. The process shown in Figure 15.3 includes grinding the meat, mixing the ingredients, and stufﬁng into small-diameter edible casings [19]. The product is put in a smoke house for a time and temperature that allows the lactic acid starter culture to reduce the pH to 5.0 or lower before drying the product. The ﬁnal step includes heating the product to an internal temperature above 137◦ F (58 ◦ C). Depending on the ingredients and processing, the above product would have a moisture content of less than 50%, a protein content of 24% for a MPR of 2.1, and a pH of less that 5.0. The microbiology of intermediate-moisture meat products is complex. The margins of safety often are not large, and breakdowns in the antimycotic

Figure 15.3 Flow sheet-beef stick snack sausage product processing.

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protection system result in mold growth. Other problems include migration of moisture into the package resulting in spotty areas of mold growth. To a large extent, intermediate-moisture meat products are relatively stable at normal storage temperatures. However, a variety of deleterious chemical reactions can occur, especially at elevated storage temperatures [7]. The ﬁrst is oxidation of the unsaturated lipids, which results in rancidity, aggregation of protein, cleavage of protein chains and destruction of vitamins and amino acids. A second common chemical reaction is non-enzymatic browning, which results in formation of dark insoluble products. A third type of reaction can occur when glycerin is used as an ingredient. It can react with many compounds, resulting in protein cross-linking (including collagen) and changes in the myoglobin (red color) spectrum.

4. OTHER DRIED MEAT PRODUCTS A large variety of freeze-dried meats and seafoods is used in shelf-stable products like soup mixes, and so on. Most are not snacks, and are usually rehydrated before consumption. The process for making freeze-dried meat is to ﬁrst freeze the meat and then remove the ice as vapor in a vacuum chamber. Dried beef slices are produced by ﬁrst curing beef in a solution of salt, sugar and nitrite until the cure solution has completely penetrated the meat. The slices are then rinsed and dried in a smoke house for several days at 90–100◦ F. Dried beef is not cooked and may or may not be smoked [20].

4.1. MEAT BARS Dehydrated meat bar products are used as components of military and survival rations. A process for making this type of product is to ﬁrst reduce the moisture content of the meat by about 90% by freeze drying. The meat is then compressed into bars at pressures about 10,000 psi (69,000 kPa). Then the bar is dried further with radiant heat in a vacuum chamber and packaged in a water-impermeable pouch with an inert atmosphere. Shelf lives of ﬁve years at room temperature have been reported [21].

4.2. SOUTH AFRICAN BILTONG Biltong is an uncooked dried meat delicacy made in South Africa and elsewhere. It is purchased in sticks or slices, and portions are cut or broken off and eaten as a snack. In making the product, fresh meat is cut in long strips with the grain and placed in brine or dry salted. Besides sodium chloride, other brine components may include spices, sugar, vinegar, nitrate-nitrite cures and preservatives such as potassium sorbate (0.1%) or boric acid. The meat is left in the

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brine for several hours, then dipped in a hot water-vinegar solution and ﬁnally air dried at room temperature for 1–2 weeks. The ﬁnal product has a pH of about 5.5, moisture content of approximately 25%, water activity of 0.65–0.85 and salt content of about 6%. A recipe for making biltong is to slice 100 kg of lean meat and rub in 4 kg salt and spices (0.06 kg nitrite, 0.12 kg chilies, 0.38 kg pepper), refrigerate, let the cure develop for 18 hours and then dry in a low-moisture atmosphere [11]. Biltong, like other low-moisture dried meat products, is stable at room temperature. The major problem with biltong is that salmonella can survive for a long time in uncooked meat products. Therefore, it is important to use meat with a low initial microbial load, sanitary manufacturing practices and to rapidly reduce water activity during the drying procedure.

4.3. TURKISH PASTIRMA Pastirma is a salted dried beef product enjoyed in Turkey and other Mideastern countries. Meat from the hind quarters of older beef animals is cut into 50–60 cm long strips with a diameter less than 5 cm. Salt containing 0.02% potassium nitrate is used to cover the strips, which are then placed in a pile at room temperature for a day. The strips are then turned, salted and stored for another day. Then they are washed and dried for days at room temperature. After drying, the strips are put in a pile and pressed with heavy weights for 12 hr. The meat strips are then dried, piled and pressed again with heavy weights before being dried for 5–10 days at room temperature. The dried meat is covered with a paste that contains ground fresh garlic and other spices. Then the paste-covered strips are stored in a pile for a day, and hung and dried for an additional 5–12 days before distribution. The ﬁnished product has a pH of about 5.5, salt content of approximately 6%, water activity of approximately 0.88 and water content close to 35% [3].

4.4. CHINESE DRIED MEAT PRODUCTS The category of Chinese dried meat products includes some produced by several techniques [3]. One type of product consists of meat cubes or strips. To prepare it, chunks of beef, pork or chicken are cooked with addition of water until tender and cut into strips or cubes. Sugar, soy sauce, monosodium glutamate and spices are added to the liquid in which the meat was cooked, and the meat-sauce mixture heated over low heat until almost dry. The meat pieces are then placed on racks for several hours at 122–140◦ F (50–60◦ C) until about 50% of the original meat weight has been lost. The product can be stored at room temperature for several months and has a water activity of about 0.7. The product has a pH about 6.0 and contains 3–5% salt, 10–15% water and sugar in excess of 20%.

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A slightly different type of Chinese product is referred to as “shredded pork,” “pork ﬂoss,” or Sou Song. Lean pork tissue is cut with the grain and cooked in an equal amount of water until soft. After the meat is removed, the cooking liquid is evaporated to 10% of its volume, and sugar, salt, soy sauce, wine, monosodium glutamate and spices are added to the liquid. The meat pieces are mashed, separated into ﬁbers and added to the prepared liquid. Low heat is applied until the liquid has evaporated, and the stirring continued for an additional hour at about 85◦ C until dry (A W ∼ 0.6). If a crisp product ( A W of about 0.4) is desired, 20% vegetable oil is added and the product stirred over low heat until a golden brown color is obtained [3].

4.5. PEMMICAN Pemmican is a dried meat and fat product that was initially produced by American Indians [22]. Its taste is not outstanding, but the product has a very high caloric density, provides all nutritional advantages of meat and is a method of preserving meat. Pemmican was made by ﬁrst heat drying meat (often buffalo) and then pounding it into small fragments. The fragmented meat was then mixed with animal fat and ﬂavor agents. The dried meat-fat mixture was originally stored in animal skin bags until eaten. There was a commercial market for pemmican as late as the 1870s. Since that time, it has been a specialty item used as survival rations by explorers, and was included in some military rations. (Armour and Company made pemmican from 1906 to 1954.) There was much variation in pemmican recipes, but a product could contain 64% dried meat, 35% fat and 1% salt [22].

5. PORK RIND PRODUCTS AND EXPANDED PRODUCTS Pork rinds have been a small niche market in the U.S. snack food industry, but are showing surprising growth. Sales grew by 16% in the year ending December 31, 1998 [23,24]. Pork rinds are sold in small bags in convenience stores and a variety of other locations, including grocery stores, vending machines, and so on. There are two parts to the industry: (1) making pork rind pellets; and (2) making pork rinds from the pellets. Pork rind pellets are made from raw pork skins, with often only the belly and fat back portion skins used. Other competing uses for pork skins include the gelatin and the leather industries. After the skin is removed from the carcass, it can be dipped for 30 seconds in a brine at 212◦ F [25]. The skin is then cut into small squares and rendered for 1–2 hours at approximately 230–240◦ F in vats of lard to remove fat and water. The squares of skin are agitated and kept submersed during the rendering process. After rendering, the pieces of skin will have decreased in size about 50%. The resulting defatted, dehydrated pieces of

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skin (pellets) are bagged and stored frozen. The quality of the pellets can be monitored by watching changes in the peroxide value of the fat. Pork rinds are made by ﬁrst rehydrating the pellets in a ﬂavored aqueous solution, followed by cooking with agitation for approximately 1 minute in fat at 400–425◦ F. During this frying step, the pellets expand (“pop”) to form a light-density product that can ﬂoat. Rendered pork fat is often used for frying. The rinds are then separated from the oil, and ﬂavorings such as barbecue, hot pepper or cheese may be added. The expanded snack can be air-dried to a brittle-hard texture. Packaging is important to avoid crushing of the product. Fat stability can be lengthened by using antioxidants and modiﬁed atmosphere in the package. Quality issues include a lack of size uniformity, texture and color uniformity, degree of expansion and variation in composition. A typical pork rind product contains approximately 70% protein and 30% fat [25]. Pork cracklings are shelf-stable products made from rendered fatty tissues. The process involves frying out (rendering) the fat from pieces of pork fat. The protein-connective tissue matrix left after the fat is removed are the cracklings. The pork skin must be removed before rendering the fatty tissue or the presence of the skin descriptively noted on the label [10]. Cracklings are consumed as a snack food or used as a condiment.

5.1. EXTRUDED STARCH SNACK PRODUCTS CONTAINING MEAT Meat can be used as an ingredient to make cereal-based extruded snacks, although it is not an ideal ingredient because of its high moisture and fat content. Studies to optimize conditions and formulas have been conducted using a starch source, soy isolate, salt, hydrolyzed vegetable protein and a pork or beef slurry at the 20% level [26]. Acceptable products, with a bland ﬂavor and light color, were produced. The use of lower-cost meat sources, including beef heart and pork shank trimmings, have also been evaluated. Other studies have examined the properties of extruded raw beef blended with defatted soy ﬂour and amylose cornstarch [27], and properties of extruded meat and potato ﬂour products [28]. A patent for an interesting expanded meat chip product has been described [29]. Ground or chopped meat is mixed with water, heated to 212◦ F (100◦ C) and combined with a mix of corn and potato starch to form a dough. The dough is cooked under pressure, cooled, and held for 8–12 hours before slicing. The slices are fried in hot oil at 400◦ F (220◦ C), resulting in an expanded chip.

5.2. EXPANDED FISH AND SHRIMP CHIPS Small amounts of ﬁsh, shrimp and other shellﬁsh mince have been mixed with starch and used to produce crisp expanded snacks. The ﬁrst step in most processes is to form a dough from starch, water, ﬁsh mince and salt. The dough

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is heated to gelatinize the starch, sliced and dried. The dried slices are expanded in an oven or by frying [30]. Fat rancidity is a problem for these products, and use of antioxidants is common. Large varieties of these snacks are common in Asian markets.

6. PICKLED SNACK FOODS Marination of meat has been used to improve meat tenderness and impart desirable ﬂavor characteristics. Several types of marinades exist, with acidic formulations common. After meat is kept in an acidic marinade for sufﬁcient time, the marinade penetrates to the center of the product, resulting in a lowering of meat pH [31]. The product can become shelf stable if the pH drop is sufﬁcient. Different types of cooked sausages have been packed in hot vinegar solutions of approximately 5% acetic acid plus salt and spices. The sausages come to an equilibrium with the vinegar solution in several days, resulting in lowering the pH inside the sausage and a weight gain of approximately 25%. Sausage types used for pickling include small individual frankfurter-like sausages, pieces of coarse-ground sausages and artiﬁcially colored (often red) small sausages. These products have good shelf life in the vinegar solutions. USDA regulations regarding sausages in vinegar require a minimum of 4 g of acetic acid per 100 cubic cm of product [10]. The vinegar pickle must completely cover the sausages, and pH maximum is 4.5. Pickled sausages and meat products are available in sealed glass and metal containers and consumed as snacks and as appetizers. Another pickled product consumed as a snack is pickled pigs feet. Several processes for pickling pigs feed are described in Matz [25].

7. DAIRY- AND EGG-BASED SNACK FOODS Some cheeses, with low moisture and very high salt content, are shelf stable but are not commonly used as snacks. Some small snack packages of cheddar, processed, and mozzarella (string cheese) are intended for eating as snacks, but usually require refrigeration. Other shelf-stable cheese-like products and spreads are packaged with or between crackers. Some puddings and dessert products contain signiﬁcant quantities of dairy components and are packaged in individual shelf-stable portions utilizing sterile processing and packaging procedure. Small dried balls of yogurt, stable at room temperature, are used as snacks in Central Asia and other parts of the world. The snack food industry uses dairy products mostly as ingredients. They include: skim milk powder, milk solids, casein, dried whey, spray-dried yogurt, cheese powders and enzyme-modiﬁed derivatives of cream and cheese [32]. Powdered cheese is a common snack food ingredient and coating for a large

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variety of snacks. Dehydrated and ground cheese products are available for these purposes, but use of spray-dried products consisting of some cheese plus dried buttermilk, powdered whey, color and ﬂavor components is more common [25]. Eggs are not common domestic snack foods. An egg snack that has lost popularity is pickled eggs. The process for making pickled eggs is to hard boil chicken or quail eggs, which are then covered with a vinegar solution containing spices. The low pH results in a shelf-stable product.

8. DRIED AND MARINATED FISH AND SHELLFISH SNACKS There are many dried and smoked ﬁsh and seafood snack products throughout the world. Many of these are salted for periods ranging from minutes to weeks [33]. Three primary salting methods are used: (1) a solid salt rub that extracts the moisture, which is drained away from the product; (2) a salt pickle, where the ﬁsh remains in contact with the extracted moisture; and (3) brining, where the ﬁsh is soaked in a concentrated salt solution for speciﬁed length of time. Smoking of ﬁsh and seafood is used to impart ﬂavor, provide antioxidant properties and inhibit microbes. Three general methods are used for smoking ﬁsh and seafood products: (1) cold smoking, where the temperature is approximately 86◦ F (30◦ C); (2) hot smoking, where the ﬁsh is cooked during the smoking operation and the temperature often is in the 131–167◦ F (55–75◦ C) range; and (3) smoke drying, where the ﬁsh is cooked and dried. Usually, products originating in Europe are brined before smoking, while products from Africa often are not brined but sometimes air dried prior to smoking [33]. Fish can be dried using many procedures, from hanging and drying in the air to using commercial drying equipment. Air drying at ambient temperature usually can be accomplished within 3 to 10 days, provided temperature and humidity conditions are appropriate. Care must be taken to avoid a crusting (case hardening) on the surface of the ﬂesh which will inhibit moisture escape from the interior ﬂesh.

8.1. DRIED FISH AND SHELLFISH PRODUCTS Dried ﬁsh consumed as snacks include: anchovies, sardines, herring, mackerel, saury, sand eel, pout and pieces of the ﬁllet from larger ﬁsh. Lean ﬁsh are usually used to reduce oxidative rancidity problems. Dried shellﬁsh snacks include: shrimp, clams, mollusks and squid [30]. The largest variety of small dried ﬁsh products is found in Japan. The small ﬁsh are dried whole, split dried or pierce dried, and can be salted or nonsalted. The salting of ﬁsh can be done using the dry salting procedure (20 to 30% salt overnight) or soaking in a 10–15% brine for 4 to 8 hours. Drying procedures include drying at high temperature, or partial drying to 44–48% moisture, plus salt curing and smoking.

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A well-known specialty from India is Bombay duck, which is dried small bumnaloe ﬁsh. During drying, the bumnaloe loses its ﬁsh ﬂavor and develops a unique roasted oil ﬂavor. The production of ﬂavored dried ﬁsh, which are made from small and medium-size sardines, saury, mackerel, ﬂat ﬁsh and sea bream is a Japanese specialty. The ﬁsh are gutted and seasoned for several hours with a combination of soy sauce, sugar, sake and monosodium glutamate, and then dried. Clams and squid are also seasoned and dried [30]. A dried “ﬁsh ﬂoss” or shredded ﬁsh product is consumed in parts of Asia as a snack food. This product is made by soaking ﬁsh in a brine, followed by cooking and deboning. The deboned ﬁsh is pressed to remove moisture and heated to further reduce the moisture content to approximately 25%. The dried ﬁsh muscle is then shredded into ﬁbers that are mixed with oil and spices and roasted. Another snack, found at times in North America and Europe, is minced white ﬁsh that has been roller dried. Dried cod that has been mechanically softened is available in small snack packages in Nordic countries. Dried shrimp and squid snacks are common in many parts of Asia. In Japan and Southeast Asia, a shrimp snack product is made by boiling shrimp in a 2% brine for 30 minutes, followed by peeling and drying. Other snack items include dried squid, dried herring, gray mullet roe and fried ﬁsh bladders [30].

8.2. MARINATED AND/OR CANNED FISH AND SHELLFISH PRODUCTS Pickled herring is a common snack and appetizer, with a 17 to 25% fat content, made from herring. The classic processes involve aging salted herring in barrels for 6 to 24 months at 39.2–53.6◦ F (4–12◦ C). Small pieces of ﬁllet are then put in glass jars with vinegar and spices. Faster processes delete the aging and marinate the herring in the jar. Shelf-life concerns may occur, depending on the procedure used, and the product is usually refrigerated. Anchovies are made from spat in the Nordic countries and anchovy in the Mediterranean countries. Whole ﬁsh are packed in containers with salt, sugar and spices and stored at 15 to 20◦ C for ripening. After ripening, the ﬁsh are ﬁlleted and packed in cans with an acidiﬁed brine marinade. Other marinated snack products include shrimp, eel, and oysters [30]. The process for making a canned oyster product is to mix raw oysters with 3 to 6% salt and boil. They are then steamed and smoked for 20 to 40 minutes and put in an oil before the canning process. Canned smoked clams are made by a similar process.

9. REFERENCES 1. Cassens R. G., 1994. Meat Preservation. Food and Nutrition Press, Trumbull, Connecticut, pp. 68–71.

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2. Iglesias, H. A. and J. Chirife, 1982. Handbook of Food Isotherms: Water Sorption Parameters for Food and Food Components. Academic Press, New York, pp. 31–35. 3. Leistner, L., 1987. Shelf-stable products and intermediate moisture foods based on meat. In Water Activity: Theory and Applications to Food. L. B. Rockland and L. R. Beuchat eds. Marcel Dekker, Inc., New York, pp. 295–327. 4. Bone, D. P., 1987. Practical applications of water activity and moisture relations in food. In Water Activity: Theory and Applications to Food. L. B. Rockland and L. R. Beuchat, eds. Marcel Dekker, Inc., New York, pp. 369–395. 5. Romans, J. R., W. J. Costello, C. W. Carlson, M. L. Greaser, and K. W. Jones, 1994. The Meat We Eat. 13th edition. Interstate Publishers, Danville, Illinois, pp. 710–765. 6. Ledward, D. A., 1981. Intermediate moisture meats. In Developments in Meat Science—2. R. Lawrie, ed. Applied Science Publishers, London, pp. 159–194. 7. Ledward, D. A., 1983. Novel intermediate moisture meat products. In Properties of Water in Food. D. Simatos and J. L. Multon, eds. Martinus Nijhoff Publishers, Dordrecht, The Netherlands, pp. 447–463. 8. Gailani, M. B. and D. Y. C. Fung, 1986. Critical review of water activity and microbiology of dried meats. CRC Crit. Rev. Food Sci. Nutr., 25:159–183. 9. FAO, 1990. Manual of Simple Methods of Meat Preservation. FAO Animal Production and Health Paper, No. 79. Food and Agriculture Organization, Rome. 10. USDA, 1996. Food Standards and Labeling Policy Book. United States Department of Agriculture, Washington, D.C. (August), pp. 107–175. 11. Ocherman, H. W., 1989. Sausage and Processed Meat Formulations. AVI-Van Nostrand, Reinhold, New York, pp. 27–28, 265–266. 12. Davis, J. M., 1990. Meat based snack foods. In Snack Foods. R. G. Booth, ed. AVI-Van Nostrand Reinhold, New York, pp. 205–224. 13. Miller, M. F., J. T. Keeton, H. R. Cross, R. Leu, F. Gomez, and J. J. Wilson, 1988. Evaluation of physical and sensory properties of jerky processed from beef, heart and tongue. J. Food Qual., 11:63–70. 14. Carr, M. A., M. F. Miller, D. R. Daniel, C. E. Yarbrough, J. D. Petrosky, and L. D. Thompson, 1997. Evaluation of the physical, chemical and sensory properties of jerky processed from emu, beef and turkey. J. Food Qual., 20:419–425. 15. Buege, D. and J. Luchansky, 1999. Ensuring the safety of home-prepared jerky. Meat and Poultry, 25(2):56–57. 16. Tompkin, R. B., 1986. Microbiology of ready-to-eat meat and poultry products. Advances in Meat Research, 2:89–121. 17. Faith, N. G., N. S. Le-Coutour, M. B. Alvarenga, M. Calicioglu, D. R. Buege, and J. B. Luchansky, 1998, Viability of Escherichia coli 0157:H7 in ground and formed beef jerky prepared at levels of 5 and 20% fat and dried at 53, 57, 63 or 68 degree C in a home-style dehydrator. Int. J. Food Microbiol., 41:213–221. 18. Holly, R. A., 1985. Beef jerky: Viability of food-poisoning microorganisms on jerky during its manufacturing and storage. Journal of Food Protection, 48:100–106. 19. Long, L., S. L. Komarik, and D. K. Tressler, 1981. Food Product Formulary, Volume 1: Meat, Poultry, Fish, Shellﬁsh. AVI Publishing Co., Westport, Connecticut, pp. 37–58. 20. Pearson, A. M. and T. A. Gillet, 1996. Processed Meats. 3rd edition. Chapman Hall, New York, pp. 351–353. 21. Varnam, A. H. and J. P. Sutherland, 1995. Meat and Meat Products. Chapman Hall, London, pp. 387–41.

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22. Binkert, E. F., O. E. Kolari, and C. Tracy, 1976. Pemmican. In 29th Annual Reciprocal Meat Conference of the American Meat Science Association, pp. 37–53. 23. McMabon, T., 1997. Living high off the hog. Snackworld, 54(11):12–14. 24. Snack Food Association, 1999. Salted snacks: Pork rinds. Snack Food & Wholesale Bakery, June, pp. S1–52. 25. Matz, S. A., 1993. Snack Food Technology. 3rd edition. Avi-Van Nostrand, New York, pp. 39–50 and 225–234. 26. Thomas, L., P. Bechtel, and R.Villota, 1989. Effects of Composition and Process Parameters on Twin-Screw Extrusion of Expanded Meat-Based Products. 1989 Annual Meeting of the Institute of Food Technologists. Abstract No. 118. 27. Park, J., K. S. Rhee, B. K. Kim, and K. C. Rhee, 1993. Single-screw extrusion of defatted soy ﬂour, corn starch and raw beef blends. J. Food Sci., 58:9–20. 28. McKee, L. H., E. E. Ray, M. Remmenga, and J. Christopher, 1995. Quality evaluation of chileﬂavored, jerky-type extruded products from meat and potato ﬂour. J. Food Sci., 60:587–591. 29. Karmas, E., 1976. Processed Meat Technology. Noyes Data Corporation, Park Ridge, New Jersey, pp. 275–276, 308–324. 30. Nielsen, J. and A. Bruun, 1990. Fish snacks and shellﬁsh snacks. In Snack Food. R. G. Booth, ed. Avi-Van Nostrand Reinhold, New York, pp. 183–203. 31. Gault, N. F. S., 1991. Marinated meat. In Meat Science—5. Applied Science Publishers, London, pp. 191–246. 32. Robinson, R. K., 1990. Snack foods of dairy origin. In Snack Food. R. G. Booth, ed. AVI-Van Nostrand Reinhold, New York, pp. 159–182. 33. Poulter, R. G., 1988. Processing and storage of traditional dried and smoked ﬁsh products. In Fish Smoking and Drying. J. R. Burt, ed. Elsevier Science Publishers, London, pp. 85–90.

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CHAPTER 16

Rice-Based Snack Foods

SHIN LU TSE-CHIN LIN

1. INTRODUCTION

T

topics are covered in this chapter: rice milling and an introduction to rice-based snack foods. Most rice snacks in Taiwan are made from either normal indica or waxy japonica rice. Rice growing has had a direct impact on Taiwanese and southern Chinese culture. As an integral part of their history, rice can be traced back to 4000 BC when the “Seed in the spring, plow in the summer, harvest in the fall and store in the winter” proverb originated. In Taiwan, 90% of all rice is consumed as cooked whole kernels. The rest is milled to produce ﬂour, which is used to make cakes, desserts and snacks, primarily for special feasts or celebrations [1]. In the United States, rice is usually classiﬁed by length of grain: short, medium and long. In Taiwan, indica rice refers to long grains, while japonica refers to short grains. The United States produces mostly long-grain and intermediategrain rice in Arkansas, Mississippi, Louisiana, Texas and Missouri. California produces medium or short-grain rice. Taiwan produces mostly japonica rice with only 10% indica, waxy indica, or waxy japonica varieties. Physical properties of major rice varieties grown in Taiwan are shown in Table 16.1. WO

2. RICE MILLING Rough or paddy rice is shelled usually using rubber rolls and aspiration to remove the hulls. The brown rice is then milled using abrasive mills (pearlers) to remove the bran. The milled (polished) rice consists of whole intact starchy

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TABLE 16.1.

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Physical Properties of Milled Indica, Japonica and Waxy Rice Varieties Grown in Taiwan [2].

Rice Varieties

1,000 Kernel Kernel Length Kernel Width Shape Weight (g) (mm) (mm) (Length/Width)

Indica TNuS 19 KSS 7 TCS 10 TCN 1 TCS 17

22.57 24.48 22.68 21.86 30.28

6.64 5.85 6.42 5.35 6.21

2.22 2.64 2.40 2.67 2.87

2.99 2.22 2.69 2.01 2.16

Japonica TK 8 TK 9 TK 5 KS 142 TNa 9 TC 189

23.36 22.76 22.47 22.65 21.60 20.99

4.75 5.02 4.69 4.76 4.64 4.93

2.99 2.86 2.83 2.86 2.90 2.88

1.59 1.76 1.66 1.66 1.60 1.71

Waxy TCSW 1 TKW 1 TCW 70

23.64 22.32 21.12

6.24 4.44 4.40

2.46 2.94 3.03

2.54 1.51 1.45

endosperm (grains) and broken pieces. The milled rice is a light, white color consisting mainly of starch and protein with low-fat, ash and crude ﬁber content. Then the milled rice is further processed by grinding to produce rice ﬂour and meal depending on the products desired. Rice is milled (ground to ﬂour or to a coarse meal) in some Asian countries as part of the process for making traditional baked or steamed products [3–6]. Rice ﬂour is used in processed foods, which include cereals, soup, snacks, candy and others. Rice ﬂour consumption in 1990/1991 was 12.2 million cwt, which was over 21% of the total domestic demand for milled rice [7]. Ofﬁcial Taiwan market statistics indicate that approximately 0.9 million cwt of rice ﬂour are consumed annually in desserts and snacks. Approximately 30% of total rice ﬂour production is used in making noodles (bi-tai-ba) which are used in main dishes. One thousand years of milling experience has produced three milling processes: dry, semidry and wet milling. These processes make different types of ﬂours depending on the amount of water used (Figure 16.1). Functional properties of ﬂours are directly related to the amylose content of their starches [5,6]. Rice starch has more physicochemical interactions than other cereal starches. The amylose content, which ranges from trace amounts in waxy types to more than 30% in some non-waxy indica varieties, signiﬁcantly affects the use of ﬂour as thickeners and breadings. Because of their higher

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Figure 16.1 Flow chart for production of dry-milled, semidry-milled, wet-milled and parched rice ﬂours.

amylose content (>27%), some indica varieties cause products to thicken and form a rigid gel during storage. Manufacturers of rice noodles and rice cakes prefer high-amylose indica varieties such as Taichung Sen 19 and Taichung Sen 17 [8–10]. Flours milled from medium or short-grain japonica (low amylose) rice are preferred for puffed rice cakes and rice crackers (arare, sen bei), which are popular snacks in Japan. The branched chains of amylopectin produce desirable, lighter, expanded texture in products. Waxy japonica rice has a stickier characteristic than waxy indica varieties. A viscoamylograph, Rapid ViscosityTM Analyzer (RVA), and/or a differential scanning calorimeter, are used to determine the cooking and pasting properties of rice. These measurements are used to select rice for production of speciﬁc rice ﬂours [11]. Storage time and conditions, milling methods and pretreatment of rice kernels signiﬁcantly affect the physicochemical and functional properties

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TABLE 16.2.

Composition and Damaged Starch Content of Flours from Taiwanese Indica, Japonica, and Waxy Rice Varieties.a Protein (%)

Ash (%)

Lipid (%)

Damaged Starch (%)

Indica TNuS 19 KSS 7 TCS 10 TCN 1 TCS 17

6.16 6.40 7.16 7.61 6.47

0.38 0.56 0.53 0.59 0.51

0.38 0.71 0.37 0.77 0.45

7.80 4.86 8.78 5.98 4.83

Japonica TK 8 TK 9 TK 5 KS 142 TNa 9 TC 189

6.68 6.67 6.64 7.10 6.30 7.47

0.59 0.47 0.44 0.49 0.61 0.54

0.95 0.64 0.69 0.70 1.14 0.62

7.79 8.66 9.19 8.89 7.51 8.89

Waxy TCSW 1 TKW 1 TCW 70

7.77 7.08 7.02

0.38 0.61 0.52

0.72 1.39 0.91

8.40 7.69 8.07

Rice Varieties

a

Means of three replicates on oven-dry weight basis.

of rice ﬂour [12–17]. Additional quality control tests, such as protein, ash, fat and microbial counts, are used to ensure the ﬂour is an acceptable ingredient in processed foods (Table 16.2).

3. MILLING EFFECTS

3.1. DRY AND SEMIDRY MILLING In dry or semidry milling, the type of mill or grinder signiﬁcantly affects the functional properties of the ﬂour. Milling with hammer mills results in ﬂours with ﬁne particles; milling with attrition grinders produces coarse particles. Genetics and environment affect the kernel hardness of rice varieties, which produce different particle sizes upon processing (Table 16.3). Scanning electron microscopic (SEM) examination of the ﬂours shows that starch granules individually separate or aggregate during dry and semidry milling, respectively (Figure 16.2). The ﬂours also differ in chemical composition and in thermal properties after grinding (Table 16.4). Differential scanning calorimetry shows relatively similar gelatinization temperature and enthalpy values for the two rice varieties when compared within each milling process. Lower enthalpy values for some processes indicate relatively high starch damage [15,16].

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Hardness Index, and Particle-Size Distribution of Fourteen Indica, Japonica and Waxy Rice Varieties and Their Milled Flours [18]. Percent on CNS Screenc PSId

Milling Temperature ◦ C

Rtb

60

100

150

200

250

Indica TNuS 19 KSS 7 TCS 10 TCN 1 TCS 17

17.5 31.0 17.1 24.0 24.4

142.2 37.2 152.8 67.5 40.5

81.3 63.9 82.4 71.9 63.4

7.0 16.8 7.7 16.6 19.2

3.1 8.9 3.7 7.9 8.5

3.2 6.3 3.3 2.6 5.4

2.4 2.6 1.8 0.4 2.2

3.0 1.6 1.1 0.6 1.3

7.3 8.7 7.4 7.8 8.6

43.2 36.3 43.4 37.9 36.8

Japonica TK 8 TK 9 TK 5 KS 142 TNa 9 TC 189

21.9 13.8 10.9 12.5 35.7 14.7

103.5 132.3 141.7 159.2 68.3 158.3

80.3 81.1 86.1 86.3 74.7 84.1

12.2 7.4 6.8 6.2 16.8 7.2

5.2 7.2 4.1 5.3 6.4 4.9

1.7 3.1 2.0 1.7 1.9 2.8

0.4 0.7 0.6 0.4 0.1 0.8

0.2 0.6 0.4 0.2 0.1 0.2

7.3 7.5 7.0 7.0 7.5 7.3

38.6 42.1 44.3 46.6 37.5 45.7

Waxy TCSW 1 TKW 1 TCW 70

25.3 25.3 31.4

136.0 101.5 111.7

82.51 79.48 80.14

7.1 12.4 10.4

5.6 5.6 7.1

3.1 2.0 2.0

1.0 0.3 0.3

0.7 0.2 0.1

7.4 7.3 7.4

41.7 40.8 43.7

a

BMHT: Brabender micro--hardness test. Rt: Resistance time. c Chinese national standard sieves. d Particle size index according to Williams and Sobering [19]. b

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BMHTa

Through 250

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Rice Varieties

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TABLE 16.3.

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Figure 16.2 SEM micrographs of TCSW1 rice ﬂours: (A) dry turbo-milled; (B) dry cyclone-milled; (C) dry hammer-milled; (D) semidry ground; (E) semidry hammer-milled; (F) wet stone-milled.

3.2. WET MILLING The rice kernels are steeped for several hours before stone grinding the wet slurries into ﬂours with desired textures. The type of abrasive mill, the ratio of ﬂour to water and speed of the mill affect the functional properties of wet-milled ﬂour [9]. Flours made by wet milling are highly desirable for most snack foods [2,9]. Optimum steeping is 6 hours at room temperature and more than 10 hours when the temperature is near 10◦ C (50◦ F) [20]. Semidry milling is an alternative way

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TABLE 16.4. Effects of Milling Methods on Chemical Composition (Dry-Matter Basis) and Pasting Behaviors of TCSW 1 and TCW 70 Waxy Rice Flours.

Milling Methods

Rice Varieties TCSW 1 Protein, % dmb Ash, % dmb Fat, % dmb Thermal Analysis T0 Tp H TCW 70 Proximate Analysis Protein, % dmb Ash, % dmb Lipid,% dmb Thermal Analysis T0 Tp H

Dry Milling

Semi-dry Milling

Wet Milling

Turbo Cyclone Hammer

Attrition Hammer

Stone

7.9 0.6 2.5

7.9 0.7 2.0

8.0 0.6 1.9

7.5 0.3 0.8

7.2 0.3 0.7

4.9 0.2 0.3

62.1 72.6 10.4

62.1 74.4 10.5

64.2 74.6 11.9

63.3 72.7 4.1

62.1 74.0 11.6

59.3 71.9 12.7

7.0 0.9 2.2

6.9 0.8 2.0

6.9 0.8 1.5

6.3 0.5 1.2

59.8 71.2 11.1

61.1 72.6 10.3

62.1 72.9 12.4

60.1 73.3 4.8

6.29 0.5 1.2 58.8 71.7 12.8

5.47 0.4 0.6 58.2 69.6 13.1

of producing ﬂour; it decreases the costs of removing excess water and reduces pollution problems [2,16].

4. SNACK FOODS Chinese rice snacks are emphasized in this chapter. The reader is referred to Chapter 17 for rice crackers and products like senbei and arare, which are major traditional baked snack foods of Japan. Several factors discourage industrial production of rice snacks. First, snack foods in Taiwan are made by secret traditional methods. Also, government controls on pricing and distribution of rice limit new developments in processing rice ingredients for new products. Snack foods are classiﬁed into: (1) products that use whole rice grains, such as puffed rice items; and (2) products that use ﬂours prepared before and after cooking of broken or whole milled kernels.

4.1. PRODUCTS USING WHOLE GRAINS Puffed rice snack products are commonly used in Taiwan. The rice kernel is expanded several fold by high pressure or by frying [21,22].

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Figure 16.3 Process for making gun-puffed rice: (A) pufﬁng gun; (B) rice pufﬁng; (C) boiling syrup; (D) mixing rice and syrup; (E) pressing; (F) cutting; (G) products.

4.1.1. Gun-Puffed Rice Gun-puffed rice products are typical Chinese rice snacks. For best results, japonica varieties with low (<20%) amylose content are chosen for gun pufﬁng [20]. Waxy-type rice has a higher water absorption index and water solubility values, resulting in soggy texture and poor eating properties. The gun (pressure cooker) is preheated for several minutes before it is loaded with 600 g rice tempered to 14% moisture content. After a short cooking time, when the pressure has reached 10–12 kg/cm2 , the gun is suddenly opened and the puffed rice kernels are collected in a metal hopper (Figure 16.3). The puffed rice is mixed with sugar or maltose syrup, and occasionally with peanuts and ﬂavorings, rolled and cut into small square pieces called “gun-puffed cake.”

4.1.2. Pufﬁng Rice by Frying (Guo-Ba) The rice is cooked ﬁrst using one of two cooking methods: traditional, where the rice is soaked in water for 30 min and boiled or steamed to obtain wholegrain cooked rice; or large-scale production, where an equal amount of water is added to the milled rice, which is soaked at room temperature for two hours and then steamed at 18 psi pressure for 10 min. Indica waxy rice varieties are preferred; the water-rice ratio is controlled to prevent the cooked rice from

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Figure 16.4 Guo-ba, puffed rice produced by deep-fat frying cooked, dried rice: (A) soaking; (B) molding/forming; (C) steaming; (D) frying; (E) resulting expansion; (F) ﬁnished product.

becoming too soft and sticky. Heating is controlled to ensure gelatinization of the rice grain to the core without scorching [16]. The cooked rice is compacted, cut into 5 cm square pieces (10 grams each), dried to 12–15% moisture and fried in oil at 220◦ C (428◦ F) for 4–8 seconds in a deep fryer equipped with a conveyor. Then, the puffed rice is packaged (Figure 16.4). Another product puffed by frying is mi-hua-tung. Milled or broken rice is washed, soaked in water and passed through a steaming and drying oven. The cooked rice is dried to 5–7% moisture using a rotating drum dryer, then fried at 240–250◦ C (464–482◦ F) for 10–12 seconds, where pufﬁng occurs [21]. The puffed rice kernel is mixed with syrup and other ingredients, placed in a mold, pressed and packaged.

4.2. PRODUCTS USING FLOURS—RICE DESSERTS AND SWEETS 4.2.1. Mochi Mochi is a popular rice cake made in Southeast Asia including Taiwan. It is prepared from milled japonica (short-grain) waxy rice by washing, soaking, wet milling into ﬂour, steaming at 100◦ C (212◦ F) for 45–60 min, kneading, cooling, dividing and packaging (Figure 16.5). Traditionally, the dough was

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Figure 16.5 Processing glutinous (waxy) rice starch into mochi: (A) waxy rice starch; (B) steaming; (C) mixing with syrup; (D) addition of ﬁllings; (E) dividing; (F) ﬁnal product.

pounded using wooden pestles in mortars to remove air from the dough and obtain rice cakes with a smooth texture. With modern mechanical kneading, air bubbles are in the dough, which produces mochi with a rough surface and a whiter appearance. Mochi is usually divided into balls, which are coated with mashed red beans or peanut grits.

4.2.2. Nien-Kuo (New Year Cake) Short-grain waxy rice is preferred for making nien-kuo. The rice is soaked for several hours and ground into a slurry using a stone mill. The excess water is removed by centrifugation, or by straining the slurry through cotton cloth bags pressed by heavy stones. The resulting material contains 45% moisture. Sugar, water and rice ﬂour (8:7:10 ratio) are mixed to obtain a batter (Table 16.5) which is steamed for 4–5 hr, cooled and packaged (Figure 16.6).

4.2.3. Bi-Tai-Ba (Rice Noodle) Several types of rice noodles, such as mi-fen, bi-tai-ba, and ho-fen, are popular in Taiwan, Japan, Southeast Asia and in overseas Chinese communities. The

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TABLE 16.5.

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Characteristics of Nien-Kuo Made from Different Formulas [23]. Ingredient Ratios (Sucrose:Water:Flour)

Characteristics

11:4:10

10:5:10

9:6:10

8:7:10

7:8:10

Hardnessa

3612 0.79 5.66 26.12 1.01 12.34

2245 0.81 5.85 29.37 0.56 ---

1801 0.86 5.84 32.70 0.45 9.12

1587 0.87 6.01 33.07 0.31 9.25

1432 0.90 6.10 34.82 0.05 10.69

AW b pH Hunter L a b a b

Measured by Fudoh Rheometer. AW : Water activity.

Figure 16.6 Nien-kuo, a Chinese New Year cake.

449

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Figure 16.7 Rice noodle preparation: (A) piston dough extruder; (B) noodle extrusion; (C) cooked noodles; (D) forming noodles by single-screw extruder; (E) cooked extruder-made noodles; (F) extrusion of green, broad noodles.

popular mi-fen is used in main dishes. Generally, it is processed to the dry state and is steamed or cooked before serving. Bi-tai-ba is a short, coarse, wet noodle made by traditional procedures by soaking high-amylose-milled indica whole and broken rice kernels in water. The hydrated rice is stone milled in water to produce a slurry, which is divided

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Figure 16.8 Fa-kuo (rice mufﬁns).

into two parts. About 75% of the rice slurry is strained through cotton cloth or sacks to remove the excess water. The other 25% of the ground rice slurry is heated to gelatinize the rice starch. Time, temperature and conditions vary with the producer and the rice used. Then the gelatinized slurry is thoroughly mixed with the ungelatinized ground rice to form a dough, which is forced through a hand or powered piston forming extruder to produce noodle strands 3 mm in diameter [Figures16.7(A)–(C)]. The extruded noodles are placed in a boiling water bath or steamed to surface gelatinize the starch, cooled and packaged. During cooling, the surface of the noodle forms a strong ﬁlm (of retrograded starch), which gives proper texture to the product.

Figure 16.9 Flow chart for making bowl rice curd.

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Figure 16.10 Preparation of bowl rice curd: (A) washing/steeping; (B) wet milling; (C) rice slurry; (D) pregelatinized portion; (E) combining; (F) ﬁlling; (G) steaming; (H) packing; (I) product.

Bi-tai-ba noodles are consumed fresh; other rice noodles are dried outside after surface gelatinization using ambient air. Some noodles are deep-fat fried into crisp snacks and used in major dishes. Bi-tai-ba is mixed with syrup and ice water in the hot season. It is served with meat, green onion and other seasonings as a main dish. Indica rice varieties with high amylose content are preferred for rice noodles because starch retrogradation is necessary for proper texture. Recently, Bi-tai-ba has been made using an extruder [Figure 16.7(E)]. Drymilled ﬂour, containing 38% moisture, is fed into a single-screw extruder, which has three barrel sections with temperatures set at 130, 100 and 50◦ C (266, 212 and 121◦ F) [24,25]. The extruded noodle strands are steamed, cooled and packaged.

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4.2.4. Fa-Kuo (Rice Mufﬁn) Fa-kuo is a mufﬁn-style rice snack consumed in Southeast Asia. Preferably, it is made from indica rice. A batter is made from dried or wet-milled rice ﬂour (100% base), plus 50–80% sugar, 3.5% leavening agent, optional red coloring and 120% water. The batter is put in bowls, steamed 20 min and cooled (Figure 16.8). The red-colored mufﬁn is mainly used for festivals. Typically, the family has nien-kuo and fa-kuo on Chinese New Year’s Day.

4.2.5. Bowl Rice Curd Bowl rice curd is a traditional, popular food consumed at breakfast in southern Taiwan. Indica rice ﬂour is preferred for its preparation as shown in Figures 16.9 and 16.10. The process is similar to the production of rice noodles, but the dough is not extruded. Mixing the proper ratio of the raw and gelatinized slurries is critical to obtain good texture and eating quality in bowl rice curd [26].

4.2.6. Kuo-Tse-Rung (Rice cake) Parched rice ﬂour is the starting ingredient in making kuo-tse-rung. This product is seldom served as a snack food in Taiwan, but is used mainly in religious ceremonies. Precooked or toasted waxy rice ﬂour is mixed with sugar, oil and other ingredients such as walnuts or almonds until sticky. Then it is transferred to a wooden mold, pressed tightly, steamed for about 40 minutes, cooled and packed (Figure 16.11).

Figure 16.11 Different kinds of rice cakes (kao-tse-rung).

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5. REFERENCES 1. Unknown, 1998. Taiwan Food Statistics Book. Department of Food, Taiwan Provincial Government, Republic of China. 2. Chen, J. J., 1998. Effect of Hardness and Milling on Particle Size Distribution and Physicochemical Properties of Rice Flours. Ph.D. dissertation, University Taichung, Chung-Hsing, Taiwan. 3. Sakurai, J., 1971. Rice as an industrial raw material for manufacture of processed and ready-toeat rice products. (Proceedings) International Seminar on the Industrial Processing of Rice— Madras, India. United Nations Industrial Development Organization, Vienna, p. 65. 4. Li, C. F. and B. S. Luh, 1980. Rice snack foods. In Rice: Production and Utilization. B. S. Luh, ed. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 690–711. 5. Juliano, B. O., 1985. Polysaccharides, proteins, and lipids of rice. In Rice: Chemistry and Technology, 2nd edition. B.O. Juliano, ed. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 59–141. 6. Chen, J. J. and S. Lu, 1997. Effect on the physicochemical characteristics of rice ﬂours by milling methods of waxy rice in Taiwan. (Abstr.). Cereal Foods World, 42:629. 7. Setia, P., N. Childs, E. Wailes, and J. Livezey, 1994. The U.S. Rice Industry. U. S. Department of Agriculture, Washington, D.C. 8. Yeh, A. Y., W. H. Hsiu, and J. S. Shen, 1991. Some characteristics in extrusion cooking of rice noodle by twin screw extruder. J. Chinese Agricultural Chem., 29:340–351. 9. Lu, S., J. S. Lin, and T. C. Lin, 1995. The effect of physicochemical characteristics at different soaking and dehydration conditions on wet-milled rice ﬂour. J. Food Science (Chinese), 22:426– 437. 10. Lu, S., W. T. Fang, and C. Y. Lii, 1994. Studies on the effects of different hydrothermal treatments on the physicochemical properties of nonwaxy and waxy rices. J. Chinese Agriculture Chemical Society, 32:372–383. 11. Lu, S. and W. J. Chen, 1988. Studies on the physicochemical properties of rice with different milling methods. (Proceedings) Symposium on Rice Quality, 310–326. 12. Nishita, K. D. and M. M. Bean, 1982. Grinding methods: Their impact on rice ﬂour properties. Cereal Chem., 59:46–49. 13. Bean, M. M. and K. D. Nishita, 1985. Rice ﬂours for baking. In Rice Chemistry and Technology, 2nd edition. B.O. Juliano, ed. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 539–556. 14. Arisaka, M., K. Nakamura, and Y. Yoshi, 1992. Properties of rice ﬂour prepared by different methods. Denpun Kagaku, 39:155–163. 15. Jomduang, S. and S. Mohamed, 1994. Effect of amylose/amylopectin content, milling methods, particle size, sugar, salt, and oil on the puffed product characteristics of a traditional Thai ricebased snack food (Khao Kriap Waue). J. Sci. Food Agri., 65:85. 16. Yang, J. H., 1994. Studies on Preparation, Processing Properties, and Affecting Factors of Semi-Dry Milling Rice Flour. Ph.D. dissertation, Taiwan University, Taipei, Taiwan. 17. Chen, J. J., 1995. Effect of Milling Methods on the Physicochemical Properties of Waxy Rice Flours. Master thesis, Chung-Hsing University, Taichung, Taiwan. 18. Chen, J. J., S. Lu, and C. Y. Lii, 1998. Thermal characteristics and microstructure changes in waxy rice using different milling methods. J. Food Science (Chinese), 25:314–330. 19. Williams, P. C. and D. C. Sobering, 1986. Attempts at standardization of hardness testing of wheat. I. The grinding/sieving (particle size index) method. Cereal Foods World, 31:359–364.

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20. Su, J. W., 1998. Effect of Steeping and Milling on the Physicochemical Properties of Rice Flours and the Quality of Rice Curd. Master’s thesis, Chung-Hsing University, Taichung, Taiwan. 21. Chang, S. M. and T. L. Chang, 1995. The characteristics of explosion-pufﬁng rice products with different amylose contents. J. Food Science (Chinese), 22:465–478. 22. Huang R. M., M. B. Chou, and C. Y. Lii, 1998. Effect of the characteristics of rice and the processing conditions on the expansion ratio of dry cooked rice. J. Food Science (Chinese), 25:383–393. 23. Lin, J. S., 1993. Studies on the Quality of New-Year Rice Cake at Different Soaking Conditions and Dehydration Methods, Master thesis, Chung-Hsing University, Taichung, Taiwan. 24. Lu, S. and C. P. Yeh, 1996. Laboratory preparation of Bi-Tai-Ba by a single screw extruder. J. Food Science (Chinese), 23:650–661. 25. Lu, S., M. S. Lin, T. Z. Lin, and C. Y. Lii, 1993. Studies on the quality of Bi-Tai-Ba and its frozen stability addition with commercial starches. J. Food Science (Chinese), 20:64–74. 26. Jeang, C. L., S. J. Wu, and T. C. Lin, 1990. Effects of treatments of different additives on the texture of frozen rice curd. J. Agriculture and Forestry, 39:145–155.

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CHAPTER 17

Japanese Snack Foods

SEIICHI NAGAO

1. INTRODUCTION

A

diversity of attractive and appetizing snack foods, different from those in the West, enriches the dietary experience of people in Japan. The large selection includes traditional Japanese confections, Western confections, harmonized Japanese and Western confections noodles and snack foods introduced mainly from the United States. Traditional Japanese snacks are classiﬁed into fresh, semifresh and shelf-stable products, and include baked, fried, molded and coated products and candies. A variety of noodles, including white salted (udon) type, Chinese (ra-men) type, instant, and buckwheat noodles are eaten as snacks as well as staples. Some of the snack products are shelf stable.

2. JAPANESE BAKED CONFECTIONS

2.1. SENBEI (RICE CRACKERS) Senbei, when applied in the broad sense, includes all traditional Japanese-type rice crackers; similar products made from wheat ﬂour are called “cracknels.” They are quite different from crackers used in Western countries. Senbei was ﬁrst introduced in Japan by a famous Buddhist, Kukai, who returned from China in 806 AD. In the early days, senbei dough was made from wheat ﬂour mixed with fruit syrup, or from rice ﬂour seasoned with salt. The dough was steamed, cut, molded into circles and baked on an iron plate [1].

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Until the 16th century, senbei was the principal rice cracker. Wheat ﬂour cracknel has become popular since the 17th century [2]. Variations of senbei were developed as processing technology advanced from the 18th century. Now, many kinds of senbei are popular as shelf stable snack foods in Japan. In western Japan, wheat ﬂour cracknels are more popular than rice crackers. Rice crackers are classiﬁed broadly into arare and okaki made from glutinous (waxy, high amylopectin) rice; rice senbei is made from non-glutinous (high amylose content) rice. Generally, arare or okaki has a soft texture and is readily soluble in the mouth, while rice senbei has a harder, more porous texture. Differences between arare and rice senbei come from the kind of rice used, the milling, dough preparation, molding processes, and the content of amylose. Many variations of arare and okaki are on the market, some of which are shown in Figure 17.1(A). They are classiﬁed as soft (3.5–4.5 ml/g), medium (2.5–3.5 ml/g) and hard (2.0–2.5 ml/g) types based on speciﬁc volume [3]. Okaki, the generic name for products of medium hardness, includes Shinagawamaki, oogaki and others. Most arare are soft, but some special hard products like kakinotane (persimmon seed) are preferred with beer or sake. In producing arare and okaki, polished and washed glutinous rice is steeped in water, drained and steamed for 15 to 20 minutes. Then it is pounded into dough, as in making rice cakes. The dough is stored in a refrigerator at 2–5◦ C (38–41◦ F) for 2 to 3 days. After storage, the stiffened dough is cut and molded into the desired size and shape, using a cutter. A roller-type cutter with several cutting edges is used to make attractive cracks on the surface of the unbaked crackers. The molded dough pieces are dried to about 20% moisture content and baked (toasted) on a parching pan over an open ﬂame at 200–260◦ C (392– 500◦ F). After baking, salad oil, soy sauce, or other seasonings are brushed or sprayed on the surface of the product. Arare, pierced with a seasoned thin slice of dry laver (edible seaweed), is a popular snack. Variety can be added to the product by mixing seasoned laver, pepper, parched sesame or parched soybean into the dough. Many kinds of rice senbei, varying in shape, size, texture and ﬂavor, are available on the market [Figure 17.1(B)]. The ﬁrst step in making rice senbei is milling non-glutinous rice. Polished non-glutinous rice is washed well, steeped in water for about an hour, drained and milled using a roller. The milled rice ﬂour is moistened and steamed in a mixer for 5–10 minutes. The material is then pounded into dough, again as in making a rice cake. A continuous steaming mixer with pounding action is commonly used. After cooling to 60–65◦ C (140–148◦ F) in water, the dough is kneaded well in a mixer, sheeted using a dough sheeter and cut to desired size and shape using a suitable cutter. The molded dough pieces are dried to 20% moisture content in a dryer at 70–75◦ C (158–169◦ F); they are kept at room temperature for 10–20 hours to become semitransparent. Dough at this stage can be stored for a long time. To

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Figure 17.1 (A) Arare (left) and okaki (right), soft rice crackers made from glutinous (waxy) rice. (B) Senbei, hard crackers made from non-waxy (high-amylose) content rice. Many kinds exist.

make the ﬁnal product, the dough is further dried in a dryer to 10–15% moisture content and baked on a parching pan, or a plate traveling over an open ﬂame at 200–260◦ C (392–500◦ F). After baking, soy sauce or other seasonings are brushed or sprayed onto the surface of the product. Rice senbei, pierced with a seasoned thin slice of dry laver, is very popular.

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Yatsuhashi is a special and very popular rice senbei in Kyoto. A typical formula for the product includes 100 parts by weight non-glutinous rice ﬂour, 100 parts sugar, honey, cassia powder and water. The non-glutinous rice ﬂour and water are kneaded well to make a slightly stiff dough, cut into small pieces and steamed. The steamed dough, mixed with sugar, honey and cassia powder, is kneaded well and sheeted to about 2.5 mm (0.10 inch) thickness. Both soybean ﬂour and cassia powder are sprinkled over the surface of the sheeted dough, which then is cut into strips. After drying both sides of the strips very carefully, they are baked on a pan under the pressure of a heavy piece of wood and molded into a curved shape by using a special wooden mold. A hard, crispy texture is characteristic of yatsuhashi, which is made without baking powder or leavening agents to avoid expansion. Rice crackers are known for their porous and crispy structure, which results from heat swelling of amylopectin in the rice starch. Thus, the swelling characteristics of rice are very important in making high-quality rice crackers. The glutinous (waxy) rice contains 100% amylopectin, which creates greater expansion during baking. The expansion decreases as the amylose content increases in the rice. Harder texture is obtained when high amylose rice is used.

2.2. WHEAT FLOUR SENBEI Many variations of wheat ﬂour senbei are also on the market. They include kawara-senbei (tile-shaped cracknel), kamenokou-senbei (tortoise shell-shaped cracknel), kuri-senbei (chestnut-shaped cracknel), shouga-senbei (gingerﬂavored cracknel), nanbu-senbei, isobe-senbei, peanuts-senbei, milk-senbei and others. Kawara-senbei, one of the most popular forms of wheat cracknel, is shown in Figure 17.2(A). A typical formula for kawara-senbei includes 100 parts ﬂour,100–130 parts sugar, 10–30 parts egg, 0.03–0.1 parts carbonic acid and 60 to 80 parts water. The sugar and eggs are whipped; the carbonic acid (dissolved in a little water) is added with the ﬂour and mixed well, followed by the remaining water to make a uniform batter. White sesame seeds or cracked peanuts are added to the batter to vary the taste. Cooking oil is brushed over the baking dies to facilitate separation of the products. The batter is poured into baking dies that are heated over a ﬁre, the dies being inverted carefully midway through the heating. Usually, 10 dies are heated simultaneously. Isobe-senbei originated in the Isobe hot springs area. Hot spring water, containing sodium bicarbonate, was used in place of water. A typical formula for Isobe-senbei production includes 100 parts wheat ﬂour, 100 parts sugar, 2.5 parts salt, ammonium carbonate and hot spring water. Today, a baking powder containing carbonate and ammonium salt is used in place of natural hot spring water to make the soft-texture product [4].

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Figure 17.2 (A) Kawara-senbei, a popular wheat-based cracknel. (B) Nanbu-senbei, wheat-based cracknel with sesame and other toppings.

Nanbu-senbei [Figure 17.2(B)] is a local specialty of Iwate, Aomori and Miyagi prefectures in northern Japan. A typical formula includes wheat ﬂour, salt and black sesame. Sugar is not used in making standard nanbu-senbei. It is characteristic of nanbu-senbei for black sesame to be spread on the surface of white senbei to give desirable ﬂavor and texture to the product. Nanbu-senbei with peanuts in place of black sesame in the formula is a new and tasty variation. Recently developed nanbu-senbei includes sugar in the formula. Ebi-senbei (shrimp cracknel) is a traditional Japanese confection. After removing the shell and body cavity parts, shrimp are ﬂattened, sprayed with dilute salt solution, sprinkled with starch powder and dried. Fried or baked shrimp is

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put in the center of each small wheat ﬂour senbei. The product has a mild and desirable ﬂavor originating from the shrimp. Successful modiﬁcations of ebi-senbei, developed by a large confectioner, were introduced in the 1970s. Presently, numerous products are popular snack foods, loved by all generations. Fried and non-fried products [Figure 17.3(A)] are available. Starch and wheat ﬂour are important ingredients in the formulas of these products. A wide range of soft wheat ﬂour may be used for making wheat ﬂour senbei. Flour containing 0.35–0.55% ash and 7–10% protein processes easily. However, high-quality wheat senbei requires ﬂour with moderate protein content and soft gluten quality. For premium senbei, soft wheat ﬂour with 0.35–0.40% ash and 7–9% protein is recommended. Crispness, peculiar to the product, is a primary quality requirement. At the same time, wheat ﬂour senbei should readily soften in the mouth without becoming gummy.

2.3. BOLO The Portuguese introduced bolo to Japan in the 16th century. Saga-bolo, soba-bolo (buckwheat-bolo), egg-bolo and eisei-bolo are produced today. Sagabolo, a well-known confection in the Kyushu area, consists of 80 parts sugar, 50–60 parts egg, 15–25 parts starch syrup and/or honey and 1–2 parts sodium bicarbonate based on 100 parts of wheat ﬂour. Starch syrup is unique to Asia and is quite popular. It is a liquid composed of dextrins and glucose, produced from corn or other starches and is more viscous than common corn syrups in the United States. Rice starch is not used in its production. The sugar and eggs are well mixed; then softened starch syrup and sugar are added to the mixture. Dissolved sodium carbonate is added next and the product mixed well. The wheat ﬂour is ﬁnally added and mixed lightly to make a dough. Because the dough is soft and runny, it is rested for 0.5–2 hours before sheeting and cutting. Vegetable oil is brushed or sprayed on the surface of the molded dough, which is baked in an oven at 210–220◦ C (409–427◦ F) for 7–8 minutes. A second-grade soft, all-purpose ﬂour, milled from a blend of western U.S. white wheat and Japanese domestic soft wheat typically is used for making saga-bolo. Soba-bolo [Figure 17.3(B)], made from a blend of wheat and buckwheat ﬂours, is a variety of bolo common in Kyoto. Eggs and sugar are used in the formula. The process is almost similar to that of saga-bolo. The dough pieces, about 3 cm in diameter, are baked to a dark brown color. The main ingredients of eisei-bolo are potato or cornstarch. Sugar and eggs are mixed well; then starch and ammonium carbonate are added to make a dough. The dough is sheeted and cut to squares 8 mm per side, or molded into the shape of sticks about 10 mm in diameter and cut in pieces about 10 mm in length. These small pieces of dough are put in a box and molded into balls by

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Figure 17.3 (A) Fried (left) and non-fried (right) modiﬁed ebi-senbei (wheat cracknels) containing shrimp. (B) Soba-bolo made from a blend of wheat and buckwheat ﬂour. (C) Hard karintou made by frying a soft wheat dough and coating with syrup.

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rotating the box forward and backward as well as right and left. The rounded dough pieces are placed side by side on an iron plate and baked in an oven at 180–190◦ C (356–374◦ F) for 6–7 minutes. Because of its light, soft texture, the product is used as an infant food [4].

3. FRIED JAPANESE CONFECTIONS

3.1. KARINTOU Karintou (fried cookie dough) is a confection originally imported from China. During the 18th century, the product was modiﬁed to meet the preference of local people. The products are soft or hard, varying in brittleness. Soft karintou is produced by yeast fermentation of hard wheat ﬂour dough, which results in a light and airy ﬁnished product. In contrast, hard karintou is made from chemically leavened soft wheat ﬂour dough, which processes into a coarser and slightly harder product. [Figure 17.3(C)]. A typical formulation for hard karintou consists of 0–3 parts sugar, 0.3 parts skim milk, 0–1 parts salt, 4–5 parts sodium bicarbonate/ammonium carbonate, and 45–60 parts water based on 100 parts hard wheat ﬂour. The ingredients are mixed to make a slightly stiff dough. The dough is sheeted, cut to proper size and shape and fried in oil at 170–180◦ C (338–356◦ F). After draining and while warm, the pieces are coated with sugar syrup, then cooled.

4. MOLDED OR PRESSED JAPANESE CONFECTIONS

4.1. RAKUGAN Rakugan is the generic name for molded Japanese confections made from parched cereals or legumes. They have a characteristic solubility in the mouth. A typical formula for making a standard rakugan is mijinko made from 320 g glutinous rice ﬂour milled after steaming and parching at 170–200◦ C (338–392◦ F), 80 g potato starch, 800 g sugar, and 50 g syrup. The sugar and starch syrup mixture is prepared by dissolving 40 parts of starch syrup in 100 parts of water. The potato starch and half of the mijinko are added to the sugar and mixed; then the remaining half of mijinko is added and mixed lightly. After sieving, the blend is placed in a wooden mold and hardened at room temperature, or the surface is moistened by steam and dried in a drying room at 40–50◦ C (104–121◦ F). The ﬁnal moisture content of rakugan is 2–3%. It has a crispy texture with a long shelf life. It has a unique, appreciated texture that is hard when bitten but rapidly dissolves in the mouth. The drying times vary.

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Figure 17.4 Pressed, molded sweet rice snacks: (A) rakugans, (B) okoshi.

Cereals other than glutinous rice and legumes can be used in place of potato starch to create variety in the product. Wheat, non-waxy rice, foxtail millet, soybeans and others are used. A formula for making mugi-rakugan consists of 100 parts mijinko, 300 parts parched wheat or barley ﬂour, 600 parts sugar, 55 parts syrup and 3 parts salt. For making kuri-rakugan, chestnut ﬂour is used in place of parched wheat or barley ﬂour in the mugi-rakugan formula given above. Soybean ﬂour is used to make mame-rakugan. Some examples of rakugans are shown in [Figure 17.4(A)].

4.2. OKOSHI Okoshi is a pressed and molded snack made from parched cereals coated with sugar or starch syrup. It originated in the 9th century, but many new and improved varieties were developed after the 17th century. Glutinous rice,

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non-glutinous rice, wheat or millet can be used to make okoshi. Parched cereal products, called okoshi-dane, are prepared by special processes. Commonly, cereals are parched after steaming and drying. Another way to make okoshidane consists of steaming glutinous rice mixed with sugar solution, pounding, extending, drying, cutting and then parching. The sugar and starch syrup is made by boiling and concentrating over a ﬁre. Cooking oil is added during the concentration step. The hot syrup is poured on the parched cereals in a wooden box, and they are mixed quickly with a wooden spoon. While it is warm, the mixed product is put in a wooden frame, cut into desired size and shape just prior to becoming hard and cooled. In the production of okoshi, the boiling temperature of syrup and the amount of starch syrup added to sugar should be adjusted to the climatic condition in the area. The amount of syrup to be added is adjusted depending on the product. Peanuts, soybean, black soybean, sesame or green laver can be added to the product for variety in taste and appearance. The softness of okoshi varies by region. It is similar in moisture content and texture to rakugan. Some examples of okoshi are shown in [Figure 17.4(B)].

4.3. GOKABOU The production of gokabou originated in a small village in eastern Japan in the 18th century. The literary meaning of gokabou in Japanese is “the treasure of ﬁve families.” The shape of the product resembles a scroll. For a typical product, 6 parts of sugar and 4 parts of starch syrup are concentrated at 115◦ C (238◦ F) to make syrup. Okoshi-dane, made from glutinous rice, and the hot syrup are mixed to make round sticks. They are wrapped with an extended dough sheet 5 mm in thickness, which is prepared by mixing soy ﬂour and boiled-down syrup (6 parts sugar and 4 parts starch syrup). The wrapped product is molded into stick shape on a plate covered with parched soybean ﬂour and cut to the desired length (6–7 cm). The product has the pleasant ﬂavor of parched soybean ﬂour, with a soft, light texture.

5. COATED JAPANESE CONFECTIONS

5.1. GENPEI-MAME Genpei-mame is the generic name for sugar-coated parched soybeans.The seasoning was salty in early days, but sugar coating has become popular since the 1870s. A typical genpei-mame formula is 200 parts sugar and 100 parts parched soybeans. Green soybeans are soaked in water, drained and parched, then coated with sugar syrup boiled down to 115◦ C (239◦ F) and dried [4].

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Mishima-mame is a local specialty in Takayama, Gifu prefecture, and was originated by J. Mishima in the 1960s. Green soybeans are used as the main ingredient for making the product, which is colored white and green by sugar and green laver, respectively. Goshiki-mame is another famous kind of genpeimame, which was originated by a confectioner named Mamemasa in Kyoto. It is a mixture of blue-, red-, yellow-, white- and purple-colored beans. These ﬁve colors were thought to purify (remove uncleanness) and were a wish for happiness [5].

5.2. ONOROKE-MAME Onoroke-mame (Figure 17.5) is a popular coated snack. A seasoned coating is prepared from glutinous rice ﬂour and wheat ﬂour. Parched peanuts are coated with sugar syrup and the coating in a rotating pan. This operation is repeated several times to enlarge the coated peanuts to the desired size; then the product is parched again. The coated peanuts may be ﬂattened to add variety to the ﬁnal product.

Figure 17.5 Onoroke-mame, a coated peanut snack.

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6. WESTERN CONFECTIONS

6.1. BISCUITS AND COOKIES Biscuits were introduced to Japan during the 16th century. They were imported on a commercial scale for the ﬁrst time in 1871, and domestic biscuit production was initiated within a year. The biscuit industry in Japan expanded rapidly between the mid-1910s and mid-1920s, aided by modiﬁcations in formulas and processing techniques to meet Japanese ﬂavor and texture preferences. With liberalization of wheat ﬂour sales in 1952, and subsequent importation of modern equipment and processing techniques, a large number of products, some unique to Japan, are manufactured in modern plants. Annual biscuit consumption totals 110,000 to 130,000 (metric) tons. Biscuits produced and marketed in Japan are classiﬁed into hard [Figure 17.6(A)] and soft [Figure 17.6(B)] types. Special soft biscuits, made using a richer formula than usual, are called cookies [Figure 17.6(C)]. Most biscuits

Figure 17.6 (A) Hard biscuits, (B) soft biscuits, (C) cookies.

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are produced mechanically in large factories using rotary formers, wire cutters, or depositors. A variety of tasty cookies [Figure 17.6(C)] introduced from the West and modiﬁed to appeal to domestic tastes are produced by large factories and small bakeries. Typical formulas for hard and soft biscuits, and for cookies, are as follows. Hard biscuits: 100 parts ﬂour, 20–25 parts sugar, 10–15 parts shortening, 0.5– 1.0 parts condensed milk, 0–5 parts eggs, 0.5–1.0 parts salt, 1.5 parts leavening (ammonium carbonate, sodium bicarbonate and cream of tartar), ﬂavorings and water. Soft biscuits: 100 parts ﬂour, 30–40 parts sugar, 25–35 parts shortening, 3–5 parts condensed milk, 0–10 parts eggs, 0.5–1.5 parts leavening, ﬂavorings and water. Rotary or wire-cut cookies: 100 parts ﬂour, 40–60 parts sugar, 25–50 parts shortening, 5–10 parts milk, 10–15 parts eggs for (or 25–30 parts for deposited cookies), 0.5–1.0 parts salt, 0–1.0 leavening and ﬂavorings. The manufacturing processes for cookies, and hard and soft biscuits, are similar to those used in Europe and the United States. First-grade confectionery ﬂour with low protein content, ﬁne granulation, and soft gluten properties is used for soft biscuit production. U.S. western white wheat, comprised of white club and soft white wheat, is the most suitable for milling into ﬂour. Cookie ﬂours are similar to those used for soft biscuits, but ﬁrst-grade all-purpose ﬂour may be used occasionally for special products. Special cookie ﬂours for baking quality products are made and sold by large ﬂour milling companies. First- or second-grade all-purpose ﬂour of moderate protein content (8 to 9%) is used for making hard biscuits. Since most biscuit manufacturing plants are highly automated, uniformity of ﬂour properties, such as protein content and water absorption, is an important requirement [6].

6.2. CRACKERS The crackers produced in Japan more nearly resemble the American type than English cream crackers. Production in Japan was negligible until the mid1950s, but consumption has progressively increased with the introduction of band ovens. Each year, 18,000 to 21,000 tons of crackers are consumed. The following formula is applicable to sponge fermentation: 70 parts ﬂour; 5 parts shortening, 0.05–0.1 parts yeast food and 25–35 parts water. The composition for the dough process is: 30 parts ﬂour, 3–5 parts shortening, 1.0–1.5 parts sugar, 2.0–2.2 parts salt and 0.5–0.8 parts sodium bicarbonate. The processing of crackers in Japan is almost identical to that in the United States. First-grade confectionery or all-purpose ﬂour is used for cracker production. It typically has an ash content of 0.36–0.45% and a protein content of 7.5–9.0%. If two kinds of ﬂours are used, sponge fermentation is conducted with the higher protein content ﬂour.

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Figure 17.7 Ice cream cones, (B) wafers.

6.3. WAFERS Wafers, another introduction from the West, are eaten especially by the very young, and frequently are processed into ice cream cones (Figure 17.7). Two parts sugar, 8 parts egg yolk, 0.5 parts sodium bicarbonate, 0.8 parts ammonium carbonate, 180 parts water and a little salt and ﬂavoring per 100 parts ﬂour is a typical formula. Another formula consists of 2.5 parts non-fat milk solids, 0.75 parts salt, 0.5 parts sodium bicarbonate, 150 parts water and a little ﬂavoring based on 100 parts ﬂour. The batter mixing and baking processes are similar to those used in the United States. First-grade ﬂour, or a blend of ﬁrst- and second-grade ﬂour, milled from U.S. western white wheat, is preferred for wafer production. The ﬂour should be

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mixed into a batter that ﬂows freely and gives a high yield of quality ﬁnished products. The wafer should be tender and dissolve readily when eaten.

7. NOODLES

7.1. WET NOODLES Noodles are very popular as a food staple and also as snacks. Noodles are eaten at home, restaurants, noodle stands, or at picnics. Many small noodle restaurants and noodle stands, widely spread over Japan, are convenient places to eat noodles as snacks. A modern noodle restaurant in Tokyo is shown in Figure 17.8(A). Numerous types of noodles, resulting from differences in raw materials, product shapes, processing methods and ways of eating, are marketed in Japan. They have also undergone changes due to the times, wheat and buckwheat supplies, technical innovations and changes in consumer preferences. Noodles were introduced from China about 1,200 years ago, at the same time as Buddhism, and gradually became widely accepted throughout the country. The manufacture of unique hand-made somen (a very thin noodle) was developed about 700 years ago. Although buckwheat ﬂour had been eaten as a substitute for rice in earlier times, buckwheat noodles did not appear until the 17th century. The development of a noodle-making machine by T. Masaki in 1884 revolutionized the manufacture of noodles. Chinese-type (ra-men) noodles originated in Yokohama at the beginning of the 20th century and were gradually popularized throughout the country by noodle manufacturers. In the summer of 1957, a new Chinese-type noodle dish, served cold, was successfully introduced in the Nagoya area. The ﬁrst instant Chinese-type noodle, called “chicken ra-men” went on the market in 1958, and many noodle manufacturers were producing similar chicken ra-men products by 1964. A packaged complete Japanese udon noodle appeared on the market in 1962. Five years later, a Chinese-type noodle, characterized by its unique taste, was welcomed by customers in Sapporo and became famous under the “Sapporo ramen” nickname among Japanese tourists. Almost all instant noodles marketed by that time were Chinese-type packed in polyethylene bags. New products, developed using styrofoam cups or bowls, were epoch-making and enthusiastically welcomed by many consumers in 1971 because of their convenience in eating. They included Chinese-type noodles and udon noodles. As the result of this development, total consumption of instant noodles began to increase again. A product using new freezing technology, to keep the taste of boiled noodles fresh and delicious for a long period, was developed commercially and marketed with new thawing technology in 1974. Consumption of high-quality hand-made so-men and hiya-mugi (thin noodles), especially as gifts, began to increase

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Figure 17.8 (A) Modern noodle restaurant, (B) dried udon noodles, (C) non-fried instant noodles.

within a few years. Freeze-drying technology was applied to the production of instant noodles in 1977. Packaged complete boiled noodles with a long shelf life appeared on the market in 1988. The annual per capita consumption of noodles, excluding Western pasta based on ﬂour, is about 9 kg and accounts for about 27% of total ﬂour consumption in Japan. The annual production of wet and boiled noodles of all types is about 730,000 tons, with 260,000 additional tons of dried noodles and 320,000 tons instant noodles. Although consumption has not increased recently, noodles are still liked by many Japanese as a staple food as well as a snack. The bland and delicate taste of Japanese noodles is considered typical of Japanese cuisine.

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TABLE 17.1.

Class So-men (very thin) Hiya-mugi (thin) Udon (standard) Hira-men (flat)

Classiﬁcation of Japanese Noodles.

Strand Width (mm)

Cutting Rolls (No.)

Dried or Boiled

1.0--1.2

30--26

Dried

1.3--1.7

24--18

Dried

2.0--3.8

16--8

5.0--7.5

6--4

Dried or boiled Dried or boiled

Manufacturing Method Hand-made (tenobe) or machine-made Hand-made (tenobe) or machine-made Hand-made (teuchi, tenobe) or machine-made Hand-made (teuchi) or machine-made

7.2. DRIED NOODLES (KAN-MEN) Noodles are classiﬁed according to the raw materials used in their manufacture, by the size of the strands, by the method of manufacture, and by the form of the product sold on the market. Dried noodles and instant noodles, eaten as shelf stable snack foods, are discussed. Japanese noodles are classiﬁed into very thin noodles (so-men), thin noodles (hiya-mugi), standard noodles (udon) and ﬂat noodles (hira-men) by the width of noodle strands as shown in Table 17.1. Dried so-men and hiya-mugi are usually cooked and served cool in the hot summer, whereas cooked udon and hira-men are eaten hot in the cool season. Kan-men is the generic term for so-men, hiya-mugi, udon, hira-men and soba (buckwheat noodle) sold in dried forms. These are storable products produced by controlled drying of uncooked wet noodle strands to about 13% moisture content. An example of dried udon noodles is shown in Figure 17.8(B). There are few dried Chinese-type noodles. Handmade noodles are very tasty, and their merits are being reviewed again. The addition of a large amount of water (40–45 parts to 100 parts ﬂour) favorably helps the development of gluten, but some maturing of the dough (relaxation by resting for a while) is needed for smooth rolling. By adding higher amounts of water to ﬂour during mixing, it is possible to produce noodles on an industrial scale with favorable texture, somewhat similar to that of the hand-made type. The basic process for making dried noodles by machines is different from hand-made products. It consists of mixing the raw ingredients, sheeting the dough, combining two sheets, rolling, cutting and drying. Formulas for Japanese dried noodles are simple: 100 parts ﬂour, 2–3 parts salt and 28–45 parts water. Salt is dissolved in the water prior to mixing. The volume of water used is carefully adjusted for ﬂour quality, type of mixer and climate. In the manufacture of typical dried buckwheat noodles, 30 parts buckwheat ﬂour and 70 parts hard wheat ﬂour are mixed with 28 parts water. Salt is not used in buckwheat noodle production lest the binding capacity of wheat ﬂour be lost. The ratio of wheat

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ﬂour to buckwheat ﬂour varies according to the type of product and the quality of the buckwheat ﬂour. The most common practice is to mix all the ingredients in a traditional horizontal mixer for 10–15 minutes to make stiff and crumbly dough pieces, but newly developed vertical mixers also are used. Other than the type and size of the mixer, mixing is inﬂuenced by the quality of ﬂour used, volume of water added, concentration of salt and temperature and humidity in the factory. The stiff and crumbly dough pieces from the mixer are divided into two, and each portion is passed through a pair of sheeting rolls to form a thin noodle sheet. The diameter of the sheeting roll is usually 180 mm (7.9 inch). The two sheets are then passed through a second set of rolls, 240 mm (9.45 inch) diameter. The roll gap at this stage is adjusted to the thickness of the original sheet to further help the development of gluten by pressure at the moment of rolling. The combined and rolled sheet is usually rested (matured) for up to 1 hour. The effect of maturing at this stage is to soften the dough sheet by stress relaxation and to make the subsequent rolling operation easier. The combining process is often repeated to more completely form the gluten network. Handmade noodles are highly valued for their delectable texture, presumably owed to the mode of gluten formation. Gluten strands in noodles made by a machine are aligned along the direction of sheeting, whereas those in handmade noodles intertwine lengthwise and crosswise. Three to ﬁve pairs of rolls, each a little smaller in diameter (240, 180 and 150 mm) with decreasing roll gaps, are used for the next sheeting process. The thickness of the combined sheet for Japanese udon noodles is gradually reduced to 2–4 mm by passing it through sheeting rolls three to ﬁve times. The thickness of a dough sheet is adjusted prior to cutting. A cutting machine is composed of a pair of rolls, a pair of cutting rolls and a cross-cutter. Two types of cutting rolls are available to produce square- or round-shaped noodles, but the square type is the most popular. The width of a noodle strand is determined by the groove of the cutter, which is established by a Japanese industrial standard. The numbers assigned to each cutting roll indicate the number of noodle strands being cut from a sheet 30 mm in width. For square-type noodles, the ratio of long and short sides of noodle strands is usually 4 (on the roll side) to 3. The noodle strands are then cut into desired lengths by the cross-cutter. Uncooked wet noodle strands several meters in length, coming from a cutting machine, are hung on rods and carried to a special chamber where the rate of drying is adjusted by controlling the relative humidity. Finally, the product is cut into lengths of about 25 cm and packed.

7.3. INSTANT NOODLES Instant noodles, easily eaten at any place, are very popular as a snack food. After gelatinizing in a steamer, noodle strands are dried by frying or by hot-air blast drying, resulting in products classiﬁed as fried instant noodles and non-

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fried instant noodles, respectively. A typical non-fried instant noodle is shown in Figure 17.8(C). Two types of fried Chinese-type instant noodles are available. In one type, the noodles are ﬂavored with various seasonings, while the other is plain and is sold with a package of soup base. Most non-fried instant noodles are plain in taste and accompanied by a package of soup base, which is applied to both Chinese-type and Japanese udon noodles. About 0.2 parts of kansui powder (a mixture of alkaline salts) is added to 100 parts of ﬂour in the production of instant Chinese-type noodles. Though their basic production is similar to fresh Chinese-type noodles, noodle strands for cup use and the non-fried instant type are cut a little thinner for faster rehydration. In producing instant noodles, noodle strands are placed in a tunnel steamer for 1 to 3 minutes at 90–100◦ C (203–212◦ F). Enough steaming is necessary to complete gelatinization of starch in non-fried type noodles. Drying by frying requires 2–3 minutes at 135–140◦ C (276–284◦ F). Hot air drying usually requires more than 30 minutes at 80◦ C (176◦ F).

8. WESTERN SNACK FOODS Corn chips, the ﬁrst Western-type snack food in Japan, were produced and marketed by a local company in 1968. Many companies began to produce American-type snack foods within the following year. Before long, some of the products were modiﬁed to meet the preferences of local consumers and were welcomed by them. American-type snack foods include potato and corn chips, pretzels, nuts, pop corn and others. The main ingredients of Western-type snack foods in Japan are potato and corn, but wheat ﬂour and rice are used in some special products.

9. REFERENCES 1. The Japan Society of Cookery Science, 1997. In The Comprehensive Encyclopedia of Cookery Science. (In Japanese). Kouseikan Co., Tokyo, pp. 304. 2. Nihon Mugirui Kenkyu Kai, 1964. In Wheat Flour: Its Material and Processed Goods. (In Japanese) Nihon Mugirui Kenkyu Kai, Tokyo, pp. 487–488. 3. Saitou, S., 1981. Manufacturing method of rice confections. In Encyclopedia of Confectionery. (In Japanese) N. Watanabe, S. Suzuki, H. Iwao and T. Obara, eds. Asakura Shoten Co., Tokyo, pp. 391–420. 4. Unknown, 1983. In Practical Knowledge of Confections. (In Japanese). N. Watanabe, A. Miyauti, and M. Ishii, eds. Touyo Keizai Syinpousya Co., Tokyo, pp. 120–127. 5. Obara, T. and N. Hosoya, 1985. In Concise Food Dictionary. (In Japanese). Jusonbo Co. Tokyo, pp. 383, 996. 6. Nagao, S., 1981. Soft wheat uses in the orient. In Soft Wheat: Production, Breeding, Milling and Uses. W. T. Tamazaki and C. T. Greenwood, eds. American Association of Cereal Chemists, St. Paul, Minnesota, pp. 276–304.

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CHAPTER 18

Snack Foods of India

SUMATI R. MUDAMBI M.V. RAJAGOPAL

1. INTRODUCTION

1.1. HISTORICAL

S

NACK foods have been known in India from time immemorial. A token gift of

pohe (ﬂaked rice), given by an indigent Sudama to his erstwhile classmate, Lord Krishna, King of Dwarka, is mentioned in the Puranas (a Hindu religious text dating before 4000 BC). Obviously, pohe was known in India at that time or earlier. The use of oil for frying was known to the Dravidians. Round cakes known as vatakas, made by grinding black gram pulses into a batter and frying, were known as early as 3000 BC. This preparation, now known as vadas, has remained almost unchanged from that time. A sweet snack, made from barley meal or rice ﬂour baked on a low ﬁre and using honey called Apupa, was mentioned as early as 2000 BC [1]. The art of preparing sweet and savory snacks has evolved over thousands of years, with each region in the subcontinent of India having its own characteristic product. Due to space limitations, only a few savory snacks are described in this chapter. These are traditional and popular throughout India, although they may have originated in speciﬁc regions. Snacks of Western origin, such as potato chips, corn (Zea mays L.) chips and pretzels, have entered the Indian market, but most people still prefer the traditional snack foods. The snacks described in this chapter are grouped on the basis of their components and method of preparation.

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1.2. PRODUCTION AND DISTRIBUTION Traditional snacks are prepared essentially in batches. Some, like chakali, murukku and thengul—different versions made from rice ﬂour (Oryza sativa L.) and black gram (Phaseolus mungo, L., also known as udid dal) dal ﬂour—are prepared on a small scale and sold through retail stores. A large cottage industry manufactures traditional snacks and employs many people, especially women who have recipes and skills for consistently making excellent products. The recipes are handed down from generation to generation. The production of some snacks is more organized. Large food cooperatives arrange to have papads made from black gram ﬂour in households according to their speciﬁcations and sell them with their brand name. Other products, like farsan, may be prepared in larger batches, 10–12 kg at a time. Factories produce fried snacks like farsan, chivda and shev in quantities up to one ton a day and distribute their products over large areas. Similar products are also prepared in small batches in the back of retail snack food shops and sold over the counter. Pohe (rice ﬂakes) is prepared only in 2.0–2.5 kg batches. The production of pohe and murmure (puffed rice) requires considerable skill and expertise passed from generation to generation, but proﬁt margins are low. These rice products usually are sold in chanawalla shops, with other snacks like daane and daale (roasted peanut and dehulled gram products). Puffed or parched products are made from other cereals (sorghum, millet) in some areas of India, usually in rural areas or smaller cities in the drier regions where rice is in short supply. Special varieties are used. Peanut, sunﬂower seed, cottonseed and palm oils are used for frying. For the most part, they are unreﬁned, ﬁltered oils. The snacks that puff during frying (papadya, kurdaya and vadam) typically are made from rice, but sometimes are extended with corn (maize) or sorghum.

1.3. METHODS OF USE The most favorite snack prepared with murmure as the main ingredient is bhel, which means a mixture. The components include daane, shev, daale, chivda (described in detail later) and a mixture of salt and red pepper. Lemon juice is added as ﬂavoring in suki-bhel (dry bhel). The other variety of bhel, which is very popular with all age groups, is served with a mixture of pungent green sauce (made from ground green chilies, coriander leaves and salt) and a sweet sauce (made from ground dates, tamarind and spices). It is topped with a thin shev, and a puri is provided for use as a spoon. Pohe was made at home until a few years ago, but with rapid industrialization and lack of time, most families now buy the ready-made product . Most traditional snacks are consumed between meals except for rice papadya, kurdaya and vadam, which are fried and served with cocktails and as

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an addendum to meals. Tea time is an important institution in India, and most traditional snacks like chivda, shev, farsan and others are served with tea or coffee to the family and guests.

2. ROASTED CEREAL SNACK FOODS

2.1. POHE (RICE FLAKES) r Ingredients. Paddy (undehulled rice), water. r Process. The rice is partially parboiled by pouring boiling water over the

paddy, which is allowed to soak overnight. The water is removed, and additional boiling water is poured over the soaked paddy. The drained paddy is then packed into gunny bags to allow equilibration of moisture. The variety of paddy used affects the size, ﬂavor and texture of the rice ﬂakes. Thus, several varieties of rice ﬂakes are available in the market. Two main varieties—thick and thin rice ﬂakes—with different textures are available. Thick rice ﬂakes are used to prepare snacks after soaking and seasoning. Thin rice ﬂakes are used to prepare chivda. The oven is ﬁred with sawdust as fuel, and the heating continued until sand in the two compartments of the oven attains an appropriate temperature. Then, the paddy is stirred into it and heated. Judgment of the appropriate temperature of sand and roasting time for paddy is extremely important to the process. The kernels are roasted within the husk, with the process completed within 2 minutes. Each batch takes about 2 kg of paddy. The sand and paddy mix is then manually sieved to remove the sand. The roasted paddy is immediately poured into the edge runner machine and passes between two rolls, which ﬂake the rice and separate it from the husk. The operation takes about 2 minutes. The husk then falls through a sieve; the ﬂaked rice on the top is packed into bags. Typically, about 1 metric ton (1,000 kg) is processed in a day. Most rice-ﬂaking mills offer the processing service to customers who bring a preprocessed paddy of their choice. It is roasted and ﬂaked in the mills and returned to the customer. The effects of process variables on composition, quality and nutritive value of pohe have been studied [2]. More research is being conducted on mechanizing and improving the efﬁciency of the operation. r Shelf Life. About 12 weeks. r Machinery. —Oven (Bhatti). The oven is made of ﬁred clay and is heated by sawdust supplied by a screw conveyor. Usually, two compartments, ﬁlled with sand and located on the top of the oven, are heated until the sand attains the desired temperature. The paddy then is mixed with the sand and

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parched at the high temperature. Then the sand is removed from the paddy by sieving and returned to the oven compartments for reuse. —Edge Runner Machine. The hot parched paddy is quickly poured manually into the runner machine, which consists of two sets of rollers separated by a small gap. Both rollers turn inward to pull the paddy between them, where the pressure ﬂattens and ﬂakes the paddy. The husk, which is pulverized, passes through the sieve of the machine. The rice ﬂakes, remaining on the sieve, are removed manually, allowed to cool and packaged [3].

2.2. MURMURE (PUFFED RICE) r Ingredients. Paddy (non-dehulled rice), salt, water. r Process. Good murmure can be made only from certain varieties of rice.

Generally, but not exclusively, they are of the waxy type. The structure of the seed is important [4]. Paddy is soaked in boiling water and left in the barrel overnight for 12 hours. Next morning, the mixture is poured into wire baskets to drain the water, and the paddy is roasted in an oven after mixing with sand. Usually about 2.0–2.5 kg can be roasted at a time. Roasting a quintal (100 kg) of paddy takes about 2.5–3 hours. Then it is equilibrated in gunny bags overnight. The next day, the paddy is spread on the ground to cool for about an hour, then shelled to remove the husks, abrasion milled to remove the brown pericarp and equilibrated (cooled) for half an hour. Next, just enough heated water is added to moisten the rice for pufﬁng. The water contains 0.5 kg salt per 100 kg rice. The moist rice is puffed by roasting in preheated sand in a shallow pan for a minute. Then the murmure mixture is sieved to remove the sand, allowed to cool and later packed. Each step in the processes for making pohe and murmure is important. Nowadays, the younger generation is moving away from manufacturing pohe and murmure because proﬁt margins are not commensurate with the required skill and labor. r Shelf Life. 6 months. r Equipment. —Oven. The same type of oven is used as for making pohe (rice ﬂakes, 2.1). —Rice Huller. A conventional batch-type rice huller is used for shelling and milling the rice. —Fuel. Wood is used for heating the water.

2.3. KHAKRA r Required ingredients. Whole wheat (Triticum aestivum L.) ﬂour, salt, water. r Optional Ingredients. Red pepper, cumin seed powder, coriander

leaves—ﬁnely cut.

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r Process. All the ingredients are mixed with just enough water to make a

hard dough. The dough is kneaded well, divided into 20 g portions and rolled into thin rounds about 5 to 6 inches in diameter. These are roasted on a thick skillet until brown. A clean cloth is used to press the rounds in close contact with the hot surface to form a dry crust. The product is cooled and packaged into packets containing 200 g or more each. r Shelf Life. 6 to 8 weeks. r Equipment. Mixing bowl, rolling pin and rolling board, thick skillet, heat-sealable ﬂexible pouches, sealer.

2.4. USES OF OTHER CEREALS Snacks are also made in speciﬁc regions of India from a wide variety of cereals, including: jowar (sorghum, Sorghum bicolor L. Moench), bajra (pearl millet, Pennisetum typhoides), ragi (ﬁnger millet, Eleusine coracana) and corn (Zea mays L.). The use of these cereals has been enhanced by the development of improved varieties. Generally, similar processes are used with adaptation for the speciﬁc cereal. These cereals are also used in blends with pulses and produce interesting variations in snacks.

3. ROASTED LEGUME SNACK FOODS

3.1. CHANE (ROASTED GRAM) r Ingredients. Whole Bengal gram (Cicer arietinum, L.), salt, turmeric

powder.

r Process. One kg turmeric powder and 2 kg salt are added to 100 kg of whole

Bengal grams and mixed thoroughly. The mixture is soaked in water for a few minutes and then mixed with hot sand in one compartment of the oven. About 2 kg of the chane mixture is roasted at a time for 2–3 minutes. About 2 hours are required to roast 100 kg or 1 quintal. The chane is taken out of the oven and sieved to remove the sand, which is returned to the oven. The roasted chane has an open split structure, with the gram hull still adhering. The product is cooled and packaged. r Shelf Life. 4–6 weeks. r Equipment. Oven (same as used for pohe, 2.1), sieve, large pans.

3.2. DAANE (ROASTED PEANUTS/GROUNDNUTS) r Ingredients. Shelled peanuts (groundnuts, Arachis hypogae L.), salt, water. r Process. 100 kg of shelled peanuts is soaked in water containing 1 kg salt,

drained, mixed with hot sand in the oven, roasted at a high temperature for

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about 2 minutes and sieved to remove the sand. Then the pink seed coat of the peanuts is removed by rubbing. The peeled peanuts are cooled and packed in bags. r Shelf Life. 4–6 weeks. r Equipment. Oven (same as for pohe, 2.1), sieve, large pans.

3.3. DAALE (ROASTED DAL OR DAHL) Dal is a dehulled gram, split into cotyledons, also known as “dahl” in English. Daale is a dahl that has been roasted as a whole gram before dehulling and splitting. r Ingredients. Whole dark Bengal gram, salt, water. r Process. It is essential that the dark variety of Bengal gram be used for

making daale. Other varieties do not make product as good. The whole dark Bengal gram is moistened with salt water and allowed to equilibrate. A 2 kg batch of soaked Bengal grams is roasted with hot sand in a preheated hot oven for 2.0–2.5 minutes, removed, and the sand separated by sieving. The roasted Bengal gram is then rubbed in a stone mortar with a wooden pestle to free the daale from the seed coat. The mixture is winnowed in a special bamboo tray to remove the light seed coat, and the daale is packed in bags. r Shelf Life. 2.0–2.5 months. r Equipment. Oven (same as used for pohe, 2.1).

3.4. ROASTED PEAS r Ingredients. Whole dry green peas (Pisum sativum L.). r Process, Shelf Life, Equipment. Same as for making daale.

3.5. PAPAD r Ingredients. Black gram dal, black pepper, asafoetida—the fetid gum resin

of various oriental plants, especially Ferula foetida, salt, papadkhar (crude sodium carbonate), oil. r Process. Black gram dal is ground into ﬂour. The roasted and powdered papadkhar and spices are mixed with the black gram ﬂour. Water is boiled with salt and ﬁltered. The ﬂour-spice mixture is mixed with the salt water and oil to make a hard dough. When available, extract of ash gourd or banana stem may be used in place of water to make a papad dough. The dough is kneaded, divided into small balls (about 10 g each) and rolled into thin circles about 2.5 inch (6.4 cm) diameter. These are individually dried in the sun. The papad are cooled and packaged in cellophane or food-grade plastic pouches.

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Papads are roasted or fried and served as cocktail snacks and with meals. A variety of papads are made by the same procedure using other dals, pohe and even jackfruit. r Shelf Life. A year or more. r Equipment. Bowl, mortar and pestle, rolling board and rolling pin, solar or electric dryer, trays for drying.

4. DEHYDRATED SNACK FOODS (SERVED AFTER FRYING)

4.1. RICE PAPADYA r Ingredients. Rice ﬂour, salt, asafoetida, poppy seeds. r Process. Dehulled, milled rice is soaked, dried, ground, and the rice ﬂour is

passed through a ﬁne sieve . The rice ﬂour, salt, asafoetida and poppy seeds are added to boiling water in the proportion of 2 parts ﬂour to 3 parts water. A quarter cup of this dough is spread on a plantain leaf or plastic sheet to make a 2.5–3.0 inch (6.4–7.6 cm) round and dried in the sun. After drying, it is cooled and packaged. The rounds are puffed by frying and served as meal adjuncts or cocktail snacks. r Shelf Life. One year. r Equipment. Flour mill, saucepan, wooden stirring spoon, package sealer.

4.2. KURDAYA r Ingredients. Rice ﬂour, salt, asafoetida. r Process. The rice ﬂour is prepared as described for rice papadya. The

sieved ﬂour is added to boiling water along with salt and asafoetida. The mixture is stirred over low heat until it becomes translucent. Then it is cooled and kneaded. The kneaded dough is put into a mold and extruded with a hand-held device onto a plastic sheet. The extruder is turned during extrusion to give a circular shape to the product. The extruded kurdaya then is dried, cooled and packaged. The product is puffed by frying in oil and becomes very crunchy. Like rice papadya, it is served as a meal adjunct or cocktail snack. A similar product can also be made from wheat ﬂour. r Shelf Life. One year. r Equipment. Same as for making rice papadya. In addition, a forming extruder is needed for shaping kurdaya. The extruder for making shaped traditional Indian snack foods is held in the hand. It consists of three parts: (1) a cylindrical body; (2) a plunger with handle; and (3) a set of plates (Figures 18.1 and 18.2). The plates are slipped into the

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Figure 18.1 Drawings of: (A) hand extruder for making chakali and shev; (B) die plate for extrusion of shev; (C) die plate for extrusion of chakali.

cylinder to ﬁt at its base. The dough is placed on top of the plate inside the cylinder, and the plunger is pressed to extrude the dough through the apertures in the plate. The extruder is moved by hand to make desired shapes from the exiting dough. The plate needed for a particular snack food is chosen from among several plates provided with the extruder. These include: (1) a plate with round holes of two sizes, small and medium for making shev; (2) a plate with round holes with smooth striations for ganthia; (3) and a plate with star-shaped holes for chakali, murukku, and vadam.

4.3. VADAM r Ingredients. Same as for making kurdaya, but powdered cumin seed is used

for spice.

r Process. Same as for making kurdaya. The product also puffs on frying and

is served as meal adjuncts or cocktail snacks.

r Shelf Life. One year.

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Figure 18.2 Drawing of screw-operated extruder for shev.

r Equipment. Same as for making kurdaya, except that a special extruder plate

is used for making vadam.

5. FRIED CEREAL SNACK FOODS

5.1. MATHRI r Ingredients. Maida (all-purpose wheat ﬂour), black pepper powder, cumin

seed powder, salt, oil or shortening, water.

r Process. The maida, spices, salt and oil/shortening are mixed, and enough

water is added to make a hard dough. The dough is divided into balls weighing 10–12 g and rolled into thin rounds, which are pricked with a fork and air dried for about 30 min. The rounds are then fried in oil to a slight brown color, drained, cooled and packaged. r Shelf Life. 4–6 weeks. r Equipment. Mixing bowl, rolling board and rolling pin, frying pan and zara (or a device to remove the fried product), sieve, heat-sealable, ﬂexible pouches, sealer.

5.2. PURI FOR PANI-PURI r Ingredients. Whole wheat ﬂour, salt, oil, water. r Process. All the ingredients are mixed to make a hard dough. The dough is

rolled into thin sheets. Pieces about 1.25 inch (3.2 cm) diameter are cut with a circular cutter and fried in oil. The puri puff instantaneously in the hot oil

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due to steam leavening. They are removed, drained, cooled and packaged to serve as pani-puri (puri with water). Three items are added to the puri when served as pani-puri: spiced water, cooked sprouted mung bean (green lentil) and cooked mashed potatoes. A hole is made on the thin side of the puri and the three items are put in the hole and quickly handed to the customer for eating. It is a delicious product. The mixture of spices used in the water imparts a unique taste to the pani-puri. Packets of puri are sold in farsan shops to customers for serving pani-puri at parties. Pani-puri is served by vendors at street corners and at beaches in Bombay and other large cities. Pani-puri is a favorite snack of people from Gujarat state and is popular with Indians from other states as well.

6. FRIED LEGUME SNACK FOODS

6.1. DALMUTH r Ingredients. Green gram, lentils (Lens esculenta), Bengal gram daale, soda,

oil, salt. Spices: green (Indian) chilies, badishop (fennel seeds), cumin seeds. Ready-made addition: thin shev. r Process. Green grams, lentils and Bengal gram daale are soaked in water for eight hours. A pinch of soda is added to each item while soaking in water to improve the texture. The grains are drained and dried on a thin muslin cloth, deep fried in a wire basket in hot oil and transferred to a colander to drain off the oil. All the spices are fried with a little oil and added to the legume mixture as seasoning. Thin shev is added to the mixture and it is packaged. r Shelf Life. 4–5 weeks. r Equipment. Same as for making chivda.

6.2. SHEV r Ingredients. Besan (Bengal gram ﬂour), oil, red or black pepper, salt,

turmeric, cumin seed. Optional ingredient: Omum (local seasoning).

r Process. All the dry ingredients are mixed; then hot oil is added followed by

additional mixing. Just enough water is added to make a dough that can be shaped through an extruder plate with small holes. The thin extruded strands are dropped into hot oil in a fryer and shaped into a circle. They are deep fried to a golden yellow color, drained, cooled and packaged. r Shelf Life. About 4 weeks. r Equipment. Fryer and frying basket, hand-operated extruder for forming the shev, plastic packets and sealer. Several extruder plates with varying diameters of holes are normally a part of the extruder (Figures 18.1 and

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Figure 18.3 Drawing of zara-type ﬂat extruder. The batter is forced through the holes by hand pressure, takes the shape of the holes and drops into oil in a deep-fat fryer.

18.2). These are used to obtain thin, medium and thick shev. The thickness of shev is determined by its end use. Heat-sealable, ﬂexible pouches are used for packaging.

6.3. GANTHIA r Ingredients. Same as for making shev. r Process, Shelf Life, Equipment. The method of preparation is the same as for

making shev, except the extruder plate has a larger oriﬁce with striations. The product is much thicker than shev and has striations.

6.4. KHARABOONDI r Ingredients. Same as for making shev, fried curry leaves. r Process. Same as for making shev, except that the besan dough is dropped

into the frying oil with a zara-type extruder (an implement with 1.25 inch diameter holes in a curved trough 9–12 inches in diameter, equipped with a handle) (Figure 18.3). The golden, round boondis fry in a minute and are removed quickly with a turner, which has round holes to drain off the oil. Boondis are drained and packed with addition of salt, spices, and fried curry leaves. r Shelf Life. A month at ambient temperature, but longer if kept at cooler temperatures. r Equipment. Same as for making shev, but a zara-type extruder is used.

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6.5. FARSAN Farsan is a mixture of several fried products made from besan. The major ingredients are shev (both thick and thin), ganthia, kharaboondi and chivda. About 40 different varieties of farsan are made by varying the proportions, texture and spices used.

7. FRIED GRAIN AND LEGUME SNACK FOODS Cereal grains other than rice are also used in some regions.

7.1. CHAKALI r Ingredients. Rice, Bengal gram dal, black gram dal, coriander seeds, cumin

seeds, sesame seeds, red pepper powder, turmeric powder, salt, asafoetida powder, oil. r Process. The ﬁrst ﬁve ingredients are roasted and ground to ﬂour, and the remaining ingredients are mixed in. Boiling water is added to make a dough, which is kneaded well. A chakali extruder (Figure 18.1) is used to shape the dough into circular forms, which are fried in hot oil. Chakali has a nice brown color when it is fried properly. After removal from the hot oil, it is drained, cooled and packaged. r Shelf Life. 4–5 weeks. r Equipment. Roasting pan, stirrer, measuring cups and spoons, extruder with chakali plate, fryer and frying basket, colander, heat-sealable, ﬂexible pouches, sealer.

7.2. KADBOLI r Ingredients. Same as for making chakali. r Process. Dough is prepared as for making chakali. It is rolled by hand and

shaped in the form of a circle. The shaped dough is fried in hot oil to an attractive brown color, removed from the hot oil, drained, allowed to cool and packaged. r Shelf Life. 4–5 weeks. r Equipment. Same as for making chakali, except that kadboli is shaped by hand and a chakali extruder is not needed.

7.3. MURUKKU r Ingredients. Rice, black gram dal ﬂour, salt, asafoetida, oil for frying. r Process. Rice is soaked in water for a few hours, drained, dried and

ground to ﬁne powder. The rice and black gram ﬂours are mixed in the

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proportion of 8:1 (volume). Salt, asafoetida; and water are added to make a dough that can be molded. A murukku plate is inserted into the extruder, and the dough is shaped in the form of a circle and deep fried After removal from the hot oil, the product is drained, cooled and packaged. r Shelf Life. 4–5 weeks. r Equipment. Same as for making shev, but the chakali plate is used with the extruder.

7.4. THENGUL r Ingredients. Same as for making murukku. r Process. Same as for making murukku, except the thengul extruder plate

does not have striations and produces straight strands.

7.5. CHIVDA r Ingredients. Thin rice ﬂakes, roasted peanuts, slices of dry coconut, roasted

Bengal gram daale, roasted sesame seeds, raisins, oil, chilies, mustard seeds, curry leaves, turmeric powder, salt, sugar, oil. r Process. Thin rice ﬂakes are roasted till they are crisp and crunchy. The oil is heated, the mustard seeds popped in it, and green chilies, turmeric, salt and curry leaves are added and stirred. Next, all the other ingredients, except the roasted rice ﬂakes, are added and stirred over low heat for a few minutes. The roasted rice ﬂakes are then added, and the entire mixture is stirred over low heat for a few minutes. The chivda is then allowed to cool and packaged in heat-sealable, ﬂexible pouches. Chivda is a genre of snack foods. A variety of chivdas are made and vary with the kind of cereal ﬂakes used (e.g., rice ﬂakes, corn ﬂakes, or wheat ﬂakes), the method of heating the ﬂakes pohe (roasting or frying), the variety and proportions of ingredients (nuts, oilseeds, dry fruits), and lastly the spices used for seasoning. r Shelf Life. One month or more. r Equipment. Large saucepan, wooden turner with long handle.

8. FRIED FRUIT AND TUBER SNACK FOODS

8.1. PLANTAIN WAFERS (CHIPS) r Ingredients. Plantains, coconut oil, salt. r Process. A special variety of plantain (called Nendrapallam) from the state

of Kerala gives the best results. The plantains are peeled and cut into thin

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wafers. They are fried in coconut oil in large frying pans, removed from the fryer, drained, cooled, salted and packaged. r Shelf Life. One month. r Equipment. Large frying pan, turner with holes to remove the wafers and drain the oil, heat-sealable food-grade, ﬂexible pouches, sealer.

8.2. YAM WAFERS (CHIPS) r The process and equipment is the same as for making plantain wafers,

except that yams are used instead of plantains.

8.3. POTATO WAFERS (CHIPS) r The process is the same as described for plantain chips, except the main

ingredient is peeled potatoes. Oil absorption is much less in all other chips compared to potato chips, possibly due to difference in type, structure and amounts of starch.

9. NUTRITIONAL VALUE OF INDIAN SNACK FOODS Most of the traditional Indian snack foods are made from cereals and legumes. The processes include roasting and frying. Parboiling, the preliminary treatment used in manufacturing pohe and murmura, ensures dissolution of the sticky layer between the husk and grain, movement of nutrients from the aleurone layer to the grain, retention of the shape of the grain, and results in a product with higher nutrient content than milled rice made from the same paddy. Thus, these products are valuable sources of protein, thiamin and niacin in the diet. The roasted products made from whole legumes (chane, daane, roasted peas) and their decorticated products (dale) are rich sources of protein, calcium, TABLE 18.1.

Product

Nutrient Contents of Indian Roasted Snack Foods per 100 Grams.a Calories

Protein g

Calcium mg

Iron mg

Thiamin mg

Niacin mg

346 325 369 570 340 290

7 7 22 26 23 19

20 23 58 77 81 80

20 7 9 3 6 17

0.21 0.21 0.20 0.39 0.47 0.35

4.0 4.1 1.3 22.1 3.5 1.7

Rice flakes Rice, puffed Chane Daane Peas, roasted Papad a

Gopalan et al. [5].

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Nutrient Contents of Indian Fried Legume Snack Foods per 100 Grams.a Product Name Dalmuth Kharaboondi Shev (bhel) Shev (farsan) Ganthia Chivda

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Calories

Protein g

Fat g

560 610 570 610 610 515

16 16 15 14 14 11

35 42 38 45 45 30

Mudambi [6].

iron, thiamin and niacin. Since roasted cereals and legume products are often consumed together, the nutritional quality of the protein is improved. The nutrients in some roasted cereal and legume products, from the nutritive value tables of the Indian Council of Medical Research [5], are shown in Table 18.1. In nutrition surveys in Bombay, the authors found that Gujarati and Maharashtrian families used snack foods purchased from farsan shops. The nutritive value tables of Indian foods did not include analyses of these foods. These were analyzed for their major proximate components by research assistants in the Department of Food Science and Nutrition, Shreemati Nathibal Damodar Thackersey (S.N.D.T.) University [6], and the values are presented in Table 18.2.

10. REFERENCES 1. Prabhakar, J. V., 1986. Amenability of sweetmeats and fried products to the application of modern science and technology. In Traditional Foods—Some Products and Technologies. Central Food Technological Research Institute, Mysore, India, pp. 49–57. 2. Ananthachar, T. K., 1980. Effect of Process Variables on the Composition, Quality and Nutritive Value of Beaten Rice Poha, Avalakki. M.Sc. Thesis, University of Mysore, Manasagangotri, Mysore, India. 3. Desikachar, H. R., 1986. Upgradation of certain traditional technologies of food processing for changing life styles in India. In Traditional Foods—Some Products and Technologies. Central Food Technological Research Institute, Mysore, India, pp. 80–82. 4. Srinivas T. and H. S. R. Desikachar, 1973. Factors affecting the pufﬁng quality of rice. J. Sci. Fd. Agric., 24:883–891. 5. Gopalan C., B. V. Rama Sastri, and S. C. Balasubramanian, 1991. Nutritive Value of Indian Foods. Indian Council of Medical Research, Hyderabad, India. 6. Mudambi, S. R., 1984. Research in Home Science. Part III Research in Food Science and Nutrition. Shreemati Nathibal Damodar Thackersey Women’s University Publication, Mumbai, India, P 3.5, 3.8, 3.9.

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SECTION IV

OPERATIONS AFTER SHAPING AND DRYING

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CHAPTER 19

Snack Food Seasonings

JON SEIGHMAN

1. INTRODUCTION

C

buy more than $6.5 billion worth of ﬂavored salty snacks in the United States annually. This is an incredibly competitive business where small regional chippers and national snack food giants go toe to toe in competing for a share of the snacking consumer’s money. Americans are snacking more than ever before. From 1993 to 1998, the percentage of adults who eat three meals a day without snacking between meals decreased from 33% to 24%. Today, more than 50% of Americans eat less than three meals per day and snack once or twice between meals. There is a growing population of Americans who snack throughout the day with no sitdown meals at all. It should be no surprise that this translates into big opportunities for snack companies. However, snack consumers are demanding. They want variety and many options. It is up to the snack food companies to provide new seasonings for chips to keep snackers interested and coming back for more. From cheese to barbecue (BBQ) to sour cream and onion, the average person consumes 8 pounds of ﬂavored chips, pretzels, popcorn, nuts and meat snacks per year. Since the mid-1980s, ﬂavor line extensions have fueled growth for many snack food producers. A reason for this is the huge expense associated with development, commercialization and marketing of new snack food brands. Developing a new snack brand is difﬁcult. Manufacturers must identify how the new brand will be different from current brands. Shapes must be identiﬁed and tested. Texture and thickness must be evaluated. New equipment and ingredients may have to be purchased. In addition, advertising budgets must be increased to inform consumers about the new brand and persuade them to buy it. ONSUMERS

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On the other hand, a ﬂavor extension of a line uses the same production equipment and brand name as existing products. Development time is shortened to the time spent formulating and testing the new seasoning. Consumers are already familiar with the brand and its beneﬁts. A new ﬂavor is easier to try and accept than a new brand. Line extensions allow the snack manufacturer to have a portfolio of products that appeal to a broad range of consumers at lower cost. Each ﬂavor can be used to extend the reach of the brand. Snack food companies may launch a new brand once every ﬁve years, but launch new ﬂavors each year. Historically, the most popular ﬂavors for salty snack seasonings have been Cheese, BBQ, Sour Cream and Onion, and Ranch. These four seasonings form the basis for the ﬂavor portfolios of most snack food brands. As a result, consumers are very familiar with the taste proﬁles of these seasonings and readily accept them on almost any snack product. A Nacho Cheese seasoning developed for tortilla chips may taste just as good on potato chips, or a Sour Cream and Onion developed for potato chips may be a great new ﬂavor for corn chips. Many snack food companies include two or more of these ﬂavor proﬁles in each new brand they introduce. The challenge for many snack food companies is deciding on the seasoning to develop after the “Big Four.” Since ﬂavor line extensions are a major source of growth, snack companies are always looking for the next great-selling new snack ﬂavor. The new ﬂavor may be a replacement for BBQ, Cheese, Sour Cream and Onion or Ranch, but is just as likely to be a reformulation of the current ﬂavor with enhancements to make the seasoning more in accord with current taste trends. For example, BBQ seasonings developed in the mid-1960s were typically hickory smoke type with high levels of torula yeast, paprika and spices. In the late 1980s, many companies reformulated their BBQ seasonings to switch from hickory smoke to mesquite smoke and made the ﬂavor much sweeter by introducing sugar, dextrose, or honey. In the 1990s, many BBQ formulas were adjusted to be spicier with more red pepper and more acidity. Similar evolutions have occurred for each of the classic seasoning types over the last 20 years, with each proﬁle changing slightly to match the changing tastes of the snack consumer. Although the classical seasonings have evolved gradually over time, at least one new ﬂavor is introduced each year as a contestant for the next classic snack ﬂavor that will withstand the test of time. Successful new snack seasonings often use familiar ﬂavors and combine them in creative ways. A review of the top-selling ﬂavored snack food products shows that many of the same ingredients are used. Cheese powder, tomato powder, onion and garlic appear in almost every ingredients statement. These ingredients appear in seasoning formulas like BBQ, nacho cheese, pizza, taco, chili cheese, or ranch. The key to successful seasoning development is creating variety in new seasonings by combining well-known ingredients in unique ways.

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2. INGREDIENTS Before discussing the formulation of seasonings, it is necessary to develop an understanding of the ingredients and their functions. As an example, one topselling snack has the following long ingredients statement, arranged in order of diminishing content: Salt, sugar, maltodextrin, dextrose, monosodium glutamate, onion powder, tomato powder, brown sugar, sour cream powder, molasses, cheddar cheese powder, Monterey Jack cheese powder, garlic powder, spices, sodium diacetate, natural and artiﬁcial ﬂavors, whey, artiﬁcial colors, natural hickory smoke ﬂavor, worcestershire sauce powder, dehydrated bell pepper, hydrolyzed proteins, beef stock, autolyzed yeast, lactic acid, citric acid, vinegar, tamarind, disodium inosinate, disodium guanylate, and yeast extract.

Seasoning manufacturers do not construct complicated ingredient declarations to confuse the competition, but rather to create great-tasting snacks with well-balanced ﬂavor and appetizing visual appeal. To accomplish this, seasoning formulators develop complex blends of ingredients that provide multiple ﬂavor sensations. Each ingredient in the formula serves a speciﬁc function to help achieve ﬂavor and appearance characteristics that attract consumers. Some ingredients provide the characterizing ﬂavor of the seasoning. The smoke, worcestershire, and natural and artiﬁcial ﬂavors are the primary characterizing ﬂavors in the seasoning, and part of the initial ﬂavor burst. They are tasted ﬁrst as the top note of the seasoning and also are part of the aftertaste. Other ingredients affect the mouth feel or texture of the seasoning. Sour cream powder, cheddar cheese powder, or Monterey Jack cheese powder are not present to introduce characterizing dairy ﬂavors that the consumer will taste and recognize, but to give a pleasant fatty mouth feel to the seasoning. The fattiness of these ingredients helps blend the harshness of the hickory smoke and meaty ﬂavors with the background ﬂavors of onion, garlic and tomato to provide a smooth transition from taste to taste. Numerous ﬂavor enhancers, including monosodium glutamate (MSG), disodium inosinate, disodium guanylate, autolyzed yeast and salt, are in the formula. These enhance the overall ﬂavor impact of the seasoning and give a mouth-watering sensation that attracts the consumer to eat more. Some snack producers avoid use of ﬂavor enhancers like these to meet consumer demands for so-called clean labels. But for seasoning formulators, this class of ingredients is very important in the development of great-tasting salty snack products. In addition to enhancing ﬂavor, ingredients are present to stimulate the basic taste sensations of sweet, salty, bitter and sour. For example, dextrose, brown sugar and molasses provide rich, sweet brown ﬂavors to the seasoning. Molasses, tamarind, some spices and yeasts, provide a subtle bitterness to the formula. A complex acid proﬁle results from the addition of sodium diacetate,

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lactic acid, vinegar and/or citric acid. The acid complex enhances the sweet brown ﬂavors described previously. The selected ingredients determine how the ﬂavor releases, what the aftertaste will be, and whether the seasoning can be applied evenly. Grouping the ingredients of a seasoning into salt, ﬁllers, spray-dried dairy and vegetable powders, spices, compounded ﬂavors, ﬂavor enhancers, sweeteners, acids, colors and processing aids helps to develop an understanding of how seasonings are formulated for salty snacks.

2.1. SALT Salt is a key ingredient in salty snack seasonings. The main purpose of salt is to potentiate the overall ﬂavor of the seasoning. Without salt, it would have a bland ﬂavor and lack intensity. The most common salt used in formulating seasonings is ﬂour salt, a ﬁne granular material with a particle-size distribution of 96% minimum through a U.S. 80 mesh (178 micron) screen. Granulated salt, ﬁne ﬂake salt, or pretzel salt may be used for snacks where only salt is added, but are not recommended for seasoning blends. The relatively larger salt particles have a tendency to adhere to the snack base differently than the other ﬁne-particle-size ingredients in the blend, and often result in excessive salt falloff or uneven distribution of the seasoning Salt typically is used in formulas at 15–25%, if the seasoning is applied to the ﬁnished product at 5–8%. The exact salt level for a seasoning should be determined through consumer testing. It is important to remember that salt also is present in many spray-dried dairy powders, hydrolyzed vegetable proteins (HVP), autolyzed yeast extracts and in some compounded ﬂavors. Also, salt perception is enhanced by the use of monosodium glutamate, disodium inosinate, disodium guanylate and some organic acids. These factors should be considered when adjustments are made to the salt level.

2.2. FILLERS The ﬁllers used in seasoning blends typically are low-cost, commodity products, bland in ﬂavor. The most common ﬁllers are: maltodextrin, corn syrup solids, wheat ﬂour, corn ﬂour and whey. Fillers are used in seasonings at 20–40%, depending on the type of seasoning and its level of application to the product. Most seasoning blends are used on snacks at 5–8%. Formulators use ﬁllers to adjust the application level of the seasoning to ensure desired coverage and ﬂavor impact. For example, if the overall ﬂavor impact of the seasoning is too strong, additional ﬁller may be added to dilute it. If the appearance of the blend on the snack is uneven, one solution may be to increase its application level. But if the seasoning use level is increased, the ﬁller should also be increased to maintain an equivalent ﬂavor impact.

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This can be shown for a seasoning which contains, among other things, 20% maltodextrin, 20% added salt and 1% compounded ﬂavor. Maltodextrin Salt Compounded flavor Other ingredients

20.00% 20.00% 1.00% 59.00% 100.00%

The blend was intended to be used at 5% on a snack base but, when applied to chips, although the ﬂavor of the seasoning is acceptable, its coverage of the product is uneven. An increase in seasoning application level to correct this is indicated. But if the blend is applied at 7%, the ﬂavor will be too strong. Therefore, the ﬁller should be increased to dilute the seasoning. Referring again to the example formula, at 5% use level seasoning, the maltodextrin, salt and compounded ﬂavor on the ﬁnished product is 1%, 1% and 0.05%, respectively. If increased to 7% without adjustment of ﬁllers, the salt content would be 1.4% and the compounded ﬂavor 0.07%, a 40% increase of each:

Ingredient Maltodextrin Salt Compounded flavor Other ingredients Total

Formula

At 7% Use Level on 100 g Chips

At 5% Use Level on 100 g Chips

20.0% 20.0% 1.0% 59.0%

1.00 g 1.00 g 0.05 g 2.95 g

1.40 g 1.40 g 0.07 g 4.13 g

100.0%

5.00 g

7.00 g

The objective is to keep the ﬂavor impact of the seasoning when used at 7% equal to the ﬂavor impact at 5%, and salt and ﬂavor in the formula are reduced. The new levels are 14.30% for the salt and 0.70% for the compounded ﬂavor. The difference in the formula is added to the maltodextrin.

Ingredient Maltodextrin Salt Compounded flavor Other ingredients Total

Formula

At 7% Use Level on 100 g Chips

26.00% 14.30% 0.70% 59.00%

1.00 g 1.00 g 0.05 g 2.95 g

100.00%

5.00 g

Referring to the previous chart, we see that the levels of ﬂavor and salt in the ﬁrst formula applied at 5% are now equal to the salt and ﬂavor applied at 7%.

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The changes in bland ﬁller will have little impact on the overall ﬂavor of the seasoning when applied at 7%.

2.3. SPRAY-DRIED DAIRY POWDERS Cheese powders, sour cream powders, butter powder and buttermilk powder are key ingredients in formulating blends for salty snacks. Their function is to provide mouth feel and ﬂavor to the seasoning. Dairy powders are manufactured by spray drying a slurry of cheese, butter, sour cream, or buttermilk, water, starch, emulsiﬁer, salt, and sometimes compounded ﬂavors. The relatively high level of butterfat in the powders, typically 15–50%, makes them valuable to the seasoning formulator. The need for dairy powders in seasonings like Nacho Cheese or Sour Cream and Onion is obvious because the named ingredients, cheese and sour cream, are required for labeling and for ﬂavor. However, the use of dairy powders is not as clear in the case of BBQ seasoning. Formulators use dairy powders in this application to provide mouth feel and to help blend all the ﬂavors contained in the seasoning. Seasonings without any fat tend to “clean up” very quickly; even well-formulated ﬂavor proﬁles, lacking fat, have this problem. Dairy fat, with a melting point below 100◦ F (37.8◦ C), readily melts and coats the mouth during eating. As the fat melts, lipophilic ﬂavor chemicals solubilize in the fat, creating a longer-lasting ﬂavor sensation in the mouth. The aftertaste of the seasoning can be affected by manipulating the fat-soluble ﬂavor components of the formula. This is useful in BBQ seasonings, which have a tendency to be harsh due to the smoky, meaty and vinegary notes present in their formulas. Spray-dried dairy powders should be used in most applications and not just dairy seasonings. Many types of dairy powders are produced for use in the snack industry, and the product for the seasoning should be selected carefully. The dairy powder should have a clean taste without signiﬁcant cooked notes. Dairy powders are relatively expensive and are priced according to cost of the starting material used, the level of butterfat in the ﬁnished powder, and whether the product is kosher or not. Dairy powders are used in seasonings at levels of 5–20%. At low levels, they help smooth out the ﬂavor, especially if the seasoning has a high level of ﬂavors and spices. At high levels, they make a signiﬁcant contribution to the mouth feel and ﬂavor of the seasoning.

2.4. DEHYDRATED VEGETABLE POWDERS Onion powder, garlic powder and chili pepper are the most common vegetable powders used in seasonings. They are produced by drying a slurry of the vegetable, usually by heat and vacuum, to a moisture content of less than 5%. The resulting powders are relatively inexpensive and concentrated in ﬂavor. Toasted

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or roasted versions of onion or garlic powders offer distinctively different ﬂavor proﬁles. Onion or garlic appears in almost every snack seasoning currently sold. They bring depth to the middle part of the seasoning’s ﬂavor proﬁle. The initial ﬂavor of a seasoning comes from compounded ﬂavors that dissolve rapidly and release ﬂavor quickly. After the initial burst of ﬂavor, the next ﬂavor perceived comes from ingredients that solubilize slower. Onion and garlic powders release ﬂavor slower than spray-dried ﬂavors and therefore are used to ﬁll the middle of the taste experience. The initial ﬂavor release can be intense in seasonings using only compounded ﬂavors, but the ﬂavor dissipates quickly. Addition of onion or garlic powder to the formula makes the taste proﬁle more complex and prolongs the taste experience. Both ingredients are versatile in most applications, and can also be used at low levels to help sustain the ﬂavor impact in cheese seasonings. However, these powders are generally higher in yeast, mold and standard plate count than most other ingredients used in seasonings, a factor to consider if the blend is used in microbially sensitive applications. Onion powder is typically used at 1–10% in seasonings, and garlic powder at lower levels, usually 0.5–5%.

2.5. SPICES Herbs and spices were the primary source of added ﬂavor in seasonings for many years. The ﬁrst snack seasoning depended on ﬂavors contributed by spices such as black pepper, chili powder, mustard ﬂour, oregano, basil and cumin. In some cases, the spices were ground to ﬁne powders to blend easily with the salt, garlic and onion powders. Some spices, like parsley, oregano and basil, were used whole to contribute to the appearance of the seasoning as well as the ﬂavor. Spices have always been an important part of seasonings, and familiarity with ﬂavor and appearance of common products is essential for any seasoning formulator. Formulators should be able to recognize by taste and appearance: anise, basil, black pepper, celery seed, chili pepper, cinnamon, clove, coriander, cumin, dill, fennel, marjoram, mace, nutmeg, oregano, parsley, rosemary, sage, savory, thyme and turmeric. All are commonly used in seasonings for snacks. Spices, like onion and garlic, add depth to the ﬂavor proﬁle of a seasoning. Ground spices are concentrated in ﬂavor, which releases slowly during the eating experience and lasts a long time, like onion and garlic. Whole spices are additionally visually appetizing. More recently, spice extracts (essential oils or oleoresins), were added to seasonings for more ﬂavor impact. Essential oils or oleoresin generally are spray dried, which accelerates the ﬂavor release to be more like compounded ﬂavors. Encapsulation increases shelf stability. Generally, ground spices are used at 0.25–2.00% in seasonings. Spice extracts, spray-dried essential oil, or encapsulated spices are generally sold as 5×, 10×

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or 25× replacers for ground or whole spices. Spices are expensive ingredients on a per pound basis, ranging from $2.00 to $5.00 per pound, but their strength makes them cost effective for use in seasonings in most applications. Like onion and garlic powders, spices have higher yeast, mold and standard plate counts than most other seasoning ingredients. Spices are generally treated with ethylene oxide or irradiation to reduce microbiological risk. The use of essential oils or oleoresins in place of whole or ground spices is a sound alternative because of the extremely low microbial risk after the extraction process.

2.6. COMPOUNDED FLAVORS In the last 10 years, compounded ﬂavors have replaced spices as the primary contributors to taste in seasonings. The need for a wider range of ﬂavor proﬁles, and stronger-ﬂavored seasonings, has led to the shift. Ground spices were not sufﬁciently stable over the shelf life of snacks, and some natural sources became too expensive for widespread use. Consumer testing indicated the need for stronger cheese ﬂavors and more authentic dairy ﬂavors, but spray-dried dairy powders no longer met the requirements. Consequently, formulators began incorporating compounded ﬂavors into seasonings to satisfy the changing marketplace. Advances in ﬂavor technology enabled the development of a wide range of shelf-stable, high-impact ﬂavors that are cost-effective for use in seasonings. Spray-dried or encapsulated ﬂavors are used in most blends. Compounded ﬂavors are used in seasoning formulas at 0.1–5.00%, depending on the application. Costs are $3.00–10.00 per pound and are highly dependent on whether the components are natural or artiﬁcial. Flavor selection has become the most important step in developing a seasoning. The potential compounded ﬂavor should be screened in the application when considered. Smelling the bottle and ﬁnger tasting are not acceptable alternatives. Each potential ﬂavor should be evaluated at two use levels, for example, the high and low levels of the usage range suggested on the container. This is necessary to see the effect of ﬂavor level on the overall ﬂavor of the seasoning. A range of ﬂavor proﬁles should be considered before making the ﬁnal selection. If the ﬂavor is a butter ﬂavor, then natural, natural and artiﬁcial, and artiﬁcial versions should be evaluated as well as ﬂavors high in diacetyl and without diacetyl. Fresh butter proﬁles should be screened versus melted butter proﬁles. It is best to understand all possible source options for the ﬂavor in question and how they interact with other seasoning ingredients and the base before making the ﬁnal selection.

2.7. FLAVOR ENHANCERS Like salt, ﬂavor enhancers are key ingredients in seasoning. The most common ﬂavor enhancers are monosodium glutamate, autolyzed yeast, disodium

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inosinate, disodium guanylate and hydrolyzed vegetable protein. Each contains a high level of 3 and 5 nucleotides, which are known to potentiate savory ﬂavors in seasonings. Flavor potentiation is important to the overall taste of the seasoning. Without one or more of these ingredients, the seasoning may have a bland or ﬂat taste. A mouth-watering response, resulting from the addition of nucleotides to the seasoning, will beneﬁt all aspects of the ﬂavor proﬁle. Use levels for ﬂavor enhancers vary according to the seasoning proﬁle, but starting levels are: monosodium glutamate, 1–5%, autolyzed yeast extract, 1–5%, disodium inosinate and disodium guanylate, 0.01–0.05% and hydrolyzed vegetable protein, 1–5%. Costs vary for these ingredients with MSG and HVP the lowest cost at $1.00–$3.00 per pound, to disodium inosinate and disodium guanylate at about $13.00 per pound. Autolyzed yeast extract is priced at $2.00–$6.00 per pound.

2.8. SWEETENERS Sugar, brown sugar, dehydrated honey solids, spray-dried molasses, dextrose and fructose are the most common sweeteners used in seasonings. As with all seasoning ingredients, the formulator should select sweeteners with small particle sizes to be compatible with the other ingredients in the blend. Each of the sweeteners gives a slightly different ﬂavor to the formulation. Sugar, brown sugar and molasses give similar sweetness perceptions. Honey solids and fructose are similar in sweetness proﬁle. Dextrose, when added to the formula, has a mouth-cooling effect and is effectively used in many BBQ formulations. Most sweeteners are inexpensive additions for seasonings. Prices range from $0.25 per pound for sugar up to $0.70 per pound for honey. Sweeteners should be added to seasonings with care because most are hygroscopic and may cause ﬂowability problems during the hot summer months. Typically, additional free-ﬂow agents are necessary.

2.9. ACIDS Citric, lactic, malic and acetic acids are the most common acids used in seasoning formulations. Additionally, the sodium salt of acetic acid, sodium diacetate, may also be used as an acidulant to mimic the ﬂavor of vinegar.

2.10. COLORS Color is added to most seasonings by use of artiﬁcial colors. The most common colors are FD&C alumina lakes including Yellow #5, Yellow #6, Red #40, and Blue #1. Alumina lakes are preferred in seasoning applications because of stability and non-reactivity. The use of pure dyes is not recommended in topical

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seasoning systems. The color dye transfers readily to hands and clothing in the presence of a small amount of moisture and becomes a nuisance in production and ﬁnal use by consumers. The lakes are used alone or as blends in seasoning formulations. Almost any color may be made from combinations of these colors. Manufacturers of seasonings have two options for adding colors to formulas: r Add directly to the seasoning blend following the addition of all granular material and any liquids. A blending step usually follows to begin dispersing the color; or r Purchase spray-dried ingredients where colors have been added to the slurry prior to drying. An example is spray-dried cheddar cheese powders with FD&C Yellow #4 and FD&C Yellow #5 added. Cheese powder manufacturers generally offer a “normal color” version for applications where high levels of the cheese are used and a “triple color” version for use if lower levels of cheese are added to the seasoning but a signiﬁcant level of orange color is desired. The major advantage of adding color directly to the seasoning blend is ﬂexibility in customizing. Seasoning manufacturers can quickly adjust color to meet customer needs for reformulation. Advantages of adding colors via spraydried ingredients is uniformity, ease of handling and weighing and avoidance of ﬂashing of individual non-lake colors in the seasoning. Both methods of adding artiﬁcial colors to seasonings are used. Extractives of paprika and turmeric may also be used for adding color to seasonings. These spice extractives are oil-soluble and must be plated onto salt, sugar or maltodextrin to distribute the color throughout the blend. Annatto can also be used to contribute a yellow or orange color to a seasoning. Caramel color is used to add brown to seasonings. All the colors, with the exception of caramel color, are relatively expensive, priced at $8.00–$13.00 per pound. However, use levels are relatively low, resulting in a low-cost contribution to the total price of the seasoning. The FD&C colors are the most stable of the colors and contribute no ﬂavor. Extractives of paprika can be light-sensitive and will fade if a stabilized version is not used. Turmeric oleoresin can change color with varying pH ranges. Caramel colors usually contain sulﬁtes, which may require declaration on the snack product label.

2.11. PROCESSING AIDS With the exception of ﬁllers and colors, all of the ingredients described thus far contribute to the ﬂavor and ﬂavor release of the seasoning. An equally important set of ingredients affects processing of the blend. These ingredients are added at different times during blending of the seasoning.

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Once the seasoning is formulated, consideration must be given to the method of its application to the snack product. Often, a tumbler coater is used in which a curtain of seasoning is spread over the snack base, allowing it to adhere to the base. The seasoning must ﬂow freely and not contain agglomerated particles; otherwise, the snack product will appear unevenly coated. Problems from ineffective use of processing aids include excessive seasoning fall-off, or clogging of the equipment and frequent shutdown for cleaning. The most common processing aids are vegetable oil and silicon dioxide. Vegetable oil is used to coat ingredients that are hydrophilic, thus reducing the tendency of these ingredients to absorb moisture. This prevents the ingredients from agglomerating or causing lumps in the blend, which makes even application of the seasoning difﬁcult. The best practice is to add the vegetable oil close after the hydrophilic ingredients in blending order, followed by a blending step of sufﬁcient duration, which allows the oil to coat the material as completely as possible. Vegetable oil is also important if the seasoning blend contains ingredients with large differences in particle-size distribution. Although it is advisable to keep the particles of seasoning formulations small and uniform in size and shape, sometimes larger particles are needed to improve the appearance of the snack, for example, dried parsley in sour cream and onion seasoning. In this case, it is important to have vegetable oil in the blend to facilitate agglomeration of the parsley with the other ingredients. The vegetable oil acts like a glue to hold the parsley in position throughout preparation of the seasoning and prevents its stratiﬁcation. Once the hydrophilic ingredients are coated with oil, it is necessary to adjust the ﬂowability of the seasoning back to its normal operating characteristics. This entails adding a free-ﬂow agent such as silicon dioxide or tricalcium phosphate to the blend. These ingredients have the opposite effect of vegetable oil. They act by coating all particles in the blend with ﬁne powders that resist agglomeration, effectively making the seasoning free ﬂowing.

2.12. ANTIOXIDANTS Direct addition of antioxidants to a seasoning formulation is not widely practiced. Incidental addition of antioxidants to oil-soluble ingredients, for example, paprika oleoresin, is more common. Such antioxidants typically are used to protect the raw material during storage, but usually are non-functional in the seasoning. Vitamin E, alpha-tocopherols, extractives of rosemary, and butylated hydroxyanisole (BHA) and/or butylated hydroxy toluene (BHT) were once used in formulations in attempts to preserve seasonings. Now, alternative processing techniques for sensitive materials are often used in place of adding preservatives. Many snack manufacturers advertise their products as preservative-free and seasoning suppliers have responded by omitting addition of antioxidants.

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High-barrier packaging ﬁlms and gas ﬂushing of packaged snacks have also eliminated much of the need for antioxidants in seasoning blends.

3. SEASONING FORMULATION Seasonings for salty snacks are blends of salt, dairy powders, vegetable powders, ﬂavor enhancers, spices, compounded ﬂavors, colors and processing aids. When the blend is applied to potato chips, corn chips, tortilla chips or other snack bases, ﬂavors in the seasoning, frying oil and the base start to intermingle. Partitioning of ﬂavors occur and prevent some from being tasted. Other ﬂavors are potentiated over time. With time, the ﬂavors smooth together to form the overall ﬂavor of the snack food. Allowing seasonings to equilibrate after blending, and allowing the seasoned snack to equilibrate after application, are important steps in evaluating seasonings during development. When starting to develop a seasoning formulation, it is useful to think in terms of building a pyramid. The characterizing ﬂavors of the seasoning are at the top of the pyramid. This is the part of the seasoning that is tasted ﬁrst, like the sour cream ﬂavor in Sour Cream and Onion potato chips, or the robust smoke ﬂavor in a mesquite BBQ seasoning for corn chips. The origin of this ﬂavor portion is typically compounded ﬂavors or spices. These ﬂavors are supported by the next level, a foundation of basic commodity materials. In the case of the sour cream ﬂavor, the supporting commodity material is generally sour cream powder, but could be non-fat dry milk, buttermilk powder, or cheese powder. In the third level of the pyramid, the commodity materials and ﬂavors are enhanced by salt, sweeteners, ﬂavor enhancers and acids. The bottom of the pyramid consists of ﬁllers, colors and processing aids to complete the seasoning blend.

3.1. TARGET SELECTION The ﬁrst step is identifying the direction of ﬂavor development by asking the following questions: r Who is the target consumer?

—Male or female? —Children, teens, adults, or seniors? r What type of ﬂavor does this consumer prefer?

—High impact or subtle? r What is needed to make this ﬂavor interesting to the target consumer?

—Is an existing ﬂavor to be duplicated, or a new ﬂavor proﬁle created? By answering these questions, the formulator reduces the development time by focusing on the most highly acceptable ideas about the targeted consumer.

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The questions should not be answerable by too many categories. It is easy to say the product should appeal to everyone. Since this is impossible, it is best practice to focus on a speciﬁc segment of total population. Obviously, in all seasoning development projects it is best to target consumers who like to eat salty snacks with ﬂavors applied to them. If the seasoning is going to be a BBQ, the product should be tested with consumers who buy BBQ-ﬂavored products. Finally, the age group to be targeted should be considered. Many companies target consumers between ages 13–35. But snack seasonings that appeal to teens do not necessarily appeal to seniors.

3.2. SEASONING DEVELOPMENT EXAMPLE A few basic concepts apply to formulating snack food seasonings: r The process is trial and error. The formula should begin with typical usage r r

r r

levels of salt, ﬁllers and enhancers, and then be adjusted as needed to suit the snack base and consumer expectations. A usage level of 6% can be assumed for the seasoning initially, with the ﬁnal level to be decided after the formula has been tested at several higher and lower levels with consumers. The existence of a product that ﬁts the ﬂavor proﬁle under development should be determined. Different products that resemble the ﬂavor being developed should be screened. If a match exists, the ingredients listing of the product should be reviewed for ideas for duplicating the overall ﬂavor proﬁle of the snack seasoning. Formulation should begin with a cost target in mind, but with enough room left in the cost allowance for subsequent changes in the formula. All the formula constraints should be considered before actual formulation is begun. Does the seasoning need to be kosher? Consist of natural ﬂavors? Is MSG allowed?

The best way to describe seasoning formulation techniques is by using an example like development of a sour cream and onion seasoning for potato chips. It is assumed that consumer research has identiﬁed the following characteristics about the target customer: r The target is teens and young adults, male and female. r The target customer prefers strong, bold ﬂavors. r The target customer eats many of the existing sour cream and onion snacks on the market, but would prefer a new ﬂavor proﬁle because current offerings are “tired and old fashioned.” r The expected usage level for the seasoning is 7%. From the ﬂavor proﬁle target, the formulator knows that salt, sour cream and onion are necessary ingredients in the formula. Simply making a blend of

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33% salt, 33% onion and 33% sour cream powder could be the beginning of a seasoning, but the formula would not be balanced. It lacks complexity and would be cost-prohibitive. The formulator must next think about the ingredients needed to balance the ﬂavor proﬁle, enhance the ﬂavor system and provide visual appeal to the ﬁnished product. Initially, several adjustments can be made to the formula based on information available at the beginning of the project. Since the application level for the seasoning will be 7%, the formulator can begin by reducing the level of salt in the formula to 22%. This results in a salt content of 0.07 × 22, or 1.54% in the ﬁnished product. The salt content for most snacks is 1.50–1.90%. This formula can start on the low side of the range because salt-enhancing ingredients will be added later. Sour cream powder is expensive, selling for $1.50–$2.00 per pound, so the formulator reduces the sour cream powder to 20%. At this level, the sour cream powder provides adequate mouth feel and ﬂavor to the seasoning blend. The onion powder is very high at 33% in the formula. Keeping in mind that the target consumer prefers high-impact ﬂavors, it is still advisable to reduce the level of onion in the seasoning, so the level is changed to 10% for the ﬁrst revision. Maltodextrin is added at 48% to return to a 100% formula. The ﬁrst seasoning formula looks like the following: Maltodextrin Salt Sour cream powder Onion powder

48.00% 22.00% 20.00% 10.00% 100.00%

Applying the blend to the potato chip base at 7% use level, the formulator observes good compatibility with the base, but it is still not a complete seasoning. The sour cream impact is too low. The overall ﬂavor impact is low, except for the onion. The next step in formulating is to begin increasing the level of sour cream ﬂavor without adversely affecting the overall cost of the seasoning. The sour cream ﬂavor impact can be enhanced by several methods besides increasing the dehydrated sour cream powder in the formula. Acidity is a key component in delivering impact to dairy seasonings. The formulator can add citric acid and lactic acid to give the impression of more sour cream. The formulator adds 0.5% citric acid and 1.00% lactic acid to increase the overall dairy impact of the seasoning. Another method is to add compounded sour cream ﬂavors to the seasoning. Numerous ﬂavors are available to ﬁt the needed proﬁle. The formulator selects one and adds it to the formula at 0.50%. In the case of sour cream, added sweetness sometimes helps increase the dairy impact. The formulator adds 5% dextrose and 5% non-fat dry milk to the seasoning in an attempt to round out the sour cream ﬂavor. The ﬁrst revised formula is:

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Maltodextrin Salt Sour cream powder Onion powder Dextrose Non-fat dry milk Lactic acid Citric acid Compounded flavor

36.00% 22.00% 20.00% 10.00% 5.00% 5.00% 1.00% 0.50% 0.50% 100.00%

Applying the seasoning to chips, the formulator can now taste elements of the appropriate sour cream ﬂavor and impact, but the seasoning lacks depth and the ﬂavor disappears too quickly. Next, the formulator adds 1.00% monosodium glutamate to the seasoning to help potentiate the overall ﬂavor proﬁle of the formula. Also, the formulator wants to make the onion part of the proﬁle more complex. One way to do this is to change to toasted onion powder instead of white onion powder, or to add hydrolyzed vegetable protein to make the overall ﬂavor meatier in character. The second revised formula is: Maltodextrin Salt Sour cream powder Toasted onion powder Dextrose Non-fat dry milk Hydrolyzed vegetable protein Lactic acid Monosodium glutamate Citric acid Compounded flavor

33.00% 22.00% 20.00% 10.00% 5.00% 5.00% 2.00% 1.00% 1.00% 0.50% 0.50% 100.00%

At this point, the formula is nearly completed. Only a few variables in the ﬂavor proﬁle remain to be optimized in this sour cream and onion seasoning. The formulator now adjusts the key variables up and down to get to the optimized formula. The ﬁrst step is to look at the sour cream level of the seasoning. In most consumer tests, responses indicate a need for more sour cream impact. Consumers almost always say they want more dairy impact in the ﬂavors used for salty snack seasonings. In this formula, the sour cream impact is affected by the level of the compounded ﬂavor, the sour cream powder level, the acid and the level of dextrose. At this stage, changes to the formulation should be bold moves, eliciting a deﬁnite response on impact. The revision should clearly be stronger than the previous formula. When impact in a formula is an issue, it is better

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to begin adjusting the ﬂavor and acid rather than the sour cream powder level or sweetness. The current levels of sour cream and dextrose in the formula are adequate. A signiﬁcant increase in the dehydrated sour cream powder would make the seasoning too expensive, and an increase in the dextrose would not signiﬁcantly increase the overall sour cream ﬂavor perception. The formulator starts by increasing the level of sour cream ﬂavor from 0.5% to 1.00%. The level of acid is also raised by increasing the citric acid to 0.75% and the lactic acid to 2.00%. The third revised formula is: Maltodextrin Salt Sour cream powder Toasted onion powder Dextrose Non-fat dry milk Hydrolyzed vegetable protein Lactic acid Monosodium glutamate Citric acid Compounded flavor

30.25% 22.00% 20.00% 10.00% 5.00% 5.00% 3.00% 2.00% 1.00% 0.75% 1.00% 100.00%

The onion ﬂavor level is rebalanced in the next step. After adjusting the sour cream ﬂavor and acid system, the overall onion impact is weaker. Also, the toasted onion powder has slightly less impact than the white onion powder initially used in the formula. The level of toasted onion powder is increased to 15%, and 5% white onion powder is added to the formula. More depth is added to the onion ﬂavor by increasing the MSG slightly to 2.00% and increasing the HVP to 3.00%. The fourth revised formula is: Maltodextrin Salt Sour cream powder Toasted onion powder Onion powder Dextrose Non-fat dry milk Hydrolyzed vegetable protein Lactic acid Monosodium glutamate Citric acid Compounded flavor

19.25% 22.00% 20.00% 15.00% 5.00% 5.00% 5.00% 3.00% 2.00% 2.00% 0.75% 1.00% 100.00%

From a ﬂavor standpoint, formulation of the seasoning is complete. However, consumers also “eat” with their eyes. So the visual appeal of the seasoning blend

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is just as important as the taste. The current seasoning blend has an off-white to beige color and becomes virtually invisible when applied to the potato chips. Consumers generally need a visual signal that the snack food is seasoned and contains added ﬂavor. As a result, the next step is to focus on appearance of the seasoning blend. Sour cream and onion seasonings historically have included a green leafy material to give a visual signal that a seasoning has been added to the chips. Looking at other similar food items, like ready-to-eat sour cream dip products, can give assistance in deciding the type of appearance characteristics to be added. In this case, dehydrated green onion, dehydrated parsley, or a fabricated soy particulate with added FD&C colors could be used to improve the appearance of the seasoning. The formulator should evaluate each possibility for use in the formula. For most snack items, dehydrated parsley is the best choice. It is bright green in color and is available in a range of sizes and prices. But parsley or green onion would not be acceptable choices if the ﬁnished product were to be exposed to light for prolonged periods. Photo-oxidation is a concern in cases where plant material containing chlorophyll can oxidize the oils to cause off-ﬂavors in the seasoning and ﬁnished product. In cases where light sensitivity is an issue (like see-through bags), the bits containing color would be the preferred material. Parsley ﬂakes are added at 3.00% for visual appeal for the ﬁfth revised formula: Maltodextrin Salt Sour cream powder Toasted onion powder Onion powder Dextrose Non-fat dry milk Parsley flakes Hydrolyzed vegetable protein Lactic acid Monosodium glutamate Citric acid Compounded flavor

16.25% 22.00% 20.00% 15.00% 5.00% 5.00% 5.00% 3.00% 3.00% 2.00% 2.00% 0.75% 1.00% 100.00%

The ﬁnal phase in seasoning development is to adjust the formula to facilitate problem-free application to the snack base. There are two parts in this step, protecting hygroscopic materials from excessive water absorption and adding free-ﬂow agent. To protect the formula from excessive water absorption, a liquid vegetable oil is added to the formula. In the sour cream and onion formula being developed, 0.5% vegetable oil is added. Partially hydrogenated soybean oil is commonly used for this purpose. The vegetable oil typically is added in the plating stage of manufacturing the seasoning, usually after the

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addition of salt, MSG, maltodextrin and any other granulated ingredients. A blending step follows the addition of the vegetable oil to adequately spread the oil across the ingredients in the blend. Any hygroscopic materials should be added to the seasoning blend following the vegetable oil. An additional blending step completely coats the hygroscopic materials, forming an effective barrier against moisture absorption. After addition of all the remaining ingredients and a blending step, the free-ﬂow agent is added as the last ingredient. The free-ﬂow agent of choice in most seasoning applications is silicon dioxide, although tricalcium phosphate also is popular. Silicon dioxide is a smallparticle-size, powdery material with a large surface area. When applied to seasoning blends, silicon dioxide coats the ingredients and reduces the tendency for agglomeration. A free-ﬂowing seasoning is necessary for even application of the seasoning to the snack base. To complete the sour cream and onion formula, 1.00% silicon dioxide is added: Maltodextrin Salt Sour cream powder Toasted onion powder Onion powder Dextrose Non-fat dry milk Parsley flakes Hydrolyzed vegetable protein Lactic acid Monosodium glutamate Citric acid Vegetable oil Silicon dioxide Compounded flavor

14.75% 22.00% 20.00% 15.00% 5.00% 5.00% 5.00% 3.00% 3.00% 2.00% 2.00% 0.75% 0.50% 1.00% 1.00% 100.00%

At this point, the basic seasoning formulation work is complete. Additional consumer testing on the use level is an important ﬁnal step. The seasoning may be good at 7% use level, but have a higher acceptability with consumers at 8% use level. This is a ﬁnal checkpoint with consumers for overall acceptability of the seasoning formulation. Once the formulation work and consumer testing are complete, the formula should be checked for shelf stability. Studies on the seasoning in its packaging material, and on the ﬁnished, seasoned, packaged snack product are recommended. These tests will indicate any ingredient interaction or stability problems with the seasoning blend. All shelf life test products should be compared to frozen control, held at 0◦ F (−18◦ C) or lower for the duration of the test. It is good practice to collect analytical data on the control before starting the test and also on each shelf life sample evaluated. After successful completion of shelf life testing, the new formula is ready for the marketplace.

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The process for developing a seasoning is similar whether it is Sour Cream and Onion, BBQ or Nacho Cheese. The same basic steps are followed: r Start with demographic information about the target audience and ask

questions about the type of seasoning these consumers prefer.

r Identify the ingredients and ﬂavors that must be in the formula. r Add the basic elements of the seasoning and begin building each part of the

ﬂavor proﬁle by adjusting levels.

r Check the appearance of the seasoning on the snack product. r Make sure the seasoning has the correct ﬂowability to ensure problem-free

application and adhesion.

r Consumer test the seasoning at several points during the development

process

4. SEASONING OF MAJOR SNACK FOODS The development of seasonings requires trial and error and repeated consumer testing. Another consideration in the development of formulation seasonings is the effects of base interaction on ﬂavor perception.

4.1. EFFECTS OF APPLICATION METHOD ON FLAVOR SELECTION The method of applying the seasoning blend will affect the formulation. The most common method for applying seasonings to snacks is to use an inclined drum tumbler. The seasoning is metered into the tumbler and introduced as a curtain of powder across the tumbling snack chips. In some cases, oil is sprayed into the tumbler to help the seasoning adhere to the chips. It is important to keep the seasoning free ﬂowing when applied in this manner. Appropriate attention to the level of free-ﬂow agent added to the formula is essential. The formula must be free-ﬂowing in the snack manufacturer’s processing facility, not just in the seasoning blender’s facility. Selection of ingredients for seasonings applied as a dry powder in a tumbler usually is limited to spray-dried and encapsulated ﬂavors. Plated ﬂavors and liquid ﬂavors may ﬂash off during the application process if the ﬂavors are volatile and the temperature of the snack chip at the time of application is too high. Spray-dried and encapsulated ﬂavors usually have a longer shelf life than plated or liquid ﬂavors. Another method for applying seasonings to snacks is to spray on a slurry of oil and seasoning. In this case, the seasoning is added at levels up to 40% to vegetable oil and then sprayed on the snack base. The seasoning-oil mixture is kept agitated to prevent the slurry from separating. Slurries are applied to snack bases at levels of 10–20%. Ingredients selected for seasonings applied

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by this method typically also are spray-dried or encapsulated for the same reason described for the dry powder method. Some ﬂavor suppliers produce seasonings in a paste form that is primarily oil-soluble and may be used in this type of application. The pastes contain ﬂavors, acid, colors and ﬂavor enhancers. They usually do not contain ﬁllers, and sometimes are referred to as ﬂavor concentrates. The slurry would consist of oil, ﬂavor paste and salt. The use of a ﬂavor paste in this manner is not common. The slurry concept is also used with water as the carrier. In this case, seasonings are formulated for mixing with water, maltodextrin and starches into a slurry that is sprayed on a snack base. The moisture is removed from the ﬁnished product in a ﬁnal drying step. The resulting product is lower in oil content than the oil slurry application method. This method is primarily used in low-fat snack products where oil spray is not permitted. The downside of this type of application is heat abuse of the seasoning ﬂavor system. The heat used to quickly dry the snack also volatilizes the ﬂavor components of the seasoning blend, resulting in an unbalanced ﬂavor or loss of impact. Encapsulated ﬂavors that are insoluble in water, and do not melt, are the best choice for formulating seasonings for this application method.

4.2. POTATO CHIPS Development of seasoning blends for potato chips is straightforward. Not many corrections are needed for this type of base. Potato chips generally are bland, carrying only the ﬂavor of the frying oil. The overall surface area of the chip may require additional consideration for use level. For example, a seasoning developed for a ﬂat, thin potato chip requires a lower use level to deliver the same ﬂavor impact than seasoning required to deliver ﬂavor on a thicker, ripple-cut potato chip. Large potato chip operations may use two-stage seasoning. All chips are salted directly out of the fryer, then split into two or more streams. Some chips go directly to packaging, others may go to a tumbler where seasoning is applied dry if used, and then on to separate packaging line. Seasoning blends for potato chips have reduced salt content compared to blends developed for tortilla chips or extruded snacks because some salt is already on the base. Two-stage seasoning is not done with tortilla chips, corn chips or corn puffs, and the rate of seasoning application on these products is typically monitored by rapid salt analysis. Seasonings are usually applied at use levels of 6–8% on salted potato chips.

4.3. TORTILLA CHIPS Yellow corn and white corn tortilla chips need additional ﬂavor impact in seasonings to overcome the taste of the corn base. When the tortilla base is made from dehydrated masa, the ﬂavor system in the seasoning needs to be much stronger to overcome the reduced ﬂavor of the corn.

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If only salt is applied, this is done downstream from the fryer. The salt contents of tortilla chip seasonings will be 22–25% and higher than for potato chips, to compensate for lack of salt on the base. Use levels for tortilla chip seasonings generally are 8–10%. In addition, 3%– 4% spray oil is added to help adhere the seasoning to the base.

4.4. CORN CHIPS Corn chips have very high fried corn ﬂavor, which overwhelms most attempts at seasoning. Stronger ﬂavors must be used in formulating seasonings for this type of base. Corn chips are generally salted in a tumbler away from the fryer. If used, the level of seasonings for corn chips generally is 8–10%.

4.5. PRETZELS Pretzels are a difﬁcult base to ﬂavor. Seasonings will not adhere to the smooth crusty surface. Manufacturers of ﬂavored pretzels must either break open the pretzels to expose the porous internal structure or apply the seasoning using a sticky adhesive that dries on the surface of the pretzel. Flavors may be added to pretzels internally, but the ﬂavor release is not as immediate as the seasoning applied to the surface of the pretzel. Pretzels generally are formulated to be low- or no-fat. This presents ﬂavoring problems because of the need for fat to help carry and sustain ﬂavors throughout eating of the snack. Low-fat bases with applied seasonings tend to have a strong initial impact, but the ﬂavor quickly disappears and the taste of the base takes over.

4.6. EXTRUDED SNACKS Extruded snacks, whether fried or baked, usually are ﬂavored using a slurry of oil and seasoning. The extremely porous surfaces of snacks absorb oil readily. This causes the ﬂavor to be masked somewhat making additional seasoning necessary. All the salt is in the seasoning, which typically has a salt content of 10–15%. The use level for seasonings applied to extruded snacks is typically 10–15%.

5. SUGGESTED READING Ashrust, P. R., ed., 1995. Food Flavorings. 2nd edition. Blackie Academic & Professional, London. Burdock, G. A., ed., 1995. Fenaroli’s Handbook of Flavor Ingredients, Vols. I and II. 3rd edition. CRC Press, Boca Raton, Florida. Heath, H. B. and G. A. Reineccius, 1986. Flavor and Technology. Avi-Van Nostrand Reinhold, New York

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Reineccius, G., ed., 1994. Source Book of Flavors, 2nd edition. Chapman and Hall, New York. Risch, S. J. and G. A. Reineccius, eds., 1988. Flavor Encapsulation; ACS Symposium Series: 370. American Chemical Society, Washington, D.C. Schay, R., 1975. Natural ﬂavors. In Fenaroli’s Handbook of Flavor Ingredients, Vol. 1. T. E. Furia and N. Bellanca, eds. CRC Press, Inc., Palo Alto, California, pp. 271–495. Tainter, D. R. and A. T. Grenis 1993. Spices and Seasonings: A Food Technology Handbook. Wiley-VCH, New York.

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CHAPTER 20

Snack Seasonings Application

DOUGLAS E. HANIFY

1. INTRODUCTION

E

all snacks are ﬂavored. This may seem obvious, but generally the various snack base products are unappetizing without added seasonings. The original, and most common, seasoning is salt. As snack manufacturers searched for product line extensions, development of ﬂavored products was a natural choice. Seasonings are compounded to add color as well as taste to improve consumer appeal of the ﬁnished product. High-impact seasonings, which are very ﬂavorful and appealing to the eye, have been developed recently. The practical objective of ﬂavoring snacks is to apply the seasoning in a uniform and consistent manner. All sides of the product should have the same appearance, which means addition of the same amount of seasoning to each piece. Usually, the seasonings are in dry form, but can also be ﬂavored oils or two-phase slurries. Slurries are produced by blending dry ﬂavors with a liquid carrier. Because not all the dry ﬂavorings are soluble in the liquid carrier, a two-phase mixture is formed. The liquid carrier usually is oil, but can be water. Oil-based slurries are common in the savory snack industry, but water-based solutions or slurries are used for sweet snacks. The principles of applying seasonings to snacks are discussed in this chapter. Time and space do not allow describing the speciﬁcs for individual products. Consequently, general methods are summarized for seasoning potato chips, tortilla and corn chips, extruded snacks, popcorn, snack nuts, snack crackers and ﬂavored pretzel products. SSENTIALLY

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2. COATING ARENAS Theoretically, it would be optimal to ﬂavor each product piece one at a time. In practice, this is not possible due to constraints of time, labor costs and work area limitations. However, equipment space must be provided for application of seasonings as product moves toward packaging.

2.1. DRUM COATING Coating drums (Figure 20.1) usually are used for ﬂavoring snacks. Also known as coating reels or enrobers, they typically are made of stainless steel. The purpose of a coating drum is to expose all surfaces of the base product to the various seasonings applied. In their simplest form, coating drums are inclined cylinders that rotate to lift the product. The drum inner wall includes product-lifting ﬂights to create the desired exposure (Figure 20.2). Product is picked up by the ﬂights near the bottom of the drum and lifted as the drum rotates. Once the product reaches a critical height, usually 90–120◦ from the bottom, it begins to turn or roll down to the bottom of the drum where the lifting process begins again. The product is transported forward because the drum is inclined downward from entrance to exit. Each time the product completes a

Figure 20.1 Snack food coating drum. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

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Figure 20.2 Interior of a typical snack food coating drum. (Courtesy of Spray Dynamics Ltd.— Par-Way Group, St. Clair, Missouri.)

cycle of lifting and falling, it moves closer to the discharge end of the drum. The extent of product exposure is determined by drum design, rotation speed and angle of drum inclination. In order to obtain an acceptable ﬁnished product, it is critical that the drum be properly designed for the speciﬁc product and process. An erroneous opinion exists throughout the industry that there is one (or possibly two) sizes of coating drum and, regardless of what is being produced, “one size ﬁts all.” In practice, drums are sized based on volumetric throughput using an assumed residence time. The residence time is determined by trial and error and experimentation, and most companies have formalized sizing criteria. Guidelines exist to determine the drum diameter and length. Generally, as the number of steps in a coating application increases, the length of the drum also increases to prevent overlapping of coating zones. Buildup can occur in overlap areas, especially when the application of liquids or slurries is followed by dry seasonings.

2.2. CONVEYOR-BASED COATING In some snack seasoning processes, it is necessary or desirable to apply coatings as the product is transported on a conveyor. Snack food examples include crackers, fabricated potato chips and sweet goods (cookies). The conveyor can be vibratory, open wire belt, closed fabric belt, or other selected types. Several principles should be considered when designing a conveyor-based coating

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system. The ﬁrst is that, without some device for turning the product over, only the top surface of the snack will be coated. However, this may be desirable in some instances, for example, the top coating of crackers. Also, because the base product seldom covers 100% of the conveyor, a means for collecting and (if possible) recycling excess seasoning is required. Separate conveyor sections should be used for each material if more than one is applied—especially for liquids. This will reduce the amount of excess carried forward to the succeeding application and onto downstream equipment.

3. TYPES OF SEASONING APPLICATIONS

3.1. SINGLE-STAGE SEASONING The simplest seasoning system is single-stage coating. When discussing single-stage coating, it is normally assumed that the material is a single phase, and not a slurry. Usually, the ﬂavoring applied is a dry seasoning, or seasoning blend. (See Chapter 19, “Snack Food Seasonings.”) Liquid seasonings typically are oil-based, but do include liquid smoke, soy sauce, or other water-based ﬂavoring materials. Dry single-stage coating is only possible when sufﬁcient liquid is present on the surface of the base product for the seasoning to adhere. Freshly oil-fried potato chips and corn chips undergo two single-stage dry seasoning applications. Typically, the unabsorbed oil on the surface of both products is sufﬁcient for adhering salt or a blended seasoning. Dry seasonings usually are brought into the coating drum using an auger feeder. The augers are either positive displacement (Figure 20.3) or an open helix. The ﬂights are ﬁlled in the supply hopper as the auger rotates, and an equal amount of seasoning is deposited into the coating drum. In this manner, the feeder is a volumetric device. Feeders can be placed on load cells (or other mass measurement devices) for loss-in-weight control. The signal from the measuring device is compared to a set point, and auger speed is automatically adjusted so the loss of material matches the target rate.

Figure 20.3 Dry seasoning auger. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

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In many applications, the seasoning discharges from the feed tube at a single point. One method for getting ﬂavoring into the coating drum is by having the auger tube discharge onto a small vibratory conveyor, which brings the seasoning into the drum. Typically, the vibrating tray only dispenses in a very small area after the entrance of the drum. In this case, the drum is used for redistribution of seasoning and not for exposure. It is desirable to enlarge the area of application if the coating drum is used for exposure. Once the seasoning is in the auger, it can be distributed by one of several means. Placing the positive displacement auger inside a horizontal distribution tube is one very common method (Figure 20.4). The distribution tube creates a “curtain” of applied seasoning. By enlarging the area of application, each product piece is exposed to the seasoning several times before exiting the coating zone. Some distribution tubes have ﬁxed-size bottom openings; this is acceptable if the seasoning application rate is constant and the openings have been designed for the speciﬁc rate. Others have adjustable openings, the advantage being that application rates can be varied by adjusting the openings for changes within seasonings and between different seasonings.

Figure 20.4 UNI-SPENSETM dry seasoning application system. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

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3.2. ELECTROSTATIC SEASONING Electrostatic application of dry ﬂavorings is a subset of dry single-stage seasoning described above. In some cases, air is used as the distribution medium. Electrostatic coating began in the paint industry, especially in the automotive arena. Dry powders were used instead of solvent-based paints. Dry paint, entrained by air, passed a charged electrode and would seek out the nearest ground. The base metal to be coated was grounded, providing the charge differential required for the process. The ﬁnal adhesion of paint to the metal surface was caused by melting the powder onto the base. To adapt this technology to the snack seasoning industry, it is necessary to ﬁrst ground the base product. In this case the coating drum is grounded and the base product also is grounded by contact with the drum. Much like in electrostatic painting, seasoning is fed into a mixing area where air is used to blow the seasoning onto the base. In this case, the mixing area has an electrode, which is energized. The seasoning receives the electrostatic charge within the mixing area and is carried onto the base product by the air. Unfortunately, seasonings are not as uniform in size as paint particles. The smaller particles that were easily carried by air often found their way out of the drum, coating any other grounded object. To solve the electrostatic application problem, it was necessary to change the appearance of the electrode and combine it with the advantages of the distribution tube. The electrode became a charged wire suspended near the falling curtain of seasoning (Figure 20.5). The seasoning picks up a charge as it passes the charged wire and then falls onto the snack food base. The obvious advantage is that gravity, not air, is the motive force, thereby avoiding problems of ﬁnes entrainment in the air.

Figure 20.5 Electrostatic dry seasoning application system. (Courtesy of Spray Dynamics Ltd.— Par-Way Group, St. Clair, Missouri.)

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3.3. TWO-STAGE SEASONING Not enough liquid is on the surface of some snack products to adhere seasonings. Thus, it is necessary ﬁrst to apply a liquid that acts as an adhesive for the dry ﬂavoring. Examples of products requiring this type of ﬂavoring system include tortilla chips, snack crackers, nuts and popcorn. In these cases, a light coating of liquid is used to “glue” or hold the ﬂavoring onto the snack piece. The liquid can be oil, which is the most common, or a solution of a polymer like gum Arabic or starch dextrin dissolved in water. The use of oil as the tack agent also has the beneﬁt of providing mouth feel. In snack crackers, more oil than is required for tacking the seasoning is added to further improve the mouth feel. A less common two-stage coating system combines a slurry (a two-phase mixture of liquid and dry components) and a dry ﬂavoring. Examples of this system include honey-roasted nuts, extruded corn curls, snack crackers, ﬂavored pretzel products and cereal-based sweet snacks. In traditional two-stage coating, the liquid application zone is separated from the dry coating zone. In this manner, the two additives can be controlled independently. Often the same production line is used for many different and varied products.

3.3.1. Liquid Addition The liquid should be added as the base product spreads out to form a bed upon entering the coating drum. As in dry-only applications, it is critical that the liquid be spread over as much of the product possible. All product surfaces should be coated in a uniform and consistent manner. Challenges occur when the amount of allowed liquid is small, as in the case of reduced-oil content snacks. If a small quantity of liquid is applied in a single spot, it is likely that the applied seasoning will adhere only in that area. Maximizing the application area is necessary, and many types of systems are used to enlarge the area of liquid distribution. r In pressure spray systems, one or several ﬁxed oriﬁce nozzles are used

(Figure 20.6). They are mounted on a header (manifold), and the pressure is created by a positive displacement pump. The design of the nozzle deﬁnes the shape of the spray pattern; a slit creates a fan-shaped spray and a circular opening creates a conical pattern. As the liquid is forced through the nozzle, it expands into the spray. Unfortunately, the desired pattern exists only at the design pressure. The limitation of ﬁxed-oriﬁce nozzles is that the spray pattern changes as the application changes. As the ﬂow rate to the manifold decreases, the pressure decreases and the size of the spray pattern is reduced. As the rate

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Figure 20.6 Positive displacement pump and manifold-mounted ﬁxed-oriﬁce nozzles for spray application system for liquid ﬂavorings. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

decreases, at some point the pattern can be reduced to a single stream. As the rate increases, the pressure in the manifold can increase beyond the design point. High pressure can cause overspray, which will carry to the surrounding area. r Other spray systems utilize compressed air that is combined with the liquid, either in the nozzle proper or immediately after the liquid leaves the nozzle. By changing the dispersion air pressure, the liquid is distributed over a larger area, creating smaller droplets. This type of system is not suitable for light-viscosity liquids like water or oil. Lighter materials can be dispersed to the point of creating only mist, resulting in many problems, including overspray and sanitation as examples. r Spray systems that use multiple positive displacement pumps in combination with self-adjusting spray nozzles allow minute changes in application rates. The resulting controllability and ﬂexibility make these systems readily usable in plant environments. Systems of this type consist of adjustable-volume, positive displacement metering pumps and corresponding nozzles. The number of pumps required is dependent on the application rate and displacement desired per pump. In this system an individual pump has a corresponding poppet nozzle (Figure 20.7). These nozzles are either mounted directly on the pump or remotely mounted (e.g., in a coating drum). The nozzles are equipped with a spring-loaded poppet that creates the back pressure required for a spray pattern. The poppet nozzles used in combination with these pumps provide several beneﬁts. As the pump displacement (output) is changed, the spring-loaded poppet adjusts to that amount of liquid. The nozzle produces

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Figure 20.7 Multiple displacement pump and self-adjusting poppet nozzle for spray application system for liquid ﬂavorings. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

the same spray pattern and droplet size regardless of the amount of liquid displaced by the pumps. It is not necessary to wait for pressure to build in a manifold, as an instantaneous increase in pressure is caused by the pump piston traveling forward. The nozzles also provide a positive shutoff, eliminating dripping common in other systems. The addition and distribution of liquid is critical for seasoning adhesion. If the liquid application is spotty, seasoning application will also be spotty. Likewise, if the coating drum is improperly designed and does not provide uniform exposure of the base product, only the side that “sees” the liquid and dry applications will be coated. The dry seasoning can be applied after the liquid has been added, in the same way as in single-stage coating. Leaving a transfer area in the coating drum to alleviate buildup is advisable.

3.3.2. Slurry Addition By deﬁnition, slurries are mixtures of liquid and undissolved solids. In savory snacks, these are usually mixtures of oil and seasoning, as is the case of cheese ﬂavoring applied to extruded corn products. In honey-roasted nuts, the slurries are mixtures of many items including honey, sugar and gums in water. Slurries cause special problems in the restrictive oriﬁce spray systems described earlier. For example, the solids in many slurries are irregular and can cause temporary restrictions and/or plugging of the nozzle. As one nozzle becomes blocked, pressure within the supply manifold increases and alters the spray pattern of the remaining nozzles. It is possible to design the system with larger nozzles, but it may not be possible to pressure the system enough to create the desired spray pattern.

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Figure 20.8 Self-cleaning nozzle for application of slurry ﬂavorings. (Courtesy of Spray Dynamics Ltd.—Par-Way Group, St. Clair, Missouri.)

Using a slurry spray nozzle that incorporates a self-cleaning feature and utilizes external dispersion air eliminates the limitations described above. A cross-section of this nozzle is shown in Figure 20.8. This system uses multiple slurry spray stations to create the area or zone of coating within the drum. The slurry mixture is pumped to the ﬂuid manifold and is dispensed through the nozzle tip. A low-pressure air supply is used to provide the dispersion air. The dispersion air ﬂows through a specially machined cavity within the nozzle cap and out through an annular opening around the nozzle tip. In this way, all the liquid is dispersed uniformly in a full cone. To avoid obstructions, the cleanout piston is forced through the nozzle tip several times per minute. Although the ﬂow ceases temporarily, the overall application is not affected. The piston also provides a positive shutoff in the event of temporary interruptions in the process. The ancillary equipment used for preparation and application of slurries is extensive. In addition to mixing and supply tanks, transfer pumps, application pumps and measurement devices, various provisions for control are required. The slurry must be constantly agitated and recirculated if it contains a substantial quantity of solids that quickly settle out. This requirement should be remembered in laying out the line and plumbing the system.

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4. CONCLUSION New product development is only limited by the imagination. Snacks will continue to be coated with a wide variety of seasonings ﬂavors and possibly new materials, whose handling will challenge equipment suppliers. Consistency and uniformity are the keys to snack production. It is imperative that the base product rate be controlled and consistent to enable addition of various ﬂavorings in a consistent manner for making products where every piece is seasoned uniformly.

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CHAPTER 21

Sensory Evaluation in Snack Foods Development and Production DENISE JACOBY CLAY KING

1. INTRODUCTION

S

evaluations are a natural part of living, with few persons aware of the processes that occur automatically when a snack food is eaten. If the product is familiar to the consumer, expectations rise when the package is opened, the product is seen again, conveyed by the ﬁngers to the mouth ﬁrst passing by the nose, and then masticated. If the product performs as expected, the consumer enjoys the reassurance that the manufacturer has again delivered consistent quality. With a new product, more curiosity and inspection occur as the product is brought to the mouth for tasting and the consumer decides whether it is liked. If so, the consumer reaches for another piece; if not, the consumer may give the product a second trial, or decide to look for a replacement on the next trip to the store. In the ﬁrst example, the brain used the senses of sight, touch, smell, taste, initial mouth feel and cleanup, and hearing (as vibrations in the inner ear when chewing crunchy food) to make an “is as expected-is not as expected” decision. A “like-dislike” decision was made in the second example. Color, tactile properties, ﬂavor consisting of taste and odor, and mouth and sound sensations were integrated. This chapter focuses primarily on methods used by sensory evaluation specialists to measure ﬂavor (taste and odor) in quantitative terms in order to deﬁne products and to control their quality during production. Information about tactile, mouth feel and auditory effects is readily retrievable from the literature. Effective sensory specialists are expected to accurately determine preferences of speciﬁc market target groups, help establish deﬁnitions (standards) for the product and ensure that in-house sensory quality control tests maintain the ENSORY

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deﬁnition rather than slide toward preferences of the in-house tasters. These are not easy tasks.

2. OVERVIEW OF FLAVOR A food normally is deﬁned ﬁrst by ﬂavor, its most recognizable feature. How ﬂavor leads to the taster’s responses is complex. Separated into basic processes, ﬂavor is a comprehensive stimulation of taste and odor receptors. The mouth detects ﬁve basic tastes: salty, sweet, sour, bitter and umami, which are combined with aromas to make up all ﬂavors. Odor is perceived when food in the mouth releases volatile compounds, which travel to receptor sites on the olfactory epithelium high in the nasal cavity. The resulting interaction triggers a speciﬁc response in the brain [1]. Scientiﬁc measurement of ﬂavor is divided into two broad categories: analytical and sensory. Instruments are used to identify and measure quantity and quality of ﬂavor for product development and quality control use. Currently, most analyses are done in the laboratory using wet chemistry methods and instruments selected for targeted products. On-line sensors, which measure attributes associated with ﬂavor and other product properties like color, are being developed and installed as proven reliable. Although only partial systems exist currently, the ultimate goal is to link on-line instruments through feedback loops to adjust and control manufacturing conditions. Sensory measurements use people as measuring tools. They are preferred because the sensors are portable, durable, often more sensitive than analytical instruments, and—most important—can integrate the various stimuli into human responses. But differences exist among people. In addition to different degrees of color blindness, taste and odor “blindness” also occur. People tire when making repeated judgments, are inconsistent when ill or have unexplainable “bad days.” As a result, their preferences change—for example, attraction for sweetness often decreases with age. Past learning experiences, especially with ethnic foods, affect ﬂavor preferences. The sensory specialist is expected to guard against many of these variations by qualifying and training taste experts, and by appropriate design of tests. A variety of sensory methods exists.

3. ANALYTICAL METHODS Instrumental/laboratory methods are able to identify the compounds present and determine their quantity in numbers. They are used for ensuring integrity and consistency of ﬁnished snack foods and for characterizations during product development. Analytical methods can determine whether the proper ingredients, in proper ratios, were used during manufacturing and the amounts of seasonings applied. As a case in point, application of a wrong seasoning may cause ill

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effects and even result in lawsuits. Consistency is vital for each snack product because consumers expect the same ﬂavor and quality each time the product is purchased. Scientists use analytical analyses to characterize competitive and new snack foods during product development, to learn about ingredient interactions and to better understand the food for future reference in case quality problems arise. The greater the variety of tests conducted on the ingredients and product, the more likely they will be fully characterized. Literature searches are used to identify newly developed methods that are more appropriate for characterization [2].

3.1. COMPREHENSIVE ANALYSES OF VOLATILE COMPONENTS Comprehensive analyses of the total volatiles are used to measure snack ﬂavor. Obviously, analysis of volatiles cannot measure ingredients such as salt, acids and non-volatile components. However, the volatile components are often responsible for the most important characteristics of a ﬂavor [3]. Gas chromatography (GC) and gas chromatography-mass spectrometry (GCMS) can separate and identify the volatile components of aroma—often the most important characteristic of a ﬂavor. Volatiles can be extremely complex mixtures, frequently containing several hundred individual components. The product formulator is interested in individual components that contribute unique characteristics or overall ﬂavor. The analysis of food aroma isolates consists of separating complicated mixtures of organic compounds into individual components and determining their chemical structure. The procedure may be complicated by extremely low levels of each component [1]. Trace components may have a larger impact on the food’s ﬂavor than other compounds present in larger amounts. Every component should be considered signiﬁcant until it is proven not to be a factor in the ﬂavor. To obtain samples for study, the scientist must remove the volatile compounds from the food, isolate them from the interfering compounds and concentrate them into a suitable form for analysis [1]. Laboratory techniques affect accuracy of the sample analysis. Care must be taken to prevent heat-sensitive compounds from being destroyed by harsh conditions. Highly volatile compounds may be lost during concentration by distillation, and low-solubility compounds may not be extracted. Many isolations rely on differences in vapor pressures of compounds for distillation, differences in solubility for extraction, or a combination of both [4]. Headspace and vacuum headspace trapping distillation techniques are used. Sophisticated headspace analysis techniques include: purge and trap, cold trap, trap with polymeric solid phase and others. Products are often heated before analysis, unless the headspace sample is taken by vacuum. Heat can destroy thermally unstable compounds, and unnatural compounds may be generated by recombination of fragmented compounds [4]. Product distillation permits

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minimum delay from sampling to analysis and minimum development of unnatural compounds introduced during sampling [4]. A sniff port may be used to determine the relationships between total ﬂavor aroma and the volatile compounds. It is used by measuring the compounds by a gas chromatograph and having a panelist simultaneously sniff the compounds from a sniffer apparatus. The panelist uses descriptive terms to describe compounds as they are released and can also quantify aroma intensity using an intensity scale as the compounds are sniffed. Gas chromatographs can detect many compounds undetectable by the panelist. In such cases, the compound is assumed not to contribute to the ﬂavor of the sample. The most important compounds contributing to tortilla ﬂavor have been indicated by snifﬁng efﬂuents from capillary gas chromatographs [4].

3.2. COMPOSITIONAL ANALYSES Compositional analyses quantify selected ingredients known to be present in a snack, but do not characterize or measure the complete ﬂavor. Depending on the product, common analyses include: salt, oil, protein, lactose, individual ﬂavors and color. These methods are used in formulators’ analytical laboratories and the quality control laboratory. For example, if concerns arise about the quality of the oil in a potato chip, amounts of degradation compounds may be measured in an extracted oil sample. If concern arises about the amount of salt on a tortilla chip, an analysis may be conducted if it is known that the salt is of consistent granulation. Otherwise, microscopic analysis of salt crystal sizes may be added. r Salt is the most common analysis in snack foods [5]. Methods are quick,

accurate and measure one of the most prevalent ingredients in salty snack foods. Methods range from a simple Mohr titration to more sophisticated automated instruments that use an ion-selective electrode, which measures chloride levels [6]. These methods are suitable for routine quality control testing in the snack plant and for analytical laboratories. Salt can be measured as an internal component in the snack food (i.e., crackers) or as applied to the surface (i.e., tortilla chips), depending on how the sample is prepared. r Oil analyses are conducted to determine the amount and quality of oil in the snack food. The most common method for determining oil is Soxhlet extraction, which uses petroleum ether. When a product contains signiﬁcant amounts of protein, it may complex with fat during high-temperature heating, rendering it unextractable. In this case, acid hydrolysis methods are used to free the fat. Critical CO2 extraction, using a specially designed instrument, has been rapidly accepted during the past ﬁve years [7]. Indirect methods to determine approximate amounts of oil in snack foods include

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nuclear magnetic resonance spectroscopy (NMR) and near-infrared resonance (NIR). These are non-destructive, rapid, and can analyze individual chips or bulk samples. Analyses that measure the extent of oil degradation include: free fatty acids content, peroxide value, hexanal content and p-anisidine value. r Protein content in the base snack food generally is insigniﬁcant, but higher levels sometimes occur in the seasonings. As an example, protein analysis is used to determine amounts of seasoning applied to cheese-ﬂavored snacks. Protein is measured by quantifying the amount of nitrogen in the sample, using the rapid Biuret method or traditional Kjeldahl digestion and subsequent titration [8]. Newer methods utilize instruments that automatically digest samples with subsequent titration. These instruments decrease analysis time and increase accuracy by removing human variability. r Lactose may be measured to determine the amount of seasoning added to the base. It is a major component of seasonings because it has a low relative sweetness, readily absorbs ﬂavors, aromas and coloring materials, and is used as a carrier [8]. Lactose is a good marker for determining how much sour cream seasoning is on a potato chip. It can be measured by extraction with solvents and analyzing by liquid chromatography. This method is accurate, but time-consuming and expensive to conduct. It is seldom the ﬁrst choice of analytical methods and is used on samples that cannot be measured by more user-friendly methods such as color or salt. It cannot be used in ﬂavor blends where maltodextrin is the carrier. r Color measurement is an indirect method to determine the amount of seasoning applied or the extent of Maillard browning in the product. Two approaches are used: (1) direct measurement of the food; and (2) extracting the color of the seasoning for evaluation. Direct measurement relies on tristimulus colorimetric methods that are highly correlated to human perception of color. This method measures chroma (saturation or intensity of the color), hue angle (red, yellow, green, blue, etc.) and lightness-darkness (the white to black range). Snack foods’ acceptability has been predicted successfully based on L, a and b values. Direct color measurement can be performed on whole or ground homogenous samples. Extracting color from the food and analyzing the ﬁltrate is a viable indirect method of determining ﬂavor. Coloring materials are extracted from products using appropriate solvents and the solutions measured by spectrophotometer. The amount of seasoning added is calculated by the difference in readings between samples with and without the seasoning. This method is used in analytical and quality assurance laboratories because of its high level of accuracy and ease of execution [9]. It is used in chips with highly colored seasonings such as barbecue and other tomato-based seasonings.

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4. SENSORY METHODS Only human subjects can comprehensively measure the sensory characteristics of foods simultaneously and translate them into meaningful responses. “Sensory evaluation” was deﬁned by the Sensory Evaluation Division of the Institute of Food Technologist [10] as: “the scientiﬁc discipline used to evoke, measure, analyze and interpret those reactions to characteristics of foods and material as perceived through the senses of sight, smell, taste, touch and hearing” [10]. The responses, of complex sensations resulting from interaction of our senses, are used to measure food quality in quality control, new product development and other programs. Sensory evaluation may be conducted by several hundred consumers or by panels of a smaller number of highly trained people depending on the type of information required [10]. Different sensory methods are used, depending on the questions asked and resources available. The most common methods include: trained descriptive panel, expert descriptive panel and consumer panels. Each method adds valuable information at different times throughout product development and life cycle [11]. Sensory evaluation facilities, product preparation, serving procedures and other management details should be standardized for both trained and consumer panels. Sensory evaluation facilities in the quality control program should also be standardized, but specialized to detect variations when comparing product with physical standards.

4.1. TRAINED DESCRIPTIVE PANEL The trained descriptive panel is designed to analyze products with a high degree of reliability and precision (reproducibility). This panel typically consists of 10–20 people, who are screened to recognize the basic tastes of salt, sweet, bitter, sour and umami unequivocally [12]. The panel has many uses including monitoring competition, screening ingredients and products during product development, determining sensory and physical/chemical relationships and establishing product deﬁnitions or standards for later quality control use [13]. Snack foods processors who do not have the necessary personnel or facilities may choose to have the work done by a consulting laboratory. The panelists are trained in developing a descriptive language to ﬁt the products they evaluate. This is done in three steps: (1) establishing a common language; (2) proﬁling the product(s); and (3) scaling the critical product attributes. The ﬁrst step in training descriptive panelists on a product is to standardize the terminology describing the attributes of the product. The terminology must be used in a way that allows panelists to communicate their evaluation to the

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Figure 21.1 Spider web sensory proﬁle of popcorn.

sensory manager. Often, the attributes chosen and their deﬁnitions are the result of panel interaction and training. Once the attributes and terminology have been explained in detail, the next step is to use the terms in practice and, where necessary, alter them after the ﬁrst level of training to incorporate what is learned during use. Once terminology is deﬁned, the product is fully characterized by determining the amount of each attribute present. This process is called “proﬁling a product.” Often, the results are arranged in a spider diagram. Different attributes such as ﬂavor, appearance and texture can be shown on separate plots. Figure 21.1 shows an example of the sensory proﬁle of popcorn. Each attribute is assigned a separate axis and scaled with “0” in the center of the spider, the level increasing as the axis radiates out. Proﬁling fully characterizes a product, and is considered the ﬁngerprint deﬁning that product. The deﬁnition is used as a historical reference to prevent product drift and to gain a better understanding of competing products. Proﬁle data are also used to compare products to determine what differences exist between them. Figure 21.2 shows proﬁles of potato chips made from fresh and stored potatoes. The attributes of potato ﬂavor, hardness and crispness are affected by potato storage. Flavor, hardness and crispiness increased in the stored potatoes; oily mouth feel, thickness, off-ﬂavor, saltiness and scorched notes were little affected. Once the product has been characterized by proﬁling, the panel determines which attributes are critical to its acceptability. This is done with consumer input. The spider diagram for popcorn (Figure 21.1) indicates that salt, butter impression and toasted corn are critical attributes. Consumers have conﬁrmed these critical attributes by comparing products with varying levels of a given attribute and determining the acceptance of each. These attributes are then positioned on a scale with anchors at each end to enable statistical analysis.

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Figure 21.2 Spider web sensory proﬁles of potato chips made from stored and fresh potatoes.

The concept of anchors is extremely important to understanding product proﬁling. They are common, reproducible foods that represent the extremes of each attribute. For example, the texture qualities of snack foods have been standardized in terminology and scales for hardness, crispness, thickness and denseness. The anchors for hardness are cream cheese, assigned “1,” and hard candy, assigned “14.5.” Examples of scales are shown in Figure 21.3.

Figure 21.3 Anchored intensity scales: (A) hardness scale; (B) expanded hardness scale; (C) denseness scale; (D) saltiness scale; (E) hedonic rating (like/dislike) scale.

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In order to distinguish differences in some products, it may be necessary to expand the standard scale to identify smaller differences, as in the texture of potato chips. Figure 21.3(A) shows the hardness scale anchored at “1” with cream cheese and “14.5” with hard candy. In the expanded hardness scale [Figure 21.3(B)], softer-textured potato chips made from early fresh crop potatoes are set at “3” and a kettle-fried, hard-bite potato chip set at “13.” What previously was a two-point difference in the standard scale has become a fourpoint difference in the expanded scale. Lay’s Potato Chips (often used as a readily available standard) have been changed from a value of “3” in the standard scale to a value of “6” in the expanded scale. A potato chip that is sliced thicker and fried longer has become “8” on the new scale, while it was only “4” on the standard scale. When scales are expanded, the anchors require reﬁnement to ensure the exact intensities of attributes are correct. Anchored denseness and saltiness scales are also shown in Figures 21.3(C) and 21.3(D), respectively. Basic ﬂavor scales and anchors have been developed for use in descriptive analyses. For example, Meilgaard, Civille, and Carr [14] developed scales and intensity values for four basic tastes (sweet, salty, sour and bitter). Often it is easier to use standard scales and anchors when training panels in proﬁling methods. But due to variability within products, it may be necessary for panelists themselves to develop the ﬁnal list of attributes, scales and anchors. Development of standardized scales for some ﬂavors may be difﬁcult because they are more complex and anchors are not as commonly known. Often, traits can be described sufﬁciently, but scaling becomes difﬁcult; the attributes a panel will agree to and communicate are evident, but the intensity in which they are present is not as precise. As seen for popcorn (Figure 21.3), salt can be described, scaled and anchored with standards that are straightforward. But other attributes, such as browned butter, are more complex and vague, making it more difﬁcult to develop a scale with appropriate anchors. A chart that demonstrates the basic tastes (sweet, salty, bitter and sour), and foods that are used to train descriptive panelist, is shown in Table 21.1 [15]. Trained descriptive panels are an inexpensive way to taste competitor products and determine if changes are occurring with their formulations or processing conditions. As soon as changes occur, panelists can alert product scientists, allowing more time to respond to market shifts. Trained descriptive panels are used to describe the complete sensory proﬁle of target products and progress in developing experimental products. The language developed in this process is also used in followup consumer panels. Product differences that can be related to differences in analytical tests can be determined and correlations developed with human perception, thus validating analytical methods and reducing the costs of human panels. In assisting quality control functions, descriptive panels can identify discernable sensory boundaries for products, track long-term trends within the boundaries and identify exceptions that trigger corrective action.

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TABLE 21.1.

Basic Tastes and Foods That Can Be Used for Training Descriptive Panelists Constructed from Reference [15]. Characteristic Foods and Potential Anchors

Flavor Bitter Sweet Salt Sour

Low Intensity Bottled grapefruit juice 2.0% sucrose/water solution 0.2% salt/water solution Natural apple sauce

High Intensity .20% caffeine/water solution 16% sucrose/water solution 1.5% salt/water solution 0.2% citric acid/water solution

4.2. EXPERT DESCRIPTIVE PANELS Expert descriptive panels operate at levels of instrument accuracy, with high reliability in judgments independent of psychological factors [12]. Panels typically consist of 3–7 people who sample products and ingredients daily and compare evaluations with their peers and with results from chemical and physical analyses. They recommend purchase of selected ingredients and determine impacts of new technologies on ﬁnished product quality and marketability of a speciﬁc product [13]. Expert panels evaluate product quality and suggest processing causes for problems. These experts do not make judgments on product acceptability. For instance, a corn chip expert will identify a bitter aftertaste and suggest the high fryer temperature is the cause, but would not decide if the aftertaste is acceptable to consumers. Expert panelists work from a list of terms often developed in association with their peers in research. The terms are technical in origin and represent existing knowledge about the chemistry, ingredients and formulation of the food product [13]. Terms are more technical in expert panels and more consumer-based in descriptive panels. For example, what a descriptive panel would describe as “green” in a potato chip frying oil would be described as “unprocessed” in an expert panel. Training of expert panelists is done on an ad hoc basis, and members usually have many years of experience and training on a particular product. They are aware that their judgments may not be included in any decision until such time as determined by the acknowledged expert. Panelists are trained to separate their opinion about preference from their opinion about the intensity of each of the attributes. Consequently, they become objective in their evaluations as often indicated by instrumental measurements.

4.3. DIFFERENCE TESTS Difference tests are used to determine if products are different from each other. They may be used when a company considers substituting lower-cost ingredients in the formulas, or when reformulation is needed for a new and

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improved statement. If a product is being improved, a difference test is used to determine if a difference exists, and other testing to determine if the changed product is better than the original. Many types of difference tests are used, depending on the purpose of the test and types of samples involved, including: paired comparisons, triangle tests, duo-trio tests, A-not-A tests. These tests are usually conducted using in-house employees. r Paired-comparison tests consist of asking the panelist if there are

differences between two samples in a speciﬁed characteristic such as saltiness, heat level, crispness or color intensity. Because it is difﬁcult to change only one dimension of the product during formulation, this type of testing is not often used. r Triangle tests consist of three samples presented simultaneously to the panelist. Two of the samples are identical and one is different. The panelist is asked to identify the different sample. Triangle tests only tell the sensory scientist if the samples are recognizably different, not how they differ. r Duo-trio tests consist of the panelist receiving three samples simultaneously. One sample is marked “reference,” and the panelist is asked to determine which of the other two samples matches the “reference.” r A-not-A tests consist of a sequential paired-difference test. It is like the paired-difference test except the samples are not seen simultaneously. This type of test is used when products are different from each other in extraneous ways (for example, color and shape), and subtle differences are not likely to be remembered by the panelist. Difference tests do not determine the types or levels of differences between two samples. They only determine if there are differences between samples. Any other questions need to be answered using alternative methods of sensory testing.

4.4. CONSUMER PANELS Consumer panels are used to determine consumer reactions to a product, for example, acceptability of products as they are being developed. Different types of consumer panels are used depending on the question to be answered. Much of the specialty of ﬂavor system design and evaluation involves asking the right questions of ﬂavor evaluators [16]. Besides knowing what questions to ask of the ﬂavor evaluators, it is also necessary to know how to ask the questions, and how to measure the responses. Several different scales are used to measure responses: r Hedonic scales are extensively used in consumer sensory analysis. They

focus on pleasant and unpleasant features of the food tested, measure like-dislike, and are used for overall, texture, and ﬂavor acceptability. The

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general form is shown in the nine-point Hedonic rating scale in Figure 21.3(E). This scale is easily used with non-trained panelists [13]. Numbers can be assigned to the different intensities, and a mean score and standard deviation calculated for each product. r Faces scales may be used when testing is conducted with children. These scales consists of faces with varying degrees of happy and sad expressions. They may also be used for people with limited reading skills. Face scales might not work with children who are intimidated or distracted by the pictures, or are not able to understand the premise behind them [13]. r “Just About Right”scale is a bipolar scale with 3–5 categories used as a diagnostic tool for consumer tests [13]. It measures how far a product is from the desired intensity on a provided line. For instance, it can be used when the formulator is determining the optimal level of salt application on a potato chip. r Semantic differential scale measures the relative intensity of an attribute, for example, cheese level of cheese puffs, sweetness of a BBQ potato chip, or salt intensity of a tortilla chip. The scientist determines the scale format to be used for the test. For instance, anchors for each side of the scale can be bitter and not bitter, or sweet and not sweet [13]. This scale can be expanded and contracted as necessary, but the scientist may risk that word pairs are inappropriate or are misinterpreted by the panelists.

4.5. TIME-INTENSITY TESTING Time-intensity sensory evaluations are used to quantify changes in ﬂavor sensations perceived during eating. The time-intensity graph of hot and spicy corn puffs in Figure 21.4 shows that, as time progresses, the intensity of salt taste decreases but the heat level builds. The sensory scientist can determine

Figure 21.4 Heat and salt time intensity graphs for spicy corn puffs.

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peak intensity—maximum perceived intensity; time to peak—time to reach peak intensity; rising slope—rate of increase from onset to peak intensity; plateau—time difference between reaching maximum and beginning of descent; declining slope—the rate of intensity decrease; half life—time to reach one half of maximum in decay portion; extinction—time at which curve terminates at base line; total duration—time from onset to return to base line, and area under the curve [15]. Formulators can use time-intensity graphs to determine how intense the heat will become and change ingredients or their levels if they are not acceptable to consumers.

5. SENSORY ASPECTS OF PROCESSING Snack food base composition, production equipment and operation, and methods of applying seasoning impact on how the products are analyzed for ﬂavor [17].

5.1. POTATO PRODUCTS The major measurements in evaluating potato snacks, made either from sliced or dehydrated potatoes, are color and oil ﬂavor [18,19]. Off-color usually is associated with after-cooking darkening due to excess amounts of sugar in the potatoes [20]. Undesirable or off-ﬂavors in products usually result from abused oil or unsound manufacturing processes. These ﬂavors can be quantiﬁed by headspace vapor analysis [21]. External and internal defects in raw potatoes lead to discoloration and reduced yields of ﬁnished products; the extent of these defects can be measured by instrumental and sensory methods. Sugar, moisture and color are common analyses for products made from dehydrated potato ﬂakes that have been combined with cornmeal, starch, gums, sugar and/or internal ﬂavors. To measure the amount of seasoning, it is necessary to measure a marker like color, sugars, salt, or other ingredients that are in the seasoning but not in the base chip. Since seasoning is applied topically, it is easy to extract. Sensory evaluations of potato products pose no speciﬁc challenges for consumer panels and trained panels. Since the ﬂavors of potatoes are mild, the panelists need to be sensitive to the subtle ﬂavors of potatoes. Cleansing the mouth between samples is recommended to eliminate excess oil and residual ﬂavors. Trained panelists should be educated on the undertones of raw potato, scorched, green oil and other ﬂavor characteristics of potato products.

5.2. CORN PRODUCTS Sensory evaluation of corn products demands close attention to the target consumer because of the many different types of corn products available.

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Consumers of corn chips, popcorn and corn puffs have distinct differences in tastes. Popcorn consumers are concerned with the delicate balance of seasoning and corn ﬂavor, while corn puff consumers are primarily concerned with the amount of seasoning on the product. Since each group of consumers is different, each test requires a unique design. Analytical preparation is dependent on the type of seasoning application. Seasonings that are applied directly to the corn product are easily extracted for analysis. Analysis is more complicated for seasonings that are incorporated into oil before application. The frying and seasoning oils must be extracted ﬁrst, and the seasoning then extracted by solvent from the oils. Additional precautions must to be taken with strong corn and seasoning ﬂavors so the ﬂavors will not affect the next sample analyzed. Having the panelist eat a bland food (crackers) between evaluating samples may absorb the remaining ﬂavors in the mouth. Trained panelists should be educated on the undertones of sour corn, scorched, lime residue and other characteristics of corn products. r Tortilla Chips. Flavor is generated in the toaster oven and the fryer (or oven)

during the manufacture of tortilla chips. High amounts of toasted corn ﬂavor developed in these chips result in distinctive GC peaks. Tortilla chips are seasoned by ﬁrst applying an oil spray and then sprinkling the seasonings onto the chips. r (Extruded) Puffs. Flavor generation during extrusion cooking of cereals results from thermally induced reactions, such as the Maillard reaction and degradation of lipids and vitamins. More than 220 compounds that contribute to ﬂavor have been isolated. Flavor can be changed by altering extrusion variables (time, temperature and moisture) [22]. These products usually have a mild taste and carry ﬂavors extremely well. Generally, seasonings are mixed with oil and applied as a slurry. r Popcorn. Many of the ﬂavor notes are lost during actual popping of corn. The resulting product has a very mild ﬂavor and carries seasonings well. Seasonings are applied in a slurry application method, or by sprinkling the popcorn after an oil spray has been applied. r Corn Chips. Traditional strong corn chip ﬂavors are generated during frying. The high temperature of the oil and low moisture content of the corn lead to many volatiles, which have been identiﬁed. The oil-and-corn ratio also affects amounts of volatiles that can be measured by GC in an aqueous system [23]. Corn chip seasonings are applied topically as with potato chips.

5.3. FRIED PRODUCTS The absorbed oil in fried products reduces the volatility of aroma compounds. Flavors for fried snack food need to be stronger than ﬂavors applied to baked snack foods. The high amount of oil damages analytical instruments and

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interferes with extraction of seasonings and sensory evaluation. Panelists evaluating snack foods with high oil content need procedures to cleanse the mouth to eliminate the oil and contaminating ﬂavors between samples. As with sensory tests of corn products, crackers may be used to absorb the oil and ﬂavors left in the mouth. Rinsing with water and added lemon further assists in clearing the mouth before the next sample.

5.4. BAKED PRODUCTS Snack foods have low levels of lipids and require lower ﬂavor aroma volatility than fried foods. However, low-moisture foods can be easily scorched during the manufacturing process and require covering of the undesirable ﬂavors with applied ﬂavorings. Baked snacks rely more heavily on internal ﬂavors; consequently, special procedures are required in analytical evaluation. Usually, the snacks are ground to make extraction easier. Time-intensity sensory analysis usually (often) is used with internally ﬂavored snacks. There is no initial ﬂavor peak when the sample is ﬁrst consumed, and enough time must be allowed for the ﬂavor to be detected [15]. Low-oil/low-moisture samples should be guarded from absorbing moisture during the time when the container is opened and sensory evaluation is conducted.

5.5. FLAVOR ADDITION Internal ﬂavors can be added in the base, either to replace a seasoning system or to enhance it. The applied ﬂavors can be inherent in the base (i.e., extra corn or potato ﬂavors), or can complement the base (i.e., a “fried” ﬂavor for a low-fat snack) [24]. Internally ﬂavored snacks have steady ﬂavor proﬁles. Although the proﬁle does not have a strong initial ﬂavor, it has a consistent impact during eating. Analytically, the samples are difﬁcult to measure because the entire ﬂavor must be extracted ﬁrst. Samples are ground to help free the ﬂavors during extraction, and solvents often are used to help.

5.6. SEASONING APPLICATION Sprinkling the dry seasoning directly onto the base in a rotating tumbler is the most straightforward way of applying seasoning. This method is used in chips with high oil levels since the oil acts as an adhesive. These types of ﬂavors have a high initial impact when consumed and are easy to evaluate analytically. The seasoning application rate on whole chips can be determined easily by measuring a marker in the seasoning as described earlier. Slurry application consists of the oil and seasoning being mixed together and then applied to the base chip. This method aids adhesion of the seasoning

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and melds the seasoning and oil to give a richer taste. It is used on foods that have a low initial oil level. In the analytical evaluation of these ﬂavors, it is necessary to grind the snack to release the seasoning for measurement by the same methods used with other seasonings. Water-based slurries are used by dissolving the seasoning in water and spraying onto the base. The base is then further dried to eliminate excess water. This type of application is used on low-fat foods, but has many drawbacks, including stale products from excess moisture and modiﬁed ﬂavor proﬁles due to excessive heat during redrying. The snacks can be analyzed by grinding and resuspension in water.

6. SENSORY EVALUATION DURING PRODUCT LIFE CYCLE The basic procedure for developing a new product, and supporting it while marketed, includes distinct steps that are constant no matter what type of product is produced.

6.1. INITIAL SCREENING Initial screening in product development roughly deﬁnes the ﬁnal product. The duration can last from several days to several years. The objective during this phase of the life cycle is to formulate and physically prepare a prototype that is close to the ﬁnal product, yet knowing the product will go through extensive optimizations. If management decides to simulate an already marketed product, deﬁnitions may be sought from a trained descriptive panel. Otherwise, sensory analysis at this stage is informal (taste as you go). Usually, the panelists are the lead scientist and a few people in the immediate area, who concentrate on screening out largely unacceptable products. Analytical tests during this stage of product development are limited. The scientist is looking for signiﬁcant differences in physical attributes. The analyses must be reproducible and accurate because the values will be used as benchmarks for further testing.

6.2. PRODUCT OPTIMIZATION The second phase of product development is optimizing the product for acceptability and production feasibility. This is the most costly phase (in money and time) of the product development cycle. The scientist must be aware of how customers perceive the product and the importance of each attribute [25]. Sensory analysis during this phase of product development is critical and includes extensive evaluation with many kinds of tests, each playing a speciﬁc

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role in optimizing the new product. Trained descriptive panels are used to characterize the ﬂavor proﬁle and other characteristics compared to what is already in the market. Consumer panels are used to determine product acceptability and aid in deﬁning the formula and product speciﬁcations for moisture, oil, salt, seasoning and oil ﬂavor in fresh and aged products. Consumer panels can be conducted by the company developing the product or by an independent consumer evaluation agency. Independent ﬁrms offer a large pool of consumers for evaluation, expertise in test design and analysis and unbiased testing. Independent ﬁrms can be expensive if used on a routine basis and conﬁdentiality may be jeopardized. Companies developing products can often conduct their own consumer panels quickly and with maximum conﬁdentiality, but the testing may become biased in favor of the desired results. It is essential that participants in consumer preference tests belong to the target group for whom the product is developed. Trained employee panels may also be used to conduct difference tests to qualify ingredients and processes. Analytical evaluation during product optimization uses feasible methods that are available and accurate. The lead scientist chooses methods based on the type of process, ingredients used, and ﬂavor application methods employed. Scientists should not limit their choices of analytical testing to what has been conducted in the past; rather, they should expand their knowledge by trying new methods. Every method used should be accurate and precise (reproducible) in repeated applications.

6.3. SCALEUP After a product is optimized in the laboratory, it is scaled up for manufacturing. During this phase of product development, the product is taken from a bench top or pilot plant environment to production on a full-scale manufacturing line. It is critical that the product ﬂavor proﬁle and other important characteristics do not change during scaleup During scaleup, speciﬁc quality assurance methods are identiﬁed and qualiﬁed for the product. Analytical evaluation typically undergoes transition from highly accurate analyses to methods that are quick and cost-effective. At this phase, sensory analyses consist of tests that compare the production samples with the optimized product. Depending on the resources available, either consumer panels or descriptive panels can qualify the production samples. Sensory speciﬁcations are also determined before the product is taken into full production. This is a time-consuming process, similar to establishment of analytical speciﬁcations. The ﬁrst step consists of screening samples that represent reasonable extremes in the manufacturing process and also represent different raw material samples. Descriptive analysis is then used to characterize the products in quantitative terms. Consumer data are used to determine

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which attributes are critical and to set acceptable limits around the optimum target. The data are graphed using a qualitative data analysis plot for ease of comprehension [25].

6.4. PRODUCTION Sensory analysis does not stop after the product has been developed and is being produced routinely, however. It is critical that products continue to be analyzed to ensure the ﬁnished goods are consistently manufactured to design criteria and that the product proﬁle does not “drift” over time. This phase is challenging because high costs prohibit many types of testing and the time available to complete the analysis is short. Typically, products and packages are inspected shortly after production in what is sometimes called a sample-cutting meeting. Many bases and their applied seasonings continue to equilibrate for several days or longer. Persons involved in evaluating freshly made products must become familiar with how products with varying characteristics age during their expected shelf life. Analytical methods used during this phase should be quick and repeatable. Many indirect measurements such as color and texture analysis are used to measure ﬂavor. Care must be taken to routinely calibrate these methods to direct methods to maintain their validity. All members of the production staff should be familiarized with “normal” appearances and odors for the product in its various stages of processing, and encouraged to bring apparent deviations to the attention of their supervisors immediately. Employees in positions that require “go-no-go” decisions, like receiving dock supervisors or on-line inspectors, should be tested for possible limitations in sensing color, odor and ﬂavor as required for job performance. Accept-reject standards, like real or synthetic samples, and color chips or photos of acceptable ingredients and products should be provided. Standard Light Boxes may be used for viewing in some applications. Traditional difference and/or variation testing should be conducted on a routine basis for quality assurance purposes. At this point, shelf-life testing should be conducted to ensure the product meets speciﬁcations throughout its code date. These tests may be conducted using employees to reduce cost and time since preferences are not being measured.

7. REFERENCES 1. Cronin, D. A., 1982. Techniques of analysis of ﬂavors. In Food Flavors Part A. Introduction. I. D. Morton and A. J. Macleod, eds., Campden Hill, London, pp.16–24. 2. Munoz, A. M., 1997. Relating Consumer, Descriptive, and Laboratory Data to Better Understand Consumer Responses. ASTM, Conshohocken, Pennsylvania.

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3. Kenny, B. F., 1990. Applications of high-performance liquid chromatography for ﬂavor research and quality control laboratories in the 1990s. Food Technology, 44(9):76–84. 4. Teranishi, R., 1998. Challenges in ﬂavor chemistry: an overview. In Flavor Analysis: Developments in Isolation and Characterization. C. J. Mussinan and M. J. Morello, eds. American Chemical Society, Washington, D.C., pp. 2–22. 5. Niman, S., 1996. Using one of the oldest food ingredients—salt products. Cereal Fds. World, 41(9):728–731. 6. Matz, S. A., 1993. Snack Food Technology. 3rd edition. Van Nostrand Reinhold, New York. 7. AOCS, 1997. Ofﬁcial Methods and Recommended Practices of the AOCS, 5th ed. American Oil Chemists’ Society, Champaign, Illinois. 8. Aurand, L. W., E. A. Woods, and M. R. Wells, 1987. Proteins. In Food Composition and Analysis. Van Nostrand Reinhold Company, New York, pp. 131–284. 9. Giese, J., 1995. Measuring physical properties of foods. Food Technology, 49(2):54–63. 10. Poste, L. M., D. A. Mackie, G. Butler, and E. Larmond, 1991. Laboratory Methods for Sensory Analysis of Food. Publication 1864/E. Research Branch, Agriculture Canada, Ottawa, Canada, pp. 15–56. 11. Stone, H. and J. L. Sidel, 1995. Strategic applications for sensory evaluation in a global market. Food Technology, 49(2):80–89. 12. Land, D. K. and R. Shepherd, 1988. Scaling and ranking methods. In Sensory Analysis of Food. J. R. Piggott, Elsevier Applied Science, London, pp. 168–170. 13. Stone, H. and J. L. Sidel, 1993. Sensory Evaluation Practices. 2nd edition. Academic Press, Inc., San Diego, pp. 87–93, 276–281. 14. Meilgaard, M. G. V. Civille, and B. T. Carr, 1987. Sensory Evaluation Techniques. 2nd edition. CRC Press, Boca Raton, Florida, pp. 174–184. 15. Lawless, H. T. and H. Heymann, 1998. Sensory Evaluation of Food. Chapman and Hall, New York, pp. 266–277. 16. Best, D., 1991. Ten “do’s” and “don’ts” of ﬂavor evaluation. Prepared Foods, 160(50):65–68). 17. Druaux, C. and A. Voilley, 1997. Effect of food composition and microstructure on volatile ﬂavor release. Trends in Food Sci. Technol., 8(11):364–368. 18. Lisinska, G., 1989. Manufacture of potato chips and French fries. In Potato Science and Technology. G. Lisinska and W. Leszczynski, eds. Elsevier Science Publishing Co., New York, pp. 166–172. 19. Kenawi, M. A., N. K. Sinha, R. Y. Ofoli, and J. N. Cash, 1992. Development of sensory characteristics of extruded ready-to-eat pre-baked potatoes. Journal Food Processing and Preservation, 16(3):175–183. 20. Leskowait, M. J., V. Barchello, R. Y. Yada, R. H. Cofﬁn, E. C. Lougheed, and D. W. Stanley, 1990. Contribution of sucrose to non-enzymatic browning in potato chips. J. Food Sci., 55(1):281–282. 21. Sapers, G. M., J. F. Sullivan, and F. B. Talley, 1970. Flavor quality in explosion puffed dehydrated potato. J. Food Sci., 35(6):728–730. 22. Bredie, W., D. S. Mottram, and R. Guy, 1998. Aroma volatiles generated during extrusion cooking of maize ﬂour. J. Agr. Food Chem., 46(4):1479–1487. 23. Buttery, R. G., L. C. Ling, and J. D. Stern, 1998. Studies on popcorn aroma and ﬂavor volatiles. J. Agr. Food Chem., 45(3):837–842. 24. Kuntz, L. A., 1997. Flavoring systems for savory snacks. Food Product Design, 7(2):59–70. 25. Thomson, D., 1988. Food Acceptability. Elsevier Applied Science, London.

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CHAPTER 22

Product Protection and Packaging Materials TOM DUNN

1. QUALITY PROPERTIES OF SNACK FOODS

C

enjoyment of snack foods results from several factors, primarily taste, texture and size. Processors’ techniques and production preferences determine these qualities at the point of manufacture. However, consumer perception and satisfaction with the product depend on the choice of protective packaging materials and the quality of the product delivered to market. ONSUMER

1.1. TASTE The taste perception of snack foods results from many factors. In particular, the choice of ingredients (carbohydrates, ﬂavorings and oils), processing conditions and in-plant handling methods control the initial taste of the product. Packaging and the other elements of a distribution system affect taste changes over time. Oils in a snack food product change rapidly. Chemical oxidation is the primary reaction leading to ﬂavor changes, which, for the most part, are undesirable. Environmental factors, in particular temperature and light, determine the rate at which the reactions occur. The ﬂavorings on the snack product can also oxidize in place. However, the more likely source of negative ﬂavor impact is the volatility of many lowmolecular-weight compounds derived from organic essential oils (“savory ﬂavorings”).

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1.2. TEXTURE Much of the appeal of snack foods results from mouth feel of a crisp and crunchy product. The moisture content of the product primarily determines texture. Processing fried snacks lowers product moisture to very low levels (less than 1%). The resulting food complex is very hygroscopic and consequently prone to texture changes from moisture uptake. Baked snacks have somewhat higher moisture content, but can still lose desirable texture with moisture gain.

1.3. SHAPE Snack foods are made to a size and shape determined by the manufacturer’s process. In virtually all cases, the consumer is meant to receive and use the product with these dimensions. Products are degraded by mechanical damage inﬂicted by shock and vibration forces experienced during distribution from the processor to consumers.

2. ASSESSMENT OF PACKAGING REQUIREMENTS With the goal of preserving product qualities as reviewed in Section I, presentday snack food merchandising has converged almost entirely on vertical formﬁll-seal bags made from ﬂexible materials as the container of choice. The amount of product sold in each package is preweighed and then dropped via a funnel arrangement into a bag-making machine (Figure 22.1). In the procedure, machines: r Unwind ﬂexible packaging materials (usually less than 0.01 inch or 250 r r r r

microns thick) of speciﬁed composition from a continuous roll; Form them into open bags sealed on the side and bottom; Fill the bags with product from the funnels; Seal the bags to make hermetic packages; and Free individual ﬁlled bags from the chain.

Precisely specifying packaging materials is a critical choice in providing an economic package and an efﬁcient packaging operation. With few exceptions, the distribution and merchandising systems used by national and regional snack foods processors are so similar that essentially identical packaging materials are used. Attempts to gain additional commercial advantages include selection of distinctive packaging, achieved by variations in materials and graphics without major packaging machinery changes.

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Figure 22.1 Form, ﬁll, seal, cut schematic of ﬂexible pouches.

2.1. TASTE Packaging materials provide protection for snacks from ﬂavor degradations that result from oxidation of oils and savory ﬂavoring components by: r Stopping the entry of environmental oxygen into the bag; r Blocking components of environmental light; and r Slowing migration of volatile ﬂavorings out of the package.

Suppliers of packaging materials can quantify barrier protection for snack food ﬂavors in terms of individual and composite (laminated) materials [1]. However, snack food processors use such measurements only for comparative purposes. The condition of the food when packaged, as well as incidental damage to the packaging material during storage, distribution, and merchandising of ﬁlled bags, are also critical factors in ultimate consumers’ taste experiences.

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Incidental damage to ﬁlled bags results from stresses on the packages. Puncture of the bag material from the inside by rigid or sharp-edged products is a common cause of failure. Compressive forces (e.g., too many bags stacked on each other in a shipping case) can cause seal failures. Expansive forces (e.g., signiﬁcant reduction of the air pressure outside a bag when snacks are groundshipped over high elevations or air-shipped in unpressurized cargo holds) can do the same. As with any structural engineering task, appropriate designs can reduce the incidence of damage. For substitutions to occur, the consequences of structural failure must outweigh the extra cost of materials able to withstand the extreme forces. Sometimes, changing other components of the delivery system to reduce extreme magnitudes (e.g., selective delivery routes and distribution areas, if possible) may be more cost-effective.

2.2. TEXTURE Moisture-barrier effectiveness is the primary measure of ﬁtness for use of materials for packaging snack foods. Signiﬁcant technical advances in producing robust, low-cost, moisture barriers, since the late 1950s, have dislodged sogginess as the usual limiting factor in distributing packaged snack foods. Even under high-temperature and high-humidity storage conditions, high-performance snack packaging can keep snacks crisp until ﬂavor degradation becomes the limiting factor in shelf life. As with ﬂavor-protecting barriers, incidental damage to the packaging material can greatly reduce its intrinsic moisture barrier properties.

2.3. SHAPE The form-ﬁll-seal snack bag—the so-called “pillow pouch”—provides cushioning that isolates its contents from compressive forces that can break snack pieces. This beneﬁt results from a slight overpressurization of the bag as it is sealed. The extra bag volume also reduces product breakage by shaking if the shipping case vibrates during transportation. The degree of damage can be managed by careful consideration of the placement conﬁguration of bags in shipping cases [2].

3. PACKAGING MATERIALS FUNCTIONALITY Most snack food packaging in the world in the late 20th and early 21st century uses oriented polypropylene (OPP) ﬁlm in one of several forms. The ﬁlm usually is printed and laminated to another ﬁlm of OPP or another material. The resulting functional performance of OPP well meets the protection requirements of many snack foods.

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Figure 22.2 Cross-section of a generic packaging material.

The barrier requirements of packaging snack foods are only one part of the task of taking commercial products to market. The elementary functions of packaging are: r r r r

Communication; Protection; Convenience of use; Containment of the product [3].

The cross-section of a packaging material in Figure 22.2 helps present these functions simply. Thickness of the layers is not shown to scale. In fact, thickness of the layers is a primary design option in choosing a speciﬁc packaging structure. A description of the layers, and how they relate to the protection requirements of snack foods, follows.

3.1. GRAPHICS CARRIER This layer, in a composite packaging material, serves more functions than simply carrying a printed image. A “reverse (inner side)-printed” packaging material, as depicted in Figure 22.2, uses this layer to protect the image from scufﬁng. It also imparts extra gloss to the package. When this layer is OPP, additional functions include: r r r r

Increased moisture barrier; Increased package stiffness; Increased puncture resistance; and Increased tear resistance.

The moisture-barrier effect of the additional OPP is calculated by the “inverse sums” method (cf. Ohm’s Law), addressed in the next section. The listed mechanical effects are more complicated. While functional effects are directly measurable, their theoretical prediction has only recently come into the literature of the packaging industry [4,5]. The lack of precise predictive models results in large part from subjective assessments of desirable levels of otherwise measurable values. The “hand” of a package is a subtle and personal norm that has traditionally described an acceptable feel among different

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packaging materials. Previously used cellulosic materials (cellophane and glassine-type paper) are stiffer (i.e., they have a higher tensile modulus) than OPP of comparable thickness. This difference, and a preference for stiffer packaging materials for snacks, delayed the industry’s acceptance of OPP technology until cost factors became compelling. The predominance of glossy, reverse-printed OPP snack packages in the market has stimulated the development of different graphics carrier layers. For example, an old-time, hand-packaged effect results from surface printing one of various grades of paper and laminating this to one or more components, which provide barrier and sealing functions to the composite material. Alternatively, matte-ﬁnished OPP and special coating techniques (applied to the outside surface of an OPP ﬁlm) are able to achieve much the same effect.

3.2. PRINTED IMAGE The information communicated by snack food packaging is substantial in amount and detail. Much serves basic marketing purposes (e.g., brand identiﬁcation, serving suggestions, identiﬁcation of ﬂavors and promotional inducements to buy). Some information (nutrition statements, net weight and producer identiﬁcation) is legally required; some is dictated by the retail trade (e.g., the Universal Product Code or UPC symbol). A pictorial representation of product inside the package is critical when opaque, light-barrier packaging is used.

3.3. ADHESIVE LAYER As with the graphics carrier, this layer can serve more than the elementary laminating function. In its simplest form (usually a separately applied coating of liquid adhesive), this layer binds a barrier surface on the layer adjacent to the ink and unprinted surface of the graphics carrier. This method, called “adhesive laminating,” is generally limited to small (less than 2 oz, 60 g) packages. An alternative process, called “extrusion lamination,” provides structural enhancement and what many consider to be superior package material “hand.” In these materials, a relatively thick (0.0005 to 0.001 inch; 12 to 25 micron) layer of polyethylene (PE) is cast in molten form (i.e., extruded) between the graphics carrier layer and the barrier layer. Adjustment of the conditions of extrusion (and sometimes the choice of a PE copolymer) can control the degree of adhesion. The extra thickness of the PE layer also has structural effects [3]. The adhesive layer can also affect the barrier functionality of the overall structure. The laminating process can use adhesives based on polyvinylidene dichloride (PVDC or SaranTM ). PVDC provides moisture- and oxygen-barrier improvements. Crystalline forms are used as barrier layers in many snack packaging structures. However, using PVDC as a laminating adhesive requires

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modifying formulations so that actual barrier performances in this form are less than those achieved by coatings. Extrusion laminating methods can impart barrier functionality by using coextruded layers. In this process, a distinct layer of barrier material is sandwiched between external layers of PE. Ethylene vinyl alcohol (EVOH) for oxygen barrier and PVDC resins would be appropriate candidates, but they have hardly been used commercially as of this writing.

3.4. BARRIER LAYER Some snack food applications do not require a distinct barrier layer. The total amount of OPP in the graphics carrier and sealant layers may provide sufﬁcient moisture barrier to maintain the snack food’s texture during distribution and sale. Some marketing systems may require more moisture-barrier or other functionalities than OPP can affordably provide. Layers of vacuum-metallized aluminum and PVDC on an OPP carrier ﬁlm are the most common types of barrier layers when OPP is not sufﬁcient. Typically in such situations, the OPP carrier also provides functionality as the sealant layer. Both types of layers can provide functional barriers to moisture and oxygen. Aluminized OPP is also a barrier to as much as 99.9% of environmental light. High-barrier, PVDC-coated OPP ﬁlms function very differently than the earlier generation of sealable PVDC-coated OPP ﬁlms. Modiﬁcations to enhance the adhesive functionality of PVDC adhesives impaired their barrier functionality, and modiﬁcations to provide sealing functionality to PVDC-coated OPP came at the expense of barrier. These coated ﬁlms had only moderate oxygen barriers and provided essentially no improvements over the intrinsic moisture barrier of the OPP base ﬁlm. Advances in the moisture- and light-barrier performance of OPP packaging materials have made oxygen barrier a much more critical factor in selecting snack packaging. Under normal packaging conditions, ambient air, containing about 20% oxygen, goes into the package with the product. The contained oxygen is more than sufﬁcient to support oxidative changes of oils and ﬂavorings to objectionable levels. A modiﬁed atmosphere packaging (MAP) process is used to take advantage of the high barrier properties of snack foods packaging materials. This involves “ﬂushing” the bag with nitrogen gas during ﬁlling and sealing. Nitrogen (most of the other 80% of air) does not react with oils and ﬂavorings. The industry seeks to lower residual oxygen levels in snack food packages to less than 2%. The MAP process produces an isolated bag of nitrogen gas in a surrounding atmosphere of 80:20 mixture of nitrogen and oxygen. Basic thermodynamic tendencies attempt to eliminate this localized oxygen-poor pocket of gas by permeation of atmospheric oxygen through the packaging material until its

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concentration is the same as in the surrounding atmosphere. Good oxygen barriers retard permeation until the package is opened for consumption.

3.5. SEALANT LAYER By deﬁnition, the form-ﬁll-seal process requires a sealable layer in fabricating a container from the packaging material. In this usage, “sealing” essentially means welding one thermoplastic surface to another. The forming part of the cycle on the bag-making machine requires that opposite edges of a sheet of material be folded or overlapped. When the weld is made with the inside of one edge overlapped on the outside of the other, the resulting longitudinal seal is called a lap seal. In the alternate format, the inside of one edge folds to contact the inside of the other, and a ﬁn seal is made. In either case, a tube of packaging material is presented to the funnel through which the premeasured product drops. During the process, metal surfaces of various shapes guide the packaging ﬁlm through the form-ﬁll-seal machine. Pinch (or “nip”) rollers, driven by various mechanical linkages, advance the ﬁlm over the guiding surfaces. Reliable and efﬁcient operation of the process requires that the surface characteristics of the ﬁlm be acceptable to both the guiding surfaces and the drive points. Fabricating a bag from the resulting tube requires making inside face-toinside face seals at the top and bottom. In practice, the bag making cycle concurrently makes the top seal of one bag and the bottom seal of the next bag and cuts the tube between the seals. Although the basics of the process are very similar, differences in package formats, sizes and manufacturing efﬁciencies throughout the snack foods industry mandate different levels of functionality in the selected materials. Simple OPP ﬁlms will not heat seal in this type of form-ﬁll-seal process. The temperatures needed to melt the polypropylene resin comprising the ﬁlm exceed the treatment (approximately 310◦ F, 155◦ C) given the ﬁlm in the orientation process. To overcome this limitation, lower melt temperature resins, typically propylene copolymers or terpolymers, are coextruded as a skin layer on a core layer of homopolymer polypropylene. To make a lap seal, a compatible sealable surface must be present on the outside (unprinted) surface of the graphics carrier layer. In such applications, the graphics carrier layer is comprised of coextruded OPP ﬁlm. This lap-type seal allows use of a narrower material width to make bags of a speciﬁed volume.

3.6. OPP AND SNACK PACKAGING The depiction of various functional layers of a typical snack food packaging material in Figure 22.2 is expanded in Figure 22.3. In the developmental path taken by OPP ﬁlm products to reach their preeminent role in the industry today,

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Figure 22.3 Multilayer coated layer packaging material

several necessary package functionalities were linked into single layers that are easily combined in making fully functional packaging materials. Figure 22.4 shows a simple snack food packaging structure in the extreme degree (effectively one layer). Stiffness requirements for large (6 oz—170 gm or more) snack food packages restrict these materials to small bags for products where light barriers are unnecessary.

4. PROPERTIES OF SNACK FOOD PACKAGING MATERIALS Previous sections described the functions required of snack foods packaging materials to protect package contents. References were made to other components of snack processing and marketing systems. A snack food processor should select packaging materials in concert with the other factors to deliver a desirable, consistent product to the market. Properties of speciﬁc packaging materials are described next to show how they provide functionality and beneﬁts. At best, this information is incomplete in today’s rapidly changing packaging materials industry and certain to be obsolete at printing. The selection of packaging materials for a speciﬁc snack application requires careful trial-and-error testing in the context of the entire commercial snack marketing system. Prize-winning snack food packages alone have done little to ensure the economic success of their users.

4.1. BARRIERS TO ENVIRONMENTAL INFLUENCES 4.1.1. Moisture Barrier Keeping crispy snack foods crisp has long been the primary objective of packaging. Theoretically complete models are available to describe the behavior

Figure 22.4 Printed, barrier-coated, single-layer packaging material.

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TABLE 22.1.

Moisture Vapor Transmission Rates for Snack Flexible Packaging Materials from Industry Data Sheets.

Material Moisture-proof cellophane (250 yield) 5 lb PVDC on 25 lb glassine Sealable PVDC-coated OPP (70 ga.) OPP 50 ga. 75 ga. 100 ga. 120 ga. Heat-sealable OPP 70 ga. 120 ga. Metallized heat-sealable OPP (70 ga.) High-barrier metallized heat-sealable OPP (70 ga.) High-barrier PVDC-coated heat-sealable OPP (70 ga.) PE (100 ga., 1 mil or 0.001 in)

Gms/100 In2 @ 100◦ F/90% RH 0.5 0.2 0.45 0.70 0.45 0.33 0.28 0.47 0.28 0.02 0.015 0.16 1.2

of moisture vapor molecules as they adsorb onto a material’s surface, begin to diffuse through that material and then desorb from the opposite side [6]. For comparative purposes, the dynamics of the process are reduced to a calculated moisture vapor transmission rate (MVTR). These rates are cited in grams of water vapor transmitted through 100 square inches of material per 24-hour period at prescribed conditions of temperature and relative humidity, usually 100◦ F and 80% (ASTM Method F372). Metric units are expressed in grams per square meter per 24 hours at indicated conditions. The MVTR calculation is a laboratory vestige with strong, but incomplete ties to actual protection of packaged snacks from environmental moisture. The unaddressed gap is the fact that commercial distribution systems for snacks between the processor and consumer do not try to control environmental temperature and relative humidity variations. MVTR values are valuable as comparative measures of moisture vapor protection. Table 22.1 summarizes how MVTR performance of various materials has improved over the years in protecting packaged snack foods. The progress has justiﬁed MAP for the simple reason that product texture stays acceptable longer.

4.1.2. Oxygen Barrier OPP by itself is a poor material for keeping environmental oxygen out of MAP snack packages. Oriented polyester (OPET) and biaxially oriented nylon (BON)

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ﬁlms intrinsically present better barriers against ingress of oxygen. Other forms of MAP packaging have used these two materials since the 1950s, particularly for processed meat and cheese products. However, only snack seed and peanut packaging typically had distribution systems requiring MAP systems during this period. By the late 1980s, development of OPP base sheets used in vacuum metallizing led to reliable metallization of OPP with oxygen transmission rates at the 3 gm/100 in2 (0.2 gm/m2 ) level at 73◦ F (23◦ C). With this barrier performance, MAP snack food packaging appreciably lengthens the acceptance periods of snack foods. Parallel improvements in high-barrier PVDC coatings for OPP have made these materials suitable for MAP packaging where a light barrier is not required. Even with these improvements, the intrinsic high oxygen permeation rate of OPP means that barrier performance can be very uncertain. The industry has developed special tests to model form-ﬁll-seal operations and predict the OTR robustness of a packaging material in actual use. Methods very similar to MVTR calculations measure and report OTR values for ﬂexible ﬁlms. Correspondingly, OTR values ﬁnd best use as comparative measures of oxygen protection. OTR performance of various materials is summarized in Table 22.2. TABLE 22.2.

Oxygen-Barrier Transmission Rated for Flexible Films. Data from Industry Data Sheets. Material Moisture-proof cellophane (250 yield) Sealable PVDC-coated OPP (70 ga.) OPP 50 ga. 100 ga. Heat-sealable OPP 70 ga. 120 ga. Metallized heat-sealable OPP (70 ga.) High-barrier metallized heat-sealable OPP (70 ga.) High-barrier PVDC-coated heat-sealable OPP (70 ga.) PE (100 ga.; 1 mil or 0.001 in.) PVDC-coated BON (72 ga.) Metallized BON (60 ga.) PVDC-coated OPET (50 ga.) Metallized OPET (50 ga.)

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Gms/100 In2 @ 73◦ F 0.5 3.5

50 100 70 120 6.0 1.7 0.3 400 0.56 0.19 0.2 0.05

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The following relationship calculates the total moisture vapor or oxygen barrier performance of a multilayered structure: T R −1 = (T Ra )−1 + (T Rb )−1 + · · · + (T Rn )−1 where: TR is the total transmission rate Tra–n is the transmission rate of the a through nth layer. As in the case of a single material’s transmission rate, such a calculated (or experimentally conﬁrmed) value is a relative indicator rather than an absolute predictor of shelf life.

4.1.3. Light Barrier Pioneering work on the inﬂuence of light energy on the chemistry of oils used to process potato chips was conducted at the University of Georgia in the 1970s. Using chromatographic methods, levels of oxidized by-products resulting from exposure of oil to light were correlated with consumer taste preferences. Since this research, potato chip processors have used packaging materials to reﬂect or absorb ambient light before it can be transmitted into a ﬁlled package. Oxidative reactions also occur in the dark, but at a much slower rate. Effects of these reactions are not as quickly noticed in corn-based snacks, so transparent packaging materials are standard for these products. The original light-barrier packaging utilized brown-colored glassine paper, or brown pigmented plastic layers in co-extruded ﬁlms, which blocked about 80% of ambient light. Metallized ﬁlms are superior in this effect, typically blocking 99+% of light.

4.1.4. Flavor and Aroma Barrier Many chemical and physical differences exist among the variety of volatile ﬂavor and aroma compounds used in foods. This makes quantiﬁcation of even relative measures of barrier in ﬂexible ﬁlms to these substances difﬁcult. As with oxygen, most of the barrier of OPP to ﬂavor and aroma migration results from metallized or PVDC coatings. Typical test protocols for aroma-barrier evaluations simplify the task by measuring the transmission dynamics of a single volatile at a time. A variety of volatiles, including allyl sulﬁde (garlic ﬂavor), has been evaluated across different materials and grades of similar materials. Unfortunately, no suitable

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volatile analogue for capsicum oil (cayenne pepper) currently supports such analyses for many of the spicy ﬂavors in snack food products. The relationship of the OTR of a given material and its barrier to a given aroma is unpredictable. Empirical measurements are necessary for even comparative evaluations. Standard methods and instrumentation have become available to industry only recently [7,8]. Earlier research found that PVDC-coated OPP is an excellent (permeability <0.1) barrier to allyl sulﬁde [9].

4.2. FACTORS AFFECTING MACHINING PERFORMANCE 4.2.1. Friction Smooth and reliable progression of the packaging material from roll form to a formed, ﬁlled bag depends primarily on the surface friction characteristics of the material. The industry typically measures this as the coefﬁcient of friction (COF). This value is the ratio of the downward force (weight) exerted on a unit area to the force required to pull it horizontally at a speciﬁed rate. Static COF refers to the relatively high force needed to start the weighted area in motion. Kinetic COF measures the (usually lower) force required to keep the weighted area in motion. COF measurements report the friction of one paired surface to another. The material’s inside-to-inside (in-to-in) surface COF, outside-tooutside (out-to-out) surface, and inside or outside surface to a metal surface are the usual COF values reported. Vertical form-ﬁll-seal equipment for the snack food industry before the early 1980s primarily depended on the outside COF of the ﬁlm. This resulted from a mechanical arrangement by which the end-sealing jaws gripped the material while a subframe assembly moved downwards unwinding it off the roll. The out-to-out COF had to be relatively low. The material also had to have sufﬁcient stiffness and strength to transmit this localized force over the distance between roll unwind and ﬁlled bag dropoff, often 5 to 10 feet of material In the 1980s, the industry took advantage of electronic motion control technology in a generation of machines that separated the end sealing process from packaging material advancement. In the newer technology, electronically controlled friction-drive rollers rotate a speciﬁed distance along their circumference to pull a like amount of material off the roll. This material is further advanced through the machine by pull belts that press against the outside of the material as it is pressed against the outside (metal) surface of the machine’s ﬁlling tube. This radically different mechanism relies on several critical, and often subtle, COF relationships. If the friction between the roll’s measuring material off the roll and the material itself is not sufﬁcient, less than a full bag’s length will be unwound. If the friction of the inside of the material against the ﬁlling tube is greater than that between the material’s outside and the pull belts, the

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material will drag, again preventing a full bag’s length from advancing. The cross-machine direction ﬂatness of the material is also critical in ensuring that the forward pull forces balance at all points of contact across the material. Because the reported values are from very speciﬁc surfaces tested with speciﬁed weights and rates of pull, at best they are relative and with limited predictive value. Managing the dynamics of material-machine surface interfaces for optimum machine performance is not simple. The best productivity improvements result from adjustments to both of the friction factors to make the overall combination more robust.

4.2.2. Heat-Seal Behavior The seals of a snack food package must balance the contradictory objectives of providing an airtight closure for the product during its distribution and a consumer-friendly means of getting into the bag after purchase. “Peelable seals” is the industry term for this material feature. The acceptable strength of a peelable seal is a personal, subjective matter. The method used to make comparisons in the laboratory involves cutting a strip (usually 1 inch or 25 mm wide) of material perpendicular to a seal line. Unsealed tabs of material are clamped into the opposite jaws of a tensile-testing machine, and the jaws pulled apart at speciﬁed rate while the seal is held perpendicular to the line of jaw separation. The force to open peelable seals for snack packages measured this way is usually 700 to 1000 gm per 25 mm width. In contrast, seals that are not peelable, such as those often used for airline peanut packaging, can measure 2,300–2,500 gm/25 mm. The process of orienting OPP ﬁlm includes an annealing operation that heat sets the ﬁlm. The temperature of the ﬁlm at this point dictates the distortion temperature at which the ﬁlm will shrink violently. The melt point of the polypropylene resin in the ﬁlm is always higher than this heat set temperature. Therefore, heat sealing of basic OPP ﬁlm is impossible. Suppliers initially addressed this critical limitation by coating sealable materials (acrylic or PVDC) onto the ﬁlm. Subsequent (and lower cost) technology involves coextruding one or two skin layers of low-melting-temperature polypropylene copolymers with the core layer of homopolymer polypropylene. The skin layers have high adhesion to the polypropylene, allowing the resulting composite to process much like normal OPP. The skins melt to form heat seals at temperatures lower than the ﬁlm’s overall distortion temperature (seal initiation temperature). Polymer technology has evolved to provide lower and lower melting point polypropylene copolymers (even terpolymers), allowing ever-wider ranges of sealing (Figure 22.5). Wider seal range ﬁlms allow faster machine speeds and higher productivity. Measured heat seal values typically depend on the temperature, pressure and time conditions used to heat materials, bring them into intimate contact

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Figure 22.5 Sealing temperatures of different polymers.

and allow their welding together. In addition, shear force can effectively mix polymers from the two sealing surfaces and result in stronger seals with lower likelihood of voids or capillary-sized leaks [10]. “Hot tack” is a measure of how quickly newly made seals, particularly the bag bottom, set up and gain their ultimate strength. Low hot tack is a limiting factor in machine speed, but its measure and management are more art than science. Seal temperatures at the lower end of the seal range favor obtaining ultimate seal strength swiftly, but may slow the machine.

4.2.3. Bag Structural Integrity After a bag of snack food is sealed, the processor depends on a combination of packaging material properties to continue protecting the product. The seals themselves can burst if overinﬂated bags experience a drop in atmospheric pressure. This is the case when product is packed at a relatively low altitude and shipped by air or by ground transport over high-altitude routes. If the seals burst, the increased air pressure when returning to normal altitudes expresses all excess atmosphere in the bags, leaving them ﬂat and, in effect, opened. Actual punctures through the body of the packaging material can result from sharp edges and corners of the snack food product. Such occurrences are rare, particularly when the material has been laminated by the extrusion lamination process. In these cases, the unoriented extruded layer resists puncture better than the OPP ﬁlms. For the same reasons, extrusion laminations are preferred for minimizing the tendency of snack packaging materials to tear down the front or back panel of the bag as a seal is opened. Proprietary techniques [5] exist to balance the forces of adhesion and tear propagation.

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5. CURRENT ISSUES IN SNACK FOODS PACKAGING Development of recloseable bags has been a major interest of the snack foods industry since the mid 1990s. The beneﬁt from this feature would be protection of remaining product in opened large snack packages from high humidity before consumption resumes. To date, reclose features have been commercialized for packaging systems other than the vertical form-ﬁll-seal. Introductory systems exist in the marketplace for non-snack products packaged on similar machines. Development is underway to adapt such technologies within costs acceptable for snack foods. Reclose features are well established for standup pouch packages, but snack products have used them only sparingly. Although standup pouches and recloseable ﬁber canisters have been used for specialty snack products, they are not popular for the high-volume mainstream products. Regulatory requirements for use of certain fat substitutes require that snack foods be vitamin-fortiﬁed to replace any vitamins that may be lost by the consumer when consuming the substitute. Retaining the bioactivity of these vitamins during distribution and display is critical in assuring consumers of the long-term wholesomeness of these products. Much of the loss of vitamin bioactivity results from light-induced chemical changes. Packaging materials can provide protection from light, and possibly other functions important in protecting against loss of vitamins.

6. REFERENCES 1. ASTM, 1998. F1249, Standard test method for transmission rate through plastic ﬁlm and sheeting using a modulated infrared sensor. ASTM Annual Book of Standards, Volume 15.09 Flexible Barrier Materials. American Society for Testing and Materials, West Conshohocken, Pennsylvania, pp. 1131–1135. 2. Marsh, K. S., 1999. The inﬂuence of product orientation on snack food packaging. Packaging Technology & Engineering, 8(1):36–84. 3. Testin, R. F. and Vergano, P. J., 1990. Packaging in America in the 1990s: Packaging’s Role in Contemporary American Society—The Beneﬁts and Challenges. The Flexible Packaging Association, Washington, D.C. 4. Morris, B. A. and J. D. Vansant, 1998. Secant-modulus in multilayer ﬁlms can skew bending stiffness. Packaging Technology & Engineering, 8(5):33–84. 5. Derkach, W., R. Hawkins, et al., 1998. Product Package Having Reliable Openability. U.S. Patent 5,829,227. 6. Salame, M., 1986. Prediction of gas barrier properties of high polymers. Polymer Engineering and Science, 26(22):1543–1546. 7. Hoch, G. J., 1997. Noses in the know: Electronic snifﬁng devices sniff out product quality. Food Processing, 58(9):42–44.

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8. Ylvisaker, J. A., 1995. The application of mass transport theory to ﬂavor and aroma barrier measurement. TAPPI Journal, 78(11):175–180. 9. Graebner, L. S., 1984. Food packaging: An opportunity for barrier coextrusions. Fourth Scotland International Conference on Coextrusion Markets and Technology. Princeton, New Jersey, pp. 25–74. 10. Bower, W. B., 1986. Heat Seal Die. U.S. Patent 4,582,555.

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CHAPTER 23

Snack Foods Filling and Packaging

CURT KUHR

1. INTRODUCTION

1.1. BACKGROUND

A

LL snack food producers must be concerned about the effectiveness of their

packaging operations in controlling costs. The types of materials used and efﬁciencies of packaging lines can affect proﬁtability as much as product formulation, purchasing, processing, distribution, marketing and other major activities of the business. Understanding and applying the proper packaging principles and systems can reduce operating costs and sometimes make the difference between ﬁnancial success and failure in today’s competitive marketplace. Packaging systems and their related support typically are a large part of production costs. Savings go directly to the bottom line. The most common areas for potential savings include reductions in: r Package materials usage and waste r Product giveaway, waste, and damage r Labor r Plant ﬂoor space requirements Other important factors in selecting appropriate packaging systems include cleanup and sanitizing expenses inherent in the design, ease of operation, including costs of training operators, and maintenance requirements. The packaging industry sometimes uses the words “bag” and “pouch” and “carton” and “case” loosely. “Pouch” generally refers to a package made from ﬂexible material, which is formed, ﬁlled and sealed in one continuous operation.

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Most snack foods are ﬁlled into pillow pouches that are not free standing. “Bag” generally means a block-bottom container, which is made from more rigid materials and is meant to stand independently when ﬁlled, as with cookies. However, pouches can be made with gussets, which also broaden their base. There are no hard rules for terminology in the packaging industry, and the machines that make pouches commonly are called bagmakers. Rather than attempting to correct a widely used vocabulary, common industry terms are used in this chapter because this is how the reader would communicate with packaging materials and systems suppliers. In similar fashion, “carton” generally refers to individual rigid retail units or packages fashioned from paperboard. The material usually is a solid bleached sulfate board (made from wood pulp), or a kraft type of board stock with a bleached or unbleached ﬁller layer in the middle and single- or double-side facings with a smooth white outer layer for printing. The term “case” generally refers to a larger corrugated paper structure, which holds multiples of cartons, bags or pouches for shipping and distribution.

1.2. HISTORICAL Although the commercial snack food industry is over one hundred years old, automation in packaging did not start until roughly 50 years ago. Prior to that time, snacks were ﬁrst dispensed to the customer from the cracker barrel at local mercantiles, and then distributed in premade wax paper bags until almost the middle of the 20th century. The bags were hand-ﬁlled and hand-sealed with a hot iron and delivered to the market, which at that time consisted mostly of small local independent merchants and pubs. As product-processing operations became automated over several decades, snack producers recognized that their packaging operations were impediments to capitalizing on the booming popularity of snacks throughout the country. The ﬁrst signiﬁcant automation in packaging occurred in the late 1940s when Daniel Woodman, founder of the Woodman Company, developed a system for the H. W. Lay Company. This semiautomatic system pulled premade bags from a magazine and clipped them beneath a series of funnels on a rotating turret where operators could easily ﬁll premeasured charges of product into the bags (Figure 23.1). The bags were then individually sealed with a hot iron. Strong consumer demand quickly outpaced the capabilities of these semiautomatic machines. The birth of regional and national supermarkets and improved transportation resulted in a widening market base. Before long, manufacturers developed the ﬁrst fully automatic packaging machines. These machines utilized very simple scale systems to weigh the product and a pneumatic/mechanical system to form the bag from a roll of ﬁlm, ﬁll it with weighed product and seal it into a pillow pouch. This was the beginning of vertical form-ﬁll-seal (VFFS)

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Figure 23.1 The earliest packaging automation used premade bags, which subsequently were sealed by hand.

equipment. From that point on, the pace of technological advancements increased and many packaging machinery companies emerged.

1.3. COMMON SNACK FOOD PRODUCTS The vast majority of snack foods today ﬁts into the following general categories. Although many variations exist in product shapes, sizes and ﬂavorings, these groupings serve to associate speciﬁc types of packaging generally suited for each application. Each category has unique packaging requirements for product protection, cost, uniformity, physical durability, marketing methods and distribution channels. r r r r r r r r r r

Potato chips Pretzels Peanuts Popcorn Pork rinds Corn chips Tortilla chips Extruded snacks Cookies and crackers Others (bagel chips, seeds and nuts, dried meat snacks, etc.)

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1.4. GENERAL PACKAGE CONSIDERATIONS AND FUNCTIONS 1.4.1. Product Protection Snack foods are highly susceptible to damage and deterioration during transit and distribution, perhaps more than any other prepared food group. As such, the structure of the package must be highly cost-effective, machinable and also hermetic to protect against physical damage and effects of atmospheric moisture and oxygen on product shelf life.

1.4.2. Distribution The package form must protect the product through all stages of distribution— from the ﬁlling machine through case loading, transportation and handling—all the way to the store shelf and the kitchen cabinet. Also, it must facilitate efﬁcient handling and automation wherever possible within the process. Package space utilization can be an important factor, as savings in transportation costs can have a signiﬁcant impact on product pricing and proﬁtability.

1.4.3. Marketing The old adage that “the package is the product” is especially true for snack foods. Product quality and ﬂavor are always the ﬁnal determinants for retaining consumer loyalty; but often it is the package, including appearance, message and visual elements (advertising, displays and photos), that attracts the customer to ﬁrst use. This places great importance on package integrity, convenience, materials, ﬂexibility and printing quality. Packaging systems must be capable of sustaining these qualities by handling specialized materials and structural features, unique high-quality graphics and precisely registered printing at high speeds.

1.4.4. Standard Sales Units The variety of standard sales units has greatly increased since the inception of automated packaging systems. Today, additional ﬂexibility is demanded of systems for handling packages ranging from small-portion packs and airline servings, to vending-machine packages, to the larger bulk sizes that now are frequently offered in institutional or club store markets.

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2. PACKAGE STYLES

2.1. FLEXIBLE BAGS The overwhelming majority of all snack foods on the market today are contained in bags (or a combination of bags in cartons) of various styles.

2.1.1. Premade Bags While rarely used for substantial production volumes, preformed bags are available from many paper and ﬁlm converters for short-run applications. These can be plain, unprinted bags to which labels can be afﬁxed, or they can be preprinted. Due to the necessity for manual ﬁlling and handling, premade bags generally are used only for limited market tests or in instances where their “home-made” appearance offers a desired market identity.

2.1.2. Pillow Pouches A pillow-style bag incorporates machine-made seals on the top and bottom and a long (vertical) seam seal in the center of the back panel. The long topto-bottom seal can be a ﬁn seal or a lap seal (Figure 23.2). Pouches are made from a roll (web) of ﬁlm or paper that is formed into a continuous tube by adhering the two edges of the roll together. The continuous tube is then pinch sealed at prescribed increments (bag length) to form a bag. The top of one bag and the bottom of the next are simultaneously created with each sealing impression. Between impressions, the desired amount of product is dropped into the tube. Most seals and materials for this type of application are hermetic or airtight. During the forming operation, a controlled amount of air is also captured within the bag to create a ballooning effect, which is essential for the protection of fragile product contents. Nitrogen ﬂushing before sealing also provides a ballooning effect and generally lengthens product shelf life by excluding oxygen, which is a prooxidant of fat. The sides of the pillow pouch can also incorporate gussets, or extra folds, which allow some expansion of the bag after it is ﬁlled.

2.1.2.1. Fin Seals Can be made of materials with sealing properties on one side only, because the heat-sealable surface seals to itself.

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Figure 23.2 The conﬁguration of the ﬁlm seal is determined by the material type, product characteristics or machine type employed.

2.1.2.2. Lap Seals Use slightly less material, but require sealing properties on both sides of the ﬁlm because the lap is made by sealing the inner ply of one edge to the outer ply of the other edge.

2.1.3. Flat-Bottom/Standup Styles A stable, standup bag (ﬂat-bottom, gable-top) is occasionally desired for shelf display characteristics and increased ﬂat facings for graphics. Nearly any type of machinable material can be used to make a pillow-style bag, but a ﬂatbottom bag requires a relatively stiff material to hold the desired shape. The basic machine for forming ﬂat-bottom bags is essentially the same as for pillow pouches.

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2.1.4. Three-Sided, L-Sealed or Four-Sided Styles Three-sided and four-sided sealed pouches typically are made on horizontal form-ﬁll-seal (HFFS) machinery. Rather than producing a continuous longitudinal seal in the center of the ﬁlm tube as with the pillow pouch, in three-sided seals the web is folded, run horizontally and pinch-sealed at increments to produce pouches, which are ﬁlled. The upper edge is then sealed (Figure 23.2). In the four-sided seal, two rolls of supply material may be used, and heat-seal stamped one on top of the other, to produce all four sides of the ﬁnished pouch. The four-sided seal pouch is relatively uncommon in snack food applications.

2.2. BAG MATERIALS Two general types of packaging materials are suitable for VFFS machines: thermoplastic and heat-sealable materials. Polyethylenes (thermoplastics) require a special bag-sealing technique. Polyethylene ﬁlms must be heated under controlled conditions until the areas to be attached to each other are melted and fused. The operation is analogous to welding metals. Heat is applied to fuse the materials, followed by a cooling process that allows the seal to set. The sequence for making good seals requires careful control to obtain quality seal integrity. Thermoplastic materials are generally used when a high degree of barrier protection is unnecessary and low material cost is important. Polyethylene materials have some porosity and are not ideal for applications where hermetic seals are necessary for good shelf life, product freshness and gas ﬂushing. Therefore, their use in snack food applications is generally limited as bags that contain multiple smaller portions of product presealed in hermetic packages. The heat-sealable or resistance seal ﬁlm materials class includes paper, cellophane, metallic foils and some coextruded and laminated products. Because these materials do not melt at sealing temperatures, they require an accompanying laminate for heat sealing under proper conditions of temperature, pressure and time. The sealant layer can be on one or two sides of the web, depending on the desired package conﬁguration.

2.3. SPECIAL BAG FEATURES Many variations of standard pouch/bag structures are possible and can often be produced on the same packaging machine with relatively minor modiﬁcation. Some of the features include: r Hangup styles can be produced with an integrated punched hole to allow for

peg-board display.

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r Headers, or extended seal areas at the top of the bag, provide additional ﬂat,

r r r

r

graphic message space in an area that does not contain product. Also, paperboard cards can be attached to the top of the bag by separate, but integrated, header applicators. Label applicators can automatically attach preprinted labels to the pouch/bag material before, during or after ﬁlling. Leaﬂet inserters can insert leaﬂets and coupons into the bag along with product as it travels down the bagmaker’s ﬁlling tube. Recloseable pouch features provide user convenience and product preservation. These are growing in popularity with consumers. They are made by attachments that apply a separate thermoplastic zipper to the pouch material before it travels through the forming operation, and by applicators that attach a wire tie or plastic clip to the bag/pouch after it is ﬁlled. Carrying handles or special hermetic seals can be produced with special tools during the bag sealing operation.

2.4. CARTONS 2.4.1. Sleeve Style or Tube Style The carton style most commonly used in packaging snack foods is produced from a blank that has been preglued into a tube or sleeve by the carton converter or supplier, who also die-cuts and prints the package. One score along the length of the carton incorporates the manufacturer’s glue seam, while the ends of the sleeve are left open for inserting the product later. Sleeve-style blanks are typically delivered to the user in corrugated cases. This style also has been referred to as an “end-load style.” Horizontal and vertical sleeve styles are shown in Figure 23.3 and Figure 23.4, respectively.

Figure 23.3 Horizontal sleeve-style cartons.

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Figure 23.4 Vertical sleeve-style cartons.

2.4.2. Top-Load or Tray Styles Top-load cartons (Figure 23.5) are produced from ﬂat paperboard blanks that have been die-cut by a carton manufacturer or converter to produce an open tray, or a tray with an appended hinge cover. Typically, the blank is not preglued by the carton converter, and the ﬂat blanks can be stacked directly on a pallet and shipped without secondary shipping cases. Hence, top-load cartons are very economical. They also allow inserting the pouch through an opening in the largest panel of the carton, greatly simplifying the loading operation.

2.4.3. Bag-in-Box Snack foods are seldom ﬁlled directly into cartons because of the need for an hermetic environment. However, some products require the extra protection provided by putting a bag/pouch inside a carton. This is particularly true for products with greater weight and density, such as cookies and crackers, which beneﬁt from the rigid outer shell. In this application, the pouches often incorporate gussets, or tucks, on both sides to maintain a rectangular shape of the ﬁlled pouch to simplify inserting it into the carton.

Figure 23.5 Top-load carton style.

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2.4.4. Double Package Similar in function to the bag-in-box approach, the double package maker (DPM) is a system that essentially lines the carton with the ﬁlm before the product is ﬁlled. A lining feed mechanism wraps the lining around a solid mandrel prior to carton forming. In this application, the non-glued carton blank is side-seamed on the DPM. These systems generally are large, complex and dedicated to a single size. Their use for snacks is limited, and they are more common in packaging products like cereals.

3. AUTOMATED BAG AND POUCH PACKAGING Automation for packaging snack foods has evolved from the early semiautomatic systems mentioned earlier to full automation, which includes unassisted product measuring or weighing integrated with automatic bag forming and sealing. Many technological advances have occurred, including the introduction of solid state electronics, followed by PLC (programmable logic controllers) or other computer controls tied to stepper and server motors with advanced motion control. Each advancement has resulted in higher speeds and improved accuracy, which beneﬁt control of package contents, materials alignment and appearance of the ﬁnished package.

3.1. INTEGRATED PRODUCT MEASUREMENT/DISPENSING 3.1.1. Bag-Filling Factors The product determines the appropriate packaging system. Machine operation is affected by product characteristics such as dust, ﬁnes, stickiness, piece size, piece weight and product volume. All of these factors affect the end result. Often, the cycle capabilities (units per minute) of the bag machine and the product measuring system are calculated independently, without considering what happens when the product moves from the measuring system down through the tube and into the bag. Achievable production rates are based on compatibility of the three components: bag machine, ﬁller and product. VFFS machinery users should supply complete information concerning products to be packaged to enable their equipment manufacturer to factually evaluate the achievable speed, weight accuracy and efﬁciency capabilities.

3.1.2. Product Fillers Several choices of measuring/ﬁlling equipment are available.

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3.1.2.1. Gross Fill Although limited in accuracy, the simplest of ﬁlling devices utilize the actual package as the measuring device. The product supply is automatically terminated when the package is ﬁlled to a prescribed level. This method is rarely used for snack foods due to inherent speed limitations and inaccuracy.

3.1.2.2. Volumetric Fill An adjustable volumetric cup is ﬁlled to volume and then emptied into the pouch/bag. This type of ﬁller generally is used for inexpensive products where high production rates are desirable and the value of product overweight given away is less important. Volumetric systems typically are very simple in concept and therefore less expensive to purchase, operate and maintain. However, when product giveaway is considered for higher value products, the additional cost of net weight systems can be quickly recovered.

3.1.2.3. Auger Filling The auger ﬁller is next in line for accuracy. It is applicable to products that are powdery or ﬁne-grained and can be handled by a screw contained inside a tube. The accuracy is dependent on bulk density control of the product throughout the auger system as well as the cycle repeatability of the chosen auger ﬁller.

3.1.2.4. Net Weight Filling Net weight scales provide the most accurate means of ﬁlling packages. The invention and acceptance of the multiple-head computer scale system in the last 25 years have literally revolutionized product weighing. Product net can be controlled to ±1 g regardless of the size of the piece or particle being packaged. This is by far the most common method of product weighing in the snack food industry. Before the application of computers to packaging machinery, net weighers relied on mechanical counterbalance technology to dribble or ﬂow feed product to the packaging machine. Systems of this type are still available, but they generally are less accurate. They simply rely on feeding a product until a speciﬁc net weight is achieved and then shutting off the supply. Unfortunately, product sometimes is in suspension when the shutoff occurs, or product ﬂow varies causing limited accuracy. With today’s computer technology and electronics, statistically controlled (or combination) weighing is preferred by far for high-volume accurate packaging of valuable products. Statistical weighers can be divided into radial combination

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Figure 23.6 Concept drawing of radial combination weigher.

weighers (Figures 23.6, 23.7, and 23.8) and linear combination weighers (Figures 23.9 and 23.10). In both cases, the principle is that several individual scales (either conﬁgured in a circle—radial, or side-by-side—linear) are ﬁlled with a charge of product that comprises only a portion of the desired total weight for the package. A computer then continuously scans the available weights in all of the scales and calculates which scales, when combined, would most accurately match the target weight. Depending on the system, it may choose two, three or four individual scales and signal them to dump their contents into the same package. The speed of the system and the accuracy it can achieve are partially determined by the number of individual scales or weigh cells in the unit. Those

Figure 23.7 Photograph of radial combination weigher.

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Figure 23.8 The computer selects and combines charges from multiple scales to most accurately meet the desired package target weight.

with more scales give the computer more potential combinations for achieving better accuracy and are able to recover more quickly between package cycles.

3.2. FORM-FILL-SEAL BAGMAKING Form-ﬁll-seal (FFS) is the process of: (1) making a bag or pouch from ﬂexible material; (2) inserting a measured amount of product; and (3) closing the bag

Figure 23.9 Concept drawing of linear combination weigher.

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Figure 23.10 Photograph of linear combination weigher.

top. Two distinct principles are utilized in horizontal form-ﬁll-seal packaging (HFFS) and vertical form-ﬁll-seal packaging (VFFS). Again, the type of product dictates which machine category is appropriate, and the majority of snack foods are handled by the VFFS method. There have not been any major breakthroughs in weighing technology during the past several years. Advancements have mainly included development of more accurately performing load cells and introduction of digital electronics. But the bagmaker side of the industry is a different story. Recent technical advancements have been made, more than doubling the bag output possible from a single machine. While the traditional VFFS machines operated in intermittent (start/stop) motion, the new machines operate in continuous motion. This means the packaging material is being advanced during the ﬁlling and sealing portions of the cycle as well as during the forming portion. The new concept enables more efﬁcient use of the time available in a packaging cycle. As a result, it is now common to hear of single-tube machines producing ﬁlled pouches at rates approaching 200 bags per minute.

3.2.1. Horizontal Form-Fill-Seal Most snack foods packaging relies on gravity to deliver product into bags at high speeds; VFFS systems are more common than HFFS. However, snacks consisting of individual items or items packaged by count—such as snack cakes, individually wrapped cookies, and dried meat snacks—often are packaged more efﬁciently on horizontal FFS systems with integrated product indexing mechanisms. Occasionally, granular or powder-type products are preferably packaged

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Figure 23.11 Typical vertical form-ﬁll-seal system with combination weigher and bagmaker.

on horizontal systems, because the extended vertical product drop in VFFS systems can generate unacceptable product dusting.

3.2.2. Vertical Form-Fill-Seal 3.2.2.1. Overview of Machine Operation A VFFS machine (Figure 23.11) produces a ﬂexible bag from ﬂat roll stock. Material from a roll with a given web dimension (Figure 23.12) is fed through a series of rollers to a bag-forming collar/tube, where the ﬁnished bag is formed (Figure 23.13). The roller arrangement maintains minimum tension and controls the material as it passes through the machine, preventing overfeed or whipping action. This handling capability becomes more critical as linear speed of the ﬁlm increases. The bag-forming collar is a precision-engineered component that receives the ﬁlm web from the rollers and shapes the ﬁlm as it travels from a ﬂat plane around a bag-forming tube. The design of the bag-forming collar can be engineered to get the optimum efﬁciency from heavy paper laminates, metallized ﬁlms and other materials. As the wrapping material moves down around the forming tube, the ﬁlm is overlapped for either the ﬁn or lap seal. With the material wrapped

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Figure 23.12 Roll-stock holder for bag/pouch maker.

around the tube, the sealing operations start and the overlapped material, moving vertically along the bag-forming tube, is sealed. Next, the tube is pinch-sealed at predetermined increments, which are equal to the bag length. The width of the resulting bag is equal to the ﬂattened circumference dimension of the tube. After the ﬁlm advance is completed, ﬁlling and bag sealing completes the remainder of one cycle (ﬁlm advance/ﬁll/seal). Two sets of seal tooling are positioned on the front of the machine. The vertical (longitudinal or back) seam seal bar is mounted adjacent to the face of the forming tube. Its function is to seal the ﬁn or lap seal that makes the package material into a tube.

Figure 23.13 Film is fed from a roll (web) and formed around a collar into a vertical tube.

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Figure 23.14 Film transport, forming and sealing tooling on vertical bagmaker.

The other set of tooling consists of a front and rear cross-sealing bridge and jaw that produce the top and bottom seals with a bag cutoff device in between. The top-sealing portion seals the bottom of an empty bag suspended from the tube, and the bottom portion seals the top of a ﬁlled bag. The cutoff device, which can be a knife or a hot wire, operates during the jaw closing/sealing operation. This means that when the jaws open, the ﬁlled bag is released from the machine. All VFFS machines utilize this principle to make a bag (Figure 23.14).

3.2.2.2. Reciprocating Carriage Film Transport The reciprocating carriage (or draw bar) style is probably the simplest of the various methods for transporting the packaging material/ﬁlm through the VFFS packaging machine. In this method, the sealing carriage moves up and

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down vertically and literally pulls the ﬁlm through the system. The ﬁlm travels in intermittent motion. Normally, the carriage is slowed during the sealing portion of the cycle and accelerated during the return and ﬁlling portions. The advantages are the simplicity of the motion and the overall ﬂexibility of the system. This style of machine can produce small bags at moderate rates of speed or larger bags at more limited speeds. The drawbacks to the reciprocating method include: (1) limited cycle speed; (2) an increased number of moving components; (3) more difﬁcult drawdown; (4) the distance of motion; and (5) the inherent stress placed on the packaging material, which may have an adverse effect on the appearance of the ﬁnished bag.

3.2.2.3. Belt-Advance Film Transport (Figure 23.15) Several variations of belt-advance bagmakers are available for producing ﬁlled bags at high rates of speed. Some of the systems operate in intermittent motion, with the ﬁlm transport hesitating while the jaws close to seal and separate the bags. Intermittent motion often has advantages for larger bag sizes, where it is necessary to advance more ﬁlm and deliver greater product volume. Other systems operate in continuous motion, with the sealing bridge and jaws moving in a slight vertical proﬁle to synchronize with the moving ﬁlm. Through programmable drive controls, some systems can operate in either continuous or intermittent motion to take advantage of either packaging method.

Figure 23.15 Belt-advance, seam-seal and end-seal tooling on bagmaker.

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Figure 23.16 Reciprocal box proﬁle sealing jaw motion.

Continuous motion systems are most common for high-speed output and efﬁciency. Several jaw movement proﬁles for synchronized sealing and cutoff with travel of the ﬁlm material exist among continuous motion sealing methods. At today’s speeds of 3+ bags per second from a single tube, this reﬁnement can have a major impact on cycles that can be achieved and quality of the bag seals. The jaw motion proﬁles currently offered include the reciprocal box proﬁle, “D” proﬁle, rotary, and a hypocycloidal proﬁle.

3.2.2.4. Reciprocal Box Sealing Jaw Motion (Figure 23.16) The major advantage of this sealing jaw motion is the extended seal dwell length and time. Its disadvantage is the abrupt change in direction during the sealing process, which can inhibit speed and result in added machine wear and operation complexity. At least a 2 axis (X and Y) motion is required.

3.2.2.5. “D” Proﬁle Sealing Jaw Motion (Figure 23.17) The second method for high-speed sealing is the “D” proﬁle. In this method, the sealing jaws follow motions similar to the shape of two opposing Ds. The ﬂat surface of the D is where the two jaws come together to seal the bag. The rounded portion of the D is where the jaws travel back to the starting position. The jaws are controlled to match the speed of the packaging ﬁlm in producing a seal, as they move vertically down during the ﬂat part of the D. This method is fairly ﬂexible, can produce various bag sizes and can operate at higher rates of speed—usually around 120 bpm (bags per minute). The main drawback of this motion is a more complicated drive system, with potential for increased wear.

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Figure 23.17 “D” proﬁle sealing jaw motion.

3.2.2.6. Rotary Proﬁle Sealing Jaw Motion (Figure 23.18) A third method for high-speed sealing is the rotary proﬁle. This system provides the smoothest and most natural movement, but at the cost of sacriﬁcing some seal dwell time. On this type of machine, the jaws are placed on rotating mandrels that are timed to coincide with the speed of ﬁlm advance. Some machines include two sets of sealing jaws. The advantage of the twin jaw system is the potential for operating at higher packaging speeds on smaller bag sizes. Disadvantages include reduced ﬂexibility of packaging style and limitation of the design to production of small bags. Some systems are offered with an option for a single jaw design, to produce larger bags or bags that are ﬁlled with hard-to-settle products. Physical changeover is required to alternate between the single and dual jaw systems. This type of sealing may also be less

Figure 23.18 Rotary proﬁle sealing jaw motion.

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Figure 23.19 Hypocloidal proﬁle sealing jaw motion.

ﬂexible in providing effective product stripping and settling—features often considered critical for efﬁcient snack food packaging. Settling ensures that all of the product has been shaken down into the bag, and stripping clears the seal area before the jaws come together to seal the bag.

3.2.2.7. Hypocycloidal Proﬁle Sealing Jaw Motion (Figure 23.19) The hypocycloidal motion is generated by a special proﬁle based on a circle rolling within the circumference of another ﬁxed circle to produce a linear output. As such, it beneﬁts from the smoothness of a rotary motion, while still providing a linear trajectory and extended seal dwell necessary for producing high-quality seals at very high speeds (Figure 23.20). Depending on the size of the package, this method can produce up to 200 bags per minute from a single tube. The sealing motion is directly driven by a servo-motor, which in turn is controlled by a PC or PLC, to allow programmable reﬁnements in the jaw’s motion to suit speciﬁc product applications.

3.2.3. Integrated VFFS Functions 3.2.3.1. Product Settling Product settlers ensure that all of the product is down in the bag and that there is room available to seal the package. This way, when the sealing jaws close they only seal the ﬁlm and not the product.

3.2.3.2. Product Stripping Stripping mechanisms, sometimes known as “product milkers,” actually clean the seal area prior to bag sealing. Both stripping and settling can contribute

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Figure 23.20 Modern high-speed continuous motion bagmaker.

signiﬁcantly to operating efﬁciencies and package integrity, especially when ﬁlling potato chips or other snack products (Figure 23.21).

3.2.3.3. Gusset Forming Some systems are speciﬁcally designed to produce gusseted ﬂat-bottom bags. These basically use the same principles of motion as the pillow-pouch systems, but include additional gusset and bag-forming mechanisms. As a rule, the additional functions result in reduced speed capabilities. Other systems are available to make either standard pillow-pouch packages or block-bottom styles on the same machine, to provide added ﬂexibility and offer the advantages of both.

3.2.3.4. Other Attachments Many other attachments can be incorporated into the design of the form-ﬁllseal system to suit individual production, product and marketing requirements (Figure 23.22). Some of those frequently included are: —Date coding—on the ﬁlm feed/transport system —Metal detection—above the product ﬁlling tube of the bagmaker —Gas ﬂushing—on the bagmaker ﬁlling tube —Seasoning applicators—on the product infeed system —Reclosure applicators—during the ﬁlm feeding or forming sequence —Product delivery and bucket elevators —Packaging system support structures and mezzanines

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Figure 23.21 Bag-forming, ﬁlling, stripping and sealing sequence.

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Figure 23.22 Mezzanines and support structures can be incorporated with the design of many form-ﬁll-seal systems for easy access.

Some of the major VFFS equipment suppliers to the United States market are Accu-Pak, Robert Bosch Corp., Eagle Packaging, Formost Packaging Machines, Hayssen Inc., Heat and Coufrol, Inc., Package Machinery Company, Rovema Packaging Machines, Inc., Sandlacre Packaging Machinery, Sasib Corp., Thiele Technologies, Triangle Package Machinery Company and The Woodman Company.

4. CARTONING Two basic types of cartoning machines exist: semiautomatic and fully automatic. By deﬁnition, in a semiautomatic machine the operator manually places the bag or pouch containing product into the carton. A fully automatic cartoner is a machine that loads the product into the carton even though an operator may place the product in a bucket or ﬂight of the infeed conveyor. Both types are available in horizontal sleeve style (Figure 23.23), vertical sleeve and toploading models.

4.1. HORIZONTAL END-LOAD CARTONERS 4.1.1. Semiautomatic Horizontal Cartoners The semiautomatic horizontal cartoner (Figure 23.24) carries the carton through the machine lying on its back panel. Because the product is inserted into the carton manually, it is classiﬁed as semiautomatic. In some models the carton

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Figure 23.23 Horizontal sleeve-style carton components.

conveyor is arranged in such a way that the carton is inclined downward away from the operator, enabling the product to be loaded more easily, that is, just slid into the carton with the assistance of gravity. The semiautomatic horizontal machine can be equipped with many different attachments, code impressers, printers and hot-melt adhesive systems.

4.1.2. Fully Automatic Horizontal Cartoners In general, this type of packaging machine (Figure 23.25) consists of a product infeed conveyor, carton feeder, carton conveyor, loading mechanism and closing system. Fully automatic machines can operate at speeds from 50 packages per minute to well over 600 packages per minute for certain items, although most snack food applications are designed to operate in the range of 100–200.

Figure 23.24 Semiautomatic horizontal cartoner.

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Figure 23.25 Fully automatic horizontal cartoner.

This type of cartoner has the advantage that all operations are automatic; that is, no operators are required to put the product into the carton. Each component is critical to the efﬁcient operation of the machine, but probably the most important is the carton feeder.

4.1.2.1. Carton Feeding Many types of feeders are used on cartoning machines, and the selection is dependent on the speed of operation and the size of the carton to be handled. The basic feeder concept for sleeve-style cartons consists of a magazine to hold a supply of unexpanded cartons, a gate or tabbing frame, which dispenses the ﬁrst carton and retains the balance of the stack, and a vacuum head(s) to place the open carton into a conveyor (Figure 23.26). The magazine can be vertical, horizontal, or inclined. In most cases, the cartons are retained in the magazine by tabbing and must be pulled free from the stack before expansion can start. A vacuum feeder arm pulls the carton from the magazine and opens it as it is delivered between the carton conveyor chains. As the vacuum is released, the carton is transferred into the conveyor ﬂights, and erection of the carton is completed as the trailing lugs travel around the head sprocket to a vertical position, capturing the opened carton. The ﬂaps on the loading side of the carton are usually guided outward to create a funnel for loading the carton. On some systems, opening of the sleeve is assisted by incorporating both top and bottom vacuum heads to positively pull the carton open. Rotary carton feeders are used extensively for high-speed operation to reduce or eliminate any reciprocal motion, which can reduce speeds and increase wear. In some instances, an air assist can be used to enhance carton opening. The carton is carried past air manifolds, which pass a high volume of air at low pressure into the carton and expand it completely while still in the transport chain conveyor.

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Figure 23.26 Rotary carton feeder pulls preglued sleeves from a hopper and deposits them onto the conveyor.

4.1.2.2. Side Seam Gluing Most cartoning machines in operation handle tubular cartons with a side seam or manufacturer’s joint preglued on high-speed in-line gluers at the carton manufacturer’s plant. The carton must be carefully packed on edge in corrugated cases by the manufacturer. If cartons are packed too tightly, they tend to lose their prebreak or become warped. Preglued cartons can also lose their prebreak or score ﬂexibility if stored for extended periods in the shipping container, developing a set that makes them more difﬁcult to open efﬁciently on the cartoning machine. As an alternative, many cartoners can be equipped to handle ﬂat, unglued carton blanks with the addition of on-machine side seam gluing. A separate gluing machine located on the cartoner can feed ﬂat blanks from a magazine, break the scores, apply hot melt adhesive to the side seam, compress the carton joint and discharge the carton into the magazine of a conventional cartoning machine. Another type of horizontal cartoner is the wraparound style, which feeds a ﬂat carton blank from a magazine, forms it and glues the seam around a three-sided mandrel carrying the product. The ﬁlled and formed carton is then transferred to a second conveyor where the ends of the carton are closed.

4.1.2.3. Product Infeed Various methods are available for automatically indexing product into the infeed of horizontal cartoners, such as overhead sweeps, “smart-belt” transfers, cross-collators and others. These are described in more detail in later discussions on bag-in-box packaging. Naturally, product can also be manually indexed into the infeed ﬂights of the automatic cartoner, but such operations essentially

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defeat the advantages of having a fully automatic cartoner compared to a semiautomatic system where product is hand-inserted directly into the carton.

4.1.2.4. Carton Loading The conventional equipment for loading cartons on a fully automatic horizontal cartoner consists of a barrel cam inserter running in synchronization with the speed of the carton conveyor (Figure 23.27). A series of sliding inserter arms are fastened to parallel chains on the inserter, with the same pitch as the carton conveyor. A cam follower/roller on each inserter arm rides against a ﬁxed cam to provide smooth transfer of product from the product infeed bucket into the carton.

4.1.2.5. Carton Closing Final carton closing can be accomplished by locking/tucking, adhesive gluing, or heat sealing the end ﬂaps of the sleeve. For practical purposes, the only method used in snack food packaging is the glue-sealing method, since tucking fails to provide the hermetic qualities necessary, and heat-sealing requires a thermoplastic carton coating, which adds to carton cost. Such coatings are generally reserved for packaging frozen foods or similar products, where their primary purpose is to provide paperboard moisture resistance and barrier properties.

4.1.2.6. Gluing A glue-closed carton may be sealed with single or double gluing. When single gluing, the two major end ﬂaps are glued together (see Figure 23.23). When double gluing, the inner major ﬂap is glued to the minor ﬂaps, and then the outer major ﬂap is glued to the inner major ﬂap. Single gluing results in a slight crack between the glued end ﬂaps and the folded side ﬂaps. This may be acceptable for internally contained products, while cartons for other products, such as exposed food, may require double gluing to protect the contents. Hot-melt adhesive can be applied by nozzles/guns, intaglio rollers, or open wheels. The glue gun can apply a strip of glue, an interrupted strip, multiple lines, or dots. A separate gun is required for each end of the carton, although only one remote glue reservoir is needed. Intaglio rollers or notched wheels can apply glue in similar patterns, but have the disadvantage of requiring a glue reservoir that is adjacent to the application wheel in an area of the machine where space and accessibility are limited.

4.1.2.7. Microprocessors Centralized microprocessors are frequently used to control and monitor the operation of cartoning machines. Encoders, working with programmable limit

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Figure 23.27 Typical automatic product loading on horizontal cartoners.

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switches, have greatly simpliﬁed operation, setup, changeover and maintenance procedures. They have replaced many electromechanical sequencers and shaftdriven cams that were previously common. Programmable devices can be adjusted remotely, set up and changed very quickly, provide better resolution, have better repeatability and generally operate at higher speeds.

4.2. SEMIAUTOMATIC VERTICAL (SLEEVE STYLE) CARTONERS The semiautomatic vertical cartoner is arranged so that the tubular carton is fed from a horizontal magazine and opened and transferred into the carton conveyor, standing on end. The bottom of the carton is closed by tucking or gluing and conveyed past one or more operators, who manually place the product in the carton. The machine then closes the top of the carton. The semiautomatic vertical cartoner is usually used for products with low production volume, where changeover to another size is frequent. It is also well suited for packages containing a variety of different items. Common operating speed is up to 120 packages per minute, although many machines of this type operate at much slower rates because of the need to place the product manually into the moving carton. The semiautomatic cartoner can be equipped with a number of attachments such as leaﬂet-feeding mechanisms or code imprinters for printing lot numbers, expiration dates, or prices.

4.3. ON-SITE TOP-LOAD CARTONING MACHINERY 4.3.1. Carton Forming The heart of any top-load packaging operation is the carton-forming machine (Figure 23.28). Although various conﬁgurations exist, the most common is a vertical system that provides overhanging delivery to outfeed conveyors or packing conveyors. Generally, these forming systems incorporate an inclined, gravity-advance magazine or powered horizontal hopper from which individual die-cut blanks are fed. Carton blanks are retained by small projections or tabs that extend slightly from the sides of a gate frame at the front of the magazine. Vacuum cups, mounted on a reciprocating feed bar, pull the individual carton blanks from the magazine and transport them in a downward arc. As vacuum is released, they are deposited in a registered position on top of a forming cavity. The carton blank is rotated from vertical to a horizontal plane during this feed cycle, with the vacuum cups contacting its inside surface. As the feed bar moves upward to feed the next blank, a plunger or mandrel moves downward to force the blank through the forming cavity. The plunger is designed so that the carton body conforms to its shape. The carton is folded, guided and manipulated by a series of metal or composite plastic ﬁngers and plows installed within the

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Figure 23.28 Top-load carton-forming machine.

forming cavity. As the plunger completes each forming stroke and begins moving upward, spring-loaded mechanical traps retain the carton and strip it or remove it from the plunger. In some cases, special carton coatings, shapes, or speeds require the use of a timed air blast system to positively eject the carton onto takeaway conveyors. Removable tooling is commonly referred to as a “forming head” (Figure 23.29). The forming head consists of (1) the forming cavity, (2) a plunger or mandrel, and (3) various components for the hopper or magazine. This tooling is portable and can be interchanged between forming machines to make different carton styles, shapes, and sizes within a speciﬁed size range, on different packaging lines. The carton body can be formed utilizing locks, adhesive, or heat sealing.

4.3.2. Carton Conveying After forming, the top-load carton is typically carried on a conveyor for loading either manually or automatically. For slow-to-moderate-speed hand packing, simple ﬂat-belt or plastic tabletop chain conveyors are frequently employed

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Figure 23.29 Carton-forming head or tooling.

and offer the most economical approach. One end of the conveyor generally is placed below the forming cavity and is independently driven with no electrical or mechanical connection between the conveyor and the forming machine. After forming, trays or cartons drop onto the conveyor and are carried downstream for product loading. The alternative to this method is a conveyor with chain ﬂights or lugs. Generally, ﬂighted conveyors are either attached to and mechanically driven by the forming machine or electronically synchronized through the use of intelligently controlled independent drive motors. Flighted conveyors offer the advantage of pacing the operators, because they are not able to individually retard cartons for loading as they can on a ﬂat belt. Flighted systems are required to achieve adequate carton control in any high-speed operation. They also allow the carton cover to be controlled during the packing operation by either maintaining a vertical position or folding it back almost 180◦ to permit loading from either side of the conveyor. Packing conveyors should be designed so that the bottom of the carton is approximately 30–34 in. (76–86 cm) from the ﬂoor. This helps optimize the efﬁciency of operators who are placing product into the cartons by hand.

4.3.3. Manual Product Loading The ﬁlled pouch or bag can be presented to the operator in many different ways in hand-pack operations. The most efﬁcient method involves bringing the

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Figure 23.30 Hand-loading product on a top-load cartoning line.

product in on a ﬂat belt or tabletop chain that runs parallel and adjacent to carton ﬂow. The bottom of the product should be elevated just slightly above the top of the carton to allow for simple sweep loading into the largest opening of the carton (Figure 23.30).

4.3.4. Automatic Product Loading Automatic loading of products into top-load cartons can be accomplished using many different standard and/or highly customized systems (Figure 23.31). Free-ﬂowing products can often be ﬁlled automatically using a volumetric system or net weight ﬁlling; however, most snack food applications require that the product be precontained in a bag or other package that is airtight. In this case, a variety of automatic product indexers or other types of transfers can be used. This includes special smart-belt indexers or sweeps much like those used for horizontal cartoning, or, special robotic systems and vacuum transfer systems, which physically lift the product from an infeed conveyor and place it into the formed carton as it travels on an intermittent or continuous motion conveyor.

4.3.5. Carton Closing Carton closing is the ﬁnal major function when hinge-cover designs are used in any top-load cartoning application. Carton closers generally are ﬂighted

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Figure 23.31 Automatic pick-and-place carton loading.

or lugless (Figure 23.32) models. On ﬂighted systems, actuation and sealing functions are timed according to predeﬁned spacing between conveyor ﬂights. On lugless systems, intelligently controlled motors and other functions react to the presence and position of a carton, as it is photo-electrically sensed on conveyor belts. In broad terms, ﬂighted systems generally provide a higher degree of carton control, while lugless systems offer greater speed, ﬂexibility and ease of maintenance. The ﬂighted closing machine is usually an independent unit with its own drive motor for slow to moderately high-speed ﬂighted operations. It is equipped with a special infeed assembly that accepts cartons at random from an upstream packing conveyor and automatically times them into the ﬂights of the closing machine. When ﬂighted systems are required to operate at high speeds (>200 cartons per minute), it is desirable to eliminate the infeed section and drive the entire packaging line from the carton forming machine. The need to retime cartons into the closer at high speeds is eliminated. This line-driven method requires use of a ﬂighted packing conveyor and ensures that positive carton control is maintained throughout. Inherently, lugless systems are independent as opposed to line-driven. Cartons are received at random and conveyed with sequential belts that have special surface traction characteristics. Both overhead and underlying conveyor

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Figure 23.32 Lugless top-load carton-closing machine.

belts may be employed to maximize control. Each sequence of the operation is powered by its own individual, intelligently controlled, drive motor so speeds and relationships between various machine functions can be readily adjusted through program controls. This allows a much greater degree of ﬂexibility and ﬁne-tuning without need for physical changeover and tool adjustments.

4.3.6. Tri-Seal Style Closure The hinge-cover carton design most frequently used is the triple-seal (tri-seal) style, also called the “three-ﬂap” or “charlotte” style. It is so named because the cover has three ﬂaps that are bonded to the body of the carton for closing.

4.4. BAG-IN-BOX 4.4.1. Concept Most snack foods are contained exclusively in a pouch/bag, or less frequently in a paperboard carton. But as mentioned in the description of package styles, heavier, high-density products require a combination of two—the added protection of an outer carton for the individual retail package. Although the technically accurate terminology is “a pillow pouch inside a carton,” the industry commonly refers to the concept as “bag-in-box.” The “box” should not be confused with corrugated “cases” that are commonly used for transportation and distribution of multiple retail packages. To obtain fully automated bag-in-box production, multiple VFFS machines can be integrated to automatically feed bags directly to the cartoner infeed (Figure 23.33). Bags are dropped onto an incline conveyor and may be

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Figure 23.33 Integrated bag-in-box operation.

conditioned while on the conveyor to distribute the product within the bag. The inclined conveyor carries them to a sweep-arm transfer device for placement into a continuously moving bucket conveyor. The VFFS machines are electrically synchronized with the cartoner, and the transfer device is mechanically driven by the bucket conveyor. An overhead paddle, driven in time with the buckets, sweeps each bag into ﬂights. At the loading position of the cartoner, the bags may be conﬁned within the carton dimensions by an overhead conveyor. To obtain high speeds, two or more form-ﬁll-seal machines may be used to feed one cartoner. The bag-in-box concept began with reﬁnement of vertical form-ﬁll-seal (VFFS) machinery. Packaging machinery manufacturers and users saw an alternative to the double package maker by coupling a horizontal cartoner with VFFS equipment. The idea of automatically end-loading a sealed bag of product into a carton includes the following important advantages compared to lined cartons: r r r r

Simplicity—fewer less complicated motions Flexibility—easier and faster size changes Higher Speeds—up to 200 packages per minute Lower Package Cost—higher speeds and lower priced machinery

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r Improved Package Integrity—bags are hermetically sealed using heat-seal

jaw

r Reduced Personnel—one operator can run the line r Less Floor Space—more compact integrated design r Wider Choice of Packaging Materials—unsupported as well as supported

ﬁlms

4.4.2. Vertical Bag-in-Box A vertical load concept offers a way of overcoming some bag insertion problems, because it relies on simple gravity and special bag-shaping techniques to drop the bag directly into the carton. The upright carton is then conveyed and indexed to position it squarely under the VFFS rectangular forming tube. The bag-forming parts produce a true ﬂat-bottom bag. The ﬁlled bag slips freely into the box. The bag cutoff is determined by product ﬁll level and, if necessary, can be made so that the top seal protrudes over the carton score line when fully seated in the box. The bag is then tucked into the carton and is indexed through a top sealer where hot-melt glue is applied to the ﬂaps. This packaging system is generally limited to speeds up to 100 cartons per minute.

5. CASE PACKING Regardless of style of the individual retail packages, multiples typically are put in cases for transportation and distribution to the retail outlet. The cases are generally constructed of corrugated cardboard, for either non-returnable or returnable use. In some applications, returnable plastic totes or trays are also used for shipping and distribution.

5.1. MANUAL PACKOFF SYSTEMS Because most snack food operations involve: (1) a product that is somewhat fragile; (2) irregularly shaped packages (bags); (3) manageable speeds; and (4) a need for ﬁnal package inspection, manual case loading often is the most straightforward and cost-effective approach (Figure 23.34). Automatic case loading may become justiﬁed when applications reach higher volumes of output, or can be dedicated to longer runs of speciﬁc package sizes and product characteristics.

5.2. AUTOMATIC CASE PACKING Several systems are available to automatically accept the output of VFFS bagmakers or cartoning systems and organize and group the individual packages

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Figure 23.34 Manual packoff from rotary table.

for loading into cases (Figure 23.35). The infeeds of these systems often utilize various forms of cross-collating or product shuttling in order to produce the correct case count and conﬁguration. The automatic case packer normally also erects the cases and seals them with glue or tape following loading. More often than not, the primary snack food package is a bag. To provide adequate product protection, these must be loaded into cases vertically (standing on end), rather than on their side, because product crushing otherwise results.

Figure 23.35 Automatic case-loading system.

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The ballooning effect of the pouch, described earlier, also helps protect the product, provided the pouches are not case-packed too tightly.

6. IMPROVING EFFICIENCY AND FUTURE CONSIDERATIONS For many producers, the ﬁrst few percentage point gains in packaging efﬁciency can be achieved simply by taking a good look at what is happening in the packaging room. If inferior bags are being made, or packaging material wasted, the supervisor should ﬁnd what the problem is and identify the best solution to minimize the waste. Some packaging rooms average between 0.5% to 15% waste or more in packaging materials alone. If each machine produces around 60 bags per minute for only one shift per day, ﬁve days per week, and material cost is U.S.$0.015 per unit, savings could approach nearly U.S.$350 per week per machine. It is easy to recognize the advantage a manufacturer operating at 99% efﬁciency has over another operating at 70% efﬁciency. Most packaging material waste is due to leaking or open seals, product seal contamination, distorted or crooked bags, or machine set up and changeover. These problems can be corrected simply by ensuring the equipment is in good operating condition and the operators know how to correctly set up and run the machine. It may be worth the expense of having a technician from the equipment manufacturer visit the facility, ensure the machines are working properly and provide additional training for the operators, if needed. Some producers are trying to increase operating efﬁciencies by using higherspeed packaging equipment. This allows them to produce more units for sale within a shorter period of time, thus realizing a faster payback on their investment. As another beneﬁt, they potentially do not have to invest in as many moderate speed machines for the required output nor have as many operators to run the machines. Other additional savings can be realized from having fewer machines. For example: (1) less time would be spent on cleaning and maintenance; (2) a smaller spare parts inventory would be required; (3) factory ﬂoor space would be released for other uses; and (4) generally, the overall costs of operating fewer machines would be lower. While true in most cases, some potential problems also go along with high-speed packaging. By nature, highspeed packaging machines are more technologically complex than standard machines and learning how to operate and maintain them can be more difﬁcult. Besides the advent of high-speed packaging machines, other technologies also have progressed to the forefront of packaging technology. New advancements include: automatic lubrication systems, web tracking systems, ﬁlm splice systems and machine timing features. Also, some systems identify certain machine or operational problems to the operator and recommend quick solutions for solving them. All these features are part of the effort to improve packaging

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efﬁciencies and provide snack food manufacturers with the most cost-effective solutions to their packaging needs. It can be beneﬁcial to select suppliers who offer an extended warranty as part of their proposal. Longer warranties typically imply higher quality and lower operating costs over time. High-quality machinery can help increase packaging efﬁciency by being more reliable and reducing downtime. Although many considerations are involved in selecting high-speed packaging machines, they deﬁnitely are the wave of the future. Usually, time, effort and money to improve packaging efﬁciency are well spent and make the operation more proﬁtable and stronger in its competitive position.

7. SUGGESTED READING 1. Brody A. L. and Marsh, K. S., 1997. The Wiley Encyclopedia of Packaging Technology. 2nd edition John Wiley, New York. 2. Bureau, G., ed., 1996. Food Packaging Technology, Vols. I and II. John Wiley, New York. 3. Hanlon, J. F., R. J. Kelsey, and H. E. Forcino, 1998. Handbook of Packaging Engineering. 3rd edition. Technomic Publishing Company, Lancaster, Pennsylvania. 4. Paine, F. A., ed., 1991. The Packaging User’s Handbook. Avi-Van Nostrand Reinhold, New York. 5. Sorka, W. G., 1998. Fundamentals of Packaging Technology. 2nd edition. Technomic Publishing Co., Lancaster, Pennsylvania. 6. Stewart, B., 1994. Packaging Design Strategy. Technomic Publishing Co., Lancaster, Pennsylvania.

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CHAPTER 24

Evaluation Methods and Quality Control for Snacks RALPH D. WANISKA

1. INTRODUCTION

C

demand safe, reliable, high-quality products at reasonable prices; they remember and continue to buy products with consistent high quality and perceived value. It is necessary that each company, no matter how small or large, implement a reliable quality assurance program. Moreover, the plan must be championed and explained by supervisors to gain the enthusiastic support of all employees. The quality assurance (QA) program makes money for a company because it provides essential management tools for dealing with critical problems that may arise, such as food safety and product consistency issues. Everyone, from top management to the lowest paid employee, must buy into and enthusiastically support the program. Training of personnel and continuous attention to all aspects of the QA program must become part of the company’s philosophy. This chapter brieﬂy reviews QA and quality control (QC) practices directed at producing safe products with consistent attributes under sanitary conditions. The purpose of this chapter is to provide essential information to enable initiation of QA/QC programs by manufacturers. A brief presentation on selected procedures, examples of how to implement QA/QC programs for making snacks and sources of information about programs are included. Gould [1–3] also provides useful QA/QC information and detailed suggested procedures for snack companies. ONSUMERS

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1.1. WHAT IS QUALITY? The major issues of quality often are divided into legal, safety and product characteristics. A functioning QA/QC program must intentionally comply with federal, state and local regulations. Next, a functioning QA/QC program must ensure product safety. Then, consistency of snack attributes deﬁnes product quality. Quality, in the eye of the customer, is the sum total of all attributes that make a product highly acceptable. It includes safety and wholesomeness, as well as physical, textural, chemical and organoleptic properties. Color, size, shape, appearance, crunchiness, oil and moisture content, and freedom from pesticides, mycotoxins and other potentially hazardous materials are involved and must be veriﬁed and controlled. Products must be clearly deﬁned in terms of measurable attributes. The research and development section of the company establishes the snack’s attributes. This enables manufacturers to vary costs of processing, ingredients, packaging, distribution and other inputs to provide snacks that meet these goals. Snacks with better quality sell because consumers repetitively buy brands they trust to deliver value and consistent attributes. Each company needs to determine and produce what is meaningful to its customers, and to have enough technical information and experience to produce snacks with the desired product characteristics consistently. Every product has potential for variances in attributes due to differences in ingredients, equipment (type, set points and maintenance), personnel, shift, season and location. An effective QC program ensures the production of snacks with qualities that fall within acceptable ranges, in spite of the variability in ingredients, processes and other changes. The range of acceptable attributes or quality standards varies with products and with customers, i.e., individual consumers, restaurants, franchise stores, and institutions.

2. QUALITY PROGRAMS Good manufacturing practices (GMP) are the basis of all QA/QC programs for producing legal and safe products. GMP refers to federal law (21 Code of Federal Regulations part 110) that is general in nature, but applies to all food categories. Personal hygiene, sanitation, design of facilities, food processing conditions and practices, storage conditions and pest control are included in GMPs. Gould [1–3] has written several useful books for snack and potato chip manufacturers on GMPs, the inspection process and quality control. Recently, GMPs have been supplemented with the hazard analysis critical control points (HACCP) program to increase the margin of safety in foods through deﬁnitive guidelines.

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2.1. HAZARD ANALYSIS CRITICAL CONTROL POINTS (HACCP) Companies in the United States are using HACCP programs to help ensure snacks are safe. Microbiological, chemical and physical hazards are the concerns of HACCP [4]. Purity of food ingredients, accurate formulation and presence of regulated chemicals and toxins within legal limits are the primary concerns in the chemical area. Removal of foreign material (rocks, metal, glass, plastic) from ingredients and processed foods is the primary concerns in the physical area. Most public attention, however, has been on the presence of pathogenic bacteria and mycotoxins. Each processing step with a potential of compromising food safety is considered hazardous and identiﬁed as a critical control point (CCP). The precautions and necessary equipment and operating parameters are deﬁned for each CCP to ensure food safety and then monitored to ensure the processes stay within acceptable range. For example, process parameters (time, temperature, moisture loss and others) need to be monitored and controlled in many primary snack processes (oven, fryer, extruder) (left side, Figure 24.1). Records must be maintained as part of the HACCP program including: CCP processing parameters, codes for all ingredients, disposition of ingredients during snack production, codes for all snacks and distribution of the snacks. Veriﬁcation is the third part of the HACCP program. Processing equipment, analytical procedures and measuring instruments are periodically checked to ensure they are working properly. Suppliers must develop their respective HACCP programs to ensure the delivered ingredients are safe before acceptance. The worst possible scenario for a QA program is a product recall [5]; a company must have a clearly written plan to deal with it. The records of a wellmanaged HACCP program are essential in a product recall. Keeping track of codes of raw materials, product codes and product distributions does this. How people respond in a crisis can be modiﬁed by training; they should be identiﬁed and trained as a crisis team, ready if needed. Only trained people should speak to the press, public and others seeking authoritative information. With an established, credible QA program, time is used wisely during a recall and consumers’ and authority’s fears are reduced. The QA program cost is always smaller than costs of losing consumer loyalty, the recall itself and associated litigation.

2.2. QUALITY ASSURANCE AND QUALITY CONTROL Before a company establishes a quality program, it must: (1) establish a corporate quality policy statement; (2) identify the legal obligations that must be met, whether or not previously realized by persons outside of corporate

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Figure 24.1 A minimal implementation of evaluation methods to address safety (hazard) and quality issues during processing of snack foods. Note: Processes with an asterisk (*) are critical control points (CCP) because they impact the safety of products.

management; and (3) ensure that mechanisms exist for dealing with these needs, as well as with product uniformity. The components of a QA program are evaluation, control and audit [5]. Evaluation includes methods to characterize ingredients, intermediate products, packaging materials and ﬁnal products. This information is provided to an “empowered corrector” to adjust equipment and

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other parameters to obtain desired product attributes. Audit is the process of verifying that purchasing, production and QC procedures are written, followed and updated to reﬂect what actually is being done. Data from QC programs are utilized to adjust or control processing equipment to produce consistent snacks. Three elements must be deﬁned and implemented to control a process and maintain desired product attributes. First, methods that yield numerical values are utilized to establish target values and a range of acceptable deviations for each method. Second, experienced personnel are needed to monitor and communicate the generated data to an empowered corrector, who, third, can restore the process to make products with acceptable attributes. These three elements need to be clearly deﬁned for each parameter being controlled. Many programs (Table 24.1) have been developed to assist companies in organizing, implementing and managing QA/QC programs [5–7]. The basics of GMPs, HACCP and quality methods are conducted in each program, but how companies involve their employees to improve company operations vary. Many industry-selected programs enhance quality of products and services, production efﬁciency, and organization and motivation of employees. International standards for QC are contained in the ISO 9000 program. It includes design, development, production, installation, servicing (9001, 9002), QC in ﬁnal inspection and testing (9003) and guidelines for quality improvement (9004). Environmental management issues are addressed in the ISO 14000 program. Each quality program in Table 24.1 varies in perspective and goals and must be modiﬁed during implementation depending on people, culture, region, facilities, products, competition, distribution and legal issues. Each quality program should improve company operations to increase consistency of products and services delivered. The Deming philosophy, Total Quality Management, and the Taguchi system have been popular quality programs during the last two decades because each has improved quality of products and company proﬁtability. QA programs are the basis for domestic and international commerce [5]. A QA program determines whether standards are being met and acts to prevent problems from occurring by controlling incoming ingredients and processes. It prescribes how the product will be produced, and the essential tests that must be conducted to monitor quality of the product to ensure that it meets manufacturing speciﬁcations. A QC program must conduct evaluation methods, use relevant information to control the processes and facilitate communication between production, management and consumers. Manufacturers usually choose suppliers on the strength of their QC programs and ability to achieve compliance with speciﬁcations. Sampling and spot checks then are done to ensure compliance.

2.3. QUALIFICATIONS OF PERSONNEL IN QA/QC Prompt decisions to ensure product safety and quality, even when it reduces production or results in loss of substandard products, exhibit a company’s

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TABLE 24.1.

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Brief Summary of Popular Quality Assurance Programs Compiled from Reference [6].

Name Continual Improvement

Deming Philosophy ISO 9000 standards

Just-in-Time

Kaizen Teams Kanban; Pull System Quality Circles

Six-Sigma Quality Statistical Process Control Taguchi System

Total Quality Management Zero Defects

Some Characteristic Properties The ongoing improvement of products, services, or processes through incremental and breakthrough improvements. 14 management practices to help companies increase their quality and productivity. A set of five individual but related international standards on quality management and quality assurance developed to help companies effectively document the elements to be implemented to maintain an efficient quality system. An optimal materials requirement planning system for a manufacturing process in which little or no manufacturing material inventory is kept on hand at the manufacturing site, and little or no incoming inspection is done. Gradual improvement by doing little things better and setting and achieving increasingly higher standards. A scheduling signal, which directs supplier product replenishment based on customer usage. Voluntary work groups that meet regularly to discuss how to improve the quality of the products and work processes. A well-controlled process, i.e., ±6 standard deviations from the mean in a control chart. Application of statistical techniques to control a process. An engineering approach that includes off-line quality control, on-line quality control and a system of experimental design to improve quality and reduce costs. A management approach to long-term success through customer satisfaction. A process where people can move closer to the goal of zero defects by committing to watching details and avoiding errors.

desire to have an effective QA/QC program. QA/QC should answer directly to top management instead of the production manager, who is more concerned about efﬁciency goals and achieving yields. People working in QC must have the necessary skills to conduct the activities, monitor the products and data generated and communicate information to an empowered corrector and to management. They need to have technical skills to conduct evaluation methods and to handle and store hazardous substances. They must exercise integrity in keeping records, charting changes in processing, handling substandard lots and

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maintaining an internal laboratory QC program. Good interpersonal relations, and ability to communicate the reasons behind their actions while conducting their essential role in the operation, are also extremely valuable skills. Outstanding personnel must be hired and retrained to perform these critical activities because an effective QA/QC program saves money and provides the basis for customer loyalty. Personnel in QA/QC, as in other parts of the company, require continuous support and training to discharge their responsibilities.

3. EVALUATION METHODS Snack companies use many methods to evaluate ingredient functionality, process control and product attributes and safety. These methods (Table 24.2) are classiﬁed into subjective, analytical, or functional methods. Subjective methods are conducted by one or more persons using sensory (sight, taste, smell, or touch) procedures to assess product attributes. These people may compare their evaluations of snack properties to reference standards or photos to determine whether attributes meet established quality criteria (Chapter 21). Analytical methods provide numerical information about chemical, physical, microbiological and toxicological attributes that are listed in ingredients speciﬁcations, manufacturing and quality control manuals and product label guarantees. Moisture, oil and salt contents of snacks are attributes determined by analytical methods. The frequency of analyzing for microbiological contaminants [8], pesticides, herbicides and mycotoxins depends on the ingredient and the process. An increasing number of ingredients are certiﬁed by suppliers, with spot checks conducted by a commercial laboratory to conﬁrm the analytical results. Functionality of ingredients, i.e., water absorption and dough viscosity, should be certiﬁed in the same fashion. For small operations, the in-plant laboratory should concentrate on the essential tests while other analyses may be done more effectively by reliable commercial laboratories. The essential tests include moisture, oil, free fatty acid (FFA) content in oil, levels of salt or seasonings, package ﬁll weights, shelf life, and organoleptic properties such as appearance, texture and taste. Products are also typically evaluated for burnt, off-color, pillow form, oily and other potential defects. These tests can be conducted quickly by skilled individuals and provide information for controlling the process. Speciﬁc examples of procedures to follow are outlined later.

3.1. SAMPLING FREQUENCY Most ingredients are evaluated upon arrival; hence, quick tests like moisture, particle-size distribution and subjective evaluations (visual and aroma) are appropriate. Some processes demand real-time monitoring, i.e., extruder screw

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Useful Methods for Evaluating Ingredients During Receiving, Intermediate Products During Processing and Quality Attributes of Snacks. Description

Source—Number

Skill

Cost

Type

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TABLE 24.2.

Receiving: Ingredients and Packaging Aroma, color, uniformity

Physical

Pasting viscosity, pasting temperature Density, particle size Moisture: Moisture balance Moisture: Near-infrared (NIR) analyzer Pesticides, chemical adulterants Mold and bacteria plate counts Aflatoxin, fumonisin Aflatoxin, fumonisin (quick tests) Metal, glass, plastic, stones Contamination, structure, composition

Chemical Toxicology

Hazard Microscope

Chapter 21, Company developed method. Company-developed methods Company-developed methods Company-selected instrument Company-selected instrument AOAC, Many methods AOAC, 990.12, 966.23, 997.02 AOAC, 993.16, 993.17, 995.15 Company-selected kits Company-selected instruments Company-developed methods

Low

Low

Subjective

Moderate Low Low Moderate Moderate Low Moderate Moderate Low Moderate

Moderate Low Low Moderate High Moderate High High Low Moderate

Functional Analytical Analytical Analytical Analytical Analytical Analytical Analytical Analytical Subjective

Company-selected instruments Chapter 21, company-developed methods Company-developed method Company-selected instruments Company-selected instrument Company-selected instrument

Moderate Moderate

Low Moderate

Analytical Subjective

Low Low Low Moderate

Low Low Low Moderate

Functional Analytical Analytical Analytical

AOAC, 925.09, 935.29C, 981.11

High

Moderate

Analytical

Processing Parameters and Intermediate Products Parameters Sensory

Temperature, time, pressure Color, taste, pillows, uniformity, friability

Physical

Bostwick viscometer Size, weight, thickness, density Moisture: Moisture balances Moisture: Near-infrared (NIR) analyzer Moisture: Drying ovens (vacuum, atmospheric)

Chemical

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Category

Chemical Oil: Oil: Oil: Oil: Oil: Oil: Oil: Salt: Salt: Moisture: Moisture: Moisture:

Source—Number

Skill

Consumer panel (color, taste, texture, friability) Expert panel (color, taste, texture, friability) Package weight; weight/piece, size, thickness color Firmness, breakage, air bubble size Density (weight/unit volume) Package fill; seal integrity

Chapter 21, Company-developed methods Chapter 21, Company-developed methods Company-selected instrument Company-selected instrument Company-developed method Company-developed method Company-developed method

Moderate

High

Subjective

High

Low

Subjective

Low Low Moderate Low Low

Low Moderate High Low Low

Analytical Analytical Functional Analytical Functional

Free fatty acid Free fatty acid (quick test) Carver press NIR analyzer Solvent extraction (ether extraction) Acid hydrolysis (if oil and proteins heated) Critical CO2 extractor Conductivity Sodium-specific electrode Moisture balance Near-infrared (NIR) analyzer Drying ovens (vacuum, atmospheric)

AOCS Ca5a-40 Company-selected kit SFA 18. B-press method Company-selected instrument AOCS, 902.39 AOCS/AOAC Ca5a-40/922.06

Low Low Low Moderate Moderate High

Low Low Low Moderate Moderate Moderate

Analytical Functional Functional Analytical Analytical Analytical

Company selected instrument AOAC, 973.40 AOAC, 976.25 Company-selected instrument Company-selected instrument AOAC, 926.12, 930.15, 935.29

Moderate Low Low Low Moderate High

Moderate Low Moderate Low Moderate Moderate

Analytical Analytical Analytical Analytical Analytical Analytical

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Type

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Physical

Description

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Description

(continued) Source---Number

Skill

Cost

Type

Several methods

Certified Laboratory

Moderate

Moderate

Analytical

Peroxide value Oxidative stability index (OSI) Active oxygen method (AOM) Head space volatiles Schaal oven Adhesion; microscopic uniformity Glass, metal, plastic, stones Dust, temperature, humidity

AOCS, Cc8--53 AOCS, Cd12b--92 AOCS, Cd12--57 AOCS, Cg4--94, Cd8b--90 AOCS, Cg3--91 Company-developed method Company-selected instruments Company-selected instruments

Moderate Moderate Moderate High High Moderate Low Low

Moderate Moderate Moderate Moderate Low Moderate Moderate Moderate

Analytical Analytical Analytical Analytical Functional Functional Functional Analytical

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Category

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speed, oven temperature, package weights, while infrequent monitoring (hourly or shift) is sufﬁcient for FFA in frying oil, salt content of snacks, or oxidative stability of oil on chips. Hence, where and how frequently analyses need to be conducted depend upon what is being measured. Conducting evaluation methods near-line rather than in the laboratory enables quicker communication of data and control of processing equipment. Many evaluations are conducted in the laboratory (in-house or off-site) because they have specialized facilities, sensitive equipment and/or skilled people. This increases the time between sampling and communication of results, but it facilitates batch analysis by skilled technicians. For example, microbiological testing has traditionally involved specialized equipment and required up to ﬁve days for results. However, microbiological test kits and other methods have been developed to measure the presence of organic matter in seconds, viable microbes in minutes and speciﬁc microbes in hours after a short enrichment period [8]. These test kits are useful for securing quick information using relatively inexperienced personnel. Some companies acquire data from on-line detectors to provide continuous or frequent sampling of process (temperature, time, pressure) or product attributes (mass, density, color, shape). On-line detectors initially are more expensive, but often quickly pay for themselves by decreasing production costs and improving product uniformity.

3.2. SELECTION OF METHODS Many evaluation methods for snacks are listed in Table 24.2 along with the relative levels of skill to conduct the analysis and the cost of the equipment/analysis. Methods that require less skill and cost are included in most categories. Several evaluation methods for snack food manufacturers are detailed in technical manuals [2,3]. The appropriate methods depend on several issues: desired precision and accuracy of the method, the skill required, the cost and maintenance of the instrument, speed, the cost per sample and the value of data generated. Data with greater value relate to safety or legal issues (left side, Figure 24.1) and/or to ingredient functionality, process control or product attributes (right side, Figure 24.1). The following sections provide several perspectives concerning selection of methods for speciﬁc snack operations. Minimal methods for addressing safety issues in a HACCP program are illustrated on the left side of Figure 24.1. They include information from ingredient suppliers, e.g., aerobic plate count, molds, mycotoxin levels, etc., on the Certiﬁcate of Analysis (COA) from a certiﬁed supplier [4]. Sieves, magnets and metal detectors remove physical hazards from ingredients and products. Sanitation of equipment and good seals on packages are important for limiting microbial contamination of snacks after thermal treatment. Records of coding incoming

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ingredients, outgoing products and product distribution, CCP process parameter and HACCP data (moisture, microbial, etc.) are retained in a HACCP program. The right side of Figure 24.1 addresses snack quality issues. Each snack has characteristics, such as color, texture, bubbles, shape, burnt spots, thickness, salt level and FFA in oil, which are important quality attributes, but often do not relate directly to safety or legal issues. Measuring and limiting the ranges of values for ingredient and intermediate product properties and processing equipment parameters yields snacks with better attributes and less variance. Methods and concepts related to these issues are discussed in the following sections, with an emphasis on needs of smaller manufacturers.

3.3. METHODS FOR RECEIVING INGREDIENTS AND PACKAGING Many evaluations use informal sensory methods supplemented with standard color charts, photos and reference samples to conduct rapid determination of ingredient attributes. If the ingredient passes the appearance, smell, taste and/or feel criteria, then inspection of the ingredient speciﬁcation sheet and rapid evaluation methods (moisture, particle size) may be useful for an accept/reject decision. When a reputable supplier provides certiﬁed ingredients, shipments are received and checked or tested for conformance to speciﬁcations. The supplier provides information (physical, chemical and microbial) that characterizes the ingredient or packaging material on the COA. This means the supplier guarantees the ingredient has these properties upon delivery; their veriﬁcation is only needed periodically. This could be done in the QC laboratory or by a commercial laboratory. Content of contaminants, i.e., microbial, mycotoxins, herbicides, pesticides and genetically engineered ingredients, is a critical issue best served by reliance on a good supplier, but samples should be taken and retained for veriﬁcation or for use in disputes. Several types of commercial kits provide rapid, economical measurement of mycotoxins [9]. However, not all the information provided by the supplier is critical for safety, legal, or quality issues. Testing and observation will determine which information relates to critical attributes for safety and for quality. That information, communicated to the supplier, is needed to negotiate improved performance in meeting attributes critical to the buyer’s speciﬁc snack operation if purchases are to continue. Measurement of critical ingredient attributes, by rapid analysis methods, before accepting the shipment is sometimes done regardless of who the supplier is.

3.4. METHOD CALIBRATION Every method requires calibration or standardization. In subjective evaluations, the ability of people to hear, taste, smell, touch and see (visual acuity, color

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blindness) and to discriminate the range of target attributes must be veriﬁed periodically. To help standardize subjective tests, charts, photos and appropriate reference ingredients and products should be retained and utilized. All instruments require calibration; this may be done internally using selfcalibration procedures, or externally using primary or secondary standards. An example of a primary standard is a 100.00 gram weight to test the accuracy of a balance. Examples of secondary standards are ingredients sealed into containers, stored in freezers and used as reference samples. This can often be done with products representative of target attributes as well as those representing typical defects. A long-range approach is to retain ingredients that yield “in spec” quality products to provide information on ingredient functionality. Several organizations (Table 24.3) develop and publish analytical methods and may have “check sample” programs that distribute samples for speciﬁc analyses. These are useful for training personnel. Participation in check sample programs veriﬁes and establishes the credibility of the lab and provides a steady supply of reference standards.

3.4.1. Moisture Content and Oil Quality Measurement of moisture content is critical in raw ingredients, throughout processing and for the ﬁnal product. Rapid methods to measure moisture include a moisture balance, near-infrared analysis and capacitance. A moisture balance [Chapter 3, Figure 3.5(A)] is recommended for obtaining reproducible moisture contents in less than 10 minutes. These instruments include a balance, a heat source (microwave, infrared, resistance, or incandescence) and a cover. These methods are calibrated using standard vacuum or forced-air oven methods [10]. Near-infrared analysis instruments determine moisture, protein, oil and other components in whole grains, meal, ﬂour, chips and intermediate products in less than a minute. Calibration equations are available for many grain and processed samples; however, adjustments must be made periodically to correct for instrument drift. These instruments can also be utilized to quantify several components of additional ingredients or products provided calibration equations are developed; however, signiﬁcant investments of time and money will be required. Certiﬁcates of Analysis are usually very reliable when oil is purchased in bulk truck or railroad car quantities from reputable suppliers, since the standard practice at reﬁneries is to deodorize just before shipping and thus deliver frying oils/shortenings with the lowest FFA and peroxide values (PVs) possible. Large commercial snack food fryer systems are designed to minimize the oil:wet product ratio and are run at full frying capacity, which results in a frying oil turnover rate of about 8 hours. Proprietary options for holding the oil over weekends and while the fryer is being cleaned are also available. Oil should not have to be discarded because of degradation in properly designed and effectively managed frying systems (Chapter 6).

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Company Defined Certified Laboratory Trade Association

Professional Society

Federal Agency Short Course Equipment Company Scientific Research

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Examples Subjective, analytical or functional methods Microbiological, chemical, physical and toxicology analyses Snack Food Association Tortilla Industry Association American Institute of Baking American Association of Cereal Chemists American Oil Chemists’ Society American Society for Quality American Society of Baking Association of Official Analytical Chemists Baking Industry Suppliers Association Federal Grain Inspection Service Canadian Grain Commission Snack, extrusion, QA/QC, etc. Technical manual, procedures, articles, etc. Published book chapters, articles, bulletins, etc.

Web Address Proprietary http://www.nhb.org/foodtech/testing/labs.html http://www.scisoc.org/aacc/dirs http://www:sfa.org http://tortilla-info.com http://aibonline.com http://www.scisoc.org/aaacc http://www.aocs.org http://www.asq.org http://www.asbe.org http://www.aoac.org http://www.bema.org http://www.usda.gov/gipsa/progser2.htm http://www.cgc.ca/prodser/labtesting1-e.htm http://www.tamu.edu/food-protein http://www.wenger.com Private and public libraries

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Category

Sources of Analytical Methods in the United States.

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However, smaller processors may only fry for one shift a day and operate more like food service or batch fryers. Even with the use of antioxidants and antifoam agent (polydimethylsiloxane, “methyl silicone”), it may become necessary to periodically recondition the oil and, eventually, discard some. A variety of systems are available for ﬁltering the oil, or treating it with a single or mixed adsorbent that reduces free fatty acid, soaps, peroxide value, heatgenerated polymers and oxidation decomposition compounds. Kits for rapidly evaluating the condition of oil (FFA, PV and other frying degradation products) in conjunction with fryer oil refreshing systems are available [11] and used by smaller commercial frying operators.

3.4.2. Sieving (Particle Size) and Paste Viscosity Uniformity of the physical size of ingredients (kernels, ﬂakes, grits, etc.) increases processing efﬁciency and improves product consistency (Chapter 3). A sample can be quickly hand-sieved and the fractions weighed to conﬁrm compliance with ingredient speciﬁcations. These tests are effective for corn meal and dry masa ﬂours. The paste viscosity of many cereal ﬂours and meals is a critical ingredient functional property that relates to processing ease and snack attributes. The paste viscosity can be included on the COA or can be measured using an inexpensive instrument, i.e., a Bostwick consistometer (Chapter 3, Figure 3.5(F)]. A slurry (50 g) is placed in the sample holder, released, and ﬂows down a channel with distances engraved on the bottom. Slurries that ﬂow farther have less waterbinding capacity that correspond to less dough cohesiveness and lower oil uptake during frying. More detailed information concerning viscosity of ingredients is provided using a pasting viscometer [Rapid ViscoTM Analyzer, Newport Scientiﬁc; Chapter 3, Figure 3.5(J)]. Results from the instrument are useful in predicting processing conditions and snack attributes of good and poor ingredients [Chapter 3, Figure 3.6(B)] [12]. A long-term approach is to characterize retained ingredients that have good and poor processing properties, using a commercial laboratory for determining target values for ingredients. Then, discussions can be held with suppliers to negotiate inclusion of the desired pasting property in ingredients supplied, as well as accompanying analyses with shipments.

3.4.3. Genetically Modiﬁed Organisms Consumers’ concerns about foods containing r-DNA are genuine. Ingredients potentially containing genetically modiﬁed organisms (GMO) include corn products, and soy, cottonseed and canola oils. Analytical methods to quantify r-DNA or speciﬁc proteins are improving [13]; however, the ability to extract and quantify introduced nucleic acids and proteins from foods decreases after

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hydrothermal treatment, chemical treatment, or reﬁning. In certain applications, it may be necessary for ingredient suppliers to indicate the level of GMO seed or material content on the COA. This needs to be veriﬁed periodically using certiﬁed commercial laboratories to determine the effectiveness of the supplier’s QC program.

3.5. METHODS FOR PROCESSING AND INTERMEDIATE PRODUCTS Equipment-speciﬁc procedures require training and periodic veriﬁcation. Equipment parameters (temperature, pressure, shear, dwell time and other parameters) require monitoring and adjusting. Even the holding times and conditions between succeeding processes affect the functionality of ingredients and product quality. The parameters from CCP equipment should be recorded and charted to detect non-random changes. Intermediate products need to be monitored for weight, size, color, oil, moisture, adhesiveness and cohesiveness using objective and subjective evaluation methods. Small electronic scales along production lines are routinely used to conﬁrm weight per unit(s). Moisture balances provide quick, repeatable values for intermediate products. Subjective evaluations of intermediate samples are frequently conducted during processing. Many of these methods are productand personnel-speciﬁc and contribute to the art of snack production. Frying operations require periodic testing of FFA, peroxide value and polar material in frying oil. Fryer heat and product moisture destabilize the ester linkages of oils and result in liberation of FFA, which causes a soapy taste in snacks and promote rancidity. Traces of cleaning compounds also cause excessive FFA production during frying. Oils polymerize during frying, resulting in decreased heating efﬁciency, increased viscosity and off-ﬂavor. Reference methods for FFA (method Ca5a-40) and peroxide value (method Cc8-53) [14] require glassware, solvents, reagents and 0.3–1.5 hours’ analysis time.

3.6. METHODS FOR PRODUCTS Sensory evaluation of snacks is discussed in Chapter 21. Consumer (untrained) panels identify the presence of differences between snacks samples. Triangle tests are used to identify the odd sample when similar snacks are presented in a quiet, controlled environment. Ofﬁce and plant personnel normally participate in sensory evaluations, but they may be too familiar with snack qualities to be representative of snack consumers. Training of an expert panel of 5 to 10 people requires time and expense; however, results from this panel will be able to more speciﬁcally identify and characterize small variations in ﬂavor, color and texture of snacks, as well as compliance with the established, deﬁned or standard product.

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Appearance (color, uniformity) and texture (friability, hardness) of snacks are quality criteria that contribute to consumers’ preferences. Subjective ratings of these properties by line personnel are routinely conducted. Objective measurements ensure consistency over longer periods. Hand-held and laboratory colorimeters enable rapid, objective measurements that relate to appearance [Chapter 3, Figure 3.5(C)]. On-line instruments enable continuous monitoring. Brittleness, hardness, friability and mouth feel of snacks change during mastication, but subjective ratings of these properties by line personnel help ensure product consistency. Since the polymers in snacks become leathery and tough at above 3% moisture, monitoring the moisture content after packaging helps ensure retention of good snack texture on the store shelf.

3.6.1. Moisture and Salt Contents Rapid methods to measure moisture content were described previously. Proper moisture content is critical in snacks, and the use of moisture meters requires care to avoid burning snacks during drying. Uniform adhering of salt and seasonings on snacks is another important quality criterion. Several rapid methods are available to quantify salt [3]. The sodium ion electrode method is accurate if calibrated, but values need to be corrected to include the chloride ion. Titration methods also measure salt on products and in seasonings.

3.6.2. Oil Content and Shelf Stability Fried snacks contain between 10 to 50% oil, which needs to be quantiﬁed periodically. A quick approach to estimating the oil content of snacks is the amount of oil pressed from a sample using a hydraulic Carver press [3]. A calibration chart must be established for each snack. Alternatively, the oil and moisture content can be measured using near-infrared analysis in less than a minute while on-line units provide real-time analysis of oil and moisture content. In ofﬁcial procedures, oils are extracted for 3–24 hours from dried samples using nonpolar solvents [14.] The use of supercritical carbon dioxide extraction apparatuses (just coming into use) shortens extraction time and permits oil analysis in less than an hour. Oil content is routinely determined gravimetrically after solvents are evaporated. Rancidity in snacks is primarily caused by oxidation of unsaturated oils during storage. Grassy, cardboard, paint aromas replace typical aromas of snacks. The ﬁrst stage in the oxidation process is the formation of hydroperoxides. The oil, extracted from snacks, can be tested for FFA and peroxide values (PV) by titration. Oil oxidation is decreased by packaging in a reduced-oxygen atmosphere (nitrogen ﬂushed) and by decreasing the exposure to light by selection of

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packaging materials. At least two packages of snacks should be retained from each shift for evaluation of shelf stability. Storing at an elevated temperature (35◦ C) can accelerate shelf-stability evaluation. Subjective evaluation of snacks at the midpoint of expected shelf life provides a measure of what the customer experiences. Distinctive rancid odors of snacks provide a good qualitative measure of oil oxidation, which can be quantiﬁed for FFA, peroxide and moisture contents and by sensory evaluation.

3.6.3. Packaging Uniformity of ﬁll, product visibility, seal integrity and ease of opening are issues that affect consumer satisfaction. Modern, high-speed weighers consistently deliver the target weight of snacks into the package with low variance. This, combined with gas-ﬁlled pillow packages to protect the snack from breakage, decreases the relative importance of ﬁll volume, but net weight claims still must be met. Snacks retain fresh characteristics longer when packaged in materials that seal efﬁciently. Seal integrity is critical for the prevention of moisture and oxygen migration into the snack, which compromises the expense of the best packaging materials. Pinhole leaks in the seal generate tiny air bubbles when the bag is submerged under water.

3.7. EVALUATION METHODS FOR SELECTED SNACKS Critical QC methods for several snacks, popcorn, fried extrusion-puffed snacks and corn tortilla chips are presented in this section. Good working relationships with the suppliers and COAs for each ingredient and packaging material help to ensure the consistency of what comes into the manufacturing plant. Speciﬁcations for common items, like salt, seasonings and packaging materials are not included in the following discussion; neither are many sensory evaluations conducted by line operators and common equipment, like metal detectors and check weighers. Items followed by an asterisk (*) should be part of the HACCP program to ensure food safety; other items refer to quality issues (Figure 24.1). Please note that some methods are needed for safety as well as for quality. r Popcorn is produced by heating corn, followed by sieving to remove

unpopped corn, seasoning, salting and packaging (Chapter 14). The corn supplier should provide a COA for popcorn that certiﬁes the kind of corn, the moisture content,∗ the popping percentage, the expansion ratio, and that the corn contains less than permitted levels of GMO,∗ mycotoxins,∗ pesticides∗ and herbicides.∗ Corn quality and moisture content need to be monitored to provide high popping percentage and consistent bulk volume. Equipment parameters of temperature,∗ dwell time,∗ sieving separation,

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scrap loss, uniformity of ﬁll, package formation∗ and package sealing∗ need to be monitored, as well as moisture,∗ salt and seasoning contents and bulk density of popped corn. r Fried, extrusion-puffed snacks are produced on a short, friction-type extruder followed by frying, seasoning, salting and packaging (Chapters 11 and 12). The COA for corn meal should include the particle-size distribution, moisture content, an index of hydration and a certiﬁcation that the corn meal contains less than permitted levels of GMO,∗ mycotoxins,∗ pesticides∗ and herbicides.∗ The COA for frying oil should ensure the speciﬁed oil species composition, and low levels of FFA, peroxides, and ‘moisture’. The hydration rate of corn meal affects extrusion performance and product characteristics. Equipment parameters of extruder temperature∗ and pressure,∗ cutter speed, fryer temperature∗ and dwell time,∗ scrap loss, and package formation,∗ ﬁll and seal integrity∗ need to be monitored. Fryer oil quality, FFA and peroxides should be checked each shift. Oil content of snacks should be estimated daily by a hydraulic press and quantiﬁed periodically by a commercial laboratory. Bulk density, expansion ratio, moisture,∗ salt and seasoning contents of fried, expanded snacks need to be monitored. r Corn tortilla chips are deep-fat fried products of alkaline-cooked and ground corn that are sheeted, baked, fried and then seasoned, salted and packaged (Chapter 10). The corn supplier should provide a COA, which indicates the kind of corn, moisture content,∗ test weight, and a certiﬁcation that the corn contains less than permitted levels of GMO,∗ mycotoxins,∗ pesticides,∗ and herbicides.∗ The shipment of corn should be sampled with a probe and analyzed for moisture,∗ test weight and uniformity. The corn sample should be divided and retained in a sealed container until the processed products from that corn are sold. Equipment parameters of temperature∗ and dwell time∗ for corn cooking, steeping, baking and frying, grinder settings, and package formation,∗ ﬁll and seal integrity∗ need to be monitored. The amount of lime used, subjective rating of masa characteristics (particle size, cohesiveness) and weight per piece of sheeted masa are critical processing parameters that need to be monitored. The moisture∗ contents of masa, baked-intermediate product and fried chips should be analyzed using a rapid moisture meter. Fryer oil quality, FFA and peroxides should be monitored using the quick test kits. Oil content of snacks should be estimated daily by a hydraulic press and quantiﬁed periodically by a commercial laboratory. Salt and seasoning contents of corn tortilla chips need to be monitored.

4. STATISTICS IN QUALITY CONTROL Statistics, an essential tool of QC, is based on comparing measures of central tendency with measures of dispersion. Central tendency is often expressed as the

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average, mean, or a term called “X-bar” represented by a large letter X capped with a line—all of which are calculated in the same fashion. The most commonly used measure of dispersion is the standard deviation, often represented by the small Greek letter sigma (␴). Despite all efforts to avoid them, differences exist between similarly made samples of the same product, resulting in a diverse product group called a population. If the different levels of an attribute, i.e., package weight, are laid out as graduations on an “X” axis, and the frequency (number of units containing each weight) is plotted on a “Y” axis, generally, a symmetrical bell-shaped curve called a Normal Distribution is generated [Figure 24.2(A)] [15]. The weight with the greatest number of packages (mean, average) will be at the peak and midpoint of the curve’s surface. Figure 24.2(A) shows that 68.26% of the samples will be within the range of the mean plus or minus 1 ␴; 95.26% of the samples within the range of the mean plus or minus 2 ␴; and 99.74% of the samples within the range of the mean plus or minus 3␴. The base of the Normal Distribution curve is asymptotic relative to a “Y” value of “zero.” That is, the curve never reaches the base. Thus, statisticians cannot be certain that all members of the population were considered and never can give a 100% guarantee that conclusions drawn about a population are infallible. Most people are willing to work within the “6 sigma” range and can draw many acceptably reliable conclusions. For example, referring to Figure 24.2(A), if the average of an attribute in the product being produced is shifted by one standard deviation away from the minimum objective (“guarantee”), quality will be compromised about one third of the time. By improving the process to make a more consistent product, and decreasing variance of the speciﬁc attribute by one half [curves in Figure 24.2(B) and 24.2(C)], a shift of one standard deviation becomes much smaller in measure, and chances that quality may be compromised are greatly reduced compared to previously. Processors making products in countries where each package must meet minimum or maximum label guarantees will only achieve 50% compliance if they manufacture or ﬁll the product exactly at the stated guarantee. But how large should the safety margins in their operations be? Since it is not statistically possible to obtain 100% compliance, depending on local laws, processors typically select a (conﬁdential) compliance target. If the target of 95% compliance is selected, the average of the product actually made must be 1.645 standard deviations (␴, sigma) higher than the minimum guaranteed on the label. Conversely, if the label guarantee is a maximum, as may occur with crude ﬁber or ash content, the average of the manufactured product must be lower than the guarantee by 1.645 ␴ to ensure 95% compliance [15]. The margin of safety in setting the target mean depends on product variability, sampling, analytical errors and company policy. Products with lower variances achieve compliance with minimal product giveaway and increased proﬁt. The

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Figure 24.2 (A) relationship between standard deviation (␴) and areas (populations) under the normal distribution curve. (B) relative areas in +2–3␴ and − 2–3␴ regions when variance (standard deviation) in distribution C is reduced by 50%.

costs of noncompliance may include product reworking, consumer issues, legal problems and possibly recalls.

4.1. CHARTS Many critical parameters (process and product attributes) are plotted on charts [15–17]. Statistical quality control charts are actually normal distribution curves

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that have been rotated 90◦ to add the dimension of time. Typically, time is on the horizontal axis and the measured parameter on the vertical axis. In a properly operating system, values posted to the chart should occur randomly relative to the mean (process average). The term “occur randomly” means that the sequence of data points should not form any recognizable pattern. The “Upper” and “Lower Control Limits” are set by management, and characterize how much of the product made is outside of the acceptable range and may have to be removed by sorting. It would be desirable for all food operations to produce products without defects, all the time [17]. However, it should be recognized that foods are made from biological ingredients, which have inherent variabilities. Thus, the seriousness of the defect must be considered. There can not be any tolerance for known disease-producing bacteria, hazardous or non-permitted chemicals, or foreign objects like glass or metal. These are “go-no-go” criteria, and statistical process control charts would not be maintained for defects as serious, and hopefully rare, as this. In contrast, a slightly darker product color than the process average target may be tolerated temporarily.

4.2. PATTERNS ON CHARTS Patterns on the QC charts that are non-random indicate something unnatural is occurring The graphs in Figure 24.3 represent several types of nonrandom patterns, but many other patterns have been described. Much can be learned about how a process is performing by watching patterns on these charts. Patterns indicating a continuing trend or cycles could result from equipment or environmental problems. Stratiﬁcation may occur when small and large particles separate while emptying from a large bin or silo. Frequent values more than two standard deviations away form the mean indicate instability, since, randomly, this should occur infrequently. Whenever a non-random pattern develops, the reason should be investigated and a means implemented to correct it.

Figure 24.3 Several non-random data patterns on quality control charts: trends, cycles, instability and stratiﬁcation.

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5. SUMMARY The QA/QC program establishes and implements protocols to consistently produce safe products in compliance with federal, state and local regulations. GMPs and HACCP programs provide the safety and legal bases of activities while company-selected quality programs, like Total Quality Management, provide the internal, organizational structure of QA/QC programs. Incoming supplies, equipment, intermediate products and ﬁnal products must be monitored to meet safety and quality issues. Improving the consistency of critical processes and ingredients effectively improves product quality and safety.

6. REFERENCES 1. Gould, W. A., 1994. Current Good Manufacturing Practices/Food Plant Sanitation. 2nd edition. Technomic Publishing Company, Lancaster, Pennsylvania. 2. Gould, W. A., 1994. Snack Food Manufacturing and Quality Assurance Manual. Snack Food Association, Alexandria, Virginia. 3. Gould, W. A., 1999. Potato Processing, Production and Technology. CTI Publications, Timonium, Maryland. 4. Pierson, M. D. and D. A. Corlett, Jr., 1992. HACCP: Principles and Applications. Chapman & Hall, New York. 5. Townsend, P. L. and J. E. Gebhardt, 2000. Quality Is Everybody’s Business. St. Lucie Press, Boca Raton, Florida. 6. Hubbard, M. R., 1999. Choosing a Quality Control System. Technomic Publishing Company, Lancaster, Pennsylvania. 7. Silverman, L. L. and L. Annabeth, 1999. Critical Shift: The Future of Quality in Organizational Performance. ASQ Quality Press, Milwaukee, Wisconsin. 8. Lightfoot, N. F. and E. A. Maier, 1998. Microbiological Analysis of Food and Water: Guidelines for Quality Assurance. Elsevier, Amsterdam. 9. Sinha, K. K. and D. Bhatnagar. 1998. Mycotoxins in agriculture and food safety. In Books in Soils, Plants, and the Environment. Marcel Dekker, New York. 10. Anon., 1998. Ofﬁcial Methods of Analysis of AOAC INTERNATIONAL. 16th edition. AOAC International, Gaithersburg, Maryland. 11. Stier, R. F., 1997. Quick quality checks. Baking and Snack, 19:72, 74–76. 12. Whalen, P. J., 1999. Detecting differences in snack ingredients quality by Rapid Visco Analysis. Cereal Foods World, 44:24–26. 13. Persley, G. J. and J. N. Siedow, 1999. Applications to Biotechnology to Crops: Beneﬁts and Risks. Issue Paper #12. Council for Agr. Sci. and Technology, Ames, Iowa, 8 pp. 14. Firestone, D., ed., 1998. Ofﬁcial and Recommended Methods of the AOCS. 5th edition. American Chemical Society, Champaign, Illinois. 15. Ryan, T. P., 2000. Statistical Methods for Quality Improvement. John Wiley & Sons, New York. www.sci.ﬁ/∼leo/Quality/mainmenu.html. 16. Whetham, C., 2000. The Red Road, (www.sci.ﬁ/∼leo/Quality/mainmenu.html), Kuikankatu 37, 33100 Tampere, Finland. E-mail: cheryl.wetham@sca.ﬁ. 17. Wheeler, D. J., 1998. A modest proposal. SPC INK, #2. SPC Press, Inc., 5908 Toole Drive, Suite C, Knoxville, Tennessee. (www.spcpress.com)

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