Practical Dehydration

Practical Dehydration Maurice Greensrnith 2ndedition

WOODHEAD PUBLISHING LIMITED Cambridge England

Published by Woodhead Publishing Limited, Abington Hall, Abington, Cambridge CB 1 6AH, England First published 1971, Food Trade Press Second edition 1998, Woodhead Publishing Ltd 0 1998, Maurice Greensmith

The author has asserted his moral rights. Conditions of sale All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. While a great deal of care has been taken to provide accurate and current information, neither the author, nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused, or alleged to be caused, by this book. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN 185573 394 3 Printed by St Edmundsbury Press, Suffolk, England.

Acknowledgements The author would like to acknowledge his debt of gratitude to his many friends in the food industry who have supplied photographs to illustrate this second edition and information on recent new technology in plant and processing. Acknowledgement is also made to Niro Atomizer for the latest technology details on tomato and coffee drying. Also Mitchell Dryers Ltd, Carlisle, have given invaluable assistance in making available their pilot drying plant in the factory for experimental dehydration trials. Mr Glenn Watters of the Western Regional Research Centre of the USDA, Berkeley, California, together with Dr Otto Silberstein of Gilroy Foods Inc have generously supplied updated information on American onion drying technology. The author also thanks the Marchese Lupi di Saragno in Vigatto, Italy, for supplying details and photographs of effluent screening technology in high density stock breeding units for meat, ham and pig meat processing in the Parma, Bologna region, particularly in the context of Parma Hams. Much information has been collated on dehydration feasibility by the author from the many studies he has carried out in the course of 12 years in countries as diverse as Egypt, India, South America and Eastern Europe, promoting interest in onion dehydration; and in Kenya, South Africa, China, Macedonia, Greece, Turkey and in Western Europe where

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vegetable dehydration in general has been taken up seriously. Poland has been involved with considerable tonnages of potato products in flake and granule form. There were, of course, instances where the infrastructure failed to meet up with the requisite parameters in horticultural terms, particularly in sub-tropical and tropical regions where irrigation and power plant were inescapably involved. Site photographs indicate where such infrastructural problems arose, notably in Northern Nigeria where attempts were made to irrigate many hectares of scrub/desert land on the southern shores of Lake Chad. Full cognisance was not taken of the lack of horticultural manpower available to take full advantage of the newly irrigated land where new skills were needed. A second example was in Pernambuco, Brazil, where the Rio Francisco offered massive reserves of irrigation water, excellent manpower training in horticulture, but not sufficient risk capital to put the irrigation and power plant in place, thereby enhancing the infrastructure to support food processing. Neither government nor private investors had the risk capital available at the time of the study. In central Turkey where cotton growing tended to be on a monoculture basis, diversification into vegetable processing failed to attract conservative farmers and there was insufficient interest to wait for some three to four years before a return on equity profit could be anticipated. Very interesting information was gained through studies in Iran where desert irrigation is very feasible, thanks to the construction possibly a century or more ago of underground ducts extending from a mountain range on the shores of the Caspian Sea to regions as distant as Khoramshaar (central Iran) from where contour irrigation is carried out efficiently by Israeli management on annual crops of tomatoes. Desert horticulture has good potential if a political solution can be found in the future. In Israel this has been undoubtedly proved and the fact that, in the case in point, international co-operation can pay off handsomely if the will can be sustained. In some of the infrastructural studies the author acknowledges the patience and invaluable help offered by Mike Cannon, Technical Manager of Mitchell Dryers Ltd, for suggesting modifications on standard drying plant design where exceptional circumstances prevailed and standard plant did not meet requirements. The author also thanks the following for their permission to use illustrative material - Dodman Ltd, Peter Holland Ltd, International Machinery Corp, Mitchell Dryers Ltd, Niro Atomizer Ltd, Nymek, Rosin Engineering Co Ltd, Rossi & Catelli, Russell Finex Ltd, Tito Manzini, Urschel Laboratories Inc, Zacmi.

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Contents PREFACE TO THE SECOND EDITION

1

ACKNOWLEDGEMENTS

3

5

1

ORIGINS, GROWTH AND POTENTIAL OF DEHYDRATION Origins; Growth; Potential; Conclusions

2

FACTORY ORGANISATION Plant location; Raw material; Labour requirements; Water; Power; Boilers; Heat raising plant; Fuels; Effluent

21

3

PREPARATION PLANT Cutters; Peelers; Washers; Blanchers; Conveyors; Miscellaneous and specialised preparation plant

39

4

DRYERS 65 Stove and cabinet dryers; Tunnel dryers; Through-flow batch dryers; Conveyor band dryers - single pass; Multi-pass conveyor dryers; Bin dryers; Air lift dryers; Rotary dryers; Vacuum dryers; Freeze dryers; Drum dryers; Foam mat dryers; Spray drying in the dairy and food industry

V

5

DEHYDRATION OF POTATO PRODUCTS Potato granules; Potato flakes; Potato cubes; Potato starch

105

6

DEHYDRATION OF VEGETABLES Horticulture; Green beans; Beetroot; Bell peppers; Cabbage; Carrots; Chilli peppers; Celeriac; Celery; Garlic; Leeks; Mushrooms; Green peas; Onions; Parsnips; Parsley, sage and leaf herbs; Spinach; Swedes; Tomato slices/flakes

121

7

DEHYDRATION OF FRUITS Apples; Apricots; Bananas; Currants; Paw paw; Peaches; Pineapples; Pears; Plums; Raisins

169

8

SPRAY DRIED PRODUCTS Tomato powder; Instant coffee; Freeze-drying of coffee; Skim milk powder

192

9

DEHYDRATION OF MEAT Raw materials; Chicken granules; Beef, mutton, ham, oxtails, kidneys; Typical buyer's specification

213

10

THE FORMULATION OF DEHYDRATED SOUP Ingredients, Formulation; Additives and artificial colours

219

11

SELECTION, PACKAGING AND STORAGE Sieves; Selection; Electronic colour sorting; Packaging; Bulk packaging

225

12

QUALITY CONTROL Laboratory analytical tests; Specifications; Methods of analysis

233

13

THE ECONOMICS OF DEHYDRATION Hours of operation; Length of season; Range of products; Staff deployment; By-products and their outlets; Costing

252

Index

vi

271

Preface to the Second Edition The first edition of PRACTICAL DEHYDRATION, published in 1971, was written primarily for the practical dehydrator, rather than for the chemist or theorist, whose interest in the industry might be more abstract or purely scientific. The text tended to concentrate on a range of products likely to be grown and processed in locations where, in the main, moderate equable climates prevailed - predominately Western Europe. Also, the scale of operation hypothesised that a plant, arguably of ’medium’ size, might be viable with an input of 70-80 tonnes of raw produce per 24hr day, or 20,000 tonnes per annum, assuming a 250 day season. Such figures were based on the author’s practical experience in the technical management of three UK plants of this size, all owned by one of the first companies in Great Britain to engage in vegetable dehydration. These operations started in Wisbech in 1934, with six further factories developing during the 1939-1945 war years, prodccing dehydrates for the Armed Services.The company’s products are still on the domestic and export market today, after more than half a century‘s growth in what was initially a wartime industry. Production today is centraliscd in one factory. However, radical changes have occurred in marketing dehydrates in the last two decades, and there has been almost a complete change in the end usage of dehydrated products, and a decline in the number of factories engaged in vegetable drying in the United Kingdom.

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This has arisen because of an escalation in operating costs in Western Europe generally, principally in wages, overheads and grossly inflated fuel costs, since the Middle East oil crisis. A change in marketing patterns has evolved, in that dehydrated vegetables have lost some popularity as ‘sui generis’ products in the domestic and catering markets but have found increasing importance as constituents in value-added products of almost infinite variety, such as snack foods, ’impulse foods’, instant soups, garnishes, ethnic specialities, sauces and health foods. Dehydrated or evaporated fruits feature very prominently in health foods and as an addition to breakfast cereals. Manifestly, this new wide range of usage, sometimes of the more exotic foods in dehydrated form, has opened u p the possibilities of processing in the developing countries of the world, both tropical and subtropical, and in this context, the chapters on fruit and vegetable processes have been expanded, covering a wider range than was covered in the first edition. These processing procedures, which are described in some detail, have been established following the author’s travels, as a consultant, to many new sources of origin of dehydrates, either in a potential context or in actual operation. This new appraisal of the industry has been arrived at by visits to South America, the Caribbean, Africa, India, Egypt, the Middle East, Western and Eastern Europe. In these areas the function has been to prepare feasibility studies for new enterprises, or to monitor existing production techniques and to guide management in their efforts to improve production methods, and to extricate some factories from difficulties arising from faulty plant design, poor lay-out, hygiene or engineering faults. It is hoped, therefore, that some reference in the ensuing text may be instructive to those who have such difficulties, and may warn others how to avoid the pitfalls which have arisen in some locations. If criticism is implied, an attempt has been made to be absolutely objective, where such problems have occurred. The revitalised market in Western Europe for value-added products has brought new opportunities for the dehydration industry in several interesting new areas, so long as the entrepreneurs accept that this growing market is largely controlled by internationally-based companies with a reputation for quality food products, and anyone seeking to supply the constituents of these products will have to give absolute priority to their own quality control methods, and to comply rigidly with the Specification Schedules which these major buyers impose on their suppliers. It is only those who recognise this concept who have a chance of succeeding in the new era of food dehydration. 2

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Origins, Growth and Potential of Dehydration ORIGINS The origins of dehydration go back into antiquity The preservation of food by drying has been an art for centuries but it is only in the middle of the present century that the art has been translated into terms of technology The old methods of utilising the sun and wind to evaporate water from foodstuffs, however, still prevail in many parts of the world, and are likely to do so for years to come, for the centuries-old crafts are not easily lost, even in the age of technology. In the coastal villages of West Africa, fishermen still salt down their catch and hang it in the sun to dry, making what is locally, and somewhat understandably, known as 'stink fish'. To Europeans, this designation is perhaps an understatement, and most would regard it as the highest built-in ptomaine poison risk imaginable. In spite of this, stink fish is highly prized by the African and, added to cassava mot meal or rice, it provides a protein constituent in what would otherwise be an unbalanced carbohydrate diet. The conditions of preparation would appear to Western eyes to be devoid of the simplest requirements of hygiene and process control, yet the author has never heard of any untoward effects arising from its consumption. In the cattle raising territories of South America the ranchers have been sun-drying beef in a similar fashion for years. Probably this was a technique originated by the Indians, and, as recently as the early part of the present century, it was not uncommon to see a side of dried beef hanging

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outside the entrance to a ranch, for migrant workers and itinerants passing by to help themselves to a few slivers, to give them sustenance for their joumey. It is more than possible that, for economic reasons, this custom no longer prevails but it was once quite common in the Argentine and Brazil. Naturally dried fish, preserved by traditional and ancient methods, is still seen in Scandinavia and other European countries where fishing is an important industry, and it is still consumed there, as are the more scientifically processed fish products. Dried ling, or 'stock-fish' , is a common sight hanging outside the village grocer's shop in the remoter parts of Ireland away from the seacoast. It forms a regular part of the Catholic diet on fast days, in the absenceof fresh fish, and, in some areas in the West of Ireland, is even preferred to the more sophisticated types of canned and frozen fish. The sun-drying of fruit also goes back for centuries and is still practised today, particularly where labour is cheap and abundant, and climatic conditions are favourable. It will, perhaps, be demonstrated in the latter chapters that to simulate the effects of these natural forces of sun and wind can, indeed, be a costly procedure, and when we think of translating the old crafts into scientific processes, then it is essential to probe very carefully into the economics of the undertaking and this is considered in some detail in Chapter 13. GROWTH The transition from craft to technology can perhaps be traced to the period during World War 1 when considerable quantities of dried vegetables and soup were shipped to the Armed Forces in Europe from the US and, to a lesser extent, from Britain. Some commercial development in dehydrated foods, particularly vegetables, had previously been achieved in the UK in the mid-nineteenth century, when dehydrated carrots and potatoes were supplied to the Royal Navy, and to troops in the Crimea. At about the same time, some early research was carried out into the manufacture of dried milk. Between the two World Wars, however, little progress appears to have been made in gaining domestic consumer acceptance of dehydrated foods. Their value under wartime conditions was undeniable but the technology was not sufficiently advanced to make any impact on the public in general. Possibly the already improved techniques in canning impeded the progress of dehydration as a popular means of conserving food. Further development obviously depended on fundamental research to give a better theoretical understanding of the underlying mechanisms, and on the creation of objective methods for assessing flavour and texture

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changes which are directly related to human sensory evaluation. World War 2 focused more attention on the industry, as the Allies were engaged this time in a type of warfare involving transportation and deployment of men and supplies over infinitely vaster areas than in World War 1. Dehydrated foods enabled many of these problems of transportation and storage to be solved, in that dried vegetables, meats and soups, pruduced for the Armed Services' use, occupied only a fraction of the space taken u p by canned and fresh food, and the weight factor was similarly reduced. A striking example of this weight/bulk economy is provided by cabbage - a vegetable with over 90 percent water content. In dehydrated form, and compressed (as was specified by the Services), it weighs only one twentieth as much as raw cabbage, and occupies about one fortieth of the storage space. Cabbage, carrots and potatoes figured very prominently in the dehydration programme set up by the British Ministry of Food in the early part of 1941 and, by 1943, there were several factories operating in the UK, the total production of which was taken by the Ministry. Quality specifications were laid down by the Government's technical officers and close liaison was maintained at all times with the factory technicians and management. In all, some sixteen major plants and about eight smaller units came into vegetable dehydration in this period, contributing very materially to the War effort. Experimentalwork was also carried out at this time on dried soup and dehydrated meat at a pilot plant in Northern Ireland and on dehydrated herrings in Scotland. These experiments all led eventually to commercial production of supplies for the Forces. Throughout this time, close contact was maintained between the Ministry and those in other parts of the world who were similarly developing dehydration, particularly in the US and Canada. In 1942a joint Ministry of Food-US Dept of Agriculture mission was appointed by the Combined Food Board to survey the vegetable dehydration industry in America and Canada, and to assess both the curxent and postwar prospects. In 1943, a mission, including both British and American members, toured Africa to stimulate the dehydration industry and to form a liaison with the many workers in the field. In the following year a similar mission visited India with the same aims in view and, as a result of all these contacts, a pool of technical information was amassed and new ideas were diffused, which provided a stimulus for further valuable experimental work that, in the ensuing years, was to provide the cornerstone for a new and important industry. The transition from a wartime industry to a viable commercial 7

undertaking in peacetime was, however, slow and it was the 1950’s before any significant progress was made. Most of the British dehydration plants ceased to operate when the Services’ requirements diminished at the end of the War, and it was left to a handful of companies to press on with the valuable research and experimentation, barely recognising, at that difficult time, the potential which was going to open up in the ensuing two decades. Contacts with enthusiastic workers in the US were renewed, and now liaison with Europe was again possible. The first major breakthrough to retail consumer acceptance of dehydrated foods was, however, to occur in America, where Potato Granules hit the market in a big way. The interest in this product was, of course, stimulated again in a military context by the hostilities in Korea, and once again the manufacturing experience gained in wartime conditions played an important part in the improvement of technology and in the upgrading of the quality of the end-product in many ways. In 1954, the research workers Cording and Willard of the Engineering and Development Laboratory in Philadelphia, produced Potato Flakes by using the technique of drum drying. The resultant product was a mashed potato almost indistinguishable in taste and texture from that of a freshly mashed potato. This was a significant step forward for the new potato processing industry, which was seeking the American consumer market. Simultaneously, considerable technical advances were made in the manufacture of potato granules, on both sides of the Atlantic, and in the 1958-59processing season in the US, 75,000,0001b of granules were produced, utilising 300,000 tons of potatoes, or 3 percent of the North American crop that year. Meat dehydration also gained some impetus this time, particularly the processing of chicken granules for soup. Chicken Noodle was one of the first varieties to be promoted and to receive wide acceptance in the retail market, which had hitherto been dominated by canned soups. The success of these novel convenience packs, with the advantages of low weight, low volume and portability, opened the way for the commercial pioneers of dehydration to improve the techniques of drying and packing of a wider range of vegetables and meats, than was ever contemplated during the War, in a form suitable for and attractive to soup manufacturers. The latter were not always dehydrators themselves but d i e d for their basic ingredients on the specialists in drying, who now recognised the potential for an ever increasing range of products. Demand now went far beyond potatoes, carrots and cabbage, and extended to the more exotic field of asparagus, mushrooms, red and green peppers, celery, leeks, tomatoes, French beans, garden peas, celeriac, courgettes, spinach and chillies. 8

Dehydrated 'packet' soups were undoubtedly here to stay from the 1950's onwards. The trend towards shopping in the supermarkets and chain stores, which involved carrying the purchases home, highlighted, to the housewife, the great convenienceof the 40g packet against the 400g can. Some of the major soup manufacturers originated from the Continent where traditional culinary skill was displayed in the formulation of soups, and a considerable service was rendered to the dehydration industry by the high standard of quality maintained in this field. Promotion of these products is now worldwide, and the future potential assured if quality is maintained.

POTENTIAL In the mid-70's the potential for vegetable dehydration in the United Kingdom appeared to experience some set-backs,and failed to achieve some of the earlier promised forecasts. This applied mainly to the demand for domestic packs of individual products, such as green peas, onions and mixed vegetables. Potato granules were vigorously marketed, supported by advertising in the National media, and held their share of the convenience food market better than most other products but currently there is only one major granule producer left in the UK and some 2000 tonnes are imported each year. The greater part of this tonnage comes from the Netherlands, the Federal Republic of Germany, Belgium and France. A small tonnage in 1986 came from Poland and Sweden. The USA, once a major source of imports into the UK, has shipped very little, due in the main to the weakness of sterling against the dollar since 1976, when the rate dropped from a high of $2.55 to the pound in 1971to $1.80 in 1976. There was a temporary rally in the value of sterling against the dollar in 1979/81but since 1976other European origins for potato granules have developed strongly and have taken up the slack arising from the decline in home production in the last decade and American imports. Potato granules still hold a substantial share of shelf space in the supermarkets where the domestic market is vigomusly promoted but an ever increasing tonnage has now found its way into value-added products in the form of an infinite variety of potatebased snack foods, soups, sauces and garnishes, and ethnic speciality foods. Taking the straight sales of granules plus the tonnage used as a constituent of other dehydrated foods, it must be recorded that in this context the trade has expanded since 1970. Where impetus has been lost, however, is in the case of the most popular green vegetable - the 'garden' pea - which in the 70's looked set to compete very seriously with the frozen pea. In spite of energetic promotion, 9

it failed to gain the housewife’s total support, in that it did not live up to some producers’ claims that the dehydrated pea reconstituted immediately by immersion in boiling water, without soaking or cooking. The promise of an instant cooked pea was not realised. The brand leaders in frozen foods were producing a frozen pea which fully cooked after three minutes simmering and, in claiming a better cooking performance for the dehydrated pea, some credibility was lost. Cumnt packs on the domestic market now recommend 15 minutes simmering to completely rehydrate and tenderise dehydrated peas, and this is nearer to reality but popularity appears to have waned. Enormous efforts have been made by the growers and processors to achieve parity with the frozen pea, by selecting cultivars particularly suited to the dehydrator but, with conventional hot-air drying, it is a difficult task. Both the freezer and the dehydrator set the same quality standard at the farm gate, in that both call for a pea with a tenderometer reading of 90100 on the scale, with round-the-clockvining to ensure a continuous flow of ultra-fresh peas into the plant. However, tenderometer readings can only be a guide to quality, not an assurance, as a random check from each delivery at the farm gate and the factory gate can only monitor a fraction of the bulk. Tenderness and maturity can vary from row to row and field to field, and can even be inconsistent in a single pod where peas at the end of the pod will vary in maturity from those in the middle. An amalgam will therefore give a mean average tenderometer reading but, when the bulk goes into process, the freezing operation is far more flexible in dealing with small variations of maturity, whereas in dehydration even a microscopic deviation can give rise to ‘case hardening’ of the outer membrane of the pea and the denaturing of the protein, which will inhibit full reconstitution and induce wrinkling. The only safeguard is to apply floatation quality graders in the factory but even this is occasionally over-ridden by an imbalance of drying temperatures in the drying cycle, as the latter have to be harmonised so very accurately to preserve the delicate texture of the freshly vined pea. There is less margin for e m r in temperaturecontrol at every stage of the drying cycle than with any other vegetable. The vagaries of the British climate invariably pose some threat to the pea harvest, which at best only lasts six weeks, and sometimes as little as five. A hot season can be equally as disastrous as a wet one, in that progressive sowings over-ride one another and, in 24 hours, fields of peas at an acceptable tenderometer reading can soar right over the top in that period of time, making them unacceptable to the processor. Conversely in a season of persistent rain, when heavy viners become bogged down and immobilised in flooded fields, thousands of tons of produce can be lost, and the IO

dehydrator's programme and the growers' bank balance become a disaster area. The 1987 pea season was, for this very reason, the worst for 30 years, and affected the freezers and canners equally badly. In the course of experiencing over 50 pea seasons in the UK the author has concluded that there is no such phenomenon as a 'normal' pea season, and the impact on the dehydrator is perhaps greater than on the canner or freezer, which may explain why in the 1987 season only one company in the United Kingdom remained in pea dehydration, using hot air drying methods, and consequently the market demands can only be met by imports from those few origins where the quality of green peas is normally acceptable -New Zealand, South Africa and the Republic of Ireland. Freeze drying produces a moE acceptable quality of pea, subject to a high standard of raw material but the pmcess is expensive and, in context of vegetables, only one processor appears to be operating currently in Britain by this method. The development of dehydration in overseas locations has been widely monitored over the period 1970-1987 by the author, through Feasibility Studies for new ventures, and visits to existing factories in India, Africa and Eastern Europe. Low world prices in the 1970's precluded much investment in new plant and machinery in factories which had been established for some years, which resulted in a decline in the quality of their products or, in some cases in Eastern Europe, a temporary cessation of production of their principal exportable product - dehydrated onions-which rank overall as the most important vegetable imported into Western Europe from all origins. Right: The author examining a heavy crop of Ventura tomtoes.

Up to 1980 the c.i.f. price for onions from Egypt, India and Eastern Europe, shipped to Western Europe, had not exceeded £950 per tonne, and it was not until the mid-80s that prices moved into the area of £1300-£1500, which made viability more of a reality, and, in addition to assisting existing producers, it began to encourage new ventures.

Onion dehydration factory - Nasik, India

Where the climate is suitable for the commercial growing of dehydrating varieties of onions, ie, cultivars with high total solids, white flesh and high pungency there is some validity in looking carefully into the potentialfor setting up a dehydration plant, because onions will invariably provide a substantial period of production run, and will combine with other vegetables, compatible with the climate, to give a throughput for the year which will meet the economic parameters to which reference was made in the Preface to this edition. A product mix which might well be considered would be onions, carrots, leeks, beans, cabbage, capsicums and tomatoes, all of which, suitably comminuted, may find a market in Europe as constituents in a large variety of value-added products. The annexed TABLE 1.1 will indicate the countries which are currently exporting dehydrated vegetables to the United Kingdom. Some stability in world prices may well stimulate expansion in this trade in countries from which the statistics show only token tonnages have been shipped. Some origins in the developing regions obviously need some confidence in the potential for export, and indeed many need an injection of new capital to bring their plants up to date in order to comply with current quality standards, and to engender more profitability. The low prices prevailing in the 70s for the staple item of dehydrated

onions, for example, inhibited many factories from investing in new plant, the cost of which was escalating at an alarming rate, whilst there was little corresponding movement in the value on the market for the dehydrated product.

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Right: Manual hydrout corm for onions

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One weakness in the asymmetry of this equation was perhaps the efforts of the food machinery manufacturers to offer their overseas clients in the developing countries plant which was too sophisticated for their needs or their ability to absorb the intricacies of the newer technology which was being introduced into food processing equipment. This undoubtedly slowed down reinvestment in new plant with many of the smaller producers and, apart from the problem of difficult exchangecontrolrestrictions and shortage of hard currency there was little incentive for expatriate investors to inject capital into overseas companies, when the cost of servicing this capital and amortisation charges imposed an impossible burden on the factories' costs. Exports from the USA, particularly onions, continued to flow but these products always commanded a premium on account of their high quality to which the trade had been accustomed for many years. For example,between 1976to 1980 the average price for kibbled onions from origins other than the USA was €750 per tonne c.i.f. European port, whereas American onions 13

varied between €1100 and E1600 per tonne. The trade always maintained that a new source of origin would have to sustain a quality equal to that of the American product consistently for five years in order to merit parity in price. In 1986, one of the more consistent Eastern European suppliers, Hungary, was selling at €1294 per tonne, against the USA at €1344. France, Holland, Germany,Yugoslavia and Turkey moved up into this price category, ranging from €1210to E1400 per tonne. Admittedly, the total tonnage shipped from these five countries combined only equalled the tonnage from the USA but the levelling up of the prices on the world market indicates that there has been an improved consistency in the quality of the onions from these European and Eastern countries, which augers well for the potential for growth here. Egypt almost equalled the American tonnage in 1986 as indicated in TABLE 1.1but the average price was only €908 per tonne. From the author’s considerable experience of the dehydration industry in Egypt, the considered opinion is that many of the old established State controlled factoriesare suffering from the aforementioned lack of investment in new plant, and the restructuring of the factories has not been given much priority, in view of demands on the country’s reserves of hard currency for more pressing developments. The most encouraging development in Egypt is, of course, the facility to operate in the private sector - an initiative promoted by the late President Sadat. The quality of the Egyptian onion crop is excellent, as the export trade in raw onions has been of paramount importance for many years, and it is scrupulously controlled by the Ministry of Agriculture. With the advent of privatisation therefore, the potential for developing the dehydrated onion industry on higher quality levels is favourable. With the excellent raw material grown in the Nile valley, the only ingredient needed is an infusion of capital for new plant suited to the prevailing conditions in Egypt. It would not be inopportune for the major European buyers of dehydrated onions to regularly visit and monitor the factories engaged in the not inconsiderable export business, so that they could assist the management in achieving that extra element of quality which would bring the industry u p a level that would ensure better stability, in world price terms. The method of restructuring and re-investing must be sensibly undertaken. An old friend of the author, who is intimately connected with the Freezing Industry in the USA, and has spent many years advising the Indian shrimp packers on how they can up-date their factories to meet USDA Food Laws applying to importations into America, made a wise comment about throwing out old plant. His comment was ’The job ahead is to 14

modernise - you don't discard a motor car with 60,OOO miles on the clock for an aeroplane -you just get a new car". In other words, improve what you have. With many operations in the developing countries, joint enterprise schemes should be considered, so long as the expatriate investor can contribute expertise as well as the venture capital, and also with the provision that, on the successful establishmentof the industry, any dividends or participatory profits to which he may be entitled can be repatriated when due. TABLE 1.2 indicates the many sources of origin of dehydrated vegetables not specifically classified in TABLE 1.1. What is interesting is the number of countries now engaged in dehydration which were not involved in 1970. Included in the tonnages declared would probably be peas, green beans, leeks, celery, beets, herbs, celeriac and a range of exotic vegetables which, for Customs purposes, are not broken down under separate headings. The figures, of course, refer only to imports into Great Britain, and behind these could be substantial exports from the country of origin to other countries in the world. For example, the figure for onions in TABLE 1.1 relates almost entirely to white onions, which are favoured almost exclusively in the UK but very large tonnages of red onions are shipped annually from Egypt to Russia and other Eastern Europe, similarly to Arab countries, where India also does a trade in red onions, both fresh and dried. So all the countries shown as suppliers on both tables are very much larger producers than the figures would indicate by taking only one country of importation. To finalise on potential in the industry, it would be invidious to preempt this development in any one country but over some ten years the author visited three continents, which were not at that time seriously into dehydration on a large scale. It appeared that the infra-structure was there, the climatic conditions were favourable, and the only missing ingredient was the return to normality of world market prices. In the wake of the oil crisis of the 70s the inflated cost of new plant and machinery bore no relation to the cash return from overseas markets for dehydrated fruits and vegetables, and what was required was a decade of adjustment to bring these two factors into some sort of equilibrium. The countries surveyed were South America, India, Egypt and most of Europe (East and West), and these warrant notice to a greater d e g e than many other regions visited for the same reason, but in the years which have since elapsed, there were difficulties, both political and financial still to be solved. 15

CONCLUSIONS

In spite of the advance of technology, there is, nevertheless, still something of an art in removing the water content from the products of nature, and science has not yet solved all the problems. There are very few constants in the raw materials of the trade, from season to season, and some rudimentary skill is still needed to process some products satisfactorily, and hand and experience have sometimes to take over from the machine. A method, meticulously followed in one season may not necessarily apply to the ensuing season, or with produce grown in a different geographical location. There are many types of dryer available, for example, for vegetables but the end results can vary widely between one plant and another. Any one machine of a number may be eminently suitable for a specific product but the quality and success of the drying operation will still depend, to a great degree, on the skill of the operator. In dehydration, the product undergoes biophysical and biochemical changes, is subject to bacteriological hazards and, to the uninitiated, can be notoriously unpredictable in many phases of the rather lengthy process. The combination of science and some of the old drying craft is, therefore, a prerequisite to success. The methods described, therefore, are given merely as guidelines - a considerable amount of skill and experience is needed to supplement mere textbook knowledge.

Irrigation canaletto, Pernambuco Brazil

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ngdom Importation of Dehydrated Vegetables for 1986

nds y (FR)

public k

via

y

Onions (Sliced/Kibbled/Powdered) Tonnes Value CIF

859 730 117 2 11 27 41 37 43 148 29 475 2140 15 15 81 2457 1 39

7283

total

€8.8million

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Potato (Sliced/Cu t /Granules/Flakes) Origin

Tonnes

France Belgium/Luxembourg Netherlands Germany (FR) Italy Irish Republic Spain Finland Switzerland Poland Israel Canada USA

Value CIF

158 40 485 782 20 96 32 18 3 281 28 10 173

------2126

total

E l .7million

Mushrooms (Including Truffles)

Origin

France Netherlands Germany (FR) Italy Irish Republic India China Taiwan Hongkong South Korea Japan USA

Tonnes 88

14 69 3 6 1 82 30 7 3 12 15

-------330

18

Value CIF

total

E2.6million

Tomatoes (Sliced/Kibbled/Powdered)

Origin France Netherlands Germany (FR) Italy Spain Morocco South Africa Chile

Tonnes

Value CIF

111 11 37 73 15 54 19 1

-

321

total

E0.9million

Carrots (Diced/Flakes/ Powdered)

Origin France Netherlands Germany (FR) Italy Irish Republic Spain Israel USA

Tonnes

Value CIF

130 285 108 16 55 22 165 134

-

915

total

E0.9million

Summary

Tonnes Onions Potatoes Mushrooms Tomatoes Carrots Other Sorts

7283 2125 330 321 915 3200 14164

Value E8.8m. E1.7m E2.6m E0.9m €1,7m E8.0m E23.7million

(Source: H.M. Customs and Excise)

19

Table 1.2 United Kingdom Importation of Dehydrated Vegetables for 1986 (Other sorts not identified in Table 1.1)

Origin France Belgium/ Luxembourg Netherlands Germany(FR) Italy Irish Republic Denmark Greece Spain Norway Switzerland Yugoslavia Turkey Hungary Morocco %YPt Ghana Nigeria Kenya South Africa Cyprus Israel Iran Pakistan India Sri Lanka Thailand China Taiwan Hongkong South Korea Japan New Zealand USA Dominica Peru Chile

Tonnes 250 27 300 590 35 62

Value CIF

14 11

83 1 1 13 189 170 1 181 4

8 1 283 11 105 73 21 8 1 1 91 53 33 1 14 11

522 1 1 29

----

3200 total E8.0million This Total is included in the summary partof Table 1.1 (Source H.M.Customs and Excise) 20

2

Factory 0rganisation PLANT LOCATION The location of the dehydration factory must be considered very carefully, because, whereas at one time proximity to the source of raw materials was of paramount importance, availability of an adequate labour force and the provision for effluent disposal will, perhaps, constitute a more pressing requirement. A rural environment is obviously better than a location in a highly industrialised area, because the operation involves the utilisation of a considerable amount of open space for the reception and storage of raw materials, particularly where vegetable dehydration is being undertaken. This chapter, in dealing with factory planning, proceeds on the premise that vegetables are the principal raw material to be processed. Fruit dehydration is dealt with in Chapter 7. On the assumption that the labour availability factor has been resolved, and co-operationfrom the Local Authority on effluent disposal has been secured, it is important that the location should be a focal point for the intake of indigenous raw material within a radius of some 80 kilome-. In the case of highly perishable vegetables, such as vined peas and green beans, availability should be within half that radius. These figures are relevant where the scale of operation presupposes an average intake of 70-80 tons of produce per day which is, in effect, a viable level upon which to work. This would be regarded as a medium size plant. Production on a larger scale would call for a wider area of raw material

21

availability but, in the ensuing chapters, it is intended to concentrate on the problems of the medium size operator, coming into the industry for the first time, or developing into dehydration from some other food processing activity. It is, perhaps, more likely,at this stage of the growth of dehydration, that development in Europe will be at this sort of level, rather than at that applying in the US, where plants with an intake capability of upwards of 500 tons a day are not uncommon.

RAW MATERIAL Once the vegetable programme has been established, an efficient procurement system is an absolute necessity, as it is vital that the plant be fed with a round-the-clock supply of raw material for many months of the year, with no hiatus or short-fall due to weather conditions, or any other circumstances. Binding contracts must be made with reliable growers to ensure this and also to ensure that suitable varieties of vegetable - ones that lend themselves favourably to the process -are grown. Random purchasing on the open market is a system not to be relied upon by the dehydrator, because wherever the price is right the variety will be wrong, and vice versa. The one exception, when this procedure is varied, is in the case of potatoes, and spot purchases are often made as the season proceeds. Whilst there is an element of risk in this particularly in a Season of low solids and a short crop - potato prices tend to be more stable than those for some other crops, and availability is spread over a much longer period. Some particular potato products, however, d o call for special varieties as a first choice. Potato granules and flakes, for example, should be made from high starch content tubers and, if these types am not grown in the traditional growing areas, special plantings under contract may have to be made adjacent to the plant location. On the other hand, some processors find that, to meet a cost problem with some potato products, they have to process culls from ware (table grade) potatoes, and, in this case, contractingis not usually possible. Grading stations can usually supply large quantities of this material, which is satisfactory for the manufacture of some grades of dehydrated pmduct, and long term arrangements can always be made for intake from such sources, provided certain basic quality requirements are covered.

Contracts The procurement contract with the grower can take one of two forms, either: (I) A contract wherein the purchaser undertakes to buy from the vendor a specific tonnage of vegetables at a fixed price per ton, delivered to the factory over a specified period, or (2) a contract wherein the purchaser 22

undertakes to buy the produce of a specific acreage laid down by the vendor, at an agreed price per acre. In the first instance, the grower must cover all contingencies arising from total or partial crop failure, and carry a not inconsiderable element of risk of the purchaser buying in against him in the event of a crop failure. The second form of contract implies that the processor takes over some of this risk but, in return, has a reasonable chance of buying his product cheaper, if he has an efficient fieldsman service to supervise the grower and ensure a high level of good husbandry. The contract, in whichever form, will specify varieties and, in some cases, the processor will elect to supply the seed at an agreed cost to the grower. Further stipulations will cover the quality standard, the rate of intake per day and the period over which intake will be accepted.The contract will also state whether the produce is to be delivered in bulk, or in containers and how accepted weights will be established. There is invariably provision for arbitration in the event of a dispute. It is important that the quality clause in the contract should be most specific, so that the grower is made aware of the standard of grading or dressing required. The processor will also underline his right to oversee, through his fieldsmen, the sowing, planting, cultivation and harvesting of the crop. Supervision must also be exercised with types of fertiliser, weedicide and pesticide used in connection with the cultivation, as dangerous residuals can sometimes affect the p d u c e at maturity. All these factors must be fully considered and covered in the document but, as this procurement procedure has been adopted for many years by canners and freezers, and has equally been accepted by growers, either individually or by their Associations, where group negotiations arise, the dehydrator should not really have any difficulty in getting all the above clauses implemented. L A B O U R REQUIREMENTS In selecting a site for the factory, the consideration of suitable labour availability will have been made. On the assumption that the location is rural, certain advantages as to quality of labour are usually apparent, in that both male and female operatives who have agricultural backgrounds and traditions often integrate very satisfactorily into vegetable processing as this is, in effect, an extension of their way of life. The labour content of the putative 70-80 ton per day plant will vary according to the type of drying plant selected and the range of products to be handled but some guide can be given if certain assumptions are made at this point. Let it be supposed that the operation is mounted on a ten months’

23

programme over the following range of vegetables: peas, green beans, potatoes (granules and cubes), cabbage, leeks, camts, celery, beetroot and turnips. The process staff will require to operate on a three shift system, usually six days per week, with a plant cleaning shift and a maintenance shift in addition at the weekend. Local custom may require that this system be covered by four teams to avoid excessive overtime at weekends but it is by no means uncommon in some factories for staff to accept this overtime, the three eight hour shifts being covered by three teams changing their shifts by rota every week. The many types of dehydration plant will be considered in detail in the following chapters but, for the purpose of assessing the process labour content of a typical medium size plant, it could be assumed that the following dryers would be required to handle the above ten month programme: For Granules: an Air-Lift dryer with a capacity of 1.5 tons of raw potatoes per hour; For peas, green beans, cabbage, celery and leeks one Hot Air Through Conveyor Band Dryer, with a capacity of up to 3 tons of prepared m vegetables per hour- the capacity will vary according to the type of vegetable and size of cut; For mot vegetables and potato cubes: one Hot Air Through Conveyor Band Dryer with the same capacity as mentioned for other vegetables. These dryers would not be operating concurrently throughout the whole of the season but would come into operation in accordance with the availability of the crops. It is vitally important that at certain times some excess drying capacity is available to cope with gluts, or a dryer breakdown, hence the advisability of duplicating the band dryer. Some important crops, which have a short harvest period, such as peas and French beans, can overlap and, in these circumstances, shortage of drying capacity can have dire consequences. The process labour to man this scale of operation, per shift, would be approximately as follows: Shift Superintendent: Foreman: Forewomen: Quality Control: Male Plant Operators: Fitters: Electrician: Boilerman: 24

1 1 1

2 10 2 (maintenance duties only) 1 (maintenance duties only) 1

Women: Permanent night men

30-50 (trimming and selection) 15-25 (Trimmingand selection)

The female labour content will vary according to the types of vegetable being pmcessed. The above numbers in any case assume that, at the selection and packing end of the pmcess, the products e being bulk packed. Where the product is intended for retail distribution in small units, a very much larger female packing staff would be required to operate filling and packing machinery. Such considerations, in this instance, however, have not been taken into account. Male operators will normally substitute for women on the lOpm to 6am shift. It is stressed that the figures given can only be taken as a mugh guide, and they are based on the manning of two particular types of dryer, the methods of operating which are efficient and particularly economical in labour content generally. The conveyor band dryer, either single or multi pass, is probably more versatile than most in the types of vegetable it will handle, and it is particularly suitable for long sustained runs of one product. Its merits, along with those of other dryers, will be described in later chapters but in the context of the present plant under review, it requires a minimum of staff to operate it. As in the canning and freezing industries, the greatest concentration of female labour is in the trimming and selection departments, and unless strict control is exercised in these areas, as to the numbers and efficiency, costs can easily overtake profits. Technology has made great strides, however, in reducing the tedium and unrewarding work of product selection, and there are now very efficient colour sorting devices on the market, which effectively select and reject blemished material in the raw state, or after drying. This reduces the labour requirement for trimming and selection, and the development of these machines to the present peak of efficiency has cut the cost of these operations very considerably. As the particle size of dried vegetables rarely exceeds lOmm by lOmm by lOmm, the electronic colour sorter can scan these particles in their trajectory through an optical box against a predetermined coloured background. Any particle, whose colour, by reason of blemish, differs from that which is acceptable, is pushed into a different trajectory by a jet of compressed air and diverted through a waste spout. These machines have a high efficiency and perform the task of selection at a fraction of the cost of hand labour. Some visual inspection is still advisable after the product has passed 25

through a colour sorter but the labour content at this point is minimal.

Intake Staff Very considerable labour economies can be effected in the vegetable intake department by the use of bulk loaders for potatoes and root vegetables, 500kg tanks for peas and large crates or tote boxes for cabbage, leeks, celery, etc. Green beans are perhaps the only vegetable for which bags or nets need to be Also, the use of storage silos for potatoes and roots reduces the intake staff to one, or two at most, per shift, and this staff can be used for fluming the raw material into the plant. This presupposes that an adequate supply of cheap water is available from an adjacent river, waterway or borehole, fmm which the processor has a prescribed right to abstract water. This need not be potable water, as it is only used as a means of moving the vegetables fmm the silos through flumes into a primary washer, and thence into the preparation plant. Such water is normally discharged from the washer into settling tanks, to remove silt and stones washed off the vegetables, before being returned to waste or recycled. In some instances, it may have to go through an effluent treatment plant before it can be discharged but the Local Authority will have to be consulted on this matter. A destoning machine is a necessary adjunct to this part of the system. The shift quality controller has an important part to play at this point, as it is his responsibility to ensure that the quality of the intake measures up

Typical box tipper

26

to the contractual requirements of the buying department. Potatoes must be examined for total solids, reducing sugar content, excess soil, blemish and grading. Vined peas are examined for quality and tested for temperature and tenderometer reading. Camts, cabbage, celery, leeks, etc, are checked for the standard of dressing which is called for in the procurement contract. Extraneous matter in vegetables, apart from the waste factor, can also do untold damage to preparation plant later in the process, and intake staff must be very vigilant on this score. The period of intake will normally extend over twelve hours of each day, except during the season when highly perishable vegetables, such as peas and beans, are being handled, then intake and quality control staff will be required round the clock on three shifts.Adequate staffing at this point is, therefore, imperative.

Warehousing Staff The staffing of the warehousing and despatch departments will depend, as to numbers, on the nature and size of the packs being produced, and whether a bulk or retail consumer trade is being carried on. If the factory is concerned mainly with bulk packs, two men per shift for stock movement will be adequate, with a daytime superintendent in overall charge.

Maintenance Staff Apart from the fitting staff detailed to cover the shift maintenance duties, it is necessary to provide for an adequate day shift maintenance staff in the field of both mechanical and electricalengineering.Dehydration plant, operating round the clock for many months of the year, demands a high standard of maintenance,' and there is invariably a heavy day shift programme of servicing equipment, both mechanical and electrical, temporarily taken out of service for a major overhaul. A minimum of six day shift fitters and three electricians would be required for the size of undertaking under review. These are supplementary to maintenance personnel working on the three shift rota. A carpenter, painter and bricklayer can also be usefully employed all the year round on the day shift maintenance staff because continuous shift operation levies a heavy toll on the buildings, particularly at the wet preparation end of the factory.

Laboratory and Horticultural Staff Laboratory staff q u i r e d , excluding the shift quality controllers, will be three as a minimum, depending on the range of products being handled. The main duties in the laboratory are the routine analytical tests on the dried 27

product, and these are supervised by a chief technician, assisted by two or more academically unqualified assistants. Some research and development will also be carried out by the senior staff. A horticultural officer and two fieldsmen are also required.

WATER For the size of plant under review, the requirements for water washing, process use, boilers, etc, but excluding any fluming operations, will be of the order of 8 million litres per week of eight hour shifts. The quality of the water is important, and it is necessary to know the temporary and permanent hardness characteristics. It may be that the local supply is not entirely suitable for every kind of vegetable to be processed and some treatment may be necessary. For example, peas require soft water for washing and blanching, as a high calcium content in the supply has a toughening effect on the skins. In these circumstancesa water softening plant will need to be installed to treat the water which is in contact with the peas in process. Conversely, potatoes, particularly when used for cubing or slicing, require a higher degree of hardness in the processing water, and it is usually necessary to treat this with calcium chloride in the blanching process. Ideal water conditions are, therefore, unlikely to be found in many locations, and perhaps a supply with 8 degrees of hardness might be regarded as a fair average, requiring less treatment overall than most samples. Consideration of the water analysis should, therefore, be treated as of some importance when choosing the factory site. Boiler water should be reasonably soft, to avoid scale formation but, where hard water conditions apply, the supply will have to be treated chemically, or a base exchange softening plant installed. With the latter, some further organic or chemical treatment will be necessary to correct excess alkalinity which is a feature of the base exchange method. It is good boilerhouse practice to =turn all the available condensate from the processing plant, ie, from dryer steam batteries, blancher and lye peeler steam coils and space heating batteries, back to the hot well in the boilerhouse, so that the feed water supply is available at a high temperature. There are several points in the factory where mains water can be conserved by recycling, particularly the washing plant. Care must be exercised here, however, to ensure that recycled water is not contaminated, and some in-plant chlorination willbe necessary to implement this recycling system.

28

Fluming Fluming water, as referred to earlier, must come from a freeor, at least, a cheap source. It is not viable to use mains water for this purpose, as the volume required for fluming, say 70-80 tons of root vegetables or potatoes per twentyfour hour day, will be of the order of 1.2 million lihes. It is, thefore, desirable that the factory be situated near a river, or waterway, and that the River Authority can be persuaded to give the necessary licence to abstract water for this particular purpose. An alternative to this sourre of supply is, of course, a borehole, or a series of boreholes capable of that sort of capacity. The sugar beet factories use this system of fluming beet into their plants, some thousands of tons per day being moved from silo to process by high pressure water jets, with a minimum amount of manual effort. It is a system well worth emulating in the dehydration factory, where large quantities of roots and potatoes have to be handled.

/.--.--v7A b.-

AI7

I r’ --___. ,*/;//,.I ,

‘rr

I

/

End elevation of root vegetable silo with centrefluming channel

Silos The construction of the silos is quite a simple matter and a typical s u e for a 100 ton unit would be 30m by 4m. The side walls are l m in height and constructed of 23cm thick masonry. Both ends of the silo are left open to allow incoming bulk loaders or tipper lorries to discharge their loads. The concrete bottom of the silo slopes from either side wall to the fluming channel in the middle. This runs longitudinally down the whole length of the silo with a fall of 50cm in the 30m length. The width of the channel is 30cm, and this is rebated to take 7.5cm thick timber cover boards which are fitted flush with the sloping silo bottom. The shallowest point of the flume channel must be not less than 15cm deep, and it is from here that the water supply is introduced from powerful centrifugal pumps with a capacity of 91,000 to 136,000 litres per hour. The cover boards are removed in that part of the silo which requires to be emptied, and the vegetables feed in a steady stream into the fluming channel, whence they are carried along with the flow of 29

water. Beyond the end of the silo, the fluming channel continues, maintaining the same rate of fall, to the prewasher and destoner. At this point the fluming water is discharged, and the vegetables are elevated into the processing plant. In setting out this system, levels have to be carefully studied, as it may not be possible to arrange for a natural fall for the whole length of the flume, and some elevation may be necessary prior to the washer. This can only be decided by the processor in the light of local circumstances. Adequate protection from bad weather must be provided, and the silos should be under cover in suitable outbuildings wherever possible. Alternatively,50 ton storage bins may be erected over the silos to discharge directly into the flume channels. A mobile elevator will be needed to fill these from bulk transport.

POWER Electricity requirements for the putative plant will be in the range 300400KW.Whilst this will normally be taken from the mains, it is a wise precaution to have some internal generating facilities, even if only to keep essential plant running in the event of a mains power failure. Downtime in a continuous process is very expensive indeed and, apart fmm raw material in mid-process being at risk, heavy standing charges have also to be met from reserves. Also, when highly perishable vegetables, such as vined peas, are being handled, every hour lost by breakdown is irrecoverable, as the vining programme on the farms is geared accurately to the plant’s optimum processing throughput, and any hold-up at the factory can result in the loss of many tons of raw material, which could be the processor’s responsibility. This situation is very obvious when it is realised that the whole season‘s pack of fresh peas has to be processed in six weeks, therefore every hour of electrical or mechanical breakdown in the working week can precipitate disastrous losses for both the grower and the dehydrator. The economics of dehydration are elaborated in a later chapter but it cannot be stressed too strongly at this point that any steps, which can be taken by way of ensuring complete reliability and continuity of the power supply, should be taken, in the full knowledge of the consequences of breakdown. It is sound practice to install electric motors rated somewhat in excess of their actual duty, and to ensure that they are adequately protected against water, steam and conditions of high humidity, remembering also that they will probably be running continuously for many hours. It is possible to spray windings, starters and switchgear with a water repellent compound, and this precaution should be taken by the shift maintenance staff as a regular procedure. 30

A spaR motor unit should be kept in the stores for all key plant and, where drives and power requirements can be standardised for several machines, this should be arranged in order to cut down the number of spares carried. Most electrical supply authorities impose a maximum demand tariff on their consumers, and as the dehydrator is involved with a considerable power Ilequirement, and the use of several high powered motors, it is very necessary to install power factor comxtion equipment in the factory to reduce the start-up load on the meters. It is usually found that the cost of such equipment can be recovered within twelve months of normal operation and this will, of course, depend on the Local Authority’s tariff, and to what extent the maximum demand rate is levied on the commercial consumer. For a stand-by supply, a 2OOKVA alternator, driven by a diesel engine or, if a steam supply is available, by a steam turbine, should be adequate to keep the principal preparation plant and the main dryers operational in the event of a mains power failure, and this supply should be arranged so that it can be fed into the mains immediately such a failure occurs. Some factories keep their steam turbine ‘stand-by’ plants continually operating, integrating the supply with that from the mains, and utilising the back p ~ s s u r steam e for process heating in the factory This is an efficient and economical method of producing, simultaneously,electricity and low pressure steam at IO-15psi from one power source, ie, the boiler. At the same time the essential plant can be kept operational in the event of an external power cut or supply failure. BOILERS Boiler plant for this scaleof operation should be rated at G O O to 7000kg per hour, at 17.5atm, with a stand-by boiler of similar capacity This boiler rating is based on the assumption that the whole of the heat requirement for drying is not expected to be taken from the boilerhouse. This point is considered later in the chapter when fuels for drying operations are specifically reviewed. Some dryers incorporate steam batteries and air fans for convection drying and, if this type is used, then the rating of the boiler plant may have to be increased but with the advent of natural gas, and the various forms of Liquid Petroleum Gas, a very much more efficient heat source for drying is now available to the dehydrator, and steam batteries are figuring less prominently in the many modern drying plants. The boiler rating stated above, therefore, takes into account the steam requirements for peeling, blanching, scalding, jacketed or coil heated vessels, steam batteries for conditioning bins (seeBin Finishing), steam hosing for sterilisation of plant and equipment, and space heating. Dryers relying upon 31

Propane combustion chamber showing burner arrangement andair control damper developed by Aeromatic Ltd.

steam heating may require a further 5000kg per hour of steam at 17.5atm. Steam usage is related to evaporation of water from the product, and it requires 1.9kg steam per kg of evaporation. HEAT RAISING PLANT Heating systems used in air drying are either direct or indirect.

Direct System Here the fuel is burned in the air stream and has direct impact on the product. This system calls for a high degree of purity and non toxic constituents in the fuel. The development of natural gas propane and butane for commercial applications has provided the dehydrator with an ideal and economical fuel for vegetable drying and, in the author’s opinion, is to be preferred against all other fuels, wheever the dryer lends itself to direct firing. LPG in the form of propane is particularly suitable on account of its very low sulphur content (0.02 percent), its consistency of composition and freedom from unsaturated compounds. It is clean and easily controlled, adjustable to special requirements and, moreover, it is relatively competitive

and widely available from the major oil companies as a by-product of refining. The combustion equipment, comprising a series of burners in an insulated chamber, thermostatically controlled and with air and flame failure safety devices built in, is relatively cheap to install and maintain. Natural gas has similar favourablecombustion characteristicsbut may not be so readily available in rural areas, and a special run of mains from the nearest pipeline may involve considerable installation outlay AThrough Conveyor Band Dryer with a raw material throughput of 3 tonnes per hour would require a combustion unit for propane with a maximum rating of 15 million Btu’s per hour. This would call for a seven burner chamber, five burners firing continuously with two on thermostatic control. Satisfactory flame conditions can be maintained with propane at a regulated pressure of 0.95atm and, whilst the fuel consumption will obviously vary in accordance with the evaporative duty demanded, this could be roughly taken at 140kg of LPG per hour, or 36cu m of natural gas. The oil industry, in collaboration with the UK Factory Inspectorate and other experts, has laid down a Code of Practice in relation to the storage and commercial usage of liquid petroleum gas, and the processor intending to use this type of fuel should familiarise himself with the regulations, particularly as to storage tanks and pipelines. Where LPG storage tanks cannot be sited at least 15m away from the factory buildings, and 15m away from the nearest roadway, they wiU almost certainly have to be installed underground, and such installation is relatively expensive compared with ground level tankage. Whilst propane will vaporise naturally from an overground installation, such is not the case from an underground tank. Here the liquid propane has to pass through a steam heated vaporiser to convert it to a gas. Very low temperatures prevail in an underground tank, as vaporisation takes place; these are not relieved by a datively high ambient air temperature as in the case of an overground installation, hence the necessity for assisting vaporisation by supplementary steam heat. Tank pressure will be 4.5 to 6.8atm and this is reduced to 1.36atm by regulators on the pipe main to the combustion plant, where the gas pxessure may be further reduced to suit required combustion conditions and drying requirements.

Indirect Systems The indirect system can be applied in several ways, and with some types of dryer there is no alternative method of heat transfer to the product. The Through Conveyor Band Dryer can derive its hot air supply from a heat exchanger used in connection with an oil or coal-fired furnace. The heat exchangercomprises a set of cast iron or steel elementsor plates, usually 33

gilled to provide the optimum surface area for heat transfer, and the gases of combustion from the oil or coal fired furnace pass across one side of the plates, transferring heat to the clean air pulled across the xeverse side by the dryer fans. The fans draw the heated air into the dryer proper, either through or across the product which is being continuously conveyed on the dryer belt. Heat exchangerscan also be constructed with a series of tubes, instead of gilled plates; this is very similar to the design of an economizer for a boiler plant. The obvious weakness of this system is that there are considerable thermal losses, in spite of the facility, and indeed practice, of recycling the gases of combustion before discharge to atmosphexe.Then there is usually a heavy maintenance factor in cleaning the heat exchanger elements or tubes, to keep the apertures through which the gases flow free from a build up of fly-ash (where solid fuel is used) and carbon and sulphurous deposits from oil. Also, at the cool end of the exchanger, where temperatures are often below the dew point, corrosion can be a pmblem. Another indinxt heat system, which can be used with band, cabinet, tunnel and bin dryers, incorporates the use of steam batteries of gilled tubes through which the drying air passes, either by induction or pressure. Here again there are some thermal losses, and the batteries require constant and careful maintenance to ensure that the air passages are kept freeand that they are efficiently trapped on the steam side. Dust is not an uncommon problem in a dehydration factory, and this can be a source of trouble on the air side of this type of steam battery.

Combined Systems With air lift and thermal venturi dryers, it is possible to use a combination of the indirect system, with steam batteries, and the direct system of LPG or natural gas - the one system supplementing the other. The use of batteries is often economical when the factory has a surplus of low pressure steam or exhaust steam from a turbine or some other part of the plant. No heat should go to waste, and every conceivable use should be made of it. Gas heat, as a supplementary source, can then be used to obtain the desired processing temperature. The drum dryer is another example of the indirect system. Here, high pressure steam passes through either one or two large rotating steel drums, and the product to be dried is fed by spraying or by feed rollers on to the outer surface of the drums in a thin layer, and heat transfer from the inside to the outside surface of each drum evaporates the water content of the product during the course of about 300" of the drum's revolution. Owing to the 34

thinness of the surface coating, evaporation is extremely rapid, the moisture being flashed off, literally, in seconds. Steam requirements are heavy for this drying method, as a pressure of at least 5.4atm has to be maintained, and the volumetric capacity of the drum is high, some being 4.6m long by 1.8m in diameter. FUELS Suitable fuels, therefore, are coal and oil for the indirect systems, and propane, butane or natural gas for the d irect systems. In no circumstances should the gases of combustion of coal or oil be used in the direct air stream when dehydrating food for human consumption. The risks of contamination by sulphur and carbon compounds are very considerable in these circumstances and, whilst this method has been used in the past for dehydrating certain food products, it should certainly be avoided in the context of modern practice. EFFLUENT The subject of waste and industrial effluent disposal is too wide and complicated tobe dealt with in depth in this volume. It has become, in recent times, a problem of national significance and importance, and the dehydrator

1

Screening solids from liquid effluent in Italy

35

must have this subject very high on his list of priorities when contemplating the pros and cons of a factory site, and he must obviously discuss all the implications with the Local Authority or River Board before any location is determined. It has already been established that for a medium size vegetable processing plant, some 1,200,OOO litres of fluming water, where applicable, and an equal volume of processing water are going to be discharged to waste each day. The authorities will need to assess the nature and quality of this discharge before any permission will be given for it to pass into any sewer or waterway. The days when effluent could be flushed down the nearest drain regardless of its ultimate destination, are gone in the Western World and disposal today can be a very laborious and expensive business, and expert advice on the subject must be sought. It is not unknown for an effluent treatment plant to cost one third of the value of the pmcess plant, because in certain conditions very intensive treatment is required by the authorities, particularly where the discharge is made into an inland waterway First, the fluming water is likely to have a high percentage of silt and vegetable matter in it, and, in the processing water effluent, there is likely to be starch, spent lye, solid vegetable matter and various chemical compounds from the blanching water. The scale of treatment required will depend on the level of contamination, and the Biochemical Oxygen Demand of the discharge, and the processor will possibly have to decide between steam and lye, or abrasive peeling of vegetables in the context of the diffenmt effects these methods will have on his effluent pmblems. Lye peeling, involving concentrated solutions of sodium hydroxide, will create a high BOD in the effluent, and the treatment cost on this account may be considerably higher than if steam peeling was used. Steam peelers involve a higher capital plant investment but this may be offset by a lesser involvement in effluent treatment, therefore no hard and fast rules can be laid down for any specific case. Abrasive peeling of potatoes releases large quantities of free starch from potatoes, and this again creates a serious treatment problem. Some large potato processors, who have been committed to abrasive peeling, have had to install expensive starch manufacturing plants to dry the free starch collected in settling tanks used as the first stage of effluent treatment, although the financial recovery from this by-product is so low that it cannot cover the capital investment or the operating costs, but the exercise has to be done as a progressive stage in the overall effluent treatment system. The method of disposal, therefore, must be considered in the light of local circumstances, and the following options may be open to the dehydrator: 36

(1)Simple screening out of solids - this is a prerequisite to all subsequent means of disposal; (2) Filtration through gravel beds: (3)Pumping into settling tanks, followed by treatment with biological agents; (4) Aeration and lagooning; (5)Spray irrigation; (6)Discharge into a public sewer, after one or other of the above treatments - this will invariably involve a charge for the volume accepted by the Local Authority; (7)Discharge into a tidal or other waterway, after whatever treatment is prescribed by the River Board.

Solid wastes can sometimes be dried for animal foods but the operating cost of this procedure must be carefully examined to ensure that it is a viable operation. The only satisfactory approach to this major problem is to engage the services of an effluent consultant at the outset of the project, and the expert is likely to fulfil the local requirements very much mo- economically than the dehydrator would do, as the latter invariably enters this field with less than expert knowledge.

--

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Contourirrigutiw Central Turkey Wastefulcontrol but low capital cost

37

Unlimited potential from Rio Francisco in Pernambuco, Brazil

Onion field trials on contour irrigated land in Pernambuco

b

Desert irrigation Khorramshaar, Iran

3

Preparation Plant Preparation plant for dehydration is very similar to that used by the canner and freezer, because up to the last stage of conservation the raw material is prepared in similar manner, other than to provide for the introduction of certain additives which are not common to either canned or frozen products. This chapter defines very briefly the type of preparation plant used in a multi-product operation, the lay-out of which will have to be arranged to suit the production flow of several types of vegetable (or alternatively fruit) without too much disturbance to the original positioning of the machines, when changing from one product to another. The description of the various machines is accompanied by photographs and the brief outline of their function will be amplified in later chapters, which explain more concisely the processing details for a wide range of fruit, vegetables and liquid products. It is stressed that some of the preparation plant described will only be required in a medium to large scale operation, because in a low budget project, full automation would be neither viable nor necessary, as such a plant may be able to be used with the simplest product cleaning facilities, a peeler, cutter and some simple conveying equipment. Some old established factories in Eastern Europe, specialising in onion dehydration, have operated for years with a minimum of preparation machinery, being convinced that hand peeling of onions, for example, produces a much better product than a 39

machine, and even their cutters have been substantially fabricated in their own workshops. However, as indicated in Table 1.l.(imports into the UK), the volume produced in this type of factory is very small, and when world prices were low in the 1970‘s many Romanian and Bulgarian factories ceased operations in dehydration and reverted to other forms of vegetable and fruit conservation. It is emphasised that the preparation plant described is ‘upstream’ of the dryer. Downstream plant is described in the chapter on selection,packing and storage. CUTTERS (a) Dicers. The dehydration process requires that produce be reduced to a fairly small particle size, otherwise the removal of water becomes an overextended operation, with consequent damage to the colour, texture, appearance and general quality of the dried product. Also the rehydration ‘factor‘ deteriorates. Dicers are cutting machines with three separate knife actions: (1) a slicing knife positioned in the machine’s impeller, which rotates at approximately 19Orpm, makes the first lateral slice as the product is fed into the machine. The thickness of the slice is adjustable but the maximum dimension is limited by the spacing of (2) the cross-cut knives, which are fixed to a spindle rotating at about 1400rpm.The impeller thrusts the first cut slices on to these cross-cut knives by centrifugal force, making strips ranging from 7.lmm to 13mm in width, pre-determined by the thickness of the first slicing cut. (3) The third cut is made with a row of circular knives that can be spaced in 3.2mm increments from 6.4 to 76mm apart. Julienne cuts are produced using circular knives spaced 4mm, 4.8mm or 6.4mm apart. For this type of cut, the cross-cut knife spindle is replaced with a slice guide roll, and the slice thickness (first cut) is adjusted to suit the circular knife spacing. A Model G dicer can be used as a slicer to produce any thickness up to 19mm. An inner chute must be used in these circumstances to guide slices across the slicing knife holder into the discharge chute. The above description, and those given below, relate to one American designed machine, noted for its high performance and reliability, and it is used internationally. 40

There are other Continental makes, built on similar lines, and the processor must judge which marque serves his purpose best in performance and cost effectiveness. The dicer is perhaps the most flexible cutter available, and will handle quite a range of products but, with a wide product mix, other types of cutter will doubtless be needed. Cutter knives r e q u k constant attention and should be sharpened every eight hour shift, especially when used on tough vegetables, such as carmts, swedes, turnips, cabbage, celeriac, etc. Failure to do this will give rise to a ragged product which will matt on the drying surface, whether it be a tray or a conveyor slat. This creates an impermeable mass which the air flow will not penetrate, and these conditions will delay drying or, at worst, will make even drying impossible. Honing machines are available for both crosscut knives, circular knives and slicing knives, and these can usually be supplied by the cutter manufacturers. In a medium to large operation, it is obviously wise to duplicate all cutters, so that by having two in parallel, the knife change will not hold u p the production flow and the product can be switched immediately, without any hold-up from one cutter to the stand-by machine. Each knife assembly can be removed with all the knives (ie, cross-cut and circular) in situ, and indeed can be sharpened as a unit, without dismantling each knife separately for servicing. This facility of course makes it possible for the smaller operator to remove and exchange a knife assembly, so long as he carries a spare assembly, and in this way he can avoid having to duplicate the whole machine but, of course, there will be some delay in the actual removal of the old machinery and replacement by the spare one, and some production time will be lost. The shift fitter must, as a priority, watch the condition of the cutting knives throughout his shift, very much as the seamer fitter in a cannery watches the quality of the double seam cans passing through a high speed can seamer at lo00 cans per minute. In both cases a lapse of attention at this point can spell trouble. Disposable knives avoid honing costs. Where cutters are duplicated, it is obviously wise to install two of identical make, so that economy in carrying spare parts is achieved.

(b)J Cutter This is eminently suitable for bulb and leafy products, such as spinach, leeks, spring cabbage, bell peppers, parsley and other herbs, celery and citrus fruit and the peel. The machine operates on the principle of a high speed belt carrying 41

the product to the cutting parts. A 152mm diameter feed roll is fitted at the feed end of the belt to the knives. This flattens the vegetable before entering the knives and forces them into the cutting area. By the arrangement of the circular and cross-cut knives, the J cutter produces square cuts ranging from 6 by 6mm to 13by 13mm, the thickness of this square being the thickness of the original product. For example a capsicum with flesh 4mm thick would emerge as a square flake 6 by 6 by 4mm or a larger square if the knives were adjusted. Strip cuts can be made by removing the cross cut knives.

(c) CC Slicer This machine will slice products up to lOOmm in diameter. Anything larger will need a heavy duty machine, such as the Model Y slicer, or the G dicer with the cross cut and stripping knives removed. The standard slice for the CC slicer is 3.2mm thick but special parts are supplied to make thicker slices, such as onions at 4mm. One benefit of the CC slicer is that the knives are disposable, and this avoids honing and sharpening and, in effect, these knives are cheaper than the cost of sharpening those fitted to other machines and the cost of down-time. They will operate for 8-12hr with normal usage and are ideal when handling onions.

(d) OV Slicer This is a transverse slicer for fruit and vegetables which are not more than 70mm in diameter. Slice thickness is controlled by using a different slicing wheel which can be selected to give a slice length (or thickness) ranging from 1.6mm to 32mm. The slicer will not handle sticky products but can be used for leeks, bananas, carrots, rhubarb, celery and asparagus. The feed must be controlled very evenly.

(e) Comitrol This is a cutter which will produce a wide range of cuts, and will comminute by flaking, slicing, shredding and dicing from 13mm down to microscopic sizes. It handles equally efficiently meat, fish, vegetables and fruit. It would have a special application in comminuting soup ingredients down to a size suitable for instant or rapid rehydration.

(f) SC Scarifier This is used in dehydration specifically for slitting the skin or membrane of fresh peas. Peas are normally scarified before blanching, and 42

alp f e d into the scarifier hopper from which they fall in a conhdled stream between a rubber roller and a row of serrated wheels, revolving at a different speed. The peas pass through in a single layer so that each pea makes contact with the slitting wheel. The slit is made at a contmlled depth - usually about 3mm as the peas pass between the rubber roller and the knives. The purpose of scarifying is fully amplified in the Chapter 5 on the ptucessing of vegetables (green peas). (g) Bean Slicer Model W It is recommended in Chapter 5, on the subject of processing Green Ekans, that slicing should be carried out after blanching, to avoid the loss of bean 'seed' in the blanching water. Round pod beans are normally used for dehydration, and the Model W slicer gives a Julienne or French-style long cut rather than a transverse cut. The beans alp f e d by a belt incorporated in the machine to the cutting head, and kept in a straight line by oscillating parallel guides. The head consists of a circular knife spindle, a stripper plate assembly and a stationary knife. The beans a= cut lengthways by the cirrular knives, removed from between the knives by the stripper plate and guided on to a horizontal stationary knife at high speed, causing them to be cut through the centre at right angles to the cuts made previously by the circular knives.

A g r m b a n snibbing line, cluster cutters and spill proof elevator

43

Left: Urschel Model G-A dicer, strip cutter and slicer

Right: Urschel Model J9-A two dimensional dicer

Left: Urschel Model RA-A for small to intermediate sized dices, strip cuts and slices

Right: Urschel Model WVF bean slicer

4

01)Bean Snipper This is a revolving drum with perforated slots around the periphery. Knives are positioned to cut along the whole length of the drum, the cutting edge being set almost up to the drum surface. The beans tumble around as they pass through the inside of the cylinder and, in course of travelling along its whole length, the ends project through the slots and are cut off by the knives. Most modem snippers are continuous in action rather than batch fed, and any unsnipped beans at the discharge end alr?returned to the feed end or, in the case of high capacity throughput, to a second machine in the line. PEELERS There are basically four methods of peeling potatoes and root vegetables: (1)Lye peeling; (2) Steam peeling; (3)Combination of heat and lye; (4) Abrasive peeling, either batch or continuous. The dehydrator will have to decide which method suits his circumstances,and with due considerationto the effect of the method chosen on the effluent problem, which can, of course, be aggravated by one or other of these methods. Provided that the effluent problem has been taken calr?of, and that suitable treatment has been organised, the preference will usually lie between steam or lye peeling, and the advantages and disadvantages of both methods can be summarised as follows:

(1)Lye Peeling One of the main advantages is the relatively low capital cost of the equipment, as it is quite usual for lye peelers to be fabricated from mild steel, no particular advantage being obtained by using stainless steel. The design is basically simple, usually consisting of a perforated metal drum, with pockets into which the vegetables are fed, rotating in a bath of hot lye (sodium hydroxide) solution of 5-20 percent concentration, according to the peeling characteristics of the vegetables being handled. Maintenance costs are low, as there are few moving parts in the machine. The system is capable of a wide variation in peeling technique to suit any particular type of raw vegetable. Some processors use the thermal shock method of high concentration and temperature, with short immersion time, whereas others prefer a lower concentration of lye and longer dwell time. In some cases, wetting agents are used in the lye tank, to cut down the usage of 45

sodium hydroxide, or to make more effective use of the standard concentration being used. Another technique to economise on lye is to allow the vegetables to pass from the peeler through a ‘retaining’ reel, which is really a reel or rod washer with the water spray equipment removed. The dwell time in this reel, which can be 10 - 15min, according to its capacity, has the effect of extending the penetration effect of the lye on the skin of the vegetable, thereby reducing the duty, and consequently the concentration of the lye in the peeler itself. From this reel, the vegetables pass normally to the washing process, which is either carried out in a second reel washer or in a rotating brush washer. On the debit side, the cost of sodium hydroxide is high, particularly when high concentrations have to be sustained. Also a considerable volume of water has to be used in subsequent washing, to a m s t caustic bum and excessive penetration of the flesh and to remove all surface traces of lye. Again, some further chemical treatment may be necessary if peeled potatoes or other vegetables have to be held in a surge hopper for any length of time prior to further processing. In these circumstances, it is usual to dose the surge hopper with 0.5 percent citric acid to neutralise any trace of alkalinity left by the lye treatment, and this, of course, adds to the cost of the operation. Where lye peeling is undertaken, very special precautions must be taken to protect operating personnel against injury by contact with lye, and it is essential that the staff engaged in this department are supplied with heavy rubber boots, gloves and outer protective clothing, and goggles must be worn at all times. Suitable warning notices relevant to the hazards must be displayed adjacent to the peeler, and first aid equipment to deal with caustic bums should always be close at hand. Very rigid control of conditions of immersion time, temperature and concentration must be exercised, otherwise heavy leaching losses will occur, which will seriously affect the ratio and yield of end product. Leaching is the loss, by extraction, of soluble solids in vegetables, which is caused by overimmersion in either the lye peeling liquor or the blanching liquor. High temperatures are also a contributory factor to leaching in some cases. (2) Flash Steam Peeling This method is extremely efficient, and has the advantage of creating

fewer effluent disposal problems than other methods. The system utilising high pressure steam at 17atm ensures that even awkwardly shaped products are evenly peeled. Steam at the pressure indicated heats the moisture under the skin of the vegetable in such a manner that, when pressure is reduced this moisture 46

Table 3.1 Relative peeling efficiency

FLASH STEAM PEELING SYSTEMS TYPE Pressure Vessel Volume, litres Door diameter, mm Support bearings, mm Steam connection, mm Air connection, BSP.T. Door seal

Speed Product per charge, Kg

100

200

100 200 60 60

200 300 75 75

300

300 300 75 75

400

400 350 100 100

550

550 350 100 100

800

800 400 125 125

950

950 400 125 125

1250

1250 450 125 125

Silicone rubber, 8mm dia. section

34

67

6 rev. per min. 100 134 200

226

333

666

Steam 25Opsi max WP (17 bar) Nominal consumptionKg/hr 100 200 300 400 600 800 1000 2000 Inlet valve, mm 25 40 40 50 50 75 75 75 Exhaust valve, mm 32 50 50 80 80 100 100 100 80 80 80 80 80 Air, psi 80 80 80 Electricity 415V, 50hz, 3 phase (power), 110V, 50hz Single phase (control) Power Pressure vessel, KW Feed Conveyor, KW Discharge conveyor, KW

1.5 2.2 2.2

1.5 2.2 2.2

1.5 2.2 2.2

1.5 2.2 2.2

3 2.2 2.2

Performance Typical example, Kg per hr 1000 2000 3000 4000 6000 Ware potatoes All capacities based on 30 cycles per hour

3 3 2.2

3 3 2.2

4 3 3

8000

10,000 20,000

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flashes off, lifting the skin with it. The final operation is to pass the product through a skin eliminator. Peeling losses can be as low as 15 to 17 percent with ware (ie, table size) potatoes. See TABLE 3.1.

A flash steam peeler

(3) Heat-Lye Peeling The combined use of lye and heat peeling has been developed in America for potatoes. Tubers are first immersed in a very light lye solution, and then pass through a gas fired infra red unit at 900°C. After the infra red treatment, most of the softened peel is removed by studded rubber rolls in a mechanical scrubber, and final cleaning is effected in a brush washer, which uses a minimal amount of water. It is claimed that caustic soda usage is cut by 80 percent and water usage by over 90 percent, using this method. There are, relatively, no waste water problems, as the system uses only 15-45 litres per minute against 7001800 litres per minute in conventional lye peeling, and the waste peel can be consolidated to a paste of approximately 15 percent solids which, after neutralising, can be used for animal feeding. 48

(4) Abrasive Peelers This type of peeler has been used for many years in all branches of the vegetable processing industry The earlier models were the ‘rumbler’ batchtype,which cannot be considered seriously for a dehydration factory, owing to the limited throughput and the fact that the abrasive action is too severe and far too much weight is lost. The new concept is to run the abrasive rollers longitudinally in a circular cage, fitted around a centre auger. This roll cage mixes and turns the vegetables to expose all surfaces, whilst the abrasive rolls also rotate at adjustable speeds to control the applied abrasiveness. Thus, control is applied on the seventy of the abrasion by instant adjustment of the roll speed, and total exposure time is governed by the auger speed.The abrasive rolls on these machines can be exchanged for brushes when handling thin skinned or delicate vegetables. It is almost inevitable that, when abrasive peelers are used for potatoes, a considerable quantity of freestarch will be released from the peeling plant, and this again can produce an effluent disposal problem. Invariably, this effluent has to be settled out in tanks before the waste peeler water can be finally discharged. It is not intended, in the foregoing summary, to denigrate or recommend any particular peeling system, as there willbe many local factors and circumstances to be taken into account by the dehydrator when he is equipping his factory but the ’pros and cons’ for each system are based on the experience of the author in several differing locations.

Tlleikpusson continuous abrasive peeler

49

Reel Washer

WASHERS

Thorough washing is essential after any of the foregoing peeling methods, and the types of washer normally used in dehydration factories are as follows: (1) Slatted reel washer, rotating on trunnions, with a centre sparge pipe fitted with water spray nozzles; (2) Rod or wire mesh rotary washer similar in action to the reel washer; (3) Rotary brush washer. Here again, the choice will depend on the degree of sophistication the processor requires at this point in the process. Reel or rod washers are both effective, provided efficient spray nozzles are fitted and the dwell time is sufficient for the weight per hour being fed through the machine. Incorrectly designed sparge pipes, with holes drilled at random along their length, to provide the necessary water spray, can give rise to a tremendous wastage of water, and this is a point which must receive very special attention. Some washers have been known to consume 20 times the volume of water that was actually required or necessary, had the proper study been applied to the washing method.

50

The capital cost of a reel or d washer is possibly only 30 percent of that of a modem brush washer but the latter is a particularly sophisticated machine, which works very efficiently with most types of vegetable and, properly controlled, will probably repay the increased capital outlay within a season. These machines comprise a trough-shaped frame, with six or more longitudinal rotating nylon tufted brushes, the bristles of which axe set in a spiral fashion to assist the movement of vegetables throughout the length of the washer. A longitudinal spray pipe, fitted with fine nozzles, is located down the middle; it is cam-operated so that it rotates through about a", directing the water sprays over the whole inner area of the washer, through which the vegetables are continuously passing. The brushing action tends to be more effective than the mere tumbling action of the simpler md washer, as it facilitates the removal of potato eyes, and excrescences and growth cracks in most t y p e s of mot vegetable are attacked with better effect. Water usage on these machines is usually very economical and, given the correct type of nozzle, a water pressure of 1.4atm is quite effective for throughputs up to 4-8 tonnes per hour. Reference has been made in Chapter 2 to the water usage to be expected in a medium size plant but this figure can be wide of the mark if proper care and attention is not given to the installationand correct operation of the washing plant.

Hot water blancher

51

BLANCHERS Blanching techniques and equipment are similar to those used by the canner and freezer, and the process is carried out either by steam or hot water. The dehydrator may have to install both types of blancher, as certain vegetables will respond better to steam blanching, whereas hot water blanching is preferred in other cases.

Steam Blanchers These can either be the rotary thermoscrew-type or a mesh conveyor passing through a steam chest. Where additives require to be used, these have to be sprayed on the vegetables as they leave the blancher. One school of thought in dehydration circles believes that steam blanching inhibits leaching losses but the latter problem has received much scientific attention in recent years, and techniques have been developed in which blancher liquors are buffered to reduce the tendency of soluble solids to dissipate in the course of this process.

Hot Water Blanchers These are invariably the rotary smw-type and are somewhat more economical in steam usage. Additives can be intmduced directly into the blanching liquor and control is usually more accurate than in the case of additives sprayed after steam blanching. An ancillary steam heated tank unit is required to make up a solution of additives (sulphite, citric acid, sodium pyrophosphate, calcium chloride, sucrose and saline solutions, etc, combinations of which are used with various types of vegetable) and this solution is usually drip f e d into the blancher, or circulated by pump, and returned back to the tank, where the required concentration is maintained at a prescribed level. Where the level of additives xquiFed is high, it is essential to heat the blancher entirely by closed steam coils, rather than by open steam injection, as, by using the latter method, the condensate will dilute the liquor, create a large volume of overflow and generally make control difficult. Open steam injection is sometimes used as a temperature booster but should not be used continuously. Blanching methods vary for each type of vegetable, as will be described later, but it is important, when selecting a blancher, to specify stainless steel construction. With many vegetables, it is customary not to drain the blanching liquor off for several days, and in these circumstances, stainless steel is the most hygienic material to withstand these particular conditions. The chemical constituents of blancher water would set u p corrosion very 52

quickly in mild steel or galvanised equipment. The desirability of retaining the blanching liquor for long periods arises from the necessity to d u c e leaching losses, which have also been r e f e d to in the context of lye peeling. Retention of blanching liquor permits solids leached out, at the beginning of the blanching process, to build u p fairly quickly to a level where fresh material passing thmugh no longer gives up its solids so readily, and a liquor of relatively high density is created. By using the buffering technique hitherto described, it has been proved conclusively that the solids content in blanched vegetables can be in excess of that in raw, unblanched material, and this can affect the ultimate yield of the dry material dramatically. An exception to this prpcedure is in the blanching of potatoes. Here the solids are in the form of free starch, released from the cut surface of the potato, and it is necessary that this be washed away, as it creates drying problems by causing a condition of impermeability to arise in the bed of material in the dryer, with serious detriment to the air flow. Also, an accumulation of starch in the blancher sometimes sets up uncontrollable foaming. In this case an anti-foaming agent can be used. Blanchers should be selected only after careful consideration has been given to their design features relating to hygiene and easy cleaning. Unlike equipment used in canneries, which may operate on a day shift basis, the blancher in a dehydration factory has to work continuously for some 150hra week, and it is absolutely essential that its construction takes this into account, and that raw material is not left behind in augers, crevices and inaccessibleparts of the machine. The inside of the blancher should be easily and quickly accessible for weekend cleaning and sterilisation. CONVEYORS The approach plant and conveying systems should all be constructed in stainless steel, wherever contact with the p r e p a d vegetables takes place. Where gooseneck elevators are used, the buckets should be of plastics or moulded rubber. Conveyor belts should be PVC-covered and manufactured to the highest sanitary standards. The conveying system from the blancher to the dryer should be arranged to allow as little delay as possible in transferring blanched material to the first stage of drying, as a high bacterial count can build up at this point, if this precaution is not taken. This condition is aggravated where cooling does not take place afterblanching. Where it is desirable to retain the additive level in blanched vegetables with a minimum of loss, water cooling after blanching is often omitted but it is essential, in these circumstances, that the drying process starts immediately and the blanched vegetables are not left

53

Left: a spiral elevator as produced by Valley Azitornation Right: A vertical destoner/washer

around for extended periods. This is one of the hazards in tunnel or tray drying, where trays of vegetables have to be filled singly and loaded on to trolleys - an operation which can take upwards of half an hour - with the consequent delay in entering the first stage of the dryer. In these circumstances cooling by cold water spray or cold air blast is essential but where conveyor band dryers are used, and a rapid transfer from the blancher to the dryer conveyor can be assured, then cooling can be dispensed with and some thermal advantage gained in the dryer. Conveyors used after the drying process do not require to be of stainless construction but again care should be taken to ensure that all equipment of this nature canbe easily cleaned as, from this point on, abrasion of the dried product and dust will be the major problems. Vibratory conveyors and elevators should always be used where possible with the dry product, as these are much more hygienic and less pmne to set up product abrasion than conveyor belts and bucket elevators. The cost of installation is relatively high but the processor is handling an expensive product and he cannot afford to make a lot of ‘fines’,by abrading away the finished material, as this by-product has very little commercial value. MISCELLANEOUS AND SPECIALISED PREPARATION P L A N T

Destoners for root vegetables: Bulk Feeders: Dry Cleaner Reels Where root vegetables are flumed into the plant, stone traps are invariably fitted into the outside washer, which is sunk into a concrete pit to suit the gravity flow of water and vegetables from the flume channels. This rugged type of washer is similar to those used in sugar beet factories. The vegetables are elevated into the bulk feeder at the intake end of the production line proper. The bulk feeder, which may have a capacity of 5 - 10tonnes, according to the required level of throughput, has a slowly moving belt built into the bottom of the bin and this, being set at an upward sloping angle, delivers the produce at a measured rate on to a m s s conveyor which transfers the material to the next machine. The bulk feeder can, of course, be fed directly by tipping farm tote boxes or stillages by means of a mechanical box tipper, or even manually if the containers are small. The bulk feeder is usually situated at the factory entrance/reception area for raw material. Where no prewashing of root vegetables has been effected by fluming, then most root lines have a dry cleaning reel installed immediately downstream of the bulk feeder, and this is a slatted reel rotary drum revolving at a slow speed; this has the effect of removing clods of earth and

55

soil adhering to the roots or tubers which may have been lifted from heavy land or in wet conditions. Roots in such a condition may be refused by the processor as not complying with the contractual quality specification by which the grower is bound but, if accepted, some deduction in weight for excess soil might be imposed, as an alternative to refusing the load. The produce then passes to the factory-based destoner. This is essentially a vertical screw elevator into which the vegetables are fed via the bottom hopper, then lifted upward through a column of water, discharging at the top, any stones or grit falling to the bottom of the machine, from where they are removed.

Preparation Plant for Beans A Pneumatic Separator is an aspirator specifically designed for beans (and peas) to remove by air flow all extraneous matter, such as skin, leaf, haulm, etc. Cluster cutters are installed specifically when beans have been mechanically harvested and clusters of beans are not separated entirely into separate pods. Such a machine is not required when beans have been manually picked. Vibratory feed to the Snippers is essential to give a controlled flow to however many snippers are in the line. The vibrating conveyor gives a gentle feed which precludes the snipper drums becoming overloaded. A bean washer is essential, especially for harvested beans and this is usually located after the pneumatic separator. A vibratory Feeder to the bean slicer (already described under the heading of cutters) is necessary, again to give an even flow to the slicing machines, so as not to over or underfeed them.

Preparation Plant for Onions A grader is essential (a) to discard bulbs under 50mm in diameter (b)

to grade the balance in the range 50mm - 60mm and those at plus 60mm. A dry cleaner is used to =move the loose skin and dry tops, and also any sand or grit brought in from the fields. A rod washer is installed with a sparge pipe and a good flow of fresh water. An Autocore topping and tailing machine with a Shufflo feed may be installed - only if the onions are full globe in shape. This machine will not handle half globe or flat onions. This latter type of onion will have to be topped and tailed (a)manually, or (b) by a Hydrout manually fed machine. These machines have a revolving 56

Right: Pneumatic separator for peas and beans

cutting/coring knife, are bench mounted with a front safety guard and have a hole messed in the centre of the guard plate into which the onion is placed. The revolving knife bores into the root of the onion which can then be reversed for removal of the top. As the onion has to be held in position by hand against the thrust of the knife, the machines can be dangerous to operate in spite of the guarding, but everything depends on the concentration of the operator. The Factory Safety Inspectoratebans these machines in some countries as being unsafe but the author has seen them used extensively in many factories. It is a matter for the management to decide. The alternative is to remove the core only by hand knife, and allow the following abrasive peeler to remove all trace of the top, which an efficient 57

machine will do if followed by a little hand trimming. A continuous abrasive peeler is probably the most suitable type for onions. These machines can be supplied with a central lubrication point for all the revolving abrasive rollers, the augur feed and all the drives. It is however recommended that, in factories where the mechanical engineering staff are not always 100 percent fastidious about lubrication, a peeler where separate grease points are fitted is a safer proposition. A small water spray sparge pipe fitted over the elevator taking the onion slices to the dryer is essential to remove surface sugar from the cut onion. This sparge pipe can be fitted as a special addition to a standard elevator.

Preparation Plant for Tomatoes and Peppers A tomato washer is a tank with high pressure water jets and water agitation by compressed air. The installation consists of a prewasher, fitted with a perforated bottom, into which the produce is fed. A rotary transfer reel or 'paddle' transfers the tomatoes to a second washer at a contmlled speed, and they are again subjected to washing in water agitated by air jets. The fruit is picked up at the discharge end by an upwards sloping roller conveyor, feeding on to roller-type sorting and inspection tables. These are elevated and the operators sit on both sides of the tables on railed platforms. Bell peppers can also be washed and sorted by the same method but in the case of peppers these are split by hand (machines are not 100 percent reliable) de-seeded and washed again in a flood washer. The double flood washer comprises two V-shaped tanks, each with a compressed air unit to agitate the water, and the produce passes through both tanks by the action of a series of paddles, which finally elevate the washed cut peppers on to an inspection belt so they may be examined for traces of any seeds still left in the flesh.

Preparation Plant for Cabbage, Spinach, Leeks and Celery Cabbage corers can be supplied with a single or double head. They are manually fed and can be adjusted to take any normal size of cabbage. A quartering machine is located alongside the corer, and this will cut any cabbage into quarters when it is too large to feed into the impeller of a Gtype dicer, as cabbage is normally diced rather than sliced. Very few dicers will accept a whole cabbage, and quartering imposes less wear and tear on the dicer knives. The main preparation plant requirement for spinach, leeks and celery is a triple flood washer, as all these vegetables are notorious for retaining soil in between leaves and follicles. 58

Preparation Plant for Peas A Tenderometer is an essential instrument for testing the maturity of peas on arrival at the plant, and this should be synchronised for scale readings with the Tenderometer on the farms. A reel washer is required to rinse the peas on arrival. A pneumatic separator will remove by aspiration any leaf or stalk left in after the farm cleaning. The latter is now usually so good that factory aspiration produces very little extraneous matter. A floatation quality grader will separate the peas into positive quality grades by specific gravity. A typical machine is illustrated. A pea pump is an ideal medium for conveying peas h m process to process in water. The rotor of the pump should be specially designed to minimise damage and, although several makes are available, the author has found that the Mono pump is very satisfactory. Special tough glass piping is used for the conveying medium. A recycling tank is fitted with a grid for separating out the peas and returning the water.

Preparation Plant For Beetroot In addition to the hitherto mentioned washing and cleaning plant for mots, beets require complete cooking before drying. There are two alternatives: (a) standard autoclaves batch fed, or (b)a Thermoscrew at 1 bar ( a m ) pressure, giving a throughput of up to 2 tonnes per hour continuously on a 20 to 40 minute cycle.

Preparation Plant Common to All Products Steam pans, stainless steel, jacketed, capacity 400 litres, with electric stirrer, are used for making up additive solutions for the blancher or for the sulphite applicator spray (see illustration of integrated unit). A dewaterer for removing surface water from products immediately before entry into the dryer. This can be used as a sulphite applicator as well by incorporating a water sparge pipe over the miprocating deck.

Services and Utilities TABLE 3.2 lists the power, steam and water consumption required to service the principal items of preparation plant in a medium/large sized dehydration factory. TABLE 3.3 lists the ancillary plant and services.

59

Additive steam jacketed pan assembly with stirrers

60

TABLE3.2 Computed Demands on Utility Services for a Range of Pmparation Plant Item

Power(Installed1 Steam Water KW Kg/hour lit./hr Bulk Feeder 8/9 tons 2 1 Bulk Feeder 4/5 tons Conveyor belts. Up to 7m 1.5 10-15m 2 Elevators 1.5 Dry Cleaning Reel 2 5ooO (if used as washer) Destoner/ Washer 3 2000 Steam Peeler (complete unit) 6 350/500 (17bar) Skin Eliminator 1.5 5o00/10,000 Abrasive Peeler: Batch 3 3000 Continuous 9 5o00 2.5 Dicer G Type 2 Cutter J Type 1.5 Slicer CC Type Slicer OV Type 2 2 Bean Slicer Pneumatic Separator 3 Horizontal Destoner 2.5 2000 Hot Water Blancher 5 500 1000/2000 700 Blancher (Draper Steam Type) 3 500 (1bar) Thermoscrew (6mxlm dia.) 3 Bean Declusterer 3 Vibratory Distributor 1 Bean Snibber 1.5 Steam Pan & Stirrer (400 lit) 0.5 100 400 Mono Pump (1001it/min) 1 Pea Pump System 2 500 Dewaterer-SO, Applicator or Starch Applicator 0.5 Flood Washer (2 section) 3 1000/1500 Flood Washer (3 section) 4.5 1500/2000 Reel Washer 1.5 1000/1500 Brush Washer 2 1500/2000 Elevator with Sparge Spray 1.5 1000 Cabbage Corer (Twin Head) 2.5 Cabbage Quartemr 1.5 61

0.25 per unit Apricot Pitter (manual) 1.5 Apricot Pitter (automatic) Pineapple Sizer (F.10) 2.5 Tomato Washer/Sorting Unit 3.5 15000 Box Tipper 1.5 'Cap Down' Shaker (Apricots) 1 Vibratory Screen 1.5 Precision Air Classifier 2.5 Turbo Mill UT 12 Model 20 Powder Sieve (Granules) 1.5 Sack Stitcher 1 Raw Vegetable Fluming Systems, Dryers, Conditioning systems (raw and dried products), boiler plant, water supply systems, effluent systems, dehumidification plant, site and factory lighting are excluded from the above figures. TABLE3.3 (Farm) Garden Pea Mobile Viner, cleaning and chilling plant, pea tanks. (Farm) Green Bean Harvester (Tractor drawn.) (Farm) Green Bean Harvester (SelfPropelled) - Alternatives Economic Boiler (complete installation) Scaled to throughput. Water Storage Tank (100,0001it/200,0001it) Water pumps to plant, and water softening and treatment plant. Plant Staging and Walkways. Effluent Screens and Pumps. Weighbridge (20 tonne) Air Conditioning Plant (if required) for vegetable storage/offices Dehumidification Plant (Packing and Milling area) Power Transformer. Factory Power and Light Installations. Site Road Lighting Standby Generator Fans/Cooling Equipment for vegetable store where applicable. Platform Trucks for Factory internal use. Forklift Trucks Factory Transport, - Trucks - Pick-up. Staff cars. Insectocutors. Laboratory Equipment. Workshop Tools. Canteen Equipment. 62

Office furniture and equipment. PVC bins and basins for factory internal use (vegetables). 15 cwt vegetable bulk boxes.

SmallFieldboxes(1Wkgcapaaty) Staff Housing (where applicable) Tenderometer (F.M.C.) The above items must be taken into account in computing the capital requirements in any project, as and where relevant.

63

4

Dryers Air drying of vegetables is still the most widely used methodand there are several options open to the dehydrator as to the type of dryer that can be used for this purpose. In the early days of the industry, tunnel and stove dryers were in general use. Designs varied widely but all of them involved the use of shallow trays upon which the material for drying was spread to a depth of 2540mm. The tray loading and unloading involved a fairly high labour content but, in spite of this, many factories throughout the world are still using this method. Continuous conveyor band dryers with single or multi-pass have, however, superseded tray drying in recent years, and this trend towards automation has obviously brought a higher degree of efficiency into modern dehydration factories and has substantially reduced the labour content of the operation. Cabinet dryers are still useful, however, for pilot runs, and for specialised products where a high level of throughput is not desired or possible. This type of dryer is, therefore, described in this chapter, as it could well fill some special requirement, albeit not in the context of the main production line. STOVE AND CABINET DRYERS Stove dryers are ideal for small to medium levels of production, and are a smaller version of the tunnel dryer, in that they operate a system of tray drying, the trays being racked on mobile trucks. The air-flow, however, is

65

cross-flow and introduced at the side of the dryer rather than at the end. The trucks may be in a single line down the length of the dryer or in double mws, side by side. Access doors are fitted to both ends of the dryer and the design is modular so that the drying compartment can be extended to meet throughput demands, within certain limits. An onion dehydration installation regularly visited in Egypt utilised 6 stoves and 12 trucks in double formation, ie, 6 pairs side by side. The stoves were used in tandem, the first stove providing the hot zone, then a space was provided for the two end trucks to be removed for ‘riffling’ over the semi dried onion on the trays, prior to moving both trucks into a second stove operating at a lower temperatuxe. As two trucks moved from the ‘hot‘ stove to the ‘cool’ stove, two freshly loaded trucks were entered into the hot stove and two trucks were removed at the end of the cycle at the cool end. The total installation, therefore, comprised six stoves divided into three pairs, in other words, three dryers each with hot and cool drying zones. The trucks carried 30 trays measuring 813mm by 813mm by 5lmm deep and each tray was loaded with 5kg of prepared onion. A 30 minute cycle was used for each pair of stoves, and in 24 hours 4 complete charges per drying unit of two stoves enabled some 43 tons of prepared onion to be handled. This equated with 6 tons of dry onion, after conditioning.

Stove dryer showing fans and heater lourves

66

This system was labour intensive but suited conditions in Egypt where labour was plentiful. One factor to recognise with any system using trucks and trays is the necessity of providing a good hardened floor surface, treated against acid and alkaline attack and the wear and tear of truck wheels passing over it continuously. It is a good precaution to lay steel tracks flush with the floor surface, where the trucks pass through the stoves in the drying compartments, and extend them out to the loading and unloading areas, and the riffling space between the dryer heat zones. The cabinet dryer is essentially a small batch tray dryer, suitable for any product being dried on a pilot scale, or small production level. They are usually of 10or 20 tray capacity, each tray measuring 813mm by 406mm by 30mm deep. The trays are supported in the cabinet on angle brackets at the sides spaced 75mm apart, with one tray per level in the 10tray dryer and two at each level in the case of the 20 tray unit. The heat source may be steam or electricity and is located at the side of the drying compartment - a fan provides a cross-flow of drying air. T U N N E L DRYERS Tunnel dryers incorporate the tray drying technique of the stove dryer on a semi continuous basis. They can be designed to give a viable commercial throughput and, as stated at the beginning of the chapter, are still used in America and Europe, in some of the older factories. As the name implies, the drying chamber consists of one, two or sometimes three tunnels, rectangular in section, up to 12m in length, with a loading aperture sufficiently large to allow the entry of trolleys, which cany the drying trays in racks up to 1.8m in height. The trays are racked in pairs on each shelf of the trolley.

Double Tunnel Dryers This type of dryer was developed in the UK in 1940 for a programme of vegetable dehydration under the auspices of the Ministry of Food. A typical double tunnel unit comprises a ’wet’ tunnel and a ‘drf tunnel running parallel. The dryers set u p by the Ministry were some 10.7m in length, and the heat source was gilled steam tubes with the fans positioned aft, so that air was drawn through the heater bank and blown through the tunnel. The trolleys entered the wet tunnel sideways, locating on a track fitted with a pusher device. In the first position, the trolley was sufficiently far away from the fan to permit adequate diffusion of the hot air stream to avoid scorching the product. 67

The blanched vegetables, racked on 50 trays per trolley, remained in the first position for 25min, then a second trolley was moved in, the pusher gear moving the first one to the second position in the tunnel. Thereafter, and at the same 25min interval, further b l l e y s entered and all moved pmgressively down the wet tunnel, concurrently with the air flow. At the end of the wet tunnel, each trolley emerged and, after turning through 180' entered the dry tunnel. Here the b l l e y s met the air stream in counter flow, the hot air fan in the dry tunnel being positioned at the opposite end, ie, alongside the wet tunnel fan. The progression through the dry tunnel was at the same 25min interval, and the whole drying cycle varied fmm 6hr to 7hr, according to product and weight of tray loading. These dryers, in the main, were used for the dehydration of potatoes, cabbage and carrots for use by the Servicesbut, after the War, many were used for a wide variety of vegetables for commefiial distribution. The inlet temperatures to the drying section of each tunnel of this type are thermostatically controlled and typical operating temperatures for root vegetables are as follows: Wet Inlet: 99' 104'C Dry Inlet: 65o 71 "C The wet tunnel outlet temperature will be in the range 57" 60'C. The air flow is controlled by louvres over the tunnels and it is possible to recycle 5@75percent of the air, by louvre adjustment, before discharging it to atmosphere. Recycling tends to slow down the drying cycle but this is usually done in the interests of economy and of restricting the demand on the fans. The capacity of this type and size of dryer, when drying potato cubes or strips at 6kg tray loading, was of the order of 25okg of dry p d u c t per hour, according to the British Ministry of Food statistics over the period when these dryers were in general use in the UK for supplying the Services' nqukments. The wet tunnel fan had a rating of 1416cu m per min and the dry tunnel fan, 991cu m per min. The construction of the tunnel walls uses engineering bricks with 28cm cavity external walls to lessen radiation losses. Both inlet and exit doors are of the counterbalanced lifting type,suitably insulated. Each tunnel has an overhead recirculation duct with louvres as previously described. Access doors are provided in the fan chambers for servicing purposes. The drying trays are ideally constructed of non corrosive metal angle with stainless bottom mesh, and the trolleys are of a size to fit neatly into the tunnel section, so that the air stream passes uniformly across the trays, and

-

68

does not by-pass round the edges of the trolley Reference has been made to the 25min cycle from trolley entry in tunnel drying, and this cycle has to be maintained at all times. If, for example, there is a delay in tray loading, due to lack of product from the blancher, or when the system is being run down, an empty trolley must be moved into the tunnel, or a series of empty trolleys, if necessary, so that the p d i n g loaded trolleys move in their proper sequence through the drying cycle.

Three 'hnnel Dryer This dryer is a variation on the double tunnel system, and comprises two wet tunnels, with the dry tunnel running down the middle. Trolley entry is at the ends of the wet tunnels, and not by sideways loading as in the case of the double tunnel dryer. The fans and heaters are mounted on the top of the dryer, and the air stream is deflected downwards by louvres on to the trolleys in the first position. The air flow is parallel or concurrent with the trolley movement, and the interval of loading is usually reduced to 20min; each wet tunnel A and B accepting a trolley alternately at this time interval. Thus, the product remains in the first position for 40min, before being moved into the second position by the second trolley On reaching the end of the wet tunnel, the trolleys again move alternately from Aand B into the middle dry tunnel, thereby shortening the duration of travel in the latter, as here the tmlleys resume the 20min cycle again. This system is equally as effective as the double tunnel but in making a choice of the type of dryer to install, the dehydrator must give full consideration to the labour content inherent in the quasi-continuous tray drying system, as against the completely continuous system offered by the Through Conveyor Band Dryer. THROUGH-FLOW BATCH DRYERS The Buttner 'Favorit' batch dryer has been used widely for many years in overseas factories for the drying of vegetables and fruits -especially where labour has been plentiful and cheap. It was used where small to intermediate levels of production were required. It comprises a single drying chamber holding either 8 or 10 trays, 3m by 2m by 150mm deep. The trays are charged on an operating stand in front of the drying chamber. The tiltable tray lifting frame slides u p and down between lateral tubular supports, with five arresting points controlled by limit switches, so that the p r o p s of the electrically lifted trays can be pn?set. A horizontal battery of heaters separates the trays in the drying chamber in two stacks. 69

I I LI-

---I d-

- _-

4

4

z

y

3

v

L

I

Sliding the tray into the drying chamber

The tray resting on the lifting frame is charged with fresh product, lifted to the top position, and slid into the chamber by operating a hand mechanism. The lifting frame slides down again to the middle, ready to support the tray immediately above the intermediate heater. This tray is drawn out and moved down a little further.The product on the tray is riffled and the tray pushed back into the chamber - this time below the heating surface. The lifting frame slides down to receive the lowermost tray of the second stack. It then moves a little way upwards and is slightly tilted so that the now dried product can be discharged. The emptied tray is moved to the bottom position and the new drying cycle commences See Fig 4.1). The drying progression, therefore starts at the top of the dryer where the higher temperature prevails, and finishes in the 'cool' zone at the bottom, from where the tray with the dried product is drawn out and discharged. Steam requirements are 600kg per hr at 7 bar for maximum throughput, the electrical load is 7KW for the heater fan and 0.7KW for the lifting device.

Double Through-Flow Dryer Thisis a demonstrablymore sophisticatedthrough-flow dryer designed by Mitchell Dryers Ltd, with twice the output of the single chamber dryer,and with less labourrequirement. This is a semi continuous dryer, comprising two drying chambers each housing 10 perforated trays 3m by 2m by 150mm deep. The product filled trays travel automatically through the drying chambers at a rate commensurate with optimum drying and product quality (See TABLE 4.1). The primary drying chamber is designed for total rejection of the saturated air. The circulation fan is mounted directly above the heater batteries at the rear of the chamber and discharges the heated air into a bottom plenum chamber and the air is then directed vertically upwards through the stack of trays to the top and into the discharge hood to be ducted away to atmosphere. The circulation fan in the primary unit handles 4OOcu m of air heated to 150°Cmaximum. The heater has a maximum heat output of 2,350,000 BTUs per hour when using steam at 2.72atm. The second chamber air circulation is provided by a fan handling 270cu m of air. The trays are automatically advanced from the bottom to the top by four hydraulic lifting jacks, connected to the lifting frame. The trays are indexed to move into their drying position automatically. At the bottom and top of the main framework there is a roller conveyor system upon which the loaded trays travel from the first chamber to the second (a) to enable an operator to examine the product at the intermediate stage of drying, and riffle over the product to effect a surface change before entering the cool chamber, and (b) on the bottom roller conveyor, to discharge 71

the product, clean the trays and recharge them befoE they re-enter the primary chamber. The trays are emptied pneumatically by an air-hose which lifts the product into a hopper, thence feeding into the conditioning bins. The air is discharged through a cyclone. If more than one unit is installed, the pneumatic emptying device can be connected to a common duct, providing discharge points from several dryers.

TABLE 4.1

7HROUGHF'DPERFORZ"CES OFl7EMITcKELL DRYERS THRWLQ DOUBLETRAYDRYER Thruflo drying units may be used where an intermediate level of production is required.They have been designed to give a good degree of automation to batch drying and to provide the facility for a staged drying technique as used in conveyor band drying, thus improving efficiency and output as well as providing a high quality product. These semi continuous dryers employ a through circulation of drying air and comprise two drying chambers each housing 10 perforated trays measuring 3m by 2m by 150mm deep. There are transfer zones between the two compartments where the trays are loaded and emptied, and also the facility to agitate the material on the trays part way through the drying cycle, which helps ensure more even drying. The product filled trays travel automatically through the drying chambers at a rate commensurate with optimum drying and product quality.

Asparagus Beans,French carrots Celery Cabbage Cauliflower Cloves Garlic Ginger Leeks

72

TYPICAL PREPARED FEED RATES 3lOkg/hr Mushrooms 54Okg/ hr Onions 570 " 500 " Potatoes 710 " 630 " 650 " Peas 470 " Peppers 600 " 450 " Parsnips 630 " 550 " Parsley 330 " 630 " 570 " Spinach 270 " 630 " Swedes 630 " 530 "

-

CONVEYOR B A N D DRYERS SINGLE PASS Reference has been made, in Chapter 2, to this type of dryer, and an ideal size unit for medium scale operation is a dryer 30-40m in length, with a conveyor width of 2.5-3m. The conveyor band dryer is used in many industries outside food dehydration, and has been standard equipment in the textile, chemical and tobacco industries for many years. Lucerne and other silage is also dried by this method, and some of the first band dryers developed for food products owed much in their design to the experience the engineers had gained in grass drying. The dryer normally has three heat zones, each of which is served by an individual fan drawing hot air from a common heat source. The latter can either be a series of steam batteries or a heat exchanger mounted on a coal or oil furnace, both indirect methods, or the air stream can be from a direct source, such as gas or LPG. The hot air stream is ducted underneath the interlocking perforated conveyor plates, which make up the continuous band, and the drying air passes through the perforations in the plates, and thmugh the mass of product which is being conveyed at a controlled depth along the length of the dryer. The plates, running the full width of the band are about 23cm wide, and are made from perforated stainless steel plate. The perforations can be either 4mm round holes or 4mm square ones at 6.4mm centres to give adequate open ama through which to pass the hot air stream. Air flow can alternate in an upward or downward direction as drying proceeds. The 23cm wide plates connect at either side with a 23cm pitch chain, which carries the band over the drive and free sprockets at either end of the conveyor. Right: Continuous band dryer for vegetables with oscillating feed arrangement developed by the parent company of Proctor Dalgleish

The blanched vegetables are delivered on to the feed end of the dryer by various methods. One is an inclined chute at about 45°, with an adjustable levelling plate running across the full width of the band to control the depth of material passing underneath it. Another loading device is an oscillating boom swinging across the width of the band and delivering the material in an even swathe at a prescribed depth. The depth to which the dryer is loaded will vary according to the type of vegetable being dried, the size to which the material is cut and the general permeability of the bed. For example, strips of root vegetable will dry at 1112cm depth, whereas 9.5mm cubes can rarely be dried on a deeper bed than 8-10cm. Cabbage, which tends to mat and create a high resistance to the air stream, may have to be reduced to a 5cm bed depth. A single pass conveyor band dryer is, on this account, not so suitable for drying cabbage but successful results are obtained with a multiple-pass dryer, which comprises a series of bands, each transferring the product to the conveyor immediately beneath it at the end of each pass. In this way the product benefits from a surface change in relation to the air stream, which facilitates drying to a very significant degree. A surface change can be effected in a single pass dryer by fitting a rotating shaft with metal tines, that just clear the band sections but rake through the product. This is fitted about one third of the way along the length of the conveyor, and such a device rotates at about 100rpm. A second pin rake may be fitted at a further distance along the conveyor.

4-stage single pass dryer

74

The heat zones are separated by transverse baffles over and under the band sections and, in this way, temperature variations can be implemented in each zone as required, and damper control in the fan ducts also gives this facility. Lower initial inlet temperatures are normally used in the first heat zone of a band dryer, as compared with those in a tunnel dryer, because the effect of passing the hot air stream through the product, rather than over it, produces a higher rate of evaporation, and the product is, in fact, exposed to a greater d e g m of heat for a longer period of time in the first zone than is the trolley of trays in the first position in the tunnel dryer. Temperatures must, therefore, be very carefully controlled to avoid scorching, case hardening and pmtein denaturation, as the evaporation rate is considerably higher in the band dryer. Temperatures in the second heat zone are usually controlled at 6"10°Clower than in the first and, in the third zone, about 10°C lower than in the second but this varies from product to product. As with the tunnel dryer, recycling is quite normal practice, so that the hot air stream is fully saturated as it passes to atmosphere. Some products with a relatively high sucmse content tend to adhere to the band plates, at the discharge end, and require a rotating nylon brush, or mechanical scraping action, to remove them completely from the plate surface. Adhesion can, however, be minimised by applying a light coating of 'dehydrator's wax' on the band plates weekly. This is normally dispensed from a hand spray gun, and will give adequate protection for about six days. The wax is specially manufactured for the dehydration industry, and modem band dryers are fitted with a continuous wax applicator device. The speed of the conveyor is infinitely variable to suit both the product and the heat conditions, and the heat zones are thermostatically controlled once the air duct dampers have been set at the beginning of a production run. This type of dryer is ideal for a long sustained run on one product as, once drying conditions have been established, it requires very little attention. The number of operators required is no more than two - the blancher operator, to periodically check the feed level of the product on to the band, and a dryer foreman, to generally supervise the overall operating conditions of the dryer. As the capital cost of this type of dryer is high, the usual practice is to take off the product at the end of the conveyor at 10-15 percent moisture content, and transfer it into bin dryers to dry down to the final specification. In this way, the drying cycle of the conveyor band dryer can be shortened to as little as 2-3 hours, the finishing in conditioning bins normally taking a 75

further 4-5 hours. Their use permits the most efficient exploitation of the band dryer, the throughput of which would be restricted by about a third if it was used to bring the product down to final moisture specification. Very low drying temperatures and air flow are required in bin drying, as it is more of a conditioning than drying process, and it is sound economics to relieve the band dryer of this duty in the last stages. MULTI-PASS CONVEYOR DRYERS This type of conveyor dryer may be either 3 or 5 pass and, because of its multi-layer construction, is more economical with floor space than the single pass dryer. They are modular in design, and therefore can be custom-built to suit the processor's throughput capacity.

There are two major European manufacturers of this type of dryer Mitchell Dryers Ltd of Carlisle, United Kingdom, and Buttner-Schilde - Haas of Krefeld, Germany and the major featuresof both are explained here.

A Buttner dryer at Erin Foods, Tuam, Co. Galway, factory

76

TheMitchellDryermodulesare1.8minlengthandthebeltWidth2.5m. An oscillatingor apron feed is optionalat the input end, and there is a standard delivery section at the discharge end. A 7 module dryer would handle a wet feed input of prepared onions at 85 percent moisture of 2091kg per hour, drying to 5 percent. With bin conditioning the takeoff moisture could be 10 - 12 percent, which would, of course, shorten the drying cycle and increase the throughput. With diced potato the wet feed input would be 3470kg per hour, assuming a raw moisture of 80 percent and an end moisture of 5 percent. Again with bin drying the takeoff moisture could be as high as 15 percent. The great advantage of multi-pass dryers is that the product undergoes 4 surface changes as it is transferred from each of the five belts, and this expedites the drying cycle time. Each module has a separate hot air circulation fan, and the belts run at different speeds to take care of product shrinkage, and the through air flow can be directed upwards or downwards, usually a combination of both directions in different sections to suit the drying characteristics of the product. For an indirect drying system, the heat exchangersare mounted on the side of the dryer, with instant access to the motors and fans but, with the increased use of Liquid Petroleum Gas or Natural Gas firing, the products of combustion can be introduced into a duct at the end of the dryer and subsequently diluted by the introduction of fresh air, thence f e d into the plenum chamber. Alternatively, a series of small individual burners can be used. The temperatures can be infinitely varied on the different levels at which the product is conveyed. Where in a single pass dryer three heat zones are created by a transfer module at two points in the conveyor travel, allowing a predetermined temperature in each of the t h e zones, the heat control in a five pass dryer can be even more sensitively predicted. Product adhesion is avoided by a built-in continuous waxing device on the belts, and hygiene is assured by a rotary brush applying hot water, detergent, etc, or a high pressure steam hose can be fitted for intermediate or continuous band cleaning. A control system, designed to achieve consistently uniform terminal moisture in the dried product is incorporated, and the whole drying operation is completely automated. One of these 7 module dryers was supplied in recent times to a major dehydrator in what was Yugoslavia (SeeTABLE 4.2 for performance details).

77

TABLE4.2 Feed Throughput Performanceof the MitchellDryer 5 Pass - 7 Module DryeE EachModule is 1.8m.long.Band Width 2.5m productsare Vegetables and Fruits prepared for drymg. End Moisture is calculated at Dryer Discharge, -before ConditioninginBins. Produce

cut

Raw Moisture

Apples (evaporated) 10-1 2mm slice Apples (flakes) 10xlOx2mm Apples (dice) 10xl0x10mm Cabbage (dice) 10xl0x10mm Carrots (dice) 10xl0xlOmm Celery (dice) 10xl0x10mm Garden Peas Scarified Green Beans Long Cut 10xlOx10mm Bell Peppers 1Ox10x2mm Leeks (flakes) Mushrooms 5mm slice 4mm slice Onions (slices) Potato (dice) 10xl0x10mm Potato (slices) 4mm slice Swedes (dice) 10xl0x10mm Parsnip Leaf 13xl3x12mm Beetroot (dice) 10xl0x10mm Parsley Chopped Spinach 13xl3x2mm Apricots (evaporated) Halves Pears (evaporated) Quarters Prunes (Plums) Whole

End Moisture

Y O

70

88 88 88 89 90 96 75 89 94 95 94 85 80 80 89 80 89 86 94 83 85 83

20 4 4

5 5 6 7 6 5 6 5 5 5 5 7 7 6 5 5 20 20 20

Feed kg/Hr 2051 1281 1795 1834 2834 1729 2992 2004 2159 1701 1733 2091 3470 2267 2699 1212 2038 973 1212 642 826 642

The Computed Raw Moistures are computed and approximate and will vary according to climatic and horticultural conditions. The end moistures may be varied by conditioning to meet any specific specification. (data courtesy of MitchellDryersLtd.) A Buttner-Schilde-Haas 5 pass 10 module dryer was observed regularly in the early 1970s in an Indian factory drying onions exclusively. 78

The manufacturers' input rating was about U3rds of the Mitchell Dryers dryer described above but under the operating conditions on site the wet input rarely exceeded lOOOkg per hour, with raw moistuE calculated at 86 percent and the end moisture 6 percent. There was no bin drying facility in this factory and the whole drying cycle averaged 7 hours. The dryer was not completely standard, in that it had no top auxiliary fans, which are now fitted on BSH dryers as standard (See TABLE 4.3). TABLE4.3 Feed Throughput Performance of Buttner-Schilde-Hass 10 Module 5 Pass Dryer: Length 28 metres: Belt Width 2.5m. Products; Vegetables Prepared for Drying. Final Moisture is calculated at Dryer Discharge; - before conditioning in Bins. Pduce

Onions (slices) Carrots (dice) Potatoes (dice) Garlic (slices) Cabbage (slices)

cut

4mm 10xlOx8mm 10xlOx8mm 3.5 - 4mm lOxlOmm

Raw Moisture

End Moisture

O/O

YO

87 90 82 68 92

6 8 8 6 6

Feed kg/Hr 1200 2240 2798 1280 1503

(Data by courtesy of Rosin Engineering Co Ltd.)

Noted Performanceofthe IndianDryer Only the top belt has a n independent drive, the other four having a common drive, which limited the retention time flexibility in the lower belts. With the side air flow, lower temperatures prevailed near the steam coil side, and a higher temperature near the exhaust and inlet side. This imbalance of temperature made it necessary to vary the product bed thickness as between one side of the belts and the other. The working conditions for the dryer in the 7 hour cycle were as under: Temperatures:

Feed depth

k t zone 2ndzone 3rdzone 4/5th zone 28-34mm

86 "C 86°C 75°C 50°C

79

Damper settings:-

Exhaust Dampers (from feed end) 2modules 80%open 3modules 80%open 3modules 70%open 2modules 60%open Inlet Dampers. All Modules 50%open. No.1 belt-45 minutes. other belts 6hr 15 minutes total cycle 7hr. Inlet Z0,000m3 per hour exhaust 24,Wm3 per hour

No.1 No.2 No.3 No.4

Retention time:

Air volume

Humidity and temperature ranges on the air inlet side of the dryer varied, according to season, as under. Relative Humidity 50 - 95% Ambient Temperature 20" - 32°C The performance of the dryer was not a criticism of the manufacturers but more of the working conditions, the non standard dryer design and the poor quality generally of the raw material. Many of the local onions were under 35mm in diameter, were ungraded when purchased, and this gave rise to problems in slicing evenly and presenting a rather impermeable bed of product on to the belts, which did not help drying conditions. A large tonnage of p d u c t was also lost by the absence of any dehumidification of the packing areas - an important factor when processing in the tropics where, during the rainy season, relative humidity reaches almost saturation point. This fault was subsequently rectified. A smaller version of the 5 pass conveyor dryer is the Imperial Band Dryer, designed many years ago by a prominent German engineering company who ultimately assigned the drawings, design, specifications and manufacturing rights to a Bulgarian company, who have marketed the dryer, still built in Bulgaria as far as is known, to Eastern European countries and have also exported some dryers to India, mainly for onion drying. The heating system, as illustrated in one of the Author's photographs of an onion dehydration plant in Bulgaria, tends to be oversimplified, in that it relies on an 8KW fan to draw air in from the building in which the dryer is located, across five steam tubes about 13cm in diameter, located longitudinally along the length of the dryer, each tube being opposite one of the five belts. In each heat zone the air is drawn across the product and subsequently exhausted to atmosphere. The volume of air from this fan is adequate on the top three belt chambers but tends to lose velocity towards 80

the two bottom belts, where the final drying takes place. This has been known to give rise to scorching,even at low temperatures, and it appeared to the author that the dryer needed some auxiliary fan power to overcome this problem. The rated wet prepared onion input is about 500kg per hour but it was observed that this figure was rarely sustained. Two Favorit through-flow tray dryers in the same factory gave a much more reliable 500kg per hr input for the pair, admittedly with a little more labour content, but a better quality end-product was usually obtained. BIN DRYERS These are used for conditioning dried p d u c t which has passed through the primary dryer - either a conveyorband dryer, Stove or ThroughFlow dryer, where the product may leave at 12 to 15 percent moisture. The function of the bin dryer is to apply a low temperature air stream through a plenum chamber at the bottom of the bin, permeating a relatively deep bed of product, and conditioning this to 5 - 7 percent moisture. The bins are l m wide and 2m long and allow up to 0.6m of working depth. The product is contained on a perforated base which allows a through draught of low velocity air at 50"to 60°C.Severalbins are normally required to allow for a conditioning time of 4-1Ohr, and are coupled up to a central air distribution duct supplied by a single fan and heater which may be either steam or electrically powered. Such units, therefore, offer a valuable intermediate storage facility between discharge from the primary dryer and subsequent packing or bulk storage.

The Mitchell Dryers engineeringspecificationfora ten-bincondition-

ing unit is as follows: The system comprises a main air circulating fan connected to a steam heater battery and a duct incorporating 10 separate docking points for the mobile bins, which are moved from the main dryer on castors. The air circulation fan is a backward curved centrifugal type with 6KW totally enclosed fan cooled driving motor. The fan is designed to handle a total volume of 283cu m of air at 15°Cand, to enable the volume of air to be reduced if all ten bins an? not used at the same time, an adjustable damper, fitted to the fan air inlet, is provided. To maintain a maximum drying air temperature of 65'C in the system a mild steel gilled tube air heater battery is provided. The heater tubes are enclosed in a mild steel flanged casing bolted into the distribution duct, and the heater is designed for a pressure of 5.4atm. The main circulating duct is manufactured in 16 gauge galvanised 81

mild steel, flanged and braced down its length to eliminate vibration. This duct is t a p e d to ensun?a constant air velocity and volume to each of the bin docking points. Ten mobile bin docking points are provided on to which the loaded bins would be clamped prior to commencement of conditioning. Each feeder point is fitted with an air control gate for sealing when the bin is removed, or at any time when the duct docking points are not being utilised. To control the heated air temperature a thermostatic controller is provided, complete with probe and adjuster, steam control valve and strainer. A dial-type thermometer is fitted for visual indication of air temperature. The bins are fabricated from 16 gauge galvanised mild steel sheets suitably braced and of robust welded construction, and each is fitted with one pair of fixed and one pair of swivel ball and roller bearing castors. The base of the bin forms an air distribution plenum chamber to match up with the feeder points on the distribution duct. The top surface of the chamber, which forms the base of the product container, comprises a perforated stainless steel diffuser screen and product support. The top of the bin is open for charging of product. At the opposite end of the bin to the air feed point a discharge gate is fitted to assist manual emptying after completion of conditioning. The bins are normally lifted and tilted into the hopper feeding the screening plant by an electrically powered box-tipper. The box tipper is of the type also used for emptying raw produce received in boxes or crates from the farm into the bulk feeder on the vegetableprocessing line. AIR LIFT DRYERS These, in the main, fall into three categories: (a) the Pneumatic Ring dryer, (b)the Thermal Venturi dryer, and (c) the Fluidised Bed dryer. Whilst these dryers are used in many fields other than the drying of foodstuffs, their main function in the vegetable dehydration plant is the secondary drying of potato granules. As will be described in the next chapter, this type of dryer performs a secondary drying operation, rather than functioning as a primary or complete dryer in itself. The Pneumatic Ring Dryer, as the name implies, comprises a q u a = sectioned metal duct, usually elliptical in shape, with a connecting duct to the heat source at a suitable point in the elliptical ring, and an entry point for the product adjacent to it. Apowerful fan draws the hot air at relatively high velocity around the ring duct, carrying the product in suspension through one or more complete cycles into a circular shaped manifold, whence it is

a2

The Rosin ring dryer

deflected into a cyclone that discharges the air to atmosphere and separates the product, through a rotary valve, for the next processing stage. The Thermal Venturi Dryer performs the same function, except that, instead of a closed ring system, a powerful hot air stream is directed upwards through a cylindrical jet section, picking up the product and lifting this at a high velocity through a tower shaped duct into a diffuser section, where the diameter increases to slow down the air stream. At the top of the diffuser the product impinges on a conical deflector and, separating itself from the 1. aimtream, falls down an outer tower with a collector chute at the bottom, where it discharges. The moist air passes out of the top of the tower to atmosphere. Another type is operated by two balanced fans - one at the foot of the venturi column where the heat source is located, and the second at the head of the column, which draws product into cyclones and discharges air to atmosphere. A vertical drying column may be upwards of 19m tall but, where the height of the building precludes this being installed, a 'serpentine' duct is equally effective.At the product entry point on these dryers, static air conditions apply, and the granulated material can be metered in freely from a vibratory trough conveyor. Both the pneumatic ring and the thermal venturi are most suitable for drying granular material, of 35-40 percent moisture at inlet, down to 10-15 percent at outlet. This performance and capability is well suited to the potato granule process, where the initial moisture in the potato is taken up by the adding back of dry 'seed' potato powder, prior to the resultant blend entering 83

the ring or thermal venturi dryer. The latter receives this blend of moist granulated material with 35-40 percent water content, and agglomeration is avoided because the product becomes immediately airborne as won as it enters the dryer. Evaporation is extremely rapid, up to 65 percent of the water content of the blend being removed in one or more orbits of the ring, or in the vertical lift area of the venturi. It is obvious, however, that these dryers are for specialised use and are not adaptable for a wide range of vegetables. Fluidised Bed Dryers are often installed as secondary dryen, following a ring or venturi dryer. Such a dryer consists of a rectangular box or trough with a porous ceramic base. Hot air is blown into a plenum chamber, below the porous base, and through a layer of granulated product, which is fed into one end of the upper dryer chamber. The air stream is controlled, through the ceramic base, at sufficient velocity to fluidise granular material, until it has the characteristics of a liquid, and moves from the feed to the discharge end at a steady flow rate, finally falling over a weir at the exit point. The capability of this type of dryer, when used as a 'finisher', will be a reduction in moisture of 7-10 percent. That is, granules leaving an air lift dryer at 12-15 percent moisture will be finished in the fluidised bed dryer at 5-8 percent moisture, as desired. ROTARY DRYERS The Rotary or Louvre Dryer is another simple type of secondary dryer, often used as a 'finisher' for granulated products. It comprises a drum, rotating on trunnions with an annular gear around the periphery of the drum and a pinion drive. The inside of the drum is fitted with louvre vanes, on the inner circumference,designed to turn the product as it passes through from the feed end. A fan and steam battery provide the heat source at the feed end, and the air stream flows concurrently with the turbulent product, which is agitated by the louvres and the slow helical movement of the drum. At the discharge end of the dryer the product passes into a cyclone, which disperses the air and drops the dry material through a rotary valve. This cyclone is sometimes fitted with a manifold and several collecting stockings, which Ieceive any fine material carried over by the air stream. Collecting stockings are sometimes frowned upon where fine powders are concerned, as the latter may possibly create an explosion hazard, and Local Authorities may insist that cyclones handling these products be exhausted to atmosphere. The evaporative capability of this type of dryer is limited, and the evaporativeduty will equate with that of the fluidised bed dryer, ie, about 710percent reduction in moisture when used as a secondary dryer in granule 84

production. These dryers are not particularly successful as a drying medium for larger particles, such as dice, as the tumbling action tends to distort the shape of the cut, and the dwell time in the drum is normally insufficient to effect any significant degree of evaporation when compared, for example, with the belt trough dryer. VACUUM DRYERS The Vacuum Dryer is not widely used for vegetable dehydration but has special applications, such as the drying of pharmaceutical products, plasma, sera, etc. It is used in America for the dehydration of citrus juices, apple flakes and for heat sensitive fruits and products where the ascorbic acid retention factor is important.The lower drying temperatures used under conditions of vacuum, and the shorter drying cycle, reduce the product's susceptibility to 'browning', denaturation, protein damage and the loss of highly volatile constituents. It has the disadvantage of being a batch system, and the equipment is costly. The vacuum shelf dryer is heavily constructed to withstand high vacuum conditions, and the ancillary plant - vacuum pumps, injectors and condensers- also involve a high installation and operating cost, in relation to the capacity of this type of dryer. This tends to confine the use of the dryer to high value raw materials, or products requiring reduction to extremely low levels of moisture without damage. The heat source can be in the form of a steam or hot water jacket around the exterior of the shell of the cabinet, or heated shelves inside the cabinet, upon which trays of product are placed. Some vacuum dryers have been fitted with dull emitter electrical rod elements to supplement the heat transmitted by the outer steam or water jacket. The construction of the shell of the dryer has to be robust enough to operate at a vacuum of 0.5 to 4 millibars, although such conditions more usually apply when vacuum drying is incorporated with Accelerated Freeze Drying, which is described later. Continuous vacuum dryers, for the dehydration of fluids, fruit juices, purees, etc, comprise a continuous stainless belt passing over rollers through a cylindrical vacuum vessel, and the product is spkayed on to the belt, sometimes with the addition of a foaming agent. Heated platens, or infra red heaters over and under the belt provide the heat source, and the product is removed from the belt at the end of the cycle by doctor knives, and ejected through an airlock valve. Where solid products are processed in this way trays are used and the 85

exit and entry method used means this again is a partial batch system - one tray has to be entered as one is =moved, through airlocks, and consequently operators have to be constantly in attendance for this simple task. An enlarged version of this dryer uses trolleys on rails, which enter and leave the vacuum chamber in much the same way as in a tunnel dryer, although, in this instance, an airlock has to be provided to contain the vacuum. All these systems can only be described as quasi-continuous, and throughput in relation to capital cost is very limited, a relatively large unit not having more than 50kg of product output per hour. Mitchell Dryers have recently introduced a refined version ofa continuous vacuum dryer by using 10 conveyor belts in a vacuum chamber. The Band Dryer consists of a vacuum chamber, 11.7m long 2.5m in diameter, (standard size for 10belts but available in alternative lengths) with ten belts passing over platens heated by steam or hot water, mounted one above the other and running longitudinally along the chamber. The feed, a viscous paste or slurry fed by a pump under pressure, is continuously distributed across the bands at one end by nozzles. The paste or slurry, distributed in an even layer across the band, dries by conduction during its passage over the heated plates into a form with a honeycombed structure. Centring and controlling the lateral movement of the bands during drying is controlled from outside the dryer either manually or automatically. The product leaving the bands at the discharge end is broken into short lengths by a guillotine, before falling into a coarse breaker producing pieces less than 15mm. Product discharge from the vacuum chamber is by double hopper system operated intermittently. The advantages of the system are (1)the form of dried material can be varied considerably by alterations to the vacuum, the feed solids of the material and the hot plate temperature; (2) The increase in mass and heat transfer driving forces enables materials with a high Esistance to diffusion to be dried; (3)Toxic materials can be dried without health hazards; (4)The risk of oxidisation is reduced; (5) Cooling of the material can easily be provided; (6) Labour is reduced to a minimum and maintenance costs are low. Product Possibilities Chocolate crumb, yeast extract, vegetable extracts, meat extracts, starch, herbal extracts, liquorice extracts, gland extracts, glucose, syrups, resins and chemicals, malted milk, malt beverages, malt extract, molasses, patent foods, hydrolysed protein, soya extract, tea and coffee extracts, fruit juices, dye extracts, Shellac and gelatine, pharmaceuticalsand food enzymes. 86

The capacity of a standard 10 band dryer operating on a milk product is a production rate of lOOOkg per hr with a capability of 150kg per hr evaporation. Pilot plant facilities for clients’ materials are available at the manufacturer’s works in Carlisle, UK where all preliminary tests can be carried out. FREEZE DRYERS Accelerated Freeze Drying (AFD) is widely practised in America, and is economically viable there on account of the large scale of operation, and the magnitude of the distribution outlets. It is viable with high cost materials, such as meats, poultry, shell-fish and certain non food specialities. It must be appreciated that the process is in two stages: fnxzing, followed by high vacuum drying. Both systems are, by themselves, expensive to operate and, as the original k z e dryer plants were based on the batch system, this again added to the operating costs, as throughput was relatively small. Continuous plants are now available but the capital cost is very high. Reduced to its simplest terms, AFD is a method of drying a p d u c t whereby the water content is first converted to ice and then changed into vapour without passing back through the water phase. In consequence, since ice has a greater volume than water, the freezing of the product causes it to expand, under pressure of the formation of ice within itself. This expansion is not followed by equal contraction as the ice sublimates into vapour under conditions of vacuum, therefore the stretchingof the capillary system in the product is permanent. This assists rapid rehydration and the product texture is very uniform. It could be argued that, following this expansion of the capillary system, much of the flavour and nutrient of the food leaches out into the cooking water and is lost. This is an argument used by critics of the method, who also refute the claim that the cost of evaporating water under vacuum requires less heat or calories per pound evaporated than at atmospheric pressure. The vacuum dryer, used in conjunction with the freezing plant, can be the batch type, as illustrated, with heated platens to carry the trays of product. Alternatively, infra red heaters can be used over the product, or, when meat is being dehydrated in slab form, heated metal spikes can be pressed into the latter. Refrigerated condensers are used in some plants to remove the water vapour from the chamber befoxe this enters the pump. Defrosting has to take place between drying cycles to ensure a passage for the evacuated air. Alternatively, the vapour can be absorbed by chemical agents. 87

The Autec freeze dryer illustrated is a batch-type with a shelf area of 36sq m which can be loaded with about 630kg wet weight of product. The drying cycle for the plant is determined by the nature of the product, and ranges from 8 to 24hr. The vacuum level is from 4 to 0.5 millibars and the vapour condenser temperature is minus 30°C.The dry output on chicken is calculated at 210kg per 24hr with an input of 630kg of prepared meat. Rossi & Catelli, of Parma, Italy, manufacture a larger batch unit with an input capacity of 3125kg of prepared produce per day for a single chamber unit, which, on the assumption that the total solids of the product is 20 percent, would produce 625kgs. of dried product per 24 hours. For larger volume production two or more units could be used as a battery, allowing more efficient utilisation of the services ancillary to the freeze drying operation, thereby reducing costs. The procedure with this type of plant is as follows: The raw produce is prepared, cleaned, washed, cut, blanched and cooled and then stored in cold moms at the required temperature. In a separate cold room there is an automatic filling plant when? the product is fed into trays, which are made of extruded and anodized aluminium. The filled trays, each with the same quantity of product are automatically conveyed and stacked on trolleys. Two or more trolleys (see illustration) are thus loaded and kept in the cold storage room. The freeze drying cycle commences by loading the trays through the open d e r of the vacuum chamber. A mechanised rail track conveys the loaded trolleys to the loading point, and a chain mechanism, integral to the trolley pushes simultaneously on to the heating plates of the chamber. This takes only a few minutes and is contmlled by one operator.

Product door Refrigerated vapour Condenser

Healing/co

Figure 4.2 Diagrammatic vapourflow chart 88

The parameters for the temperature of the condenser, the degree of vacuum and the heating gradient of the plates in the chamber are all set at the commencement of the operation, and are automatically controlled by a programming device for the duration of the cycle, which ends when the Right: Batch freeze dying plant - tray loading product into the freeze-drying chamber on to heated platens Below: Batch freeze drying plant- end of tray washing plant followed by automatic transfer of trays into the cooling room

89

product reaches the pre-determined end-moisture. The services are disconnected and the vacuum in the chamber is broken. The back door of the plant is opened and the trays with the dry p d u c t are pushed out simultaneously again by the chain mechanism provided in the chamber onto another trolley situated in a room with conholled low humidity atmosphere. the plant is then free to start another cycle. A single operator is required, and his direct intervention is necessary only at the end and begining of cycles, which normally follow one another at 15-20minute intervals. For the major part of the cycle time, the function of the operator is limited to occasional supervision of the control instruments and he is therefore available for other duties.

n a y Emptying In the low humidity room there is an automatic tray emptying device again programmed electronically From the trolley each tray is automatically taken in turn and taken over to the storage tank, where it is overturned, shaken by a vibratory and scraping mechanism to ensure complete emptying, and sent out of the dry room. The empty trays are then taken up automatically and stacked on a storage rack awaiting cleaning, or they can be taken immediately and put through the washing, sterilising and cooling machine, then t r a n s f e d into the cold mom ready to be filled again with the frozen product. All these handling operations are automatic, and no labour is invofved except for supervision of the equipment. Service requirements are as follows: Electricity per 24 hours 5OOOKW Fuel per 24 hours Wkg 750~3 Water at 18°Cper 24 hours Operators 1 per shift. Filling trays 2 per shift. The plant is designed to freeze-dry any p d u c t under pressure of up to 50 microns, if necessary

In conclusion, this method of drying cannot be recommended unequivocally for all vegetables but is viable for meat, shell fish, some fruits and high cost vegetables, such as asparagus, mushrooms, etc. D R U M DFWERS Drum Dryers also have specialised applications, and are used in the main for the drying of potato flakes and bananas. Milk and tomatoes are 90

almost exclusively spray dried now. Drum dryers can either be single or double drum units. Each drum is heavily constructed, and capable of withstanding an internal steam pressure of u p to 7atm. Its diameter is lm to 1.8m, and the length can be anything between 3m and 4.5m in standard machines. The principle of drying by this method is that the liquid, or semi liquid, is coated on to the surface of the drum, which rotates slowly and, in the course of about 300' of one revolution, the moisture in the product is flashed off and the dry material is peeled offthe drum surface in flake form by a series of doctor knives. In the case of a double drum dryer, the two drums are sited paraUe1 and in close juxtaposition to each other. The f e e d is usually from a trough,

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B N I P F E E D - Simplest type of feed suitable for milk and many other such materials

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F E E D ROLL - Suitable such as starch and flour.

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DOUBLE APPLICATOR ROLL- For heatsensmve materials. The materml I S in contacl w i t h the hot roll for the minimllm poss,ble rime.

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SPLASH F E E D - Especially useful for materials with a high rate of sedimentation.

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S I N G L E DRUM D R Y E R - Used lor increasing film Ihkckness for cereais. potaio llakes. etc.

Figure 4.3 Typicalfeed arrangement developed by Richard Simon G.Sons Ltd for their drum dyers

91

situated above and running longitudinally between the two drums, which rotate away from one another, one clockwise and the other anticlockwise. Feed rollers, also running along the periphery of the drums, rotate and even out the feed material to a uniform thickness on the drum surface. There can be three to five of these feed rollers on each drum. The steam inside the drums, at 7atm, produces intense heat on the surface, flashing off the moisture in the few seconds' travel between the feed position and the doctor knives at the lower part of the drums. The dried material is taken off in the form of a fine curtain, which falls into a scroll conveyor and is reduced, by the action of the latter, to flake or coarse powder form. With a single drum dryer, the feed is usually at the top, where the drum passes through a shallow trough of the feed material, and the doctor knives are located to meet the dried material at a point where the drum has moved through about 300° of one revolution. The drying time for potato flakes with this system is about 20sec, the raw material at the feed point being 80 percent moisture, and the dry material 6-7 percent. In the case of both double and single drum dryers, the water vapour is extracted through a hood over the drums, either by natural flow or fan assistance.

Typical drum dryer for potato fIakes - input: 2.5T/Hr of prepared potatoes. Dry output: 550kg/Hr

92

FOAM MAT DRYERS Foam drying is a system used in America for citrus fruit juices. It can be extended to any non particulate foods in puree or slurry form. The plant consists of a continuously moving stainless steel belt, which passes through a heating chamber. Steam condenses on the underside of this belt, and heated air passes over the top. Fruit juice, in concentrated form, is pumped into a foam generator and the foamed material is distributed evenly over the surface of the belt at an average thickness of 0.05in. After exposure to the heat, the concentrate dries to 1.5percent moisture and then passes through a cooling section. Here it crystallises and, at the end of the belt, a doctor knife removes the crystals, which are conveyed to the packing station. Operating costs using this method are claimed to show a considerable reduction when comparwl with vacuum drying. The recently improved technology, as demonstrated in modem spray dryers, may eventually take precedence over foam mat or vacuum drying of fruit concentrates.

SPRAY DRYING IN THE DAIRY AND FOOD INDUSTRY

Introduction Basically, spray and fluidized bed processing are well known techniques for production of powders in the dairy and food industry. However, advanced pre-processing of feed products, peculiar rheological properties and delicate thermal sensitivity of materials have prompted the development of new, tailor-made processes and controls. Powder manufacturers demand increased throughput and flexibility of spray and fluid bed equipment for production of specialty products, and the end users require an increasing control of functional properties. Particle size and bulk density must be well defined. Dustiness, dispersibility and flowability, are required to be controlled within specific limits, too, all in order to ensure adequate added value of the produced products. Last - but not least - producers, consumers and legislators require careful considerations in respect of health, hygiene, safety and environment. During the past 20 years considerable development of the spray drying and fluid bed technology has met these demands in a number of ways of which a few examples will be given.

93

Demands The most important demands made by the dairy and food powder producers of an up-to-date spray drying plant are: 0

0

Flexibility , i.e. it must be possible to produce a large variety of products in the same plant. The plant must produce high quality powder with specific physical/chemical, functional and bacteriological properties i.e. dustless, stable, defined density, etc.

APV Anhydro Spray D y e r installed in the milk Marketing Board Creamery, Kendal, for the drying of mi& products

9

It must be possible to have long production periods of the plant between cleaning, i.e. without the occurrence of deposits of any significance in the process equipment. Fast and effective cleaning of the plant must be possible. Automatic control of the plant, with small deviations in relation to selected parameters and automatic start, stop and cleaning. 0

Low energy consumption and low operation costs.

Development In short, the most important development has taken place within the following fields: One-stage dryers have been replaced by two or multi-stage drying plants. Atomization and agglomeration techniques have been improved. 0

Load on environment and energy consumption have been reduced.

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Hygiene and CIP cleaning have been improved.

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Control and automation have become sophisticated.

Today, spray drying is a flexible process with many possibilities of controlling the operating parameters in order to obtain the desired powder quality. Powder production consists of a number of different processes, e.g. homogenization, concentrate preheating, atomization / agglomeration, drying, lecithination, rewet agglomeration and final drying/cooling which all may be controlled in one single dryer system.

One process Many functional powder properties, e.g. wettability, dispersibility and viscosity, are closely related to the method of agglomeration, the process of forming porous clusters of single particles. Agglomeration can take place by return of fine particles to the atomizer or to the fluid bed, by means of particle impingement around the atomizer nozzles or by rewet agglomeration in the fluid bed. Instant properties of agglomerated fat-filled powder, required for reconstitution at temperatures below the melting point of fat, are achieved by lecithination in an external fluid bed prior to powder cooling. Drying and agglomeration are performed in one process in the spray bed dryer, a spray dryer with a fluid bed integrated into the bottom of the chamber. Developed for dustless powders in the late seventies, this system

95

has since then been sophisticated for widespread use in the dairy and food industry. In the spray bed dryer a concentrated feed product is atomized by a system of pressure nozzles or by a centrifugal atomizer into a downward stream of hot air. Moist powder particles collide with dry particles in the upper part of the dryer chamber and form porous agglomerates that fall down by gravity into the fluidized bed. The fluidized bed acts as a second drying zone and as a classifier in which very fine particles are removed from the formed agglomerates. The spent drying air exits at roof level, and entrained fine particles are separated in cyclones and can be re-injected into the wet atomization zone around the nozzles, in order to form porous agglomerates here, too, in a second agglomeration process. Figure 4.4 shows a computer generated simulation of gas stream lines and gas velocity profiles above the integrated fluid bed in this process.

Axial velocities

FiPre 4.4 Profile Of a spray bed dryer showing air--owstreamlines and vertical air velocity 96

Fig ure 4 .5 Spray bed dryer with external fluid bed with rewet for two-stage agglomeration for production of infant formulas y

As a matter of nature, the amount of recirculated fine particles, the formation of agglomerates and the process of drying in the integrated fluid bed are not independent variables. Therefore, an optional nozzle with water or feed may be placed above the powder in an external fluid bed which performs a fully independent third agglomeration process directly in the bed, for example to make instant whole milk powder. Here too fine individual particles are blown off continuously, which makes the produced powder dustless with a desired and uniform particle size, selected within a broad range. The external fluid bed acts at the same time as an after-dryer and cooler. The spray bed drying plant is compact with short powder conveying ducts and only one cyclone system, from where the powder can be recycled either to the internal fluid bed, to the external fluid bed or to the atomizer.

Flexibility The mentioned principles of agglomeration in the spray bed dryer system make it extremely flexible in respect of production of controlled and unique functional powder properties: 0

0

0

0

The fraction of fine particles recirculated for agglomeration can be controlled separately. The velocity of the fines returned can be controlled within a wide range so as to obtain a defined site and relative velocity of collision between particles and droplets in respect of desired agglomeration. An adjustable direction of the nozzles allows for a controlled collision and agglomeration of droplets. Rewet-nozzles allow for agglomeration and an optional lecithination of fat-rich powders in the external fluid bed.

Further it has been shown that by such control of the return of fines to both atomizer and external fluid bed it is possible to agglomerate with addition of much less water than what has hitherto been possible. Further control and improvement of the quality of agglomerates may be performed in a multistage counter current air classifier in which - by means of a rising gas stream - introduced particles are separated into two size fractions. The coarse fraction of a predetermined particle size is withdrawn as the agglomerated product. The undersize fraction is entrained in the exit gas stream from the classifier and is returned to the atomization

9

Figure 4.6 Spray bed dryer with nozzles, integratedjuid bed, air classifier and with fines return for production of agglomerates with low dust content 99

zone as fine particles for formation of agglomerates. Figure 4.6 depicts an illustration of the classifier from which fine particles are returned to the atomization zone while agglomerated particles are withdrawn from the valve at the bottom. In this way it is possible to produce agglomerates with a low dust content and excellent fluid-mechanical properties. Some products are very difficult to dry and tend to stick to the chamber wall. This can be prevented by an optional rotating arm which blows compressed air through slits against the wall. The rotating arm gives a prolonged period of time between cleaning intervals of the spray bed dryer, and makes possible the drying of some products which previously were regarded as unsuitable for spray drying.

Hygiene Detachable insulation cladding is becoming a market standard in order to enable inspection of the chamber walls from the outside with the purpose of detecting leakages or micro-cracks, Fig. 4.7. Such panels combine the

Figure 4.7 Easily detachable insulation panels for inspection of the chamber wall against leakages or micro-cracks 100

advantage of an air gap between chamber wall and insulation and the totally encapsulated cladding, thus ensuring the best possible conditions for protection against bacterial growth. The insulation panels may be made of foamed-up polyurethane covered on both sides with stainless steel. Conclusion The spray bed dryer offers a unique possibility of flexible production of high quality, tailor-made powder products -including concentrates and products with high contents of fat and properties according to customers' wishes and to international standards, such as: Infant formulas Milk protein contentrate Caseinate Fat-filled whey Cheese Coffee whitener

Ice cream mix Whey permeate Lactose Yoghurt Whey protein concentrate

101

T h o Stage Spray Dryer During drying the atomised particle experiences two separate phases. The first is the constant drying rate period when the unbound moisture is removed. Surface moisture is rapidly evaporated, and so is the moisture within the particle, which can move by capillary forces quickly to the outside. The second period is the falling rate when bound moisture diffuses to the surface for evaporation. The rate of diffusion decreases with the moisture content and so the time required to remove the last few percent of moisture takes a major part of the residence time with a single stage dryer. High outlet temperatures,are needed to give a sufficiently large driving force to remove this moisture and this adversely affects the thermal efficiency of the process.

Figure 4.9 TWOStage Spray dVeY

I02

Three-stage spray dryer The Anhydro three-stage dryer, consisting of a spray dryer with integrated fluid bed and an external fluid bed, is the most flexible system for production of a large variety of agglomerated and non-agglomerated dairy and food products. The atomization principle can be either nozzle or centrifugal. The internal fluid bed normally works as second stage dryer, and the external fluid bed as third stage dryer and cooler or, for products with high fatcontent, as cooler only.

Figure 4.10 Three stage spray dnjer

103

Performance Comparison Table 4.4 shows an example of typical figures for the 3 systems with an evaporation capacity of 2000kg per hr. Drying Process Single

Two

Three

S tage

Stage

St a p

kg/h kg/h

2000 1980

2000

%

48

'C

210 100 3.5 8811 167 205

2000 1980 48 230 85 6.5 7453 151 90

Unit

Water evaporation total Powder production Solids in feed Inlet temperature to spray dryer Outlet temperature from spray dryer Water content from spray dryer Heat consumption Electric consumption Cooling consumption Operating hrs. per year Heat costs (0.03E/MJoule) Electric costs (0.04f/kWh) Cooling costs (033f /MJoule) Energy costs per Yr Investment costs, total Investment costs (deprec. 20 years, interest 10% per year) Energy and investment costs Index (energy + investment cost)

'C 46

MJoule/h kW MJoule/h

6Ooo

6ooo

f/Yr E/Yr E/Yr f E

379,436 40,080 68,600 488,120 666,700

320,940 36,240 30,066 387,246 766,700

306,360 39,360 21,000 366,720 833,400

E/Yr f/Yr

75,000 563,120

90,000 477,246

96,700 463,386

100

85

TABLE 4.4 Comparatize operating wsts in spray d y i n g

I04

1980 48 240 78 9 71 14 164 63 6Ooo

82

6

Dehydration of VegetabIe s The vegetable cultivars quoted in the following process data are, in the main, those bred in temperate climates, the USA and Western Europe and, in the case of pulses, the Antipodes. However, with the growth of dehydration in the developing countries, with tropical or subtropicalclimates, these regions, along with Eastern Europe, Egypt and China, who have had a dehydration industry for many years, have, through their Horticultural Institutes and Ministries of Agriculture, developed indigenous varieties which have been processed with considerable success. It may not be possible to identify all these varieties but in the author’s experience, great assistance has been afforded by the field officers working with these Horticultural Institutes in setting u p field and seed trials for the benefit of processors, and they are becoming increasingly knowledgeable in the characteristics required in vegetables for processing. They have afforded, also, valuable information on the infrastructure required for setting u p a processing plant, along with the disposition of labour, local building requirements for food factories and the pattern of irrigation practices. The processes set out assume an intermediate size operation with a reasonable measure of automation but, of course, in each case the throughput may be cut down to meet capital budgeting requirements, and whilst most of the preparation plant is geared to a raw throughput of some 1.5 to 3 tonnes per hour of prepared material or 300 to 350 tonnes of raw produce per week, adjustments can obviously be made, introducing more hand labour in

121

preparation and using Stove or Through-Flow Tray Dryers instead of a Conveyor Band Dryer, either single or multi-pass. Whilst a product-mix should be arrived at to give the maximum number of days work in a season, it is wise to concentrate on those vegetables which are available for several months of the year, either from seasonal sowings, or by having storage facilities at the factory or farm. Too many change-overs from product to product are costly, often entailing moving plant around, but what is more important is knowing the market demand for those vegetables for which the climate and growing conditions are ideal. HORTICULTURE It is difficult to guide the processor in horticultural procedures, as climate and soil conditions will vary considerably from region to region. The company agronomist must assess all the requirements and problems on the spot, and in a new venture it is absolutely essential to carry out field trials for every vegetable to be processed. However, the author has appended some horticultural guide lines for seven of the more popular vegetables grown for dehydration, and these follow the processing data in this chapter. The guide lines are based on actual field trials and commercial scale cultivation in several locations varying from temperate to subtropical climatic conditions. In most cases irrigation was available, either contour or overhead spray.

GREEN BEANS (1)Flow-Sheet

Feed to Line

I Pneumatic Separator I Washing I Cluster Cutting (only for machine harvested beans) I Inspection I Snipping I Inspection

I Blanching I22

I Sulphiting

I Slicing (long cut)

I Dewatering I Drying

I Conditioning I Screening I Inspection I Packing (2) Varieties

Tendergreen, Processor, Bush Blue Lake (3)Product Handling The bean pods are either harvested by hand or, in the case of large acreages, by mobile bean harvesters. They are fed to the line in a bulk feeder from where the pods are delivered into a pneumatic separator to remove extraneous matter. They are then transferred to a reel washer which, in the case of machine harvested beans, feeds in to cluster cutters, to 'single' any beans not separated from their stalks in the harvester. This machine is not necessary for hand harvested beans. After inspection on a conveyor belt, the beans are conveyed on a vibratory trough belt and ploughed off into a battery of snippers. The number of snippers willdepend on throughput,as each machine will handle about lOOOkg per hour. At the exit end of each snipper an unsnipped bean removal reel takes care of any beans not topped and tailed and returns them to the snippers. Snipped beans are then visually inspected on a conveyor belt and delivered into the blancher. This can be either a hot water or steam type, depending on what other products are to be catered for. For example, if cabbage or leaf vegetables are included in the product mix, it would be advisable to opt for steam blanching as this is more suitable for brassicas. Sulphiting is effected by pumping from sulphite make-up pans into the blanching water, in the case of hot water blanching. If steam blanching is I23

used, sulphiting is carried out in a sulphite dip tank situated at the discharge end of the blancher, and the solution of sodium sulphite is made u p in the pans alongside. Anhydrous sodium sulphite is always used for green vegetables and sodium metabisulphite for root vegetables,where sulphiting is permitted under prevailing Food Laws. Whole beans are fed on a vibratory conveyor to slicing machines (long cut) with a capacity of 2000kg per hour each, the slicing taking place after blanching to prevent the seed of the pod being washed away in the blanching process. After dewatering, the cut beans pass into the dryer, thence to conditioning bins. The dried slices are elevated to the screen for sifting to remove broken pieces and fines, and then to the final inspection tables. Packing should be in poly-lined cartons or drums, rather than paper bags, to avoid breakage. (4) Drying

Conveyor Band dryer scaled to throughput Temperatures (input): 85"/ 77"/ 60°C Conditioning: 5Oo-52"CDry to 6% Overall ratio: 13.1 Drying ratio: 9.1

Cultivation Guidelines for Geen Beans (1) Sowing:

150kgperHa.Sowinsinglerows7.5-lOcmapartat4lcmcentres.Sow50mm deep in fine tilth. (2) Fertilisers. On irrigated land use N40/P80/K60 plus 2.5 tonnes of organic per Ha., if available. (3)Herbicides. Preforan or Granoxone or Dachtal. (4) Pesticides. Dimethoate or Diazinon; for caterpillar attack, use Folithon or Diazinon. (5)Disease Control. Botrilex against Southern Blight or Root Rot. Afucan or Benlate every 7 days against powdery mildew. Kocide, Perenox or Cupravit against bacterial blight or rust. (6) Maturity Pick every second day to avoid over-maturity. 8mm is the maximum pod diameter (measured across a section of the bean) for processing. Harvest is about 60-70 days from sowing. Plant population: 430,000 per Ha. I 24

BEETROOT (1)Flow-Sheet Semi - Continuous Process I Feed to Line

I Destoner-Washer

Batch Process

a Autoclave cooking

2

Semi-Continuous Pressure Cooking Washing

Skin Removal

I Inspection I Cutting I Dewatering

I Drying I Conditioning

I Screening

I Inspection

I Packing (2) Varieties

Detroit Red Globe (3)Product Handling Beets should be selected 50-75mm in diameter, with the tops wrung off (not cut off) at the farm. Care must be taken to avoid bruising and 'bleeding'. From the bulk feeder they pass through a dry cleaning plant to remove soil, then to a destoner-washer or alternatively a flood washer, if free of stones. Two options are open to the processor: (a) to feed the beets into a batch thermoscrew operating at 1.2atm steam pressure. A Thermoscrew 6m long by lm diameter should batch-cook young beets in a 20-40 minute cycle at a I25

rate of 1.5-2 tons per hour; (b) the second alternative is to cook the beets in batches in an autoclave, or a series of autoclaves according to quantity of input. Again pressure will require to be at 1 to 1.2atm. Cooling from the semi continuous cooker will be in a slat washer reel and, if from autoclaves, the cooling water will be applied to the bottom of the autoclave and allowed to circulate until the pressure has dispersed and the autoclave baskets can be removed. The cooked beets, when cool enough to handle are fed on to a stainless steel belt where the skins are removed by hand. The batch system is the one most often used, as a continuous pressure cooker is a very expensive machine. Stainless steel belts should be used when handling beets, as rubber or PVC belts will stain badly and are difficult to clean. The red pigment is betanin, which will leach out if the beets are subjected to washing after peeling and dicing. This should be avoided. Before the beets are transferred to the cutters, any root or fibre remaining should be removed on a second inspection belt, or this can be done by the skinning operators, if the belt is sufficiently long to accommodate both functions. It is most important that the beets are fully cooked before cutting and drying. Some processors have attempted to peel beets in a standard steam peeler but the short residence time suitable to soften the skin of vegetables, such as carrots and potatoes, is insufficientto soften the beet to the centre of the root, and partly cooked beets when reconstituted after drying are not acceptable.When the skin is removed, therefore, it is necessary to check that the beetroot flesh is tender to the centre, and it is only by extended cooking under steam pressure, either in autoclaves or a semi automatic steam peeler with a controlled residence time, that the right tenderness can result. Peeling and trimming losses will amount to 20 - 30 percent. Beet is usually cut into 9.5mm dice if used subsequently for pickling. No blanching or sulphiting is required. After dewatering the dice, they are fed into the dryer. (4)Drying. Conveyor Band Dryer scaled to throughput, or Stove dryers. Inlet temperatures: 99"/ 82"/ 71 "C Condition in Bins to 5 - 6%at 54"- 57°C Raw moisture 89% Overall ratio: 14:l to 15:l Drying down ratio: 7:l Note. A.K.Robins &CoIncof theUSA,and alsoFoodMachineryCorporation, make suitable semi automatic beet peeler-cookers. The Robins machine is particularly suitable, as the time under steam pressure can be extended as I26

desired to achieve complete cooking, and it incorporates a second tank where rubber rollers rub off the skin without damage to the flesh. Where autoclaves are used, these can be the standard canner’s horizontal type, with front loading. The standard retort crates should not be used, however, as the depth of beets will be too great for the heat to penetrate into the centre of the mass and proper cooking will not take place. Small stainless baskets with perforated bottoms should be used, of suitable size to fit in layers inside theretort crates but spacer battens should be used between each row of the small baskets to allow a free flow of steam around and through the product. In this way the residence time for cooking and skin softening can be substantially reduced and an even penetration of heat obtained.

BELL PEPPERS (1)Flow-sheet Feed to Line I Double Flood wash I Splitting I Deseeding

I Double Flood Wash

I Inspection I Cutting I Sulphiting

I Drying I Conditioning

I Screening I Inspection I Packing I27

( 2 ) Varieties.

Yo10 Y. - California Wonder. - Bell Boy.

(3) Product Handling

Peppers may be processed whilst green, or can be left to ripen to red. Intermediate g r e e d r e d peppers are sometimes processed but d o not command the top market price for the dry material. The peppers are fed from field boxes into a bulk feeder, then elevated to a double flood washer which has compressed air fed into its base to aerate the water. Whole washed peppers are fed to a three channel inspection belt where they pass down the outer lanes for deseeding, and the halves are then delivered down the centre channel to a second flood washer which washes out the remaining seeds. Cleaned peppers are elevated from the flood washer on to an inspection belt where any residual seeds or pith are taken out manually. It is possible to core and deseed peppers by machine but, unless the shape and size are very regular, these machines are not 100 percent effective, and manual handling is often preferred. If tomatoes are included in the product mix, then a tomato washing and sorting line can be used for both products as indicated in Chapter 3. The peppers are then elevated toa J typecutter, which is particularly suitable for peppers, leaf vegetables and leeks. After cutting into flakes with the J cutter (capacity 2000kg per hr.) the product is elevated into a sulphiting bath with the solution of sodium metabisulphite controlled to give a residual level of 1250ppm(+/- 250ppm) in the end-product. After dewatering, the flakes pass to the dryer, then to conditioning bins. After drying, the flakes are elevated to a vibratory screen for removing fines, and thence the main product is fed by vibratory conveyor on to an inspection belt. The number of belts will depend on required throughput. Each 7 metre belt should handle 1.5-2kgof product over the total area of the belt at any one time. At a belt speed of 4 metres per minute, 60-80kg of product can be handled per hour, per belt. (4) Drying Conveyor Dryer or Stove or Tray Dryer scaled according to a desired throughput. Input temperatures 85°Cin first stage reducing to 50°Cat end of cycle. Conditioning at 52"- 54°C. Dry to 6% to 7% Ratio overall (Raw material as received: dry = 22:l.) Drying Down ratio (Prepared material: dry = 14:l.)

I28

Cultivation Guidelines for Bell Peppers (1) Sowing Nursery Bed spacing: 6.5cm. Plant out: 23-30cm apart in 75-100cm rows (2) Fertilisers Apply 500kg per Ha of 12:12:17+2 at planting and side dress at 4-6 week intervals with 250kg per Ha of Sulphate of Ammonia or 12:12:17+2. (3)Herbicides Apply Dymid liquid formulation at 11 litres per Ha. (2kg active) or 2kg Diphenamid 8OW (Dymid), either pre or postemergence, to clean ground. (4) Pesticides Diazinon 60 EC against Leaf miner: Thrips: Aphids Endosulfan against flea beetles and caterpillars. (5)Disease Control Kocide 101 against bacterial leaf spot. Dithane M45 or Antrocol against mosaic virus. If virus is severe, uproot affected plants. (6) Maturity California Wonder should be picked green but allowed to bc fully mature before harvesting. If picked too young the fruit will wilt. Yo10 Y is left to mature to bright red. Harvesting is 12-14 weeks from sowing/planting, onwards. Plant population 30,000 per Ha.

CABBAGE (1) Flow-sheet

Feed to Line

I Trimming

I Coring / Quartering

I Rod washing I Flood Washing I Dicing I Steam Blanching I I29

Sulphiting

I Dewatering I Drying

I Conditioning

I Screening

I Inspection

I Packing ( 2 ) Varieties As cabbage is now used mainly as a constituent in soups, both for flavour and eye appeal, it is necessary to select cultivars of bright green appearance when reconstituted. Another important requirement is that the head should be compact and ideally the core should not exceed 7 - 8 percent of the total trimmed weight. Very heavy trimming losses can arise from heavily cored ballheaded varieties, such as Primo and Winnigstadt, and these should be avoided. Small compact heads, such as Celtic, Ice Queen, and January Queen are useful Savoy types with good colour. Hispi and Offenham are good early varieties, and Wiam a dark green mid-season type. Cabbage is grown almost worldwide and there will be many indigenous varieties which could process well, subject to the parameters set out on colour and absence of heavy core. Dry matter is all important and 9 - 11 percent total solids is a figure to be aimed at when selecting raw material. (3) Product Handling Cabbage is brought to the factory in crates or tote boxes, and special attention should be given to the condition of these in the reception area, to ensure that wooden containers are not splintered. Splinters of wood can cause damage to cutters, apart from contaminating the product. Cabbage nets are also a hazard as they tend to shed fibres, which are difficult to detect in the dry product. Cabbage should never be stored for more than ten hours at the factory before processing. As much trimming as possible of outer leaves should be done at the farms to avoid bringing extraneous waste matter into the factory. The first operation is to trim the cabbage of its four outer leaves on a suitable conveyor

I30

belt. Where a lot of knife work has to be done, it is advisable to have a narrow hardwood bench running along the length of the trimming belt - on both sides - to prevent damage by knives to the belt fabric. After trimming, the heads are conveyed on to a coring machine, preferably one with two heads, thence to the quartering machine which cuts the head into 4 segments. These pass through a rod washer, and then through a double flood washer, in which the aerated water will disperse any grit or soil trapped between the leaves. Cutting follows,and cabbage is now mostly diced rather than shredded in view of its use in soups or other composite vegetable meals. The size of the dice will depend on market specifications. Blanching is preferably carried out in flowing steam, either in a Thermoscrew-type or a Draper or belt conveyor blancher. Sulphiting is carried out in a sulphiting dip tank, or on a reciprocating screen over which sparge pipes spray on the sulphite solution. The latter is made up in an adjacent steam pan fitted with an electric stirrer. Sulphite solution is made up from sodium sulphite (anhydrous) to achieve a level of 2000ppmin the dry product. The addition of sodium carbonate, bringing the alkalinity of the liquor up to pH 8.5 - 9, enhances the colour of the product but this is optional if the cabbage has a bright natural green colour. The dice pass over a dewaterer before passing to the dryer. A lot of surface water adheres to cabbage, and a thorough dewatering will make the drying operation much easier. Some plants centrifuge cabbage after blanching and before drying but this tends to revert to a batch process and breaks the flow into the dryer. (4) Drying Conveyor dryer scaled to desired output. Temperatures (inputs) through zones: 80"/75 "/65"C Conditioning: 50" - 52°C Moisture down to 5% maximum, as cabbage is hygroscopic. Cabbage is easily damaged by high drying temperatures and the above levels should not be exceeded, particularly in the middle and end heat zones. The phenomenon of 'browning' in cabbage arises from improper blanching, sulphiting or drying. Browning arising from processing faults must not be confused with scorching by high temperature in the dryer, although the appearance is similar; the stalk fraction being more affected than the leaf. It is thought that the condition is caused by the heat decomposition of certain soluble constituents in the raw cabbage. There is a big shrinkage loss in drying cabbage, and it is necessary to have a dryer of ample drying capacity at relatively low temperatures,

131

otherwise the dry output will fall below an economical level. The dried cabbagemay be aspirated at the time of screening to remove any excessive stalk content. This breaks u p the particles which may have a tendency to mat together. Packaging should preferably be in air-tight drums, with 500 guage polyethylene liners. Nitrogen flushing is also recommended. Drums give better protection than poly-lined sacks, as some product abrasion takes place in transit with the latter. Ratio: Overall 17:1 Drying 10.5:l

Tray loading cabbage prior to cabinet drying

Cultivation Guide Lines for Cabbage (1)-Sowing Direct drilling: 1.7kg per Ha. Transplanted: 550g per Ha. Final spacing: Early: Mid-Season: 37cm in rows by 30cm centres Late: (Savoy):-60 cm in rows by 60 cm centres (2)Fertilizers: On irrigated land use N100:P40:K60 plus 2.5tonnes per Ha organic (3)Herbicides: -Propachoor (Pre-emergence) or Dynid. (4)Pesticides: -Dimethoate: Hostathion: Fundal: Galicron: Prosuel: Princidid:-Diazinon. (5)disease Control: I32

Calomel Dust and Garden Lime on transplanted roots if Club Root is endemic. Benlate against Leaf Spot. (6)Maturity: -Cut before ‘cracking’occurs. If rain follows cracking, heads will rot. Harvest is 12-15weeks after drilling, or 14-17weeks with transplanted crops. About one third of the above time is in the nursery bed. Plant population:-Mid-~eason:-87,000 per Ha -Savoy:-27,000 per Ha

CARROTS (1)Flow-Sheet

Feed to Line

I Dry Cleaning I Destoner-Washer I Flash Steam Peel I Skin Elimination

I Inspection Trim

I Cutting I Inspection

I Blanching

I Sulphiting

or Starch Dip

L

Dewatering Drying

I Conditioning

I Screening I Inspection I33

I Packing

(2)Varieties Colour and high total solids are the most important factors in selecting carrots for dehydration. Up to the 1970's Chantenay was perhaps the most favoured variety in Europe because of its stump rooted shape, which made for economy in dicing. It was practically coreless and had an orange-red colour, which was reasonably bright when dehydrated. It did not prove very hardy in the winter in Europeand rarely survived without frost damagebeyond December, when processors reverted to the more hardy Norfolk Giant and Danvers. Chantenay also failed to reach full colour if not allowed to mature properly. The author experienced a severe problem in Cyprus in the early 70'5, when a particularly wet winter had encouraged good growth in carrots and potatoes (even the early spring potatoes produced tubers 13-14cmlong and 7-8cm in diameter) but the crop of Chantenay carrots being grown on contract for a multi-national processor in the UK failed completely to develop an acceptable red colour, due to the non development of the carotene in the early stages of growth, following a very cool wet spring. Today, the selection of carrots for dehydration has become a specialist exercisefor the seed breeder and severaluseful cultivars now being produced come from Dutch seed breeders, and the following have been favourably regarded by European dehydrators: the suffix RZ indicates the seed breeders - Rijk Zwaan of Holland. Karotan RZ

Bordeaux RZ

Kartal Tosto RZ

Furon RZ

These are related by a succession of cross breeding to a German variety, Kieler Rote, which the author introduced into the UK in the late 1960's for field trials but which, although they meet the parameters of a bright scarlet colour and very high solids, failed in context of its long tapering shape, which made it uneconomic for dicing. The above new varieties, now bred to the Kieler Rote colour characteristics, should provide an excellent choice for the dehydrator. In the USA the Ventura type carrot is used successfully. Ventura is, however, a region and not a specific cultivar but several varieties which meet the colour and solidsrequirements are available from Californian seedsmen. (3) Product Handling The removal of the tops and crowns of the carrots should be carried out on the farm or at a preprocessing washing and 'topping' station, to avoid I34

bringing tops and extraneous material into the factory processing areas. Once 'crowned', however, the carrots must be processed without delay, otherwise they will become rubbery and their quality will deteriorate. Removal of the crowns will create a 10- 11percent weight loss, according to the size of the root, and this will be reflected in the factory price, as will the labour cost of the out-workers. The carrots will be fed from tote boxes into a bulk feeder, unless a fluming system is used, in which case they will pass through a prewasher in the flume discharge pit, be separated from the fluming water, and then elevated into the bulk feederin the factory.If thecarrots havebeen prewashed, then the dry cleaning reel is not required, and they will pass on to the destoner. If the carrots are delivered dry into the bulk feeder, they will pass through the dry cleaning reel and then to the destoner-washer. Peeling is preferably by 'flash' steam peeler at 17atm pressure and the skin is then removed in a skin eliminator. If lye peeling is used, this must be followed by passage through a brush washer. Peeled roots are then inspected on a 'merry-go-round' conveyor for trimming where necessary, then elevated to a G Dicer, set for 9.5mm dice, half dice or flakes 9.5 by 9.5 by 2mm. For instant reconstitution soups, the cut may have to be reduced to 6 by 6 by 2mm. It is normal to blanch in a hot water blancher, with the additives (SO, and buffering agents, such as sugar and salt)being metered into the blancher at a prescribed rate to sustain an SO, level of 1200ppm in the end product. The use of SO, in carrots has now been superseded in American factoriesby using a steam blanch in a Draper-type belt blancher followed by a dip in 2 percent food grade corn starch. This retards colour and quality loss, and is regarded as better than sulphiting only but their specification usually permits a maximum of 500ppm of SO, in the dry product, or less than half the European level. Dehydrated carrot was originally packed in nitrogen-flushed hermetically sealed tins against Armed Services indents, as it is recognised that the colour deteriorates rapidly after 3 months storage in poly-lined containers - the dice turning pink and giving off an odour reminiscent of violets. The starch dip method has partially overcome theoxidation problem but it is necessary to hold the product in cool storage (under 5°C) if it is required to be stored for 6-9 months. The end moisture also affectsdurability, and should not be more than 5 percent. (4) Drying Conveyor dryer scaled to a throughput of 2 tonnes per hour upwards. Through-flow or stove dryers for 500kg per hour upwards. Temperatures (inlets) through zones: 104"/ 93"/ 88°C.

I35

Conditioning: 50" - 52 "C Moisture maximum 5% Raw moisture basis 90% Overall Ratio: 15:l Drying Ratio: 9:l The Overall Ratio is based on the factory gate weight, ie, with tops and crowns removed to the dry weight.

Cultivation Guide Lines for Carrots (1) Sowing To produce large roots : sow 1.7kg per Ha. 50mm spacing in single rows at 37cm centres. Deep soil cultivation. (2) Fertilizers 260kgperHaof 12:12:17+2beforeplantingandrepeatas a topdressing ifleaf shows sign of yellowing. Organic 1500kg per Ha. (3)Herbicides Pre-emergence: Prometryn 50 WP at 2.5kg per Ha. Post-emergence: Herbicidal oil (Kerosene) 500-750 litres per Ha., after first true leaf appears. (4)Pesticides Diazinon or Dimethoate against aphids and leaf miners. (5)Disease Control Spray regularly with Daconil or Benlate against alternaria and leaf spot. (6) Maturity Roots should be allowed to grow to 40-45mm minimum across the crown. Do not lift until carotene is developed and full colour is achieved. Ensure that the crown is covered by the soil to prevent greening. Harvest is about 14-16 weeks after sowing but lifting can continue for several weeks after this. (7) Plant population 530,000 per Ha.

CHILLI PEPPERS (1)Flow Sheet Feed To Line

I Washing I Inspection

I Shredding I I36

Drying I Conditioning

I Inspection I Packing (2) Varieties Anaheim Long Green Chili (Californian) Jalapeno Green (Mexican) Floral Gem Grande Yellow /Red (Californian) Birds Eye Red (miniature - 13-19mm long) (Africa - Papua). (3)Product Handling Only fully mature pods are picked at time of harvesting. They are brought to the plant in bulk or tote field boxes and fed into a feed hopper. They are washed through a flood washer or washing reel, inspected on a conveyor belt and fed toa J type cutter for cutting into 25mm slices.Birds Eye small red chillies are dried whole, usually in the sun, or they can be artificially dried. The cut or whole peppers are fed into the dryer for low temperature drying, conditioning, aspiration, inspection and packing. Dried chilli peppers may be ground down for chilli powder but for this purpose they must be dried to 3-4 percent.

(4) Drying

Conveyor or Stove Dryer according to scale. 6 hour cycle for slices - 10-12 hour for whole. Temperatures (input) through zones: 71 "/65"/62 "C Conditioning: 49 "-50 "C Moisture down to 6-7% for sliced chillies. 4% for whole (small) Drying Ratio = 5:l Raw Moisture = 80% Overall ratio: 6:l

CELERIAC (1)Flow Sheet

Feed to Line

I Dry cleaning

I Destoner-Washer

I Steam Peeling I I37

Skin Removal I Inspection I Dicing I

Blanching I Sulphiting I

Dewatering I Drying I Conditioning I Screening I Inspection I Packing (2) Varieties Smooth skinned root cultivars: Giant Prague - Alabaster (3)Product Handling As in the case of many vegetables, much of the rough preparation should be done externally to the factory, particularly as celeriac has a considerable amount of leaf and stalk. The latter should be cut well back to the root crown as, whilst some of this can be used in the fresh state for salads, it serves little purpose for dehydration. The trimmed roots are therefore fed into a bulk feeder and elevated into a dry cleaning reel. The roots pass into a washerdestoner and on to the steam peeler. Peel is then removed in a skin eliminator and the roots pass on to an inspection and trimming belt. Cleaned roots are elevated to a G model dicer (capacity u p to 6OOOkg per hour for lOmm dice). Alternatively the roots may be cut into strips 40mm x 6mm x 6mm. Blanching may be carried out in a hot water blancher, in which case the sulphite is fed from a make up pan and metered to give the requisite level of SO,. Alternatively a steam blancher may be used and the sulphite solution sprayed on to the diced product on leaving the blancher. When setting up a root vegetable line, it is probably advantageous to opt for steam blanching, provided potatoes are not included. Potatoes release considerable amounts

I38

of starch after cutting, and water blanching permits this to be removed from the surface of the blanching liquor by arranging a flow of hot water continuously through the blancher. On the other hand water blanching leaches solids from carrots, swedes, turnips and all green vegetables, and consequently better drying ratios are achieved i f steam blanching can be used in these cases. If potatoes are a major part of the product programme, however, then hot water blanching may have to be used in the root vegetable line, as the expense of two blanchers in parallel may not be justified. 5-6 minutes is required, adding up to 1percent citric acid in the blanching liquor to assist whitening. This is combined with the SO, treatment in hot water blanching. The blanched material is dewatered before passing to the dryer, then to the conditioning bins. Screening, sorting and packing proceed as for other vegetables. (4)Drying Conveyor Dryer scaled according to desired throughput. Temperatures (input) through zones: 104"/loo"/ SO"/ 75"/ 50°C through the zones. Conditioning at 50"-55"C Overall ratio: 15:l (subject to acceptable trimming losses). Drying ratio: 9.5:l

CELERY (Leaf and Stem) (1)Flow Sheet Feed to Line

I Flood Wash

I Trimming

I Flood Wash

I Inspection

I Cutting I Blanching I Sulphiting I Dewatering I39

I Drying

I Conditioning

I

Aspirating I Kibbling\Milling Inspection

I Packing ( 2 ) Varieties

(White) Lathom or Golden Self-blanching (Green) Pascal or Utah 52-70 (3)Product Handling Celery should undergo a good washing process on the farm to avoid bringing unwanted soil and dirt into the factory. It should also be well trimmed down to the root and have coarser outer leaves removed, leaving very little green top. The field boxes of trimmed and washed celery are tipped into a bulk feeder, from where it is elevated into a double flood washer. After washing under pressure the roots are elevated on to a trimming belt, or ‘merry-goround-system’conveyorwhere any discoloured stalks or leaves are removed. Large roots are cut longitudinally so that no root is greater in diameter than 70mm. This assists removal of soil in the second wash. Trimmed celery then passes through a second double flood washer and on to an inspection conveyor. Thence it is conveyed to a J type cutter, or alternatively a Model O V Transverse Slicer. The celery should be cut into 9mm squares on the former J machine or transverse slices on the OV. The green part is aspirated out after drying. The celery pieces are blanched in steam for 2 minutes, and then dipped in a sulphiting tank for a few seconds in a solution of SO2 and 1percent citric acid. The level of SO2 concentration is such as to give a final concentration of 1OOOppm in the dry product. Up to this point, it is essential that all equipment shall be of stainless steel to prevent blackening of the product. Thecut celery is dewatered and conveyed to thedryer, then conditioned. The bins of dry material are fed into a precision air classifier to separate the green leaf from the slices or squares. If the celery is required for powdering or kibbling for soup, it is diverted to a Turbo-Mill or Kibbler - otherwise on to inspection tables prior I 40

to packing. (4) Drying Conveyor Dryer scaled to desired throughput. Temperatures (input) through zones: 82"/ 76"/ 65°C Conditioning: 5Oo-52"Cto 6% moisture Overall ratio: 221 (for well trimmed roots) Drying ratio: 14.2:l

GARLIC (1)Flow-Sheet Feed to Line I Bulb Cracking I Screening 1 Aspiration I

Flood Washing I Dewatering I

Inspection I Slicing

I Drying I Screening I Aspiration I

-

Inspection Kibbling

Milling for Powder 250 microns

I

Packing (2) Varieties

California Late, California Early, Creole or indigenous (3)Product Handling The garlicbulb, which may contain from &36cloves,is broken into individual 141

cloves by passing between rubber-covered rollers that exert enough pressure to crack the bulb without crushing the cloves. The loose paper shell is then removed by screening and aspiration. The cloves pass through a flood washer to float off the root stubs. After dewatering, the garlic is inspected, sliced and loaded on to trays for drying. After drying the pink skin, which adhered to the fresh clove, will have been loosened sufficiently to be removed by screening and aspirating. After inspection, the clove slices can be kibbled down to a smaller particle size, or milled in a Turbo Mill fitted with a 250 micron screen. (4)Drying Stove or Through-Flow dryers are used Temperatures (inlets) 70°C reducing to 50°C Moisture down to 5% for kibbled and 4% for powder. Preparation losses will be approximately 40% - 600kg prepared material from each 1 tonne received. Overall ratio: 4:l Drying ratio: 2.4:l Note: Much of the garlic processing plant has been designed by the major processors themselves, particularly in the USA where production is in the main confined to California, and the larger onion processors.

Horticulture Yields in the USA are u p to 9.5 tonnes per hectare. The garlic is cured on the field in windrows after lifting. Bulbs are topped and sorted (to remove diseased bulbs) on the field. Sometimes grading precedes delivery to the factory. The bulbs may be stored but at more than 70 percent R H they may start to mould.

LEEKS (1)Flow Sheet Feed to Line

I Inspection

I Flood Washing

I Cutting 1 Inspection

I Sulphiting

I I42

Dewatering I Drying

I Conditioning I Aspiration I Screening I Inspection I Packing ( 2 ) Varieties

Autumn Giant, Goliath Super RZ, Bastion RZ, Giant Musselburgh, American Flag, Autumn Mammoth Carantan, Winterreuzen, Giant Winter, and many indigenous varieties having thick stems and a good proportion of white bulb to green top. (3)Product Handling Like celery, leeks also require a considerable amount of cleaning and trimming on the farms. The roots should be cut right back to the butt of the bulb, and only about 30 percent of the green leaf should be left on the bulb. Further cutting back may be necessary if the leaf is discoloured. In effect, the leek should be prepared on the farm to the quality expected on the fresh market in context of washing and trimming back the green leaf. This is essential to avoid extraneous matter being brought into the factory, and it is far better to leave vegetable waste on the land than to create a waste disposal problem in the factory working areas. If necessary, a premium should be paid to the grower for this extra service. The trimmed leeks are fed promptly from the bulk feeder to the inspection belt for final trimming and examination, and it is important that the leeks are handled quickly as they are a perishable vegetable and will not hold well once lifted. If storage is necessary leeks can be held for a limited period at 0°C at 90 - 95 percent RH. The leeks pass through a double flood washer to ensure that any dirt or silt still remaining in the crotch of the leaves and follicles is washed away by the aerated water in the two washer tanks. If the leeks are very thick stemmed, it may be necessary to split them longitudinally on the inspection belt before the washer. A J type cutter is used with knives set to produce flakes of a predetermined square size, the thickness being that of the leaf and follicles. I43

Alternatively they may be diced to 9.5mm. Sulphiting follows in a sulphite applicator, the solution being made up in an adjacent pan at a concentration to achieve 750-1000ppm in the end product. The concentration of the liquor is 1- 1.5 percent. After dewatering, the flakes proceed to the dryer. Green and white flakes are not separated at this stage. After drying, the flakesare transferred to the conditioning bins. Before screening the product is then fed into an aspirator which can be accurately adjusted to separate the green leaf from the white bulb flakes. Screening will remove fines and, after a final inspection, the product can be packed. If required the product can be milled for powder on a UT 12Turbo Mill fitted with a 250 micron screen, as there is a good demand for powder as a soup ingredient. (4)Drying Conveyor Band or StoveDryer, scaled to throughput. AThrough-flow Dryer may also be used for medium scale operation. Temperature (inlets) through zones 82"/ 76"/ 65 "C Conditioning: 50"- 52°C.End moisture 5 - 6 % Overall ratio 14:l Drying ratio 8:l - with a raw moisture of 88 %

Cultivation Guide Lines for Leeks (1) Sowing Nursery Beds: Drill 2.5kg per Ha, Transplant 15cm apart in single rows at 45cm centres. ( 2 ) Fertilisers A rich soil is essential, with 1000- 1500kgper Ha. organic manure ploughed in before drilling/planting. Otherwise applications of artificial manures is as for onions. (3)Herbicides Pre-emergence: Dachtal W75. Post-emergence: Nitrofen 14 days after emergence of first leaf. (4) Pesticides Diainon, Leptopros, Permethrin. (5)Disease Control Benlate, Kocide 101 (6) Maturity Drillsshould beregularlyearthed up tofacilitateblanchingof the bulb. They should not be lifted until the bulb is upwards of 40mm in diameter. The root and two thirds of the green top should be trimmed off in the field when lifting, before delivery to the plant for processing. Plant population: 143,000 per Ha. I 44

MUSHROOMS (1)Flow-Sheet Feed to line

I Washing

I Inspection

I Cutting

I Blanching

I Drying

I Conditioning

I

Screening

I

Inspection

Milling (boletus edulis)

Packing

Agaricus campestris (cultivated mushroom) Boletus edulis (field mushroom) (3)Product Handling Both types of mushroom are handled more or less in the same way, although the wild or field mushroom is picked fully open, exposing the dark pores on the underside instead of the gills characteristic of the cultivated mushroom, or champignon. Thorough washing is necessary in a reel or drum washer to remove all traces of soil. Inspection on a conveyor belt follows. The champignon-type mushroom is usually sliced in a CC Slicer to 0.8 - 3.2mm thickness. If the mushrooms are large then a G type dicer set for 6.4mm dice is favoured. In thecaseofBoletus edulis,eitherasmallcutisrequiredif theproduct is going to be used as a whole particle ingredient in dried soup mixes, or a random cut if thedried material is to be milled for mushroom powder, which is also used as a base for mushroom soup. Whole mushrooms of whatever size are rarely air dried, as the drying cycle is too protracted. With both varieties, the stems are left on, unless there are some of the root fibres left, in which case the latter should be trimmed off on the inspection table but ( 2 ) Vareties

I45

anything u p to 1.5in. of stem may be left on. Blanching in flowing steam or hot water takes from 2 to 5 minutes. After drying and conditioning to 5 percent moisture, the product is inspected and packed, or diverted to a mill for grinding to powder. The particle size should be 250 microns (60 BSM sieve). (4) Drying Air drying never produces a really first class product suitable for use as a straight vegetable for grilling or frying, and this quality can only be achieved by freeze drying. On account of the high value of the raw material and the price obtained for the end-product, this is one of the very few vegetables which will support the high cost of this process. (See Autec Process in Chapter4). However, if colour and presentation is a secondary consideration and a considerable percentage of the product is going to be milled for powder, then air drying can be considered. A major problem with mushrooms, by the nature of their cultivation, is a very high total bacteria count, and excessive levels of yeasts and moulds. This can be circumvented to a degree, by reversing the heat zone temperature in the dryer, ie, controlling the inlet temperatures in the usual 'hot' zone to not more than 65 "C and finishing at a higher temperature of 80°C.In this way the bacterial level can be substantially lowered. Mushrooms are about 93%moisture, and drying should be down to 5%end moisture. Overall ratio 16:l Drying ratio 14.5:l

GREEN PEAS (1)Flow Sheet Farm

Vining

I Dry Cleaning I Pneumatic Separation I Washing I Cooling Factory Washing

I I46

Pneumatic Separation

I Quality Grading I Inspection I Scarifying I Blanching I Dewatering I Drying

I Conditioning I Aspiration I Screening I Inspection I Packaging ( 2 ) Varieties

Early: Sparkle Banff Main: Scout Tristar Pujet Markardo (3)Product Handling (a) Farm handling It is invariably essential, with the general use of viners nowadays, that the grower assumes responsibility for the greater part of the precleaning and cooling process, which enables the processor to handle peas on a 24 hour a day basis, without deterioration of the raw peas held in bulk at the factory. Some years ago it was necessary to process vined peas within two hours of

their being shelled. To do this, podding machines, and later viners, were installed as static machines outside the factories, and the cut haulm was transported on bogies fiom the farms, and podding or vining was controlled to handle peas with a minimum of delay once the peas were shelled. The transport of vine/haulm and the disposal of the threshed haulm eventually proved so cumbersome and costly, that mobile viners were developed, whereby the shelled peas were collected in trucks on the field running I47

alongside the vining drums, and the waste haulm was discharged from the rear of the mobile viner on to the field and subsequently ploughed back into the soil.

Mather & Platt’s super mobile viner working in the field. Obviously some solution to the holding of shelled peas in bulk had to be found to prevent the rapid spoilage that arises from the heat generated in the pea which has been subjected to stress by the beater-paddles in the viner drum. The grower, therefore, had to assume the further responsibility of cleaning, washing and chilling the shelled peas so that they could be safely held in bulk tanks of 10 - 12cwt capacity for anything up to 8 - 10hr. Hence the somewhat elaborate process incumbent on the farmer to install a dry cleaning drum to remove loose pods, stalk and haulm from shelled peas, then a pneumatic separator for finer cleaning, followed by a reel washer, and finally passing the peas through a fluidised bed chillerfreezer to bring down the temperature of the peas to about 2°C.In this way the grower can be a few hours ahead of the factory’s demands and provide a round the clock service with little or no fear of quality deterioration. At the point of filling the holding tanks, an automatic Avery scale is fitted, to register the exact weight discharged into the tanks, and this is the basis of payment for the crop to the grower by the processor, subject to a sliding scale taking into account the maturity of the peas, if applicable. Peas for dehydration must meet quality levelsof maturity determined by a Tenderometer. This machine must be installed by both grower and processor. It is the last quality test at the grower's end and the first at the processor's. All peas for dehydration should fall into the category reading up to 100 on the Tenderometer scale. Any peas above that reading are normally rejected by the dehydrator, (and similarly by the commercial I 48

freezer processor) and are used for canning. A cross-check is made at the factory on arrival of the load. It is sometimes the practice to pay the grower a premium for peas at lower levels of tenderometer readings, say 90 maximum, to compensate for lower yields in the field. (b) Factoy Handling Dehydrated peas are regarded as a quality product, and anything less than a bright green pea which will reconstitute rapidly and hold its tenderness will rarely find a market outlet - therefore the cleaning process already carried out on the farm is almost repeated to ensure a first class product requiring the minimum of manual handling. Incoming tanks are emptied through a bottom gate into a gooseneck elevator with nylon perforated buckets that deliver the peas into a rotary cleaning/washing reel, thence to a pneumatic separator to remove any particles of stalk or skin left behind in the farm cleaning operation. The peas next pass through a flotation quality grader, whereby any over-mature peas are diverted to a separate processing line for catering quality packs. Any separation should be minimal, if quality control at the farm has been strictly observed. This fraction will need to be held over in chill conditions and put through the line at suitable intervals. After a visual inspection on a conveyor belt, to remove any discoloured peas, the product passes through a scarifier, which makes a shallow incision of 3mm in the outer membrane of each pea. This assists evaporation of the moisture during drying, and prevents the denaturation of the protein and case hardening of the skin. Without this process it is very difficult to achieve a good quality pea that will rehydrate quickly and have the level of tenderness required to compete with a frozen or canned pea. Scarifying will cause some leaching loss in the blancher but this can be minimized by the use of additives, such as sugar and salt, in the blancher liquor. The use of the latter was the subject of a Patent some years ago but the process is now universally available. Hot water blanching is preferred for peas, especially if the 'buffering' technique is used. The blancher must be heated with closed steam coils, open steam injection only being used to bring the blancher up to operating temperature. Buffering agents - sugar, salt, sodium carbonate, sodium sulphite - are made u p in solution in two stainless jacketed pans fitted with electric stirrers. One is in use being pumped into the blancher whilst the second one is being prepared. The solution passes through a small pump, capacity 45-90 litres per minute, into the blancher water at a low level. Treated blanching water flows out from a top overflow pipe by gravity back into the make-up pan and the cycle continues, the additive levels being regularized by half hourly or hourly additions of dry additives into the pan in use. After 8 hours it is normal to change the blancher water completely as

I49

it will have become very discoloured and sour smelling. Anhydrous sodium sulphite is used for sulphiting, to give a final residual level of 1250ppm in the dried pea. It may also be advantageous, especially where the water is hard to add sodium carbonate to sustain a pH of 9 to 9.5 in the blanching liquor. Sugar levels may be held at 1to 1.5percent, salt at 1percent and sodium sulphite 1.2 percent. Addition of 0.5 percent of sodium carbonate may be necessary to arrive at a pH of 9. The blanching liquor temperature should be controlled at 97°C and the dwell time 1to 1.5minutes for peas with a Tenderometer reading of 100, reducing to 1minute for younger, lower reading peas. Adequate blanching is testedat 30minuteintervalsbycheckingthat thereisanegativeperoxidase reading. A positive reading indicates that either blancher temperature or dwell time is too low. No cooling is necessary if the peas pass quickly to the dryer but it is essential to pass them over a dewatering screen. Drying and conditioning follow. The dry peas are then aspirated, to take out splits and skins. They are then screened for size, and sorted visually on 7m belts with metal detectors. Packing is normally in 25kg poly-lined paper (multi-layer) sacks, or poly-lined fibre drums. (4) Drying Conveyor Dryer scaled to desired output. Temperatures (input) through zones: 82"/76"/65 "C Conditioning; 50 "-52"C Moisture down to 6 - 7% maximum Drying ratio: 5:l to 6:l according Tenderometer readings. Higher ratios are linked with low readings and highest quality. The product is highly sensitive to light after drying, and black pigmented polyethylene liners of 300 gauge and 5 ply extra strong quality paper bags are recommended for packing.

ONIONS Onions represent some 50 percent of all dehydrated vegetables, excluding potatoes, used in one form or another in the United Kingdom, and this percentage is reflected in consumption figures for Europe and the United States. In America about half the Californian onion crop is contracted to the dehydrators, who handle some 100,000tons per annum, yielding 10,OOOtons dry. This is supplemented by imports from Egypt and Mexico. In view of the importance,therefore, of onions in the production programme, the processing I50

data hereunder is supplemented with some horticultural data, in-plant storage methods and details of the varieties used in countries visited in recent years. (1)Flow Sheet Feed to line

I Grading - (discard minus 50mm bulbs)

I Loose skin removal (slat reel dry cleaner) I Washing (reel)

I Topping - Tailing

I Peeling

I Inspection I Slicing I Inspection I Rinsing I Dewatering I Drying I Conditioning I Screening I Kibbling to flakes Inspection I I Inspection Packing I Packing

151

(2)Varieties USA & Europe

South Africa Egypt

India Bulgaria Romania

Long- Day Southport White Globe Dehyso Dehydrator 14

Short-Day White Creole

Intermediate Primer0

Dehydrator 3 Dehydrator 4 Dehydrator 6 Dehydrator 8

F1 Hybrid Gilroy

Sphinx Alba Fahoumy Guiza 6 Winter Nile Bombay White Gorna Oryakhovitsa Ranoresk

Note: Long-Day varieties signify 14-15hr photo-period. Intermediate varieties signify 13 1/2hr photo-period Short-day varieties signify 12-13hr photo-period (3) Horticulture It is of the utmost importance to know the day length and prevailing temperatures in the environment where the onions are to be grown. At ordinary temperatures in moderate climates, all bulbing onions require a certain day length to initiate bulbing. Late maturing varieties need longer hours of daylight to induce bulbing than those that mature early. Temperature also influences the amount of ‘bolting’, and this occurs more frequently with winter crops. It is essential, therefore, for the processor and grower to consult with the local Horticultural Institute or Research Station in the growing region to select suitable cultivars and to know the conditions under which they will give optimum results. Field trials are of the utmost importance to establish the parameters before a full scale dehydration operation is contemplated. White or brown skinned onions are preferred. Demand for red skinned onions is limited. (4) In-Plant Storage Onions may be delivered direct from the farms for immediate processing, or may be diverted into controlled temperature storage sheds to build up a reserve stock, so as to extend the period of processing. The storage facility is important where harvesting periods are limited by climatic constraints.

I52

Windrowing onions mechanically.

In the USA the regions where most of the onions contracted to processors are grown have a wide range of climatic conditions. Crops mature very early in the southern regions of Louisiana, Texas and Southern California, and mid-season to late season in areas north of the 36"parallel. This gives a longer processing season than most countries enjoy. Bulk storage of onions may be undertaken at the factory, or at an outside location if space is more cheaply available.The preference, however, is to locate the stores on the factory site to take advantage of the installed utilities, like electricity, heating, etc, and to have the benefit of centralised supervision. As a guide to the logisticsof onion storage, the following details were noted from an actual installationof storageunits, each holding approximately 750 tonnes of onions. The method of delivery is in stillages, each holding 750kg, and the dimensions of these bulk boxes used for conveying the onions from the fields were 1.2m long by l m wide by 1.2m deep. They were fitted with perforated metal bases of heavy gauge and two strong wooden battens on the underside, so that when the stillages are stacked an air space is created to allow circulation of either warm or cold air. The onion store building was a pitched roofed shed 22m wide by 23m long by 5.5m high to the eves of the roof, designed to hold 720 stillages stacked 4 high in rows of 12across the full width of the building. This lateral I53

row of 12by4 stillagesis added to by a further 14rows running longitudinally down the 23m length of the building, accounting for the full capacity of 12 by 4 by 15 stillages, or 720 in total. The first row of 4 stillages high docks into a plenum chamber, connected to 2 air fans, running the full width and height of the end wall. At each docking point there is a 'letter-box' aperture in the plenum which directs the flow of conditioning air through the space created by the battens. This flow is diverted upwards through the perforated bottom of the boxes and through the onions by fitting a block of timber in the air gap at the end of the longitudinal rows. This deflects the air upwards at any point where the baffle is fitted, even if the row is not completed to the front of the building. When the store is fully loaded the baffles will be at the end of the 15th row, allowing circulation along the full length of the store. Stillagesare placed in position by forklift trucks, and each stack of four must be carefully located to ensure that there is an uninterrupted length of air flow gap as the rows are completed longitudinally. The temperature at which onions can be efficientlystored is extremely critical, and American tests published by Copley and Van Arsdel on Southport White Globe onions over four months storage periods at differing temperatures disclosed that the optimum yields of sound bulbs after this period of storage were obtained by utilising temperatures of 2°C (85 percent yield) and 30°C (79 percent yield). In designing and operating the store, therefore, it is vitally important to be aware of ambient temperatures at all times during the period of storage, and to judge whether a cool or warm air flow is to be used. This will vary according to whether the plant is operating in temperate, tropical or subtropical climates. It should be noted that, at temperatures of 10"to 20°C the quality of the bulbs deteriorates rapidly, yields falling from 49.9 percent at 10°C to 36.5 percent at 20°C. (5)Product Handling After feeding to the line, the onions are graded for size. Where labour is plentiful this is sometimes done manually, as the illustration of the Indian factory demonstrates. Bulbs measuring under 50mm in diameter are discarded, and in some instances are diverted to the fresh market. The quantity of this size of onion should be minimal, as the specification in the purchasing contract should clearly specify that bulbs must measure more than 50mm. The processing grades are 50 - 60mm upwards, and the reason for dividing into these grades is to accommodate an automatic topping and tailing installation, if such automation is desired. Where this method is used it is customary to feed u p to two grades into

I54

separate Autocore machines, each provided with a Shufflo feed. These units are supposed to handle 1000 to 1500kg per hour each, with two operators who are required to orientate the onions manually into cups on a metal conveyor, which presents the bulbs to a top-cutting and root-coring operation at a rate of 140 bulbs per minute. It must be stressed, however, that these machines are only efficient with full globe-type onions, and half-globe and flats are difficult to handle mechanically . Reference has been made in the chapter on preparation plant for onions to the Hydrout machines, which are manually fed but the processor is advised to investigate the safety factors involved in the operation of these machines. The peeling operation in most of the factories visited has been by abrasive machines, either batch or continuous. One of the major Californian dehydrators has indicated that American methods have changed in recent years, in that the onions having been cured in the field, are subjected to supplementary curing in the plant by applying an air blast of 35o - 38 "C for the purpose of thoroughly drying out the skin, roots and tops, so that the bulbs can be mechanically cleaned as much as possible before coming in to contact with water. After this additional curing and on their way to the processing area, the onions pass through brushers, scrubbers and toppers. During this operation, skins, roots, tops and dirt clods are removed. Onions are then flumed into the plant and pass through various types of high pressure washer, the bulbs being conveyed on roller-type conveyors so that the high pressure water jets impinge on all surfaces. After drying, any remaining particles of skin are removed by efficient aspiration. Much of the specialised plant for scrubbing, washing and curing has been developed over the years by individual factories - they are not products of food machinery manufacturers. To revert to the more standard process, after grading, the onions pass through a dry cleaning reel with wide wooden slats in order to remove the outer skin and loose tops and soil, and are then washed in a standard washer reel. If an Autocore machine is not going to beused, topping and tailing must be done manually or by Hydrout (See Chapter 3 with reference to this machine). The onions are then peeled by abrasive peeler, preferably in a continuous model, although for small production a batch peeler may be used, provided it is a high efficiency machine. After peeling, the onions are inspected before being elevated to the slicing machines, which are set to produce a 4mm slice. A CC slicer with disposable knives may be used, or a more robust slicer, such as a modified cabbage slicer. If the latter type is used, it will be

I55

essential to sharpen the knives every 8 hours, as indicated previously. The slicing process releases sucrose on the surface of the cut onion and it is necessary to give the slices a gentle rinse - usually by a water sparge pipe fitted over the elevator feed at the end of the inspection belt on which the slices have been inspected. The slices are dewatered before entering the dryer.

Elevator feed to five pass dryer - onion dehydration plant, Nasik, India.

(6)Drying Conveyor Band Dryer scaled to throughput for medium to large scale operation: 200kg per hour upwards of prepared material. Stove or Through flow Dryers for throughputs up to 1500kg per hour of prepared onions. Number of dryer units will depend on input required. 82°/ 76°/ 65°C Temperatures: Inputs through zones: for Conveyor Band Dryers 70°C first zone Tray Dryers - Stove or Through flow 50°C second zone Conditioning: 50° to 52°C Dry to 6% moisture Overall ratio: 10.1 Drying down ratio: 6:1 to 6.5:l

1

The drying down ratio represents the weight of fresh prepared onion in kg required to produce l k g of dried product. This is calculated by the formula:

100 - End Moisture = Evaporative Factor Raw Material Moisture - End Moisture 100 = Water evaporated from lOOkg Evaporative Factor of fresh material

100 - Evaporated water

= Dry Material from 100kg fresh prepared.

100 = Drying down ratio Weight of Dry Material Example: Calculation of drying down ratio with onions containing 84 % moisture and drying to 6% end moisture is as under: 94 100 -6 - =1.205 (Evaporative factor) - = 84 - 6 78

-

loo =82.987kg Evaporation 1.205 100 - 83 = 17kg dry material 100 _. = 5.88 Drying down ratio 17 Note This figure i s somewhat theoretical as there are some hidden losses in handling the raw material through all the wet processes, and losses of dry material between the discharge from the dryer and the point of packing off. These losses arise from 'fines' being emitted into the atmosphere by the air flow from the dryer fans, the conditioning bins, abrasion of product in sieving, handling and minor spillage. As part of the onion slices may be converted to kibbled onion or onion powder, there are further small losses in these operations. Taking these into account the drying down ratio for onions of the quality and total solids assumed in the example would be nearer to 6.0 to 6.5 : 1 but the formula provides a rule of thumb method for calculating a gross figure for drying down ratio. In practice, adjustments must be made for losses a s identified above. (7)Kibbling and Powder Production Whilst onion slices are usually at a premium on world markets, it is inevitable that a percentage of dried slices will break down in handling, and it is usual to divert this material into a kibbling machine. This broken material will manifest itself when the slices are screened over a large gauge I57

sieve, and the 'through' material can then be kibbled down and screened out as 5mm or 7mm kibbled flakes (ie, sieve size). Onion powder is generally produced from fines created by sieving the primary product, and from undersized particles caused by kibbling. A Turbo Mill is strongly recommended for producing powder. The Baumeister mill has proved very efficient for this purpose, having a wide range of adaptability in output, fineness of particle size (no problem in grinding onions to minus 250 microns), and arrangement to suit the availability of floor space or geography of any factory. The mill must be housed in a separate room in the factory, sound insulated, and the cyclone vented air discharged to atmosphere. A typical installation to handle the powder production for a medium size plant would be a UT 12model, powered by an 18KW motor. The cyclone and supporting framework, including filter-bags require a height of approximately 5 metres in the designated building. Vegetable dust can create an explosion risk but the design of this mill has many safety factors built-in, which minimise this danger. ( 8 ) Packing Whilst most onions of overseas origin have been packed in poly-lined cartons, the American processors now use multi-ply bags hot melt sealed, as these are easier to handle than lined cartons. The use, generally, of the latter type of packing will depend on availability in the country of operation. Cartons and liners are normally available in most locations, and the specifications for these are as under: Cartons: constructed of double walled corrugated fibreboard with a minimum bursting strength of 17.5kg per sq cm. The carton should be constructed with the long flaps butting together. The flaps must be glued and taped, and the carton cross banded with nylon banding tape. A typical carton size for sliced or kibbled onions would be 60cm by 40cm by 30cm. The opening must be the 60cm by 40cm dimension. End opening cartons are not acceptable. Bulking is 83 cartons per tonne = 6 . 2 5 m ~ ~at 12kg per carton. Liners: These should be 500 gauge low density polyethylene of sufficient size to twist at the neck and tie with twine. Metal or other closures should not be used, nor should the liners be heat sealed, as this method tends to entrap air in the pack. Two liners filled with product are accommodated in each carton. Dehumidification: It must be stressed again that the packing area should be dehumidified and cooled, especially in tropical areas, to avoid entrapping

I58

hot humid air in the polyethylene liners. Relative humidity should be reduced to 25 - 30 percent and the product temperature should be no higher than 12°C.These conditions should also apply in the milling area. Powder Packaging: Onion powder should be packed in metal-topped drums containing 25kg. As onion powder is very hygroscopic, it is necessary to nitrogen-flush wherever possible, or failing this to incorporate u p to 2 per cent of anticaking additive.

Cultivation Guide Lines for Onions (1)Sow either in nursery beds or direct by precision drill: Seed approximately 6.6kg per Ha. Twin lOcm rows by 46cm centres (planted from nursery beds lOcm apart.) Plants per row: 19.7 per metre. Density: 66 plants per square metre. Plant population 661,000 per Ha. ( 2 ) Fertil:.sers Organic: 2000kg / Ha. Sulphate Ammonia: lOOkg/Ha. Phosphates: 15Okg/Ha. Potash: 75kg/Ha The above will be subject to soil analysis and requirements. (3)Herbicides and Pesticides. Post-emergence application: Linurin or Aflon - 4.2 litres per Ha. Apply Calomel Dust against onion fly. Benlate or Dithane against botrytis. (4) Irrigation Total precipitation in growing period: 80cm. 70 days irrigation at 5-6 day intervals. (5)Maturity After lifting, bulbs should be cured in rows on the field until the tops wither. Size of bulbs for processing should be from 60mm upwards. PARSNIPS (1)Flow sheet Feed to line I Dry Cleaning

I Destoner Washer I Steam Peeling

I I59

Skin Removal

I Inspection

I Dicing

I Blanching

I Sulphiting I Dewatering

I Drying

I Conditioning

I Screening

I Inspection I Packing (2) Varieties Any smooth white skinned variety resistant to canker, short root-type preferred. (3)Product Handling The parsnips are fed into the line from a bulk feeder, having been well trimmed at the farm and topped at the shoulder. Next they pass into a dry cleaning reel to take off excess soil, etc, then toa destoner-washer.They are steam peeled and the skinremoved. Inspection follows and here it is important for the operators to look for any incidence of canker, large roots should be sliced in half, so that any trace of canker can be seen. Such roots must be discarded. Theparsnipsare thendiced inaGDicer,eitherasl0mmxlOmmxlOmm cubes or 1OmmxlOn-tmx2mmflakes. Blanching can be either in hot water or in steam. SO, is metered into the blancher from a make-up pan if a hot water blanch is used, or, if steam blanched, the dice are passed through a sulphite applicator tank, supplied by the make-up pan. The product is then dewatered. Blanching is for 3 minutes, or as long as necessary to produce a negative peroxidase test. Drying is by conveyor dryer, followed by bin conditioning. The dice are elevated to a screen for grading, with a 6mm sieve to take

I60

out small particles and fines. Inspection is camed out on conveyor belts fitted with metal detectors. Packing is in 25kg multi-ply paper sacks with 300 gauge polyethylene liners. (4) Drying Conveyor dryer scaled to throughput. Inlet temperature 93'C reducing to 87' and 70°C in the last stage. Dry down to 12% in the conveyor dryer and condition to 7% in bins. Raw moisture = 83% Overall ratio = 9:l to 11:1 Drying ratio: 6:l

PARSLEY, SAGE and LEAF HERBS (1)Flow Sheet Feed to line I Reel Dry Cleaning I Triple Washing

I Inspection

I Drying I Cutting (Stalk separation first stage) 1 Inspection I Aspiration I Screening - Milling I Packing (2) Varieties

Parsley - Moss Curled Sage - Broad-Leaved Thyme - Broad-Leaved (3)Product Handling Herbs are fed into the line 'on-stalk' and passed through a dry cleaning reel to remove dirt and extraneous matter. They are then triple washed in a flood washer with three tanks, or passed through two double tanks in line. Herbs are examined on a wide conveyor belt where the operators remove 161

any yellowed leaves or debris. Herbs then pass into the dryer, usually a conveyor, single-pass unit with three heat zones, and drying is usually completed in a 45-60 minutes cycle. Cutting into granules or flakes takes place after drying, and a standard method is to hand-feed stalk-first into a J type cutter and, if the discharge chute is removed, the flaked leaves tend to separate from the stalk, which shoots out beyond the leaf.This is effective with parsley but other herbs may need to be separated from the stalk by aspiration. The flake or granule size will be determined by market requirements and can be regulated by the knife spacing on the cutter. After inspection, the dried leaves pass into a Sortex air separator which finishesanyremovalofcomminuted stalkleftbehindby themechanical separation in the cutting operation. The material is then size graded by a screen and packed. Mixed stalk and leaf may be milled for powder, if there is a demand. ( 4 ) Drying As thedryingcycle is short, a single-pass dryer is preferred,scaled to desired throughput. Alternatively stove dryers may be used. Raw moisture of parsley is 84435%and it is particularly important to retain the fresh green colour in the dried product, hence the necessity to keep temperatures fairly low, 80'/ 70"/ 65°C through the zones. Dry to 5% Overall ratio = 121 Drying ratio = 7 1

SPINACH 1) Flow Sheet

Feed to line I Precleaning

I Washing (triple)

I Inspection

I Cutting I Blanching I Sulphiting I I62

Dewatering

I Drying I Conditioning

I Aspiration

I Screening

I Inspection

I Packing

(2)Varieties. Winter Prickly - Medania Summer Spinach. (or indigenous varieties) (3)Product Handling. Spinach is usually cut by hand on the farm and delivered to the factory in crates or field boxes. These must not be allowed to stand for any length of time, and should be loaded lightly into a bulk hopper allowing air to circulate freely. Precleaning is done by hand and consists of removing crowns, large stalks, wilted leaves, weeds, etc. Extremely efficient washing is required, hence the need for a triple washer. This hasthree sections,each with a good flow ofwater that isaerated by compressed air. A good flow of fresh water is needed in the last section and any overflow can be pumped back into the second section. If any grit remains after triple washing, the spinach may be put through a final reel washer, or alternatively held in tanks with a through-flow of fresh water, before feeding into the triple flood washer. This will release some of the soil or grit and ease the washing process in the threecompartment flood washer. A further inspection is made to reject any blemished leaves or extraneous matter, before cutting. This can be done on a J dicer, hand fed, and it is usual to cut strips by removing the cross cut knife spindle. Feed fingers are used between the circular knives to ensure positive transfer of the leaf. Blanching should be in flowing steam for 3 - 4 minutes at 95°C. The product is then sulphited by a dip in a sulphite applicator tank. Dewateringisveryessentialas thereisa lot ofsurfacewateron theleaf. If this cannot be removed by a reciprocating screen dewaterer, then the leaf strips will need to be centrifuged in batches. This will ease the initial drying I63

problem. Drying is by conveyor dryer scaled to throughput. Conditioning in bins. The dried strips are fed into a Sortex air separator to remove any unwanted heavy stalk. If required, the product can be screened to take out fines but possibly the aspiration will have been adequate. Inspection over belts with metal detectors. Packing in multi-ply paper sacks with 300 gauge polyethylene liners. (4) Drying. Inlet temperatures: 82"/ 74"/ 65°C dry to 7% Conditioning: 50°C dry to 5% Raw Moisture: 94% Overall ratio: 17.1 - 19-1 Drying ratio: 13:l

-

SWEDES White Turnips 1) Flow-Sheet Feed to Line

I Dry Cleaning I Destoner-Washer I Steam Peeling I Skin Removal

I Inspection I Quartering I Dicing

I Blanching I Sulphiting

I Dewatering I Drying

I I64

Conditioning

I Screening

I Inspection I Packing (2) Varieties:

Swedes Purple Top - Green Top

White Turnips

Early Snowball - Green Top White

(3)Product Handling The swedes, which ideally should be not in excess of 13cm in diameter, are fed into the line from a bulk feeder. It is essential the roots be well trimmed on the farm, with tops cut off and the root trimmed well back to the butt. They are fed into a dry cleaning reel to remove any soil or extraneous matter, then transferred to a destoner-washer before steam peeling. The peel is removed by a skineliminator, and the swedes inspected and trimmed where necessary. If the swedes are in excess of 13cm diameter it is advisable to quarter them on the inspectionconveyor. This willdisclose whether any are infected withroot canker, to which swedesaresometimes prone. The main reason for quartering large swedes, however, is to reduce them to a suitable size for feeding into the dicer. The roots, either whole or quartered are elevated into a G type dicer, set for 9.5mmx9.5mmx9.5mm dice or 9.5mmx9.5mmx2mm flakes. Occasionally swedes are cut to flakes 20mmx20mmx2mm.The G dicer has acapacityof6000kg perhourof9.5mmdiccbuta lesser throughout on flakes. The knives require changing every 8 hours and should be honed and sharpened. This applies to all root vegetables. Blanching is either in hot water at 99°Cfor 3-4 minutes, or in flowing steam. If a water blanch is used the sulphite is metered in from a make-up tank, along with other additives to inhibit leaching losscs (sugar and salt).If steam blanched, the sulphite solution may be sprayed on, or the dice can pass through a sulphite dip tank. Steam blanching will require a dwell time of 5 minutes, or until such time as a negative peroxidase result is achieved. The sulphur dioxide level in the end product is 1000ppm. After dewatering, the dice or flakes pass into the dryer, thence to the conditioning bins, and screening is through a 6mm sieve toremove fines and small particles. Packing is usually in 25kg multi-ply paper sacks with 300 gauge

I65

polyethylene liners. White Turnips are processed in exactly the same way. (4) Drying. Conveyor band dryer scaled to throughput. Temperatures (inlets): 110"/ 9 5 " / 85°C Conditioning to 7% in bins: 52"/ 54°C. Raw Moisture: 89 - 91% Overall ratio: 12:l to 14:l Drying ratio: 9:l Dehydrated swede should be bright yellow. Any tendency to 'browning' indicates temperatures too high in the second and third dryer zones. Turnips should be creamy white and free from browning and blemish.

TOMATO SLICESFLAKES. (1)Flow Sheet. Feed to line I Washing-Sorting I Removing Calyx I Washing I Slicing I Inspection I Dewatering I Drying I Conditioning I Kibbling I Screening I Inspection I Packing

I66

( 2 ) Varieties.

Cal J - PeteMech - Roma (all oblate types - USA seed) (3)Product Handling. The tomatoes are discharged from field boxes, or bulk, into a bulk feed hopper.Theyare thenelevated intoa tomato washer integrated witharollertype inspection conveyor, where damaged or unsuitable fruit are removed. This process is followed by a second inspection conveyor with three channels on which the operators remove the calyx and the fibrous top of the core. The latter operation can be done mechanically, if throughput warrants the installation of a battery of manually fed Hydrout corers. This is a similar machine to that used for onion coring but in some countries they are not permitted under factory safety regulations. A secondary washing follows in a flood-type washer, and then the prepared tomatoes are fed into a CC slicer set to cut 4mm slices. After a further inspection, the slices are dewatered and placed on the drying trays of a double or single tray dryer. During the transfer from the 'hot' zone to the 'cool', the slices must be turned on the tray to prevent adhesion to the mesh and to expedite drying. The slices are then transferred to bins for conditioning down to 5 percent. The reason fordrying down to5 percent is that the tomato is very hygroscopic and can pickup moisture if there is any delay in final processing, ie, kibbling, screening and inspection. Tomato slices are rarely sold as such, and invariably are converted to flakes by kibbling in a suitable machine. Flaking by roller drying is rarely practised nowadays, as the resulting colour is poor owing to the high drum temperatures, and the particle size is nearer to a coarse powder, which even after sieving is much inferior to spray dried tomato powder made from tomato concentrate. The kibbled material is fed on to a vibratory screen to eliminate fines, then inspected and packed. To avoid too much breakage of thc flakes, they are packed either in poly-lined cartons or fibre-board drums. (4) Drying. Tomato slices can only be dried on trays, owing to the necessity of turning or riffling the product halfway through the drying cycle. This is not really feasible on a conveyor dryer. The trays must be waxed regularly to prevent product adhesion. The total drying cycle, excluding conditioning will be 4 - 5hr and temperatures will range from 80°Cin the hot zone to 60'C in the cool zone. Conditioning is at 50" - 52°C to 5% Raw moisture = 94-95%

I67

Overall ratio: 201 to 221 Drying ratio: 161 to 17:l

Cultivation Guide Lines for Tomatoes (1)Sowing Direct: 890g per Ha. Nursery Beds: 190g per Ha. This method is recommended in tropical climates. All seed should be dressed with fungicide and stored at 4'C until used. Spacing 45cm apart in l00cm rows. (2) Fertilisers Farmyard or other organic manures are desirable, applied at the rate of 6 tonnes to 12 tonnes per Ha. Apply 500kg per Ha of 12:12:17+2 at planting. Supplement 250kg per Ha. of Sulphite of Ammonia after fruit has set. (3)Herbicides Dynid: Metrobromuron: Dachtal50 percent WP. (4) Pesticides Dimethoate: (against midges) Endosulphan against Leaf miners. ( 5 ) Disease Control Koccide 101: Cobox: Cuprovit; alternates with Dithane N45 or Antrocol for bacterial spot, mosaic virus, stephylium and blossom end rot. Flower drop can be controlled by a fine mist of water when the fruit sets. (6)Maturity Picking must be at regular intervals when full colour is achieved. Avoid bruising. Harvesting 12 - 14 weeks after planting. Plant population: 25,000 - 30,000 plants per Ha., according to variety. Yield anticipated 40-50 tonnes per Ha.

I68

5

Dehydration of Potato Products

Potato Granules Potato granules are more usually commercially designated as Instant Potato or Potato Mash Powder. This product was first manufactured in the UK, on a commercial scale, some 55 years ago. As the name implies, precooked potatoes are dehydrated into granular form and, when hot water is added, they revert almost instantly to cooked mashed potato. This product has been widely developed as a convenience food in America and Europe, and is almost certainly the most popular forin of dehydrated potato on the market today. It features extensively in snack foods. There are several methods of producing granules but the generally accepted commercial method is the 'add-back' process. Several improvements have been made in the manufacturing processes since World War 11, and some of these are referred to in British Patents No.683,604 (1952) and N0.740~711(1955).The basic process goes back to, and is described in, earlier Patents - No.496,423, No.525,043 and N0.601~152. The following description of the process explains the basic commercial add-back method but makes no reference in detail to the refinements and improvements, introduced in recent times, by individual pmcessors, many of which were originally patented.

I05

Flow Sheet Feed to Line I Dry Cleaning I Destoner Washer I Peeling I Skin Elimination I Washing I Inspection - Trimming I Slabbing (Slicing) I cooking I Mashing - Mixing I

Add - Back Mix I Sulphiting + Additives I Granulating - Conditioning I + 1.5mm rejected k r e e n i n g d 65%add-back granules I to mixer by bulk Secondary Drying (35%)by bulk I 250 micron sieve Final Sieving through I Overtails return Primary Packing to mixer Nitrogen Flushing I Secondary Packing in poly-lined sacks

7

I06

A Lockwood self feed hopper in to which potatoes are being tipped from a swivel head fork lift truck

Varieties of Potato Suitable for Granules The main requirements are (1) high solids content, (2) low reducing sugars, (3) freedom from aftercooking darkening, (4) immunity to wart diseases, and (5) shallow eyes. In America and the UK, the preference is for white fleshed varieties, whereas in Western Europe, cream and yellow fleshed potatoes are more popular. The following varieties are, therefore, in general commercial use for this process.

USA:

Russet Burbank, Katahdin, Kennebec, Cobbler, Chippewa I07

UK:

Europe:

Aran Comet, Aran Pilot, Home Guard, Estima, Pentland Javelin, Pentland Crown, Maris Peer, Cara, Maris Piper, Pentland Dell, Bintje, Iris, Lenino (West and East) Record, Uren, Wilja, Desiree.

PROCESS The important factor to be observed at all points of processing is the prevention of cell rupture in the raw material. Every individual cell that is damaged in peeling, cooking, granulating or drying will release free starch, which will mitigate against satisfactory reconstitution, and will produce a sticky gelatinous mass instead of a light fluffy mashed potato. Peeling should be by lye or the steam method, and the potatoes should be well sprayed with cold water afterwards. This can be done in a rod washer, or preferably in a brush washer as described in the chapter on preparation plant. Batch abrasive peelers are wasteful, and tend to create the very conditions of cell damage which should be avoided. More recently developed continuous abrasive peelers, with sophisticated control of the depth of peeling, may well meet the requirements of minimal cell damage, therefore the processor has a reasonably wide choice of equipment for this part of the process, but Flash Steam Peeling is preferred. From the peeler and washing plant, the potatoes pass over an inspection belt where they are trimmed. With average quality raw material, ten women at the trimming belt should handle 16 tons in eight hours. At the end of the trimming and inspection table, the small to medium size potatoes go straight to the cooker, whilst tubers of 44mm upwards are diverted to a slicing machine for slabbing into 20mm slices before returning to the main flow into the cooker. If required, the trimmed and sliced potatoes can be delivered into a surge tank prior to cooking; this has the effect of removing surface starch, and also provides buffer storage to keep the line running where there are breaks in the preceding process for some reason or another. Cooking, in continuous cookers, may be in atmospheric steam for 45-60 min, or alternatively the potatoes may be partly cooked in hot water, cooled and then transferred to the steam cooker (Cording and Willard method: 1955). From the cooker, which is usually a rectangular steam cabinet with a stainless steel mesh conveyor belt, the potatoes now emerge, thoroughly but not overcooked, and fall into a paddle mixer. This is normally of the U trough-type, with a rotating shaft fitted with T-shaped paddles at intervals

I08

along the length. The angle of the paddles to the line of the shaft is variable, so that the flow of material can be accelerated or decelerated, as may be required, to thoroughly mix the product. Mashing, and mixing in the add-back granules or ‘seed’ powder at this point must be gentle to avoid cell rupture, and the speed of the mixer is critical. The seed powder is continuously f e d into the mixer at the point where the cooked potatoes enter, at a rate in excess, by weight, of the potatoes. The average proportions might be 35 percent potato to 65 percent seed powder but this can only be established by practice, and will vary according to the solid matter in the raw potato, and, conversely the moisture content of the seed. The ultimate objective is to obtain a blend with 35-40 percent moisture; the arrangement whereby the seed powder is available continuously at the mixer is described later. The blend of cooked potato and add-back seed fills up the trough mixer, and is then allowed to fall over a weir, through an aperture in the endplate, into a second mixer of longer but shallower proportions. The purpose of this second mixer is to extend the mixing period, at the same time allowing the blend to cool as it travels along the trough. As stated before, the rate of travel is controlled by the angle of the paddles, and thorough granulation will take 25-35 min. Sulphite and other additives, which may be required, are added to the blend by a suitable metering device, during the mixing process. No general rule can be applied as to the additives, as Food Laws differ from country to country, and the processor must familiarise himself with what is permitted, and what is not, in his own particular market. Additives may include sodium metabisulphite, acid sodium pyrophosphate, monostearates, anti-oxidants, flavourings and milk powder. Sulphur Pyrophosphate, anti-oxidants, and sometimes milk powder are mixed with potato granules to make a ’master mix‘ whereby the metering into the mash can be more accurately gauged and, by dilution, can be assimulated more evenly than small quantities of separate ingredients. Glycerol monostearate in solution is metered in. At the end of the second mixer, the blend again falls over a weir and passes to a conditioning bin, where the material cools to about 24°C in an hour. Two bins are normally used, one being filled whilst the other is ‘conditioning’.This conditioning is a most important stage in the process, as it assists granulation and retrogradation of the starch. From the bottom of the conditioning bin, the blend feeds into the first stage of drying. The primary dryer can be either (a) a pneumatic ring dryer, or (b) a thermal venturi dryer, both of which were described in Chapter IV. A suitable feeding arrangement is required for the particular type of dryer I09

used but it is important that this should provide a consistent, regular rate of feed, compatible with the rate of throughput from the mixing plant, and a proper balance must be achieved at this point. There must always be an adequate reserve of blend in the conditioning bins because, if the feed to the dryer is too fast or too slow, the whole system will break down. DRYING The air velocity of the dryer must be carefully controlled from the outset, otherwise cell damage can occur here. The function of the primary dryer is to reduce, rapidly the 35-40 percent moisture in the blend to 12-15 percent as the powder, which it now more correctly resembles, leaves the collecting cyclone. At this point, the powder is screened and coarse material Left: A Finex 22 sieving machine which is ideal for potato granules or vegetable powders

l lO

- plus 1.5mm mesh - is removed. Of the finer material which passes through this mesh, approximately two thirds is conveyed back by auger or belt as seed powder to meet up with the cooked potatoes in the first mixing process. The proportion fed back must be carefully metered to provide exactly the c o m t proportion in relation to the quantity of potatoes passing through the cooking stage. As explained before, this proportion will be of the order of 65 percent. The remainder of the powder, having passed through the screen, now passes to a secondary dryer, which ideally is (a) a fluidised bed dryer, or (b) a rotary louvre dryer. This secondary drying reduces the powder to 6-7 percent moisture content. The secondary dryer discharges into a collecting cyclone and it is customary to locate the latter in a cooling system. An air ring, similar in design to the ring dryer, but utilising cold air, is ideal for this purpose, and this cools the product down to about 16°C. From the cold air cyclone, the powder discharges through a rotary valve on to a final screen fitted with a 250 micron stainless steel sieve, and the 'through' material is the final product which then goes to pack-off. Any overtails from the final screening are returned back as seed. It is essential that a permanent cascade magnet be fitted on the outlet of the last screen, to remove any ferrous metal contamination. A Finex 22 sieve with 2 decks as illustrated is ideal for this purpose, and a Finex 48 sieve for the initial screening. From the foregoing description, it is seen that the process involves the continuous feeding back of part of the dried material, which is used to absorb in excess of 50 percent of the initial water content of the cooked potato. The processor must therefore, always retain a stock of seed granules to start up the system at the beginning of a new season. It must also be remembered that the rate of pack-off of the final powder can only equate with the input of raw potatoes, and if this is wrongly estimated, the seed will gradually bleed out of the system, and the process will eventually come to a halt. This balance can only be achieved with experience, and the constant attention of the dryer operative. Product should be packed in nitrogen-flushed drums for prolonged storage, or 25kg polyethylene-lined sacks for 6-8 weeks storage in temperate conditions. RAT10 Expected ratio of final product at 6 percent moisture content, using potatoes with 20 percent solids, would be expressed as about 6:l.

111

Single drum d y e rfor potatofldkes (courtesyofMitchell Dryers Ltd) POTATO FLAKES Flow Sheet

Feed to Line I Dry Cleaning

I Destoner-Washer

I Peeling I Skin Elimination I Washing

I Inspection-Trimming I Slabbing (Slicing) I Hot Water Cooking

I Cooling

I Steam Cooking

I Ricing I Additive Addition

I Drying I Flake Breaking I Inspection I Antioxidant addition or

I Antioxidant addition or Primary Packkg (Nitrogen Flushing I Nitrogen Flushing I Secondary Packing in poly-lined sacks The production of Potato Flakes was developed in 1954 by Cording and Willard at the Eastern Utilisation Research and Development Division of the Agricultural Research Service in Philadelphia, USA. Potato flour had been produced on single drum dryers for at least 70 years but it was not until 1954 that the technique was perfected, whereby the drum dryer could be used to produce a product, which, on reconstitution with hot water, gave a mash equal in texture and appearance to freshly mashed potato. The success of the process lay in minimising the rupturing of the starch cells, and the special steps, taken in precooking and cooling, to retmgrade or reduce the solubility of the amylose fraction of the potato starch. (See Potato Granules cooking method.)

Varieties of Potato Suitable for Potato Flakes The required characteristicsare similar to those for granules, therefore all the varieties listed for the latter product are suitable for flaking. Process Peeling is by lye or steam methods as a general rule, followed by a thorough brush washing and cold water spraying to remove surface starch. After inspection and trimming, which must be very thorough, so as to remove all eyes and blemishes, sizing and slabbing follows, as for granule I13

production. The cooking procedure is most important, and this is the main part of the process as set out by Cording and Willard. The first stage is precooking in hot water, and for this purpose, a continuous auger-type cooker is often employed. The dwell time is about 30 min at 71 °C. Cooling takes place in a similar vessel, circulating cold water to sustain a temperature of 10°C for 20-30 min.

Section of the Erin Foods plant at Mallow, Eire - potato flake process showing Gouda roller dryer

The potatoes then pass to a continuous atmospheric steam cooker with a cycle of 35-50 min. Overcooking destroys texture, and this must be carefully controlled. High solids potatoes require less cooking than low solids varieties. Ricing, or mashing, follows the cooking process. This is achieved by feeding the cooked potatoes through rolls into a rotatbg cylinder, perforated with 6mm holes. The cooked slices are gently forced through the perforations, and a ribbon screw on the inside of the cylinder discharges the product at one end. This equipment was designed in the US but there are equally acceptable alternative methods in Europe. Additives are introduced after ricing to improve stability, texture and colour. As in the case of granules, these may comprise sulphite, glycerol monostearate, sodium pyrosphosphate, citric acid, etc. Sometimes antioxidants are also used but legal restrictions on their use apply in some countries. Skimmed milk powder is used in small quantities by some manufacturers.

l l4

Sulphur dioxide content in the final product, where permitted, is usually controlled at 250 ppm with a legal limit of 500 ppm in the UK. DRYING The riced potato is fed on to a single drum dryer, as described in Chapter 4. Single drum dryers are used mow frequently than double drums, as it is believed that a better bulk density is achieved by this method. Potato Flakes have a bulk density of about half that of potato granules, and this may be considered somewhat of a disadvantage in the context of packaging costs. The delivery from the dryer is usually by auger, which breaks down the curtain of dried potato to flake form, and the flakes then pass over an inspection belt for removal of any residual blemish. It is important, as in the case of all dehydrated products, that the flakes flow under and over permanent magnets, or other metal detection devices, before packing. Some drum dryer installations provide for a flake breaker, or Floconeuse, which is reputed to produce more uniformity in flake size.

Packing This is usually in 15kg polyethylene-lined multi-ply paper sacks, or, for prolonged storage in nitrogen-flushed air-tight drums, with anti-oxidant added.

Ratio Expected ratio is 6.5:l.

POTATO DICE

Feed to Line

I Dry Cleaning I Destoner-Washer

I Peeling

I Skin Elimination

I Washing I Inspection-Trimming I15

I Dicing I Blanching I Sulphiting + Additives I Dewatering I Drying I Conditioning I

Screening I Inspection I Packing There is a growing market for Potato Dice (9.5mm cubes) half dice (9.5 by 9.5 by 4.8mm) and ‘Thins’ (9.5 by 9.5 by 2mm), and this product features prominently in most dehydrators’ production programmes. Apart from catering outlets, potato pieces figure prominently in soups and vegetable mixtures, and there is an off-take by the bakery trade for meat and vegetable pie manufacturing. The dehydrated product is very uniform in quality, and offers the manufacturer of composite food products some advantages over fresh potatoes, especially in the preparation stages.

Varieties of Potato Suitable for Dicing There is a fairly wide choice open to the processor and, indeed, the latter may have to spread his production programme to take in the second early varieties, as well as the main crop varieties. The important requirements in potatoes for dicing are: (1) Good solids content (2) White fleshed, although the preference on the Continent of Europe is for cream or yellow flesh (3) Free from after-cooking darkening (4) Low reducing sugars, (under 2 percent) (5) Firm texture after reconstitution, with the dice retaining their shape after cooking. I16

To meet the latter requirement, some of the varieties with a high starch content, which are ideally suited for granules and flake production, are not so suitable for dicing because of their tendency to 'fall' or mush in cooking. Whilst high solids are economically desirable, a compromise may have to be made by selecting a variety which will not disintegrate in cooking but which will have a solids content of at least 20 percent in a normal growing season. Matching this potato against a variety with, say, 22 percent solids, the processor will lose about lkg of dehydrated product for each 5Okg of peeled potatoes through the production line but, if the texture stability is right, this compromise is worthwhile in the interests of improved product quality. Varieties, which are borderline in this respect, can be firmed up in processing by the addition of calcium chloride in the blanching process, and it is good practice to use this technique for all potatoes used for dicing, in varying degree, according to their natural texture and tendency, to ensure they keep their shape during cooking. The exact level of calcium in the blancher will be determined, therefore, in the light of experience of the stability of the finished product. Potatoes for dicing should be large and uniform. Small tubers are wasteful, in that they do not cut economically into dice, and they give a lot of bits and off-cuts, which, when dried, have a low sales value. The following varieties are used commercially for this product:

U S A Early varieties: Irish Cobbler, Chippewa. Kennebec, Katahdin Russet Burbank. Early varieties: Arran Comet, Arran Pilot, Home Guard. Second Early: Estima, Pentland Javelin Maris Peer Main crop: Wilja Maris Piper Pentland Squire Cara Pentland Dell Pentland Crown. Main crop:

UK:

I17

Process After washing and destoning, potatoes should be well peeled by lye or steam. If lye is used, an immersion time of 3 min at 92"C, and a sodium hydroxide concentration of 15-18 percent should give adequate msults but, again, times and concentrations will have to be varied according to the time of the season and the varieties. Stored potatoes are usually more difficult to peel than those freshly lifted. Peeling losses will range from 20 to 30 percent. Peeling is followed by washing under a powerful water spray in a brush washer or reel washer. The former method is preferred by some processors, as the brush action is particularly effective in scouring and cleaning growth cracks and other excrescences softened by the lye h-eatment. Alternatively flash steam peeling may be used, and this is now usually preferred. The peeled potatoes pass from the washer on to trimming and inspection belts. Inspection must be very thorough here, and particular watch must be kept for grit, or foreign matter, which may have escaped the precleaning operation, as, if these enter the cutters, considerable damage will be done to the dicing knives, which are quite expensive to replace. With good quality raw material, well peeled, each person on the trimming belt should be able to handle 170-180kg per hour. The trimmed potatoes are conveyed to the cutters. A standard size of dice for dehydration is 9.5mm cube but this can be varied by changing the first, or slicing, knife position to give a thinner initial cut (down to 2mm) or the spacing of the stripping and the dicing knives can be altered to change the other two dimensions. It must be remembered, however, that reducing the thickness of the cut may create a dense 'bed' condition in the dryer, necessitating a lighter loading per square foot of drying area. A 9.5mm cube, therefore, is the ideal size for optimum throughput, as this particle size forms a satisfactory permeable bed in the dryer with the minimum restriction to the air flow through the product. The dicer knives must be kept very sharp at all times and it is good practice to change these once per eight hour shift. They should then be honed and reassembled on the carrier block Eady for the next change. The dicers should be lubricated by a flow of water, through the feed hopper, to assist with the removal of starch from the cut surfaces of each potato. Blanching is carried out either in a steam or a hot water blancher. As sulphite is invariably added to the product, steam blanching will need to be followed by a sulphite spray. 3-6 min in flowing steam at 99°C should be an adequate steam blanch for potato dice, and this is followed by sulphiting to a level of 250 ppm in the final product. As, however, most dehydrators use additional additives, such as I18

calcium chloride, citric acid or sodium pyrophosphate, it is perhaps simpler to use a hot water blanch, whereby the additives can be drip-fed from an auxiliary tank, at whatever rate is required. Hot water blanchers should always be heated by a closed steam coil system, with live steam injection used only for boosting the blanching water to operating temperature. The liquor should not be recirculated through the additive make-up pans but allowed to over-flow to waste to avoid excessive foaming created by released starch. The blancher water should be changed at least once a day - depending on build up of excess starch. The adequacy of the blanch is constantly checked by the peroxidase test. One of the purposes of blanching is to inactivate the surface enzymes of the cut vegetable and, by using an indicator solution of Guaiacol and hydrogen peroxide on a sample of blanched vegetable, this can be gauged and, as long as negative peroxidase conditions are shown, blancher dwell times and temperatures are adequate. If the blanched dice discolour, turning brown when immersed in the Guaiacol solution for less than one minute, it is an indication of positive peroxidase, arising from underblanching. If no colour contrast develops within the minute, then peroxidase is negative and blanching conditions are adequate. Underblanched potato shows up immediately the product dries, and this is manifested by the white, chalky appearance of the dice half-way through the drying cycle. On leaving the blancher, the dice should be sprayed with fine jets of cold water, again for the purpose of removing starch, then dewatered. DRYING Suitable dryers for potato dice are (a) the tunnel dryer @) the through-conveyor band (c) stove or through-flow tray dryer. With all types of dryer, finishing is usually carried out in bin dryers. Drying temperatures and times will vary according to the type of dryer used but typical 'wet' inlet temperatures for an efficient 3-heat zone conveyor band dryer would be: Zone1 107°C Zone2 99°C Zone3 85°C Outlet temperature would be 65°C - 71°C with efficient evaporative conditions. Finishing temperatures in bins range from 57'C to 60°C.

Sizing and Selection After drying, the dice are conveyed to a vibratory screen with an adequate sieving area and the 9.5mm dice or half dice are usually screened I19

out, standing on a 4.5mm or 6mm hole perforated sieve. The ‘throughs’ are the smaller cut-off pieces, which are diverted for use in soups or vegetable mixes where a very quickly reconstituted product is required. With careful attention to the dicers, however, this fraction only represents about 5 - 10 percent of the pack-off material. The main product, after screening, passes to inspection belts for manual selection and removal of blemished pieces, which may have escaped the earlier trimming operation. Or, as is more common practice today, the dice are electronicallysorted by colour sorters. These machines have reached a very high standard of performance in recent years, and one machine has the capability of sorting as much weight of product as that sorted by eight to ten women in a given time. The product should pass under and over magnets before packing.

Ratio The expected ratio from raw material with 20 percent solids content would be 7.5:l to 8:l. POTATO STARCH Starch is not a primary product of the dehydrator, as its production from ware grade potatoes is not by any means economically viable. Some simple means may have to be resorted to, however, to recover and process starch in a plant handling large quantities of potatoes for dehydration, solely for the purpose of relieving a critical effluent problem. The release of large quantities of starch into factory effluent systems can give rise to expensive treatment bills, and one method of dealing with this is to separate out the freestarch in settling tanks, and to contrive some inexpensive means of drying it. The slurry can be centrifuged to dewater it, and from that point drying can be effected by any one of several types of dryer, which may be available, but the economics will preclude this product taking any priority in the overall dehydration programme. It is convenient if any waste heat in the factory can be ducted into a simple home-engineered dryer to cope with this problem. Potato starch production is, in itself, a highly specialised industry, and is only possible in areas where large tonnages of potatoes can be diverted, by giving subsidies to growers, for this purpose. Several starch plants operate in America, Germany and Holland, producing a wide range of high quality specialised grades for the paper, textile, adhesive and food industries. It is not an exercise, however, to be recommended to the dehydrator, other than as a means to an end, and that is invariably for the purpose of reducing effluent disposal problems.

I 20

7

D ehydration of Fruits The United States is by far the largest producer of dried fruits, raisins and prunes being the most important tonnage-wise, with figs, apples, apricots, peaches and pears followingin order of tonnage produced. Other countries with a substantial export trade in dried fruits are Greece (producing 90 percent of the world's currant supply), Iran, Turkey, Portugal, Iraq, Algeria, Australia, Argentina, Egypt and South Africa. Of the above, the Middle East countries are particularly important in the drying of figsand dates. Sun drying has always been important as a drying technique for fruit and it is still carried on extensively, other than for apples, prunes and some types ofraisin. Withcut fruits, particularlyapricots,pearsand peaches, it has long been considered that using solar energy to remove the water from these fruits produces a superior quality to that obtained by artificial drying, and in a dry harvesting season there are cost advantages, which have been critically pin-pointed since the fuel crisis in the 70's. However, reliance on sun drying brings the risk of inclement weather at harvest time and the difficulty of maintaining a high degree of sanitation in the process. Consequently processors have made considerable efforts to improve quality in artificial drying, particularly with cut fruits, (apricots, peaches and pears) by introducing the Dry-Blanch-Dry method, to which detailed reference is made in the process data on apricots which follows.

I69

This method has been devised by Lazar, Barta and Smith of the Western Regional Research Laboratory, US Department of Agriculture, Albany, California, where promising tests have been made on apricots, peaches, pears and raisins. Apricots, particularly, responded well to this method, the dried fruit retaining a bright translucent colour instead of the dull red-orange of the sun dried product. The best results were obtained by reducing the blanching temperature to under 100°Cat the 50 percent weight reduction point the primary drying. Such a system was also effective with raisins, whichsuffer fromsplittingof skinswitha 100°Cblanch,and this was eliminated by a temperature reduction to 92°C.

Sulphiting The use of sulphur houses was ordinarily, but not necessarily, exclusively associated with sun drying methods, and sulphite dipping with mechanical drying. A sulphuring house is always erected away from the main factory building. The fruit is spread on trays which are racked on trolleys in a similar manner to that used in tunnel drying. The trolleys are pushed into the sulphuring shed, which is fitted with a sulphur burner at the bottom end, with adequate venting to atmosphere, either by natural draught or by fan, through the roof. 2 to 3kg of sulphur are burnt for each ton of fruit treated, and the exposure time is varied according to the absorption characteristics of the fruit. The latter must be tested regularly but, as a guide, the concentration of SO, in thesulphur shed should be maintained at about 2 percent. Residual SO, in the dried fruit will range from 1500 to 2000ppm. An exception to the use of sulphite can be exercised with Thompson Seedless grapes for the production of 'natural' raisins instead of the more common 'golden-bleach' raisins which contain levels of SO, u p to 2000ppm and are mostly artificially dried. Processing All the fruit processing described in this chapter except currants and peaches relates to artificial drying in either Conveyor Band, Tunnel or Stove Dryers,and whilst the Dry-Blanch-Drymethod is prescribed for Apricots on the basis of the author's trials, it could equally be used for Pears and Peaches, Apple Rings and natural Raisins.

Apples (Rings and Flakes) (1) Flow Sheet

Feed to Line

I70

I Washing I Grading I Peeling-Coring I Trimming I Sulphiting I Cutting I Re-sulphi ting

I Drying I Inspection I Packing ( 2 ) Varieties

Baldwin, Delicious, Jonathan, U K Bramley Seedling (Cooking variety)

USA

Permian,

Winesap

Left: A Fruit Washer produced by the Bead Engineering Company

171

Eastern Europe: Red Delicious, Golden Delicious, Jonathan Turkey: Arap Kisa (Cooking variety), Delicious Note: The more acid cooking varieties soften more readily when rehydrated, which can be an advantage. However, in practice, more dessert types are generally processed. This is mainly on account of their more symmetrical shape, which makes mechanical peeling easier and less wasteful. Of the dessert varieties listed above, Delicious, both red and golden types, are the least suitable for processing, on account of their tendency to break down in preparation and low acidity. However, they are grown more widely in America and Europe than almost any other dessert apple, and may be used in seasons when there is a shortage of apples of higher acidity. (3) Product Handling

The apples are brought to the plant in field boxes and, if pesticides have been used in the orchards, it is necessary to tip the fruit into a washing tank, or subject it to water sprays. It is essential to grade the apples, and the more accurately this is done, the less waste will occur in peeling and trimming. The following table gives the approximate number of each grade of apples (by diameter) per kilogram. Grading Diameter in mm. 50 60 70 80 90

Weight per fruit in g 70 85 115 155 210

No. per kg

No. per tonne

14.286 11.765 8.696 6.452 4.762

14,286 11,765 8,696 6,452 4,762

Subject to slight variation as between varieties.

Peeling and Coring There are three options: (a) Hand peeling ($)Steam flash peel (c) Mechanical peeling With hand peeling a substantial labour force will be required,and this may only be viable with a small scale operation. With careful control and skilled operators, peeling losses can be as low as 33-35 percent. Flash steam peeling can be carried out in a short immersion steam peeler operating at 17atm, and normally 15 seconds exposure time is

I72

necessary. The apples then pass through a skin eliminator with powerful waterjets. Losses by this method vary from 45 to 47 percent for medium sized apples, including coring losses. Mechanical peeling can be carried out by a battery of semi automatic ‘Pease’ peeling and coring machines. Each machine has 4 paring and coring heads, and is fed by one operator at a rate of 80 apples per minute at 100 percent efficiency but, in practice, 75 percent of the manufacturer‘s rated throughput is more realistic. More manual trimming is often required after the machines, and 50 percent losses are usual. The following table gives the theoretical and proven outputs (factory test) of one 4 head unit. Throughput/hour Throughput per @ 75% efficiency 8 hours

Diameter in mm

Throughput/hour @ 100%efficiency kg

kg

kg

50 60 70 80 90

336 408 552 744 1008

252 306 414 558 756

2016 2448 3312 4464 6048

From the above factory figures, based on an actual day’s production, 4 units produced 6.5 tonnes of prepared apples averaging 70mm in diameter. 30 trimmers were employed on the inspection belt.

A better type of mechanical peeler with automatic feed is available from Atlas-Pacific. This will handle 110 apples per minute (at 85 percent efficiency) or 700kg per hour of 80mm apples. Peeling losses are claimed to be 35-40 percent, and with regular shaped apples of good quality, few trimmers are required -approximately one third of the number needed with 4 semi automatic units. The principle of mechanical peeling and coring is that the apples are offered u p to, and impaled on a rotating spindle and a spring-loaded ’floating’ peeling knife follows the contour of the rotating fruit, removing a narrow strip of peel. A circular coring knife then lifts in an arc in a simultaneous movement and removes the stem, calyx and seed cells in one operation. The peeled and cored apple is then mechanically ejected from the spindle down a chute and on toa discharge conveyor which delivers it to the inspection and trimming conveyor. As soon as the apple is peeled and trimmed it must be submerged in either a 1.5 percent salt solution or sulphite solution to prevent browning and oxidisation. This is most conveniently done in a flume which delivers I73

the fruit to the cutting machines. The fluming solution is recycled from a collecting tankat thepointwheretheapplesareseparatedout from the flume liquor, and from here they are conveyed to the cutters. Cutting The method of cutting will depend on whether ‘evaporated’ rings, or segments are being processed - or whether the apple is going to be dried down to low moisture (4 percent) as flakes. For the former a slicing machine will be required - either a CC model as described in Chapter 3, or a heavy duty slicer; if segments are required, a machine with radial knives is used, the number of knives depending on the size of segment required and the size of the fruit. The apples are held in position by a rod through the core opening. With slices it is desirable, as far as possible, to use a machine which cuts at right angles to the centre axis. A slice of TO-12mm in thickness is customary. Too thick a slice will prolong drying. If flakes are required, the apples are fed into a G type dicer and cut in 1Omm by lOmm by 2mm pieces. Re-Sulphi f ing The Rings or Flakes are passed through a sulphite bath to bring the residual SO, level in the end-product u p to 1500ppm (2000ppm is the legal maximum permitted. Dewatering Excess water is removed with as little delay as possible, otherwise leaching losses will occur. A leaching loss of 5 percent can occur with an immersion time of one minute when fluming and sulphiting. These losses of totalsugars and other soluble flavour constituents will reduce the weight of the final product, as of course the percentage of total solids in the prepared material as it enters the drying process is the whole key to viable production. Once the apples are peeled, therefore, they should not in any circumstances be stored in surge hoppers or tanks awaiting further handling. (4)Drying Conveyor Band, Stove or Tunnel Dryers, scaled to throughput. Inlet temperatures not to exceed 70°C in first zone, 50°C in last zone. Dry Rings and Segments down to 20-22% moisture Dry Flakes down to 4% moisture Raw moisture is assumed to be approximately 88%. Overall ratio 13:l and Drying ratio 7:1 for Apple Flakes. Overall ratio 10.5:l and Drying ratio 5.3:l for Rings.

I74

(5)Storage Freshapplesmaybestored inchillroomsat-1 "Cto+3"Cat85-90%RH for u p to 8 months.

Apricot (Halves) (1)Flow-sheet Feeding to line

I Dip (whole) in SO, + citric acid

I Pitting

I Dip (Caps) in SO, + citric acid

I First Stage Drying I Blanching

I Second Stage Drying

I Inspection

I Packing (2) Varieties (recommended) Blenheim. (USA)

Matalya (Middle East)

(3)Product Handling Feeding to line is by bulk feeder, whence the fruit i s elevated into a sulphitedip tankholdinga solutionof 2percent sodium metabisulphiteplus 0.5 percent citric acid, duration 5 minutes. Fruit is dewatered on a stainless screen and fed on to an inspection conveyor for pitting by hand, or alternatively elevated into an apricot pitting machine. Manually fed machines are also available from FMC. Caps are elevated into a second sulphiting tank with the same concentration as the initial dip, duration 1 1 / 2 minutes, followed by dewatering. First stage drying is carried out on trays (stainless mesh) the halves being in 'cup-up' position, ie, cut surface upwards. Trays are transferred to a steam blancher (belt-type) with transit time I75

giving exposure to steam for 4 to 5 minutes. Trays are transferred to a secondary dryer and in the final stage caps are reversed to 'cup-down' position. This reversal can be effected mechanically. Bin Drying to achieve moisture equilibrium. Inspection and Packing. Inspection belts should always be fitted with permanent magnets and metal detectors (non ferrous). (4) Drying

Stove or Tunnel Dryers should be used in view of the lengthy drying cycle and the necessity of primary and secondary drying as separate operations. First stage drying is for 2 1 / 2 - 3 hours with tray loading at lOkg per sq m. In this stage the weight reduction is 50% of the feed weight. Inlet temperature 71 "C cup-up position. The second stage drying is for 5 1/2 - 7 hours at 71 "C reducing to 65°C half-way through the cycle at which stage the cups are reversed to cup-down position. Bin Conditioning at 49-50°C to achieve moisture equilibrium at 20-22%. Overall ratio: 8 : 1 Drying down ratio. 7.46 : 1. (5)Equipment

Mechanical and manual apricot pitters and cup-up and cup-down machines can be supplied by Food Machinery Corp of San Jose, Cal. or FBR SrL of 43100 Parma, Italy.

Banana Flakes (1) Flow-sheet

Feeding to line

I Hand Peeling I Buffer storage in SO, I

Dewatering

I Pulping

I Pasteurisation I I

7

I

Mixing

I Homogenizing

I Drying

I Packing (2) Varieties Gros Michel

Cavendish

(3) Product Handling Single fruits are fed to the line, the stripping from 'hands' being handled outside the factory in sheds or at the farms, peeling and trimming off pith and dark flesh on a 'merry-go-round' conveyor. The peeled whole fruit is collected in buffer storage tanks (two required) with SO, solution 0.05-0.1 percent for u p to an hour. The fruit is dewatered and fed into a comminuting machine with a 0.5mm mesh screen to remove the seeds and fibre. Use an Urschel Comitrol machine with homogenising head SH 200084N (capacity 2000kg per hr) Feed pump into an auger-type steam blancher and pasteurise for 8 to 10 minutes in live steam. Collect pulp in a U-Trough mixer. Add SO, solution,reducing original total solids from 25 to about 20 percent. Level of SO, will be regulated to arrive at a residual SO, level in the end-product of 150ppm at the discharge point. Feed the pulp into a colloid mill for secondary homogenization. Elevate by auger feed to a drum dryer, with drum temperature of 171"C drying to 4 percent moisture. Inspect flakes on belt conveyor, with metal detectors (ferrous and non ferrous). Add u p to 2 percent anticaking additive and pack in airtight cans ( 4 ) Drying

Single drum dryer on which the maximum product temperature should not exceed 93°C and the drum temperature 171°C. Ratio overall: 8:l Drying ratio: 4.4:l Final moistures of flakes is maximum 4%

Currants Almost 90 percent of the world's currant supply comes from Greece, and from grapes grown in the Aeghion-Patra and Korinthos region. The best quality currants are produced from the Vostizza grape I77

peculiar to this part of the Greek mainland. The fruit is grown sometimes on relatively small farms as well as on the larger estate farms, and the whole crop is contracted to a handful of merchants, in Patra mainly, and these process the crop after the farmers deliver it to the storage and processing factories. Currants are not produced,in quantity to the author’s knowledge, outside of Greece, other than small tonnages in Australia and South Africa, therefore the methods described come from knowledge acquired on visits to the Patra region. All the fruit is sun dried and this operation is carried out by two methods: (a)by stripping the grapes from the vine and laying them on concrete floors outside the farmsteads, protecting them by sheets of paper underneath and with gauze or nylon net on the top to protect them from birds and other predators, and also from the rays of direct sunlight at the hottest time of the day. (b)by taking off the bunches and hanging them on the shoots of the vine to dry under the protection of the foliage. This is labour intensive but is practised by the smaller growers, or others who have abundant cheap labour. This method produces a premium quality currant and commands a higher price from the proccssor. The fruit is dried down to about 14 percent moisture in the farm yards, and is then stripped from the stems to a tolerancc of 6 percent waste matter before delivery to the processing factories. Secondary Processing The dried fruit is assessed for quality on delivery to the warehouses, and is piled in heaps on the concrete floors, sometimes up to three or four metres deep. The currants, as delivered, are then prc-riddled to remove stalks, dirt, stones and other extraneous matter, and are aspirated in a second stage of dry cleaning. They then pass on to a ’breaking’ machine, which separates the fruit where it has becomc compacted. Fruit then goes to grading machines which separate it into three sizes -small, standard and ’jumbo’. The first grade is set aside for catering outlets, the standard for retail and other premium outlets, and the over-size fruit normally go as a by-product for the production of alcohol. The separate grades are washed by fluming over riffle plates, and pass to a spin drying machine which removes the exccss water centrifugally. Fruit is then packed in lined wooden boxes, or cartons, which finally go into

I78

a fumigation shed for methyl-bromide treatment. This has to be repeated at regular intervals during storage, and before shipment. The process has not changed radically over many years, and at first sight would appear to be primitive. However, with the demands for rising quality standards by the importers and users of dried fruit, it is almost universal practice for the fruit to be re-selected, washed and re-dried when it arrives in the buyers’ premises. The number of dried h i t importers in the United Kingdom is relatively small but they arebig companies with excellent processing facilities and, being ‘brand conscious’, they invariably market a high quality and hygienic product. This applies to importers in Europe and elsewhere equally rigidly.

Paw Paw (Carica Papaya) (1) Flow-Sheet

Feed to Line

I Washing I Inspec tion I Peeling

I Quartering

I De-seeding

I Inspection

I Cutting

I Drying I Conditioning

I Inspection

I Packing (2) Varieties

Indigenous

I79

(3)Product Handling Whole fruit is washed and inspected before peeling, quartering and de-seeding; the latter will most probably be done manually. Thebest type of belt for the latter processes is a stainless Sandvik-type conveyor rather than a rubber belt, for reasons of hygiene. The quartered fruit is then cut into small segments or dice by a Model C dicer set for 6 by 6 by 6mm cubes upwards to 13mm After drying and conditioning the material is inspected, screened and packed. (4) Drying Stove dryers are normally used with an inlet temperature of 88°C for 1hour, reducing to 65°Cin the second and final stages. End moisture should be 6%. Raw moisture 92-94%.

Peaches (1)Flow Sheet Primary Processing Feed to Line I Grading I Washing I Dewatering I Pitting/Halving I Sulphuring I Drying

I Sweating Secondary Processing Inspection

I Washing I Sulphuring

I Grading

I80

Right: A manual apricot pitter

I Inspection

I

Packing ( 2 ) Varieties

Freestone Peaches should be used - not Clingstone. The main variety in California is Muir, followed by Rochester, Hale's Early, and Peregrine. There are many Mediterranean varieties which are equally suitable. (3) Product Handling

Fruit is harvested in fully ripe condition and must be handled with care to avoid bruising. The peaches are first graded and inspected toremove damaged or diseased fruit and then washed to remove dirt and skin 'fuzz'. After washing, the fruit is dewatered. Freestone peaches d o not require peeling in the manner that Clingstones are handled for canning, ie, lye dipping. Pitting and halving may be done by hand for a small operation but for larger throughputs machine pitting and halving is essential. l8l

The caps are then placed on wooden trays, cap uppermost in a single layer, and the trays are racked on to trolleys and placed in the sulphuring shed. 2.5kg of sulphur is burned for each tonne of fruit loaded in the shed. The exposure time is 4 to 5 hours or such time as is required to obtain a residual SO, level of 2000 to 2500ppm at the end of the cycle. The trays are stacked singly in the drying yard, on racks about 25 cm from the ground and exposed to the sun for 10-12days, according to climatic conditions; the fruit is dried to about 18 percent moisture in this period. After sun-drying the fruit is transferred to curing or 'sweating' boxes to equalise the moisture. Alternatively, it may be spread out on a clean concrete floor and turned regularly. Any wet fruit is returned to the traysand spread on the racks again for further sun-drying. Secondary Processing After preliminary inspection of the halves, they are washed in a rotary reel washer torender the fruit pliable,and in the course of this washing about 10 percent moisture is re-absorbed. The fruit is finally spread on the sulphiting trays again and then returned to the sulphuring shed, where it is exposed to the burning sulphur for a further 4 hours. Final moisture is controlled at 22 - 25 percent. The fruit is graded again into six sizes determined by the diameter of the caps. (4)Drying The drying method described is sun-drying, as the drying cycle is so prolonged as to make artificial drying in tunnels too protracted. Experiments have been conducted, however, by the Agricultural Research Service of the US Department of Agriculture on drying by the DBD method (Dry-BlanchDry) with some success - using tunnel dryers. Whilst this method has been proposed for commercially drying apricots, based on the author's practical trials, no personally collated data on DBD is available, hence sun-drying only has been proposed. The US trials on DBD disclose the following information: Sulphiting Time 1st stage drying 3% S 0, Dip 8 mins 4.5hours 68'C

Blanch

2nd stage drying

6mins

17 hrs 63 68'C

Product Analysis. Moisture S O , 16 % llOOppm

@1Oo"C

The Research Institute reports that no commercial drying of peaches

I82

by this method is currently being carried on at the time of the experiments but that the results were sufficiently encouraging to promote larger scale tests.

Pineapple (1) Flow-Sheet

Feed to line

I Washing

I Grading

I Sizing-coring

I Inspection

I Slicing

I Dicing: Segmenting, Sulphiting, Drying I Conditioning I Inspec tion

I Packing

(2)Varieties Smooth Cayenne (3) Product Handling Pineapples are usually processed in cans and on a large scale, involving high speed and highly specialised plant manufactured by two American Corporations, FMC of San Jose, Cal. and The Carter Co Inc. of Hawaii, the traditional home of pineapple canning. Evaporated pineapple is processed therefore on a much smaller scale. After washing, which should be carried out in a flood-type washing machine to avoid bruising, (probably a tomato washing and inspection line would be most suitable for a medium sized operation), the fruit is graded. Most h i t will fall into the range 1.6 to 2kg (with crowns) and the crowns represent 16-20percent of this weight. Diameter will range from 7.6 to 14cm and length from 18to 22cm. Possibly the smaller fruit will be most economical

I83

for drying and the operation would be more viable if it were combined with canning, where the larger diameter fruit could be diverted for this purpose. The standard high speed high capacity Honiron pineapple grader, made by the Carter company, has a capacity of u p to 60 tons per hour; therefore, for a smaller operation, a simple fruit or vegetable grader would have to be adapted. Sizing and coring is usually carried out on a Honomach Ginaca machine set for a specific size and operating at 120 pineapples per minute. Alternatively, if small fruit are going to be used the Carter C o can offer a small Sizer-Corer to handle 7cm fruit at half the price of the Ginaca. After sizing and coring, which implies the removal of the skin and coring down the centre of the fruit, a cylinder of fruit is left, which passes on to a stainless steel conveyor belt for inspection and trimming if required. The trimmed cylinders are then conveyed into a pineapple slicer, thence to a Honiron segment cutter, which will produce dice, spears, titbits or chunks. This is a relatively small capacity machine but is probably relevant in context of a medium sized drying project. The comminuted pieces are then sulphited by immersion in a sulphiting tank, dewatered and passed to the dryer. After conditioning, the fruit is inspected screened and packed. (4) Drying

For a medium sized operation, probably a double tray dryer or stove dryer is most suitable, and again a lower temperature is often used in the first stage - 63°C - finishing at 65°C - 68°C.This tends to prevent caramelisation of the sucrose in the fruit. Raw Moisture is about 85%. Moisture content in the end-product ranges from 15 to 18%. Drying ratio: 6:l Overall ratio depends on crown weight and sizing losses, which could be up to 50%. This would create a n overall ratio of 12:l. (5) Equipment Suppliers

Special pineapple plant: Carter Co Inc 91-060 Hanua Street, Ewa Beach, Hawaii 96706. or FMC International AG 1459 Coleman Avenue, Box 1178, San Jose, CA 95108 USA.

Pears (1)Flow-Sheet

Maturing

I i 84

Feed to Line I Grading

I Washing

I Inspection

I Peeling-coring I

Halving/Quartering

I Inspection/Trimminlj

I Sulphiting

I Dewatering I Drying I Inspection I Packing (2) Varieties Williams Bon Chretien (Bartlett)

(3)Product Handling Whilst William's are probably the best variety for processing they are somewhat difficult to produce for processing at the criticalstageof maturity, and it is almost impossible to pick off the tree and transfer to the factory at this stage, as in 2 to 3 days after ripening they soften and become flavourless and rapidly deteriorate. i t is necessary, therefore to pick them green at a specific Maturometer reading, hold in store in boxes at 16" to 18°C in 85 percent humidity. They are tested daily with a Maturometer,and fed into the plant when exactly ripe for processing. Pears for dehydration should not be too large, as this would prolong the drying cycle. 50 to 60mm diameter is about the top limit for size, and 45mm the lowest calibration. The graded fruit is separated into two sizes, which are transferred separately into a fruit washer, then inspected for damaged or blemished pears. I85

The fruit is then conveyed into an Atlas Pacific Pear peeling, coring, and halving unit with waste conveyors. If required the fruit could be quartered instead of halved. Each Atlas unit requires one operator and handles 750 - 800kg per hr depending on the size of fruit. As there is an hydrofeed tank in the Atlas Pacific plant, the preliminary wash may not be thought necessary, and is therefore optional. The cut pears are then passed over an inspection belt for trimming so that any seed cells which may have been missed by the peeling plant, or any discoloured flesh are removed. The product is then sulphite dipped and dewatered. A sulphite solution vessel and stirrer are located alongside the applicator tank to make u p the concentrated solution, which is metered in, to maintain the SO, level. Drying is by stove or tunnel dryer, as the cycle is 12-18 hours depending on piece size. Low drying temperatures must be observed in order to retain the cream colour of the pears. The dried halves or segments are inspected and packed in the same way as for apples and apricots. (4) Drying Tray loading is about lOkg per square metre. Inlet temperatureat the hot end should not exceed 65°Cand 57°Cat the cool end. Conditioning at 49°C to 50°C. Dry down to 20 - 22%. Raw moisture = 85%. Overall ratio = 10.5:l to 11:l Drying ratio = 5:l

(5)Equipment Suppliers Complete pear peeling, coring and cutting plant: Atlas Pacific Engineering Co 67th and Hollis Street, Emeryville, CA 94608 USA. Maturometer (hand machine): FMC. Pear core trimmers: FMC (hand tool).

Plums (Prunes) (1)Flow-Sheet (A)Drying

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(B) Processing

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I Sorting I Packing (2)Varieties Oregon-type Red Plums (3) Product Handling The plums are fed from a bulk feeder to the washing plant, which is usually a reel washer with a powerful water spray. If the fruit carries an exceptional amount of soil and extraneous matter a second flood wash may be necessary. The plums then pass over an inspection belt on which defective fruit and any remaining stalk or leaf are removed. They are then loaded on to drying trays for drying in a stove dryer or a twoor three pass tunnel dryer. As thcdrying cycle is 24- 36hr- occasionally up to 48hr for large fruit - this is the only type of dryer suitable. Drying tends to be uneven hence it is necessary to transfer the prunes on to tables for conditioning and here to remove any wet fruit for secondary drying. The prunes are then transferred into boxes to be held for what is described as 'processing'(B). The second flow-sheet describes this supplementary handling. Theprunesare passed througha dry reel tobreakdownany 'clumping'. They are then graded into sizes dictated by the count per kg weight. The largest fruit may be 55 per kg and the smallest 330 per kg. The local type of plum will dictate, by its average size, how many grades will be required to produce an acceptable presentation. To limit the number of grades, some blending of near equal sizes is done from the holding boxes of primary graded plums. Moisture is then stabiliscd by some rehydration in steam to arrive at 20-22 percent moisture, then dewatering. Where permitted by food laws a

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spray of potassium sorbate solution is applied to give a residual level of 400ppm. A final inspection is given before packing in 14kg cartons. (4) Drying Inlet temperatures in the first zone should not exceed 75°C otherwise there may be some problem of fruit bursting. Drying temperatures reduce progressively to50”Cin the finishing zone, and theend moisture is normally in the range 16 to 19%.In reprocessing the steam rehydration brings this u p to the 20 to 22% referred to earlier. The dual process permits the initial drying to be done during the harvesting period, and the secondary processing is done out of season as the product is required for marketing. Raw moisture of plums is 83%. Drying ratio can be expected to be about 6:l Overall ratio will depend very much on the condition and size of the raw material but should fall between 8:l to 10:l.

Raisins (Golden Bleached) The Thompson Seedless Grape is used mainly for the production of raisins, although Muscat and Sultinana grapes are processed in some localities. California is the major producer, with Greece, Australia and Turkey also being substantially involved. There are several methods of production, namely soda-oil or sodium hydroxidedip before sun-drying (California)rack-drying (Australia),natural sun-drying without pre-dip, sulphur bleach, and golden bleach. The soda dip involves immersing the fresh grapes in a 0.25 percent solution sodium hydroxide at a temperature at 94°C for a few seconds, then rinsing in cold water before sun-drying. The lye treatment removes the bloom and checks the skin to hasten drying. A second method used in Australia is to dip them in a solution of 0.3 percent lye, 0.5 percent potassium carbonate and 0.4 percent olive oil at 82°C for 2-3 seconds. This is not rinsed off before drying. For the last two to three days of drying, the fruit is placed in direct sunlight to effect a colour change from dull green to yellow or light brown. The process which follows, however, concerns the process for Golden Bleach Raisins in which the grapes are dried mechanically in a tunnel dryer. This type of dryer is rccommendcd in view of the long drying cycle of 24-25 hours.

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(1)Flow-Sheet (Primary Process) Feed to Line

I Inspection I Lye Dip I Washing I Tray Loading I Sulphuring I Drying I Fumigating in Sweat Boxes (Secondary Process) Feed to Line I

Dry Screening I Stemming (1) I Screening I

Aspiration (1) Stemming (2) I Aspiration (2) I Washing I Dewatering I Stemming ( 3 ) I Sorting I Packing I89

Fumigating (Flowline by Courtesy Van Arsdel, Copley and Morgan - Food Dehydration 1973) ( 2 ) Product Handling

This is done in two stages

Stage 1. Inspection. The grapes are inspected when fed to the line, and diseased and damaged fruit removed. In some instances, large bunches are broken down to smaller ones to facilitate quicker drying. Dipping. The grapes are dipped for 2-3 seconds in a lye bath (94°C)in a solution of 0.25 percent sodium hydroxide, then washed in cold water. Tray loading. In California the fruit is loaded on to wooden trays which are racked on to trucks and transferred to the sulphuring house. Sulphuring. The trucks are held in the sulphuring house for about 4 hours, exposed to the fumes of burning sulphur - 2kg of sulphur being used per tonne of grapes in the chamber. Drying. The trucks are then transferred to a tunnel dryer, where they remain until dried down to about 12 percent moisture. The trays are loaded 19kg per square metre, or 3 1 /2-41b per square foot. The inlet temperatures in the first tunnel must be kept low, otherwise SO, losses by heat will cause discolouration. 74°C should be adequate in the first stage, with a finishing temperature of 55°C. An SO, target of 2000ppm should be aimed at to maintain the bright colour desired. The dried fruit are then stored in ’sweat’boxes until they are ready for secondary processing. During this period the boxes should be fumigated at two weekly intervals to kill any infestation, and the ‘sweating’ is merely a process of conditioning the fruit at ambient temperature and allowing it to reach equilibrium by moisture diffusion through the mass of product. The effect is similar to that in conditioning vegetables in bins after primary drying except in the case of fruit there is no heated air-flow and conditioning is natural at ambient temperature.

Stage 2. The raisins are fed from the sweat boxes on to a rotary/aspirated screen to remove extraneous matter. Sfemming.They pass into a stemming machine which mechanically removes the raisins from the panicles by a strigging action. The fruit must notbe higher than 12 percent moisture,otherwise thestems will be too soggy

I90

and may clog the machine.

ScreeninglAspiration. This is a further cleaning operation to remove any trace of stem left behind by the previous operation. Stem Capping: Aspiration. Stem capping removes the small stem adhering to the individual raisins and these stems have to be removed by aspiration. If at any stage stemming proves to be difficult due to the residual moisture being slightly too high, some further rapid drying may be necessary in a stove or cabinet drying, at 50"-55°C. for 3-4 hours. Washing. This is a rapid rinse to finally clean the fruit and will increase the moisture to maximum 17 percent. The raisins are then dewatered. Inspection. At this point the fruit is inspected to remove any residual cap stems and imperfect fruit. Grading. This may be necessary if a retail pack demands a specific size of fruit. In this case the larger fruit will be screened out for this purpose and the smaller grade for catering packs. Packing. Catering packs are normally 301b (or 13.5kg)and retail packs

500g. Fumigation. This should be carried at regular intervals by methyl bromideina fumigatingchamberat thcrateof2.1 kg per 1OOcumofchamber space. This applies to the sweat boxes and to the final packs. BIBLIOGRAPHY W.B. Van Arsdel and A.I.Morgan. jr. Food Dehydration 1973 Californian Golden Bleach Raisins 11 :I73.

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Spray Dried Products TOMATO P O W D E R Tomato powder is much in demand by dehydrated soup manufacturers, and is now produced in many countries where tomatoes are an indigenous outdoor crop. The heavy cropping Italian plum tomato is ideal for drying down to powder, and this is grown in most areas with a ‘Mediterraneantype’ climate. Tomatoes have a very low solids content - not more than 6 percent - and dehydration must be preceded by evaporating the pulped tomatoes down to a paste containing 30 percent solids. Drying to a powder then follows by one or other of the methods described.

PROCESS Fresh ripe tomatoes are delivered into a water soaking vat, from which they are conveyed by roller conveyor to a spray washer. After washing, the fruit is discharged to a sorting conveyor where bad tomatoes are removed manually.

PULPING At the end of the sorting conveyor, the tomatoes are pulped in a chopping machine, eitherby the ‘hot break‘ or ‘cold break‘ method. The former is more often used with tomatoes for dehydration. The tomatoes are preheated rapidly to about 88°C prior to pulping, and this rapid heating destroys enzymes which prevent decomposition of the pectin. The latter’s retention helps to give body to the paste. The cold break method, by which thc fruit is pulped at room temperature, produces a paste which is easier to spray but, when dried, the

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powder will not reconstitute so well, the solids tending to settle out rather than remain in homogeneous suspension. The cold break method has some merit in the manufacture of tomato juice, in which it often produces a better colour and flavour but it invariably has a tendency to cause separating out.

STRAINING From the pulper the material passes to a holding tank, thence to a series of strainers with perforated plates, reducing consecutively from 1mm holes to 0.7mm and finally to 0.4mm. This process removes the skin and seeds, amounting to 5 percent of the weight of the fruit. Strained pulp is then transferred to storage tanks.

EVAPORATING The juice is concentrated under vacuum from 5 to 30 percent solids, as a preliminary stage to drying. A double-effect evaporator is normally used, with a finishing pan in the final stage. From here, the paste is transferred to a feed tank where it is constantly mechanically stirred.

SPRAY DRYING OF TOMATO POWDER The flow-sheet drawing Fig. 8.1 showsanoperation whereby the production of tomato powder is continuous and concurrent with the evaporation of the fresh pulp. In practice, however, some producers of tomato powder make their product out of season, and in the case of a plant in Portugal, which the author has visited, the company bought in most of their concentrate from a nearby tomato paste factory where there was a surplus, over and above what was contracted for export, as concentrate in 5kg cans. The cans were delivered to the drying plant in standard 5kg packaging, opened by a piston-type automatic can opener, which ejected the paste into the storage vat serving the dryer, at the same time crushing the empty cans and baling them for disposal. In this case the process commenced at Figure 19 on the Flow Sheet - Feed Tank for the Spray Dryer. In this particular instance the concentrate was made by the hot break system with concentration to 30-32 percent solids. Cold break pastes, concentrated to 36-38 percent concentration before drying, are sometimes used.

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Fig.8.1: Process flowsheet for producing tomato powder from fresh tomatoes by spray dying

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Key to Figure 8.1 17. Intermediate storage tanks with 29. Drying air disperser Soaking vat Roller conveyor stirrers 30. Spray-drying chamber with Spray washing vat 18. Transfer pumps double wall 19. Feed tank for spray dryer 31. Exhausted drying air duct Air compressor Sorting table 20. Water tank 32. Cooling air fan for item (3 1) Chopper 21.Three way valve 33. Cyclone with pneumatic Preheater 22. Feed pump to atomiser transport conveying at base 23. Atoiniser (rotating vaned disc 34.Exhaust drying air fan Intermediate holding tank 35. Exhaust duct and air hood 9. Transfer pump tY Pe) 24. Supply air inlet (cooling spray 36. Band conveyor (air conditioned) 10. Coarse mesh strainers 37. Packing room (air conditioned) drying chamber walls) 11. Medium mesh strainers 25. Supply air from atmosphere 38. Air conditioning unit 12. Fine mesh strainers 13. Holding tanks 26.Supply from air filter 39. Powder sieve 40. Powder packing box on scale 14. Doublehriple effect evaporator 27. Supply air fan 28. Steam-air heater (indircct oil- 41. Chamber for packing in an inert 15. Finishing pan 16. Transfer pump gas air heaters arc altemativcs) atmosphere

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

By couvtesy ofNiro Atoiniser

Above: Batch evaporator plant

Niro Dryer There were two of these dryers in parallel in this particular plant, and the Niro dryer is specially designed to cope with the properties of tomato powder, with a drying chamber of non standard construction as compared with other types of spray dryer. The conventional chamber design would create problems on account of the thermoplastic and hygroscopic properties of the powder, and continuous drying would be difficult. The co-current drying chamber (30) has a jacketed wall for air cooling and a conical base. Ambientair isdrawn through the jacket prior toentering thechamber via the air heater (28).Cooling air intake is controlled to enable close maintenance of a wall temperature which, in the range of 38'- 50°C, allows continuous operation. Paste is pumped to a rotating vaned-disc atomiser (23) located within the air disperser (29).The vaned disc has multi-vanes to achieve complete atomisation of the heavy paste feed. Paste is sprayed into the drying air entering the chamber at a temperature of 138'- 150°C.The drying air to the 195

heater (28) is supplied from the cooling air wall jacket supplemented by atmospheric air intake. The location of the atomiser within the roof air disperser creates optimum spray/air contact conditions. Moisture evaporation is rapid but controlled. Product settles out of the air-flow on the chamber wall, building u p to loose layers (15 - 25mm thickness) before breaking away and falling as nodules to the base of the chamber. The build-up is important for completion of evaporation. For the removal of the remaining moisture from a tomato particle, much resistance to mass transfer is apparent. The necessary long second period of drying is accomplished by the residence timeon the cooled wall. Increased drying temperatures cannot be used as heat degradation wouldresult.15-20percentof the throughputdoesnot settleon thewalland passes out of the chamber with the exhausted drying air. The entrained product is recovered in a cyclone, and conveyed from the cyclone base in dehumidified air. The bulk of the production falls from the chamber base into an enclosed band conveyor (36). Cool dehumidified air flows counter-currently slowly over the surface, and the product nodules are cooled on the conveyor. Ata temperatureof24"-3OoC,the nodules become brittle,and readily shatter into powder as they fall from the conveyor on to a sieve (39).This conveyor exit and sieve are installed within an air conditioned packing room kept at a low humidity. The plant under review dehumidified this area to 30 percent RH, with the temperature at 15°C. Insome plants this dehumidified area is treated with sodium fluorate, which is introduced into the air flow to provide a sterile atmosphere. Finalmoistureof the powder is3 to3.5 percent, and to maintain this low level in a hygroscopic material, it is preferably packed in nitrogen-flushed sealed polyethylene-lined drums or tins. Whatever container is used it must be air and moistureproof. Atmospheric packing in very dry air conditions was practised at the factory visited but this is recommended only for limited storage periods. Anticaking dessicants can also be used, in the form of silica gel envelopes placed in each pack.

Overall Ratio: range from 20:l to 22:l (Raw material to powder)

Whilst the drying plant was equipped to process from 5kg cans of concentrate, a more economical method of packing of the concentrate by the supplier would be in asceptic 225 litre barrels. These are filled at the concentrate plant by flash sterilising the paste at 95"C, cooling to 40°C and filling intopresterilised barrels under reduced pressure. A vacuum is drawn through a 20mm aperture in the top, and filling is through a second 50mm

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aperture. In the event, the latter method was advised and implemented the following season.

Above: Spray dryer for production of tomato powder

INSTANT COFFEE

C L E A N I N G AND B L E N D I N G The first step in the processing line is a thorough cleaning of the green coffee beans, to removedefectivebeans and extraneous matter. Blending is usually carried out to achieve optimum flavour development in the roasting stage.

RO&TIJXGANDGRINDING Roastingenhances the flavourand aroma and may be carried out batch-wise or continuously.The latter continuous method is more cost effective.Grinding to a particle size most suitable for the extractionprocess follows.

EXTRACTION This is eithercontinuousorbatch. Thecontinuous method employsa tiltable jacketed pressure vessel containing two helicoidal conveyors. Hot water enters the top end and the extract flows through the trough by gravity. The dwell time is from 30 to 40 minutes. In two stage extraction, atmospheric pressure is used in the first stage and pressure in the second. Batch extraction is carried out in a counter-current column battery unit featuring split extraction under closely controlled conditions, and yields of over 48 percent can be achieved. The first stage produces a prime quality extract, which is held separately pending final pretreatment and drying. The second stage produces a high overall extract yield but with low solids and this has to be subsequently concentrated.

CONCENTRATION Two methods are used, eithera two stage falling film evaporator with aroma recovery section, or a rotary thin film evaporator designed uniquely by Niro for heat sensitive products. Both types of evaporator operate undcr vacuum, thereby maintaining low extract temperatures.

SPRAY DRYING The concentrated extract is pumped to the pressure nozzle in the drying chamberwhereit isatomizedand contacted with hot air. Drying temperatures are low in order to preserve aroma and flavour in the dry product. An in-line spargesystem operating with inert gas in the feed system allows adjustment of powder bulk density and colour. The enlarged conical section of the drying chamber separates the dried coffee from the drying air so effectively that virtually all the powder leaves the base of the chamber, where it is cooled, screened and passed to storage, packing or agglomeration.

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Efficient cyclones clean the air, preventing the emission of coffee fines to the atmosphere. Heat recovery systems can be installed to preheat the inlet drying air, whereby energy savings of 15 to 20 percent can be made. As related in Chapter 4 (Dryers)energy costs can be cut by recovering the spent grounds from the extractor plant, to produce a cheap fuel for steam generation, if the boiler plant is normally fed by fossil fuels.

AGGLOMERATION This is carried out by wetting the instant dried powder with either water or coffee extract and after-drying in a fluidised bed dryer. The degree of agglomeration is controlled to give the product the appearance of regular ground coffee. Agglomeration improves the solubility factor, and simulates fairly closely the appearance of freeze-dried coffee. The Figure 8/2 shows a production line without agglomeration. A medium sized plant would perform as under: Green coffee (10% moisture) input Roasted coffee (6% moisture) input Extract solids content (split extraction) Green Coffee yield: 2.38:l ratio = Concentrate solid: Spray Dried powder rate: @ 3% moisture. Annual production: based on 270 days/6500 hours production time =

An agglomerator

595kg per hour 520kg per hour 10 / 25% 42% 36% 250kg per hour 1625 tonnes.

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SKIM MILK POWDER Skim milk powder accounts for about 80 per cent of the global production of milk powders; dried whole milk, butter milk and whey comprising the balance.

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In 1987 it was reported that some 100,000 tonnes were in EEC intervention storage, being surplus to commercial consumption requirements. The latter fluctuate widely from year to year. Milk quotas throughout Western Europe have been adjusted to correct this surplus situation but the technology in spray drying has recently been so much improved that new outlets for dried skim milk are being progressively created. Whey powder also has found many new uses with manufacturers - in ice cream mixes for flavour enhancing, in bakery products as a shortening agent, in soup and sauce mixes, and in dessert topping products. The new technology in spray drying has also given more choice to the buyer in that, for specific end uses, he can now specify low heat, medium heat, or high heat powder. This is made possible by the introduction of multi-stage dryers, as indicated in Chapter 4 (Anhydro Spray Drying Systems). The process herein described is based on the author’s contact with skim milk production in 1981, and whilst the spray dryers in this particular plant were not of the design described in Chapter 4 they were efficient and met the requirements of the processors, who were a company manufacturing a milkbased value-added product, and the Dairy Marketing Board, who absorbed any tonnage surplus to commercial sales. PRODUCT HANDLING It is customary for most drying plants to be located alongside the dairy in which the whole milk is processed, either for straight consumption, or conversion to cream, butter and cheese. In this particular case the dairy is located some 500 metres from the drying plant, both companies being in separate ownership. The drying plant has a long term contract with the dairy to supply 70 million litres of skim milk (or 92 percent of the creamery’s capacity) per annum. This is fed into the drying plant by a pipe line, and subsequently into buffer storage tanks, refrigerated to 5°C. The incoming skimmed milk has a minimum 8.8 percent solids and its specific gravity is 1.035. The supply is subject to seasonal peaks and troughs, which precludes continuous operation throughout the year at 100 percent capacity. In some circumstances, this could be corrected by an intake of skim milk in tankers from other creameries but the location is isolated and not contiguous to other creameries to make this a viable operation. Shifts are therefore reduced from 3 to 2 in the late winter months, and the late autumn. In the normal way, had the company been dependant only on the sale of straight skim milk powder, this partial restriction of supplies would have been less than economic but the additional production of a value-added item balances out any loss which might be occasioned by an interruption of the spray drying process.

This production unit in Northern Ireland was monitored by the author for the purpose of a valuation and viability, commercially. The process is set out as follows: The Skim Milk was evaporated with a 'falling film' evaporator to a concentration of 45-46 per cent total solids. The falling film concept made it possible to operate with low temperature differentials and to achieve high thermal efficiency. Manual supervision of the equipment was minimal, and the start-up, shut-down and C.I.P. could be automatically performed. The evaporator serving the first of two spray dryers was a 4-effect unit, with a three stage instantizer, following the second spray dryer. Initial pasteurization time before evaporation was at 71°C for 15 seconds. This No 1plant handled 19,350kg of skim milk (at 8 per cent total solids) per hour yielding 1,820kg of powder at 4 per cent moisture per hour The maximum inlet temperature of the drying air was 93°Cwith an outlet at 82°C. At these temperatures the evaporation was approximately 1,865kg per hour and the yield of powder at 4 per cent was 1,820kg per hour - a conversion ratio of 10.63:l. The steam consumption was 3,950kg per hour for the dryer and for the evaporator 3,045kg per hour. Installed power was 240KVa. The No 2 plant was smaller with a two stage instantizer. The efficiency of the dryer was similar to the No 1 plant with an input of 7,727kg per hour and a yield of 650kg per hour, although the evaporator was slightly less efficient in that it consumed rather more steam per kg of water evaporated. Steam consumption was 1,600kg per hour for the dryer and 1,900kg per hour for the evaporator. Installed power was 95KVa. Packaging was in polyethylene-lined multi-ply paper sacks. Bulk storage silos had a capacity of 70 tonnes, and the warehouse had a capacity for 2,000 tonnes of product. The storage of raw milk as previously indicated only provided for 28 hours reserve, and comprised 4 stainless tanks - 2 of 114,000 litres capacity and 2 of 91,000 litres, and this feed stock was maintained at 5°C. HYGIENE Clean down procedures were carried out daily on the evaporating plant; 4 hours wash-down after 20 hours running. The spray dryers were cleaned down as necessary at least every 4 weeks.

QUALITY CONTROL Tests on raw milk include: acidity, total solids, water adulteration, temperature and full bacteriological tests. In-process tests include total solids in the concentrate.

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STAFFING Total personnel, including management, is 67 at peak production times, of whom 28 are permanent staff. The balance are, in this instance, seasonal workers. Whilst the foregoing relates to an established spray dried milk plant in operation for some 13 years, a processor intending to engage currently in such a project, should obviously evaluate market conditions, and furthermore study the evolution of spray drying plant as recently outlined by APV Anhydro and set out in detail in Chapter IV. The author has always endeavoured to set down in the text the experience gained from practical contacts with operational plants but the reader should also be aware that technology advances almost day by day, and practices of even a year ago may be approaching obsolescence today. A mere guide to processes and disciplines is all, therefore, that can be achieved in a text book of this nature. P O T E N T I A L USES F O R S K I M M I L K POWDER Agglomerated Skim Milk has been boosted in recent years by the public’s trend to reduce their intake of fatty dairy products -butter, cream, cheese and full cream milk - on health grounds. A high fat diet has been regarded, along with other factors, as contributing to obesity and heart disease. High fat and sucrose intake by children is thought by some nutrition experts to affect behaviour patterns and mental concentration capacity. Specimen diets, studied by medical specialists in nutritional problems, and containing high fat and sucrose constituents have also indicated a deficiency of certain vitamins and chemical trace elements which are necessary for a ‘balanced’ diet. The validity of these claims has yet to be proved by a wider field of investigation than has hitherto been undertaken but the low fat diet theory appears to be well founded and accepted by many people. This has given an impetus to the sale of liquid low fat milk and aggressive advertising has created a substantial market for dried agglomerated skim milk. Agglomeration ensures the immediate dispersal of the milk solids in water, and the product is instantly soluble by the addition of cold water. The bakery and ice cream industries are substantial users of skim milk powder, in addition to the other creamery by-products, whey and butter milk, which in dried form have many uses. In the light of the still-mounting stocks of milk powder in intervention storage, the author has been involved in seeking interest in projects for reconverting milk powder into liquid milk, by rehydration and the addition of butter fat, then sterilising it and marketing the product in regions of high population in the developing countries, where little or no fresh milk is available. One project was in Cairo, which has a population of some 10,000,000,

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increasing at times to 12,000,000, by an ingress of some two million 'floating' population. In 1982 there was only one small processing plant involved in the rehydration of milk powder in the manner suggested, and the food stores have insufficient fresh milk to sell owing to the few dairy herds in existence. The small reprocessing plant, packing reconstituted milk into 1 litre UHT retail packages, which require no refrigeration, seems to fill a definite need. An expanded scheme for Cairo and other major centres of population was the subject of a feasibility study which envisaged a plant producing 8000 litres of UHT milk per hour from skim milk powder with 6 percent of the productive capacity of the plant diverted to the manufacture of ice cream and yogurt. The project purported to show that the reconstituted milk, brought up to the required butter fat content, could be produced at a price more than competitive with fresh milk locally produced or imported. UHT milk would be available to millions of people at a price they could afford, in a market which is somewhat short of reasonably priced dairy products. This scheme envisaged the production of the following products: (1) UHT 1 litre packs of milk manufactured from skim milk plus anhydrous milk fat and water, this product to be either plain or flavoured. (2) Evaporated Milk, Sweetened Condensed Milk, Recombined butter and butter-type spreads, Baby Foods, Recombined Cheeses (3) Yogurt - either zero-fat yogurt, or maximum 2 percent fat hard, 'scoopable' ice cream yogurt. (4) Ice Cream and Ice Cream Mixes

MARKETS Investigations showed that supermarkets, stores and hotels would accept these products, not only in Cairo, but in Alexandria, Ismalia and other major centres of population.

EXPORTS Exports might eventually be feasible to other Middle East countries. The process and plant for 'recombined' milk, as it is technically described, has been developed by a multi-national dairy engineering plant company, and is described hereunder, and is also referred to in Modern Dairy Products (1975) published in the USA. Four stages are involved: (1)Mixing of raw materials: (2) Uperisation: ( 3 ) Aseptic Tank Storage: (4) Packaging.

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MIXING To produce a recombined milk with 3 percent butter-fat content, the raw material required for 16 million litres (assumed production per annum) would be 1616 tonnes Skim Milk Powder 480 tonnes Butter Oil. The raw material mix, therefore, will be 77.1 percent milk powder and 22.9 percent butter-oil. Mixing is effected in a Liquiverter - a stainless steel hopper, incorporating a rotary impeller in the base, which feeds the material in the above proportions into two reconstitution tanks with paddle agitation. Circulating pumps and a steam heated circulation heater provide the energy and heat for this operation. Water flows from one of the reconstitution tanks to meet the dry material fed into the Liquiverter, where lumps are broken down by the impeller before the flow is reversed and the mixture pumped back into the tank. During the circulation the heater raises the temperature to 55". The mixture is then transferred to the Uperisation unit, whilst the second reconstitution tank is brought into use for the following batch mix. UPERISATION This is a method of continuous sterilisation by injection of clean live steam into the product. Vapour equal to the amount of steam injected is removed during cooling - thus preventing dilution of the milk or over-concentration. Rapid heating and cooling, with a short holding time ensures that flavour and appearance are not affected. After preheating to 77-80°C the milk is pressurised by a booster pump before passing into the Uperiser, where steam is injected, raising the temperature to 150°C.After a short holding time, the product is 'flashed' off into the expansion vessel, and cooled to 80°C. In this vessel the same amount of vapour is removed as was injected by steam. The milk is then homogenised, cooled in a plate cooler and transferred to the aseptic tank system. ASEPTIC TANKS These provide a buffer store of milk between the Uperiser and the packaging Machines. In operation, the tanks and associated pipework are first flushed with sterilising fluid, and the sterile condition is maintained by sterile air. Constant air pressure ensures a steady flow from the tankage to the packaging plant.

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Figure 8.4 - Key to Figure 8.3 1. The roll of packaging material is located in a cassette at the back of the machine. 2. A photocell, which gives a signal when it is time to insert a new roll of packaging material. 3. Rollers which soften up the creases in the packaging material, thus facilitating final shaping of the cartons. 4. Stamping device, which stamps the packaging material with the date or other marking. 5. Bending roller. 6. When the splice between two rolls of packaging material passes this point, this is registered by the machine. The carton which is subsequently sealed by the spliced packaging material and the two succeeding cartons are discharged through the drop chute 20. 7. Strip applicator, in which one edge of the packaging material is provided with a plastics strip. This is subsequently sealed to the other edge of the packaging material. 8. In the sterilizing bath, the inside of the packaging material is wetted with hydrogen peroxide. The wetting process is monitored by a built-in control function. 9. Rollers which mangle away any surplus hydrogen peroxide. 10. Cover for collection of air rising from the paper tube. This hot air is returned to the sterile air compressor and, in conjunction with this, any residual hydrogen peroxide in the air is removed by washing with water which is collected in a special separator. 11. Upper bending roller. 12. The product to be packed is introduced through the stainless steel filling tube, which is jacketed by a second tube through which sterile hot air can be blown into the paper tube. The current of air is deflected upwards upon reaching the lower edge of the tube heater. 13. As an initial stage in the sealing of the longitudinal seam, one edge of the packaging material passes through an element which is heated by hot sterile air. 14. The longitudinal seam is sealed in this forming ring where both edges of the packaging material are pressed together. 15. The tube heater consists of a coil-shaped electric element that heats the inside of the packaging material with radiant heat. This radiant heat sterilizes the packaging material and at the same time a sterile atmosphere is created above the liquid level. 16. Liquid level in the paper tube. 17. The liquid level in the paper tube is regulated mechanically by a float SO

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18. 19.

20.

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that it is always higher than the mouth of the filling tube. By this means, frothing is avoided. Filling-tube mouth. The cartons are finally sealed below the liquid level and are thus completely filled. Sealing is carried out by a system of jaws, which also separate the cartons. Upon commencement of a production run, and when the packaging material contains a splice, the cartons are discharged here. The finished cartons are discharged from the machine, either to the right or to the left, and carried by a conveyor to the place where they will be packed in transport packaging.

Fig 8.5 Sterile air system for 1 litre packs

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Key to Figure 8.5 1. The compressor which creates the necessary pressure in the sterile-air system is of the water-ring type, implying that in order to function it requires a continuous water supply at a rate of approximately 8 litres per minute. The water serves a twofold purpose: not only does it afford a seal between the rotating impeller and the pump housing but it also washes away any residual hydrogen peroxide contained in the air sucked in from the upper part of the machine at 17. 2. Water inlet to compressor. 3. Separator for removal of water from the air. 4. While the machine filling system is being sterilized prior to commencement of production this valve is open and the water is discharged to the drain. During production, the water is used as coolant in the cooler 17, after which it is discharged into the drain. 5. Heater in which the air is heated to approximately 350°C. 6. Some of the heated air is conducted to the strip applicator and longitudinal sealing element of the machine. 7. Cooler, in which the air temperature is lowered to approximately 80°C. 8. This valve is open while 1 litre cartons are being produced and conducts the sterile air into the space above the liquid level in the sealed paper tube. On machines for making smaller carton sizes this valve is closed during production. 9. The filling system is sterilized with hot air before commencement of production, and during the process this valve is open. 10. Filling tube for the product to be packed. 11. The sterilized air is supplied through this tube which completely encases the filling tube. 12. The electrically heated, coil-shaped tube heater element emits radiant heat which sterilizes the inside of the packaging material. 13. At this point, the current of sterilized air in the paper tube is deflected upwards. The vaporized sterilizing liquid is removed, and at the same time a sterile atmosphere is created in the sealed paper tube. By this means, re-infection from the air in the premises is prevented. 14. Liquid level in the sealed paper tube. 15. Float which regulates the liquid supply through the filling tube. This float communicates with valve 16. 16. Throttle-type valve. 17. Cover which collects the air rising from the sealed paper tube. This air is returned to the compressor 1, where it is mixed with water which washes away any residual hydrogen peroxide. The water is then collected in the separator 3.

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9

Dehydration of Meat The dehydration of meat and poultry in granule form for soup ingredients is dealt with in this chapter, as being of more practical importance than the drying of meat in larger cuts, such as slabs, dice, etc which can only be dehydrated by the AFD method. Outlets for the latter products are relatively limited in Europe, whereas there is a worldwide market for soup-making materials. Meat granules and powders can be air dried or freeze-vacuum dried. The latter system has the undoubted advantage of quick rehydration, which is beneficial for soup mixes but, as previously stated, it is an expensive system and, therefore, the air dried product still finds wide acceptance in what is a very competitive market. It is on this system that the following processes are based. The dehydrator will require to have a completely separate plant for the handling of meat and poultry, as this cannot be carried out hygienically alongside vegetable processing. Ideally, the premises should be separate as well or, at least, properly subdivided if the two activities are carried on under the same roof. Otherwise, the required standard of hygiene cannot possibly be maintained. The local Health Authority should always be consulted before setting up a meat plant of any description, as there will inevitably be several by-laws in this context, which will have to be observed. It is also essential to have adequate cold storage in the factory, both for short and long term storage of raw materials. Where the latter have to be bought in at special times of the year, in order to gain a seasonal purchasing price advantage, low temperature storage (-29°C) will also be a necessity.

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R A W MATERIALS Beef and mutton should be brought into the factory boned out and ready for processing, either frozen or fresh, as available. Oxtails, kidneys and other offal are usually bought frozen and held in cold storage until required. Poultry is bought plucked and eviscerated, either prefrozen or fresh, according to availability. The preparation of meat and poultry for processing, ie, the boning out of quarters, and the plucking and eviscerating of birds, is specialist work better carried on outside the dehydration factory, and there is little or no good reason for the dehydrator to tackle this, or involve himself with the additional equipment and labour concerned with this part of the work. A strict procurement specification for meat products should be set out, and there should be no difficulty in having this complied with by the suppliers as to fat content, trimming and quality generally, if reliable sources are contacted. CHICKEN GRANULES The poultry is thoroughly defrosted and the carcasses cleaned and prepared for the precooking. Well fleshed hens with a good flesh to bone ratio are the best for this purpose.

Cooking Stainless steel jacketed vertical autoclaves, with perforated metal baskets, which lock on to a central spindle, are loaded with the chickens, and steam is applied to the outer jacket at 5.5atm. A small quantity of water is required in the bottom of the autoclave to start the cooking process, and the internal pressure of the vessel is brought up to 1 .2atm, after first venting the air. The chickens are cooked for 30-35min, or until such time as the flesh falls freely from the bones. The condensate and juices are drained off from the bottom of the autoclave, at the end of the cook, into a lower tank, where the fat and bouillon are separated. The fat is recovered, rendered and hardened for subsequent use as an ingredient in chicken soup. The bouillon is transferred to a stainless steam jacketed boiling pan and concentrated until 75 percent of the excess water has been removed. This is held for subsequent addition to the flesh. This concentration may alternatively be carried out in a vacuum pan.

Fleshing The chickens then pass to a fleshing table where the operators remove the cooked flesh from the bone, transferring it to sterilised trays.

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Mixing The flesh, which must be scrupulously examined for small bones and gristle before leaving the fleshing tables, is then transferred to a steam jacketed mixer, and the bouillon from the batch of chickens just cooked is added back in its condensed form. The mixer is fitted with a ribbon-type blade, which rotates very slowly, thoroughly mixing all the flesh. The heat in the mixer jacket and the retention time are judged to reduce the bulk 15 percent by evaporation. If permitted by the specification, salt may be added at this point in the process. Mincing The meat is taken from the mixer-dryer and minced through a 2.4mm, 4.8mm or 9.5mm plate, according to the size of granule required. Drying With a small scale operation, drying is usually carried out in a stove dryer by the simple hot air convection method, although medium sized conveyor band dryers can be used equally well. Where a stove dryer is used, the meat is spread 25mm deep on previously sterilised trays, and the latter are racked on trolleys of a suitable size to fit the stove dryer. As a preliminary to drying on trays, however, where considerable handling of the meat has taken place, it is necessary to sterilise it, and one method of effecting this is to move each trolley, with the trays racked in position, into an autoclave of rectangular shape - similar to those used in the canning industry. Here, the product is sterilised with live steam at latm for about 20min. This is a necessary precaution to reduce the bacteriological count arising from handling, exposure to room temperature and general conditions which encourage bacterial growth. When using a conveyor band dryer, where no tray loading or predrying delays are involved, sterilisation may be omitted. In this case the meat granules are transferred directly on to the band dryer plates at a 7.5cm bed depth. Drying temperature is 66°C at the inlet, and the time of travel through the heat zones is 30-40min. From the dryer, the product passes through a cooling section, which reduces its temperature to 23°C. A suitable size of through conveyor dryer for this purpose would be 9m long and 1.5m wide, with a 3m cooling section. This would handle up to a ton of raw material an hour. Final moisture content should be 5 percent and the free fat content 35-40 percent.

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Packing Hermetically sealed 4gal. tins, nitrogen-flushed, are almost invariably used for this and all meat packs. Ratio With well fleshed hens, this should be 3.5:l to 4:l. BEEF, MUTTON, HAM, OXTAILS, K I D N E Y S The process for these meat products follows that for poultry very closely, in principle. For beef products, cow and bull beef is the best material to use for dehydration. Beef loins are a suitable cut, having relatively little fat. Oxtails must be defatted after cooking, and these will normally require precooking for 45-60min at 1.4atm in the autoclave to tenderise them sufficiently to allow removal of flesh from the bone. If difficulty is experienced in defatting, it is usually an indication that insufficient heat has been applied in the precook, and this must be controlled to obtain the best results on the fleshing and defatting tables. Well trimmed tails should be insisted upon in the procurement contract, as there is no recovery value in a large percentage of fat. Drying techniques are the same as for poultry, and similar drying temperatures are applied. Ratio 71 may be expected from lean tails. T Y P I C A L BUYER'S S P E C I F I C A T I O N

- USA

C H U N K STYLE D E H Y D R A T E D C O O K E D C H I C K E N Description: Chunk style dehydrated cooked chicken, produced from fresh or frozen poultry. It is free of extraneous parts, such as hearts, gizzards, livers, kidneys, cartilage and bone. Ingredients: Cooked chicken, salt, MSG and anti-oxidant. Specifications: Physical and Chemical: Moisture 5% Maximum Fat 35% Maximum 3% Maximum Salt MSG 2% Maximum Protein 55% Minimum 10.0 millequivalents maximum per kilo of fat PH Less than 0.02% of the fat portion as BHA and Anti-oxidant

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Colour Particle size Flavour/Aroma

Propyl Gallate. Other anti-oxidants may be used to meet customer requirements or foreign Government Regulations Golden brown Standard 1/4in. may be adjusted to meet customer requirements Characteristic of cooked chicken

Microbiological: Less than 10,000 organisms per gram Standard Plate Count Coliform, Yeast and Mould Negative in log tested Negative by approved testing procedures Salmonella General Requirements: The product conforms to all current USDA Regulations Governing the Inspection of Poultry and Poultry Products. T Y P I C A L BUYER’S S P E C I F I C A T I O N - U S A .

C H U N K STYLE D E H Y D R A T E D C O O K E D BEEF TYPE 1 Description: Chunk style dehydrated cooked beef, prepared from fresh and/or frozen beef. Ingredients: Cooked beef, beef broth, salt and MSG Specifications: Physical and Chemical: Moisture 5% Maximum Fat 35% Maximum 4% Maximum Salt MSG 3% Maximum 50% Minimum Protein 5 millequivalents per kilo of fat PH Colour Medium brown Flavour/Aroma Characteristic of cooked beef Standard 1/4in. may be adjusted to meet customer Particle size requirements. Microbiological: Less than 10,000 organisms per gram Standard Plate Count Coliform, Yeast and Mould Negative in log tested Negative by approved testing procedures Salmonella

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General Requirements: The product conforms to all current USDA Regulations Governing Meat Inspection. TYPICAL BUYER’S SPECIFICATION

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USA. C H U N K STYLE D E H Y D R A T E D C O O K E D HAM

Ingredients Cooked ham. Normal curing ingredients: Sodium Nitrite, Sodium Nitrate, Sodium Erythorbate, salt, MSG, Disodium 5- Inosinate, Disodium 5Guanylate, smoke flavour and anti-oxidant. Specifications: Physical and Chemical: 5% Maximum Moisture Fat 35% Maximum 50% Minimum Protein Salt 6% Maximum MSG 2%Maximum Colour Pinkish Flavour/Aroma Characteristic of smoked ham Particle size Standard 1/4in.may be adjusted to meet customer requirements Anti-oxidant Less than 0.02% of the fat portion as BHA and Propyl Gallate. Other anti-oxidants may be used to meet customer requirements or foreign Government Regulations Microbiological: Standard Plate Count Less than 10,000 organisms per gram Coliform, Yeast and Mould Negative in log tested Salmonella Negative by approved testing procedures General Requirements: The product conforms to all current USDA Regulations Governing Meat Inspection.

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Selection, Packaging

and Storage SIEVES The size grading of dehydrates is an important function, both in the interests of quality and presentation, and also for the purpose of obtaining the optimum return on products undersize, or less than the standard cut. With almost all cut vegetables and fruits, there will be off-cuts from the dicers or cutters, which can be effectively separated from the primary product by the use of effective sieving machines. The recommended type of sieve for all dehydrates, whether whole product, diced, sliced or comminuted, is a high centrifugal force vibratory screen with adjustable amplitude and pitch. The Russell Finex 22 as illustrated in Chapter 5 is ideal for screening potato granules in the final stage of sifting the potato mash powder through a 250 micron or even finer mesh, whilst the Finex 48 Vibro Separator with two decks is highly recommended for the initial stage of screening the blend from the primary dryer, from which point one fraction returns to the mixing plant and the other to the secondary dryer and then to the final screening. The Finex 48 is also very effective as a screening machine for all vegetables and fruits after bin drying and aspiration (where applicable) and before the final inspection and packing. Again, this machine has adjustable amplitude and pitch for any desired flow pattern, which is absolutely necessary to obtain perfect size separation. Deblinding devices can be fitted

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to both types of screen for products which are prone to ’blind’the mesh during extended usage. The illustrated self-loading sieve is also suited to handling granules and powders, which are fed into the lower bin and then drawn up to the dust-tight gallery above the mesh of the self-loading sieve by vacuum. The air is separated from the material via an integral filter mounted in the lid of the sieve and taken away either by a venturi or electric vacuum pump. A timer control switches off the vacuum and sieved material drops into a suitable container sited below which, in the case of potato granules, could be end packaging sacks and liners. This type of arrangement may suit some lay-outs but is invariably regarded as more suitable for granules or powder than cut products. A useful range of sieves for dehydrated vegetables and fruits is as follows: Round-hole screens: From 4mm to 9mm in increments of 0.4mm - stainless steel. Slotted screens: 19mm by 2.5mm and 25mm by 3mm - stainless steel. Woven wire screens: 1.5mm, 1.2mm, lmm, 0.85mm - stainless steel. The above would cover the screening of most types of fruit and vegetables. For Potato Granules and Powders the sieves range between 350 microns to 150 microns. A 250 micron screen is commonly used for the pack-off granules in the final sieving. Powder screens may be stainless steel or occasionally nylon. The processor must select the size of screen most suitable for the product being graded, bearing in mind what outlets there are for the ’through’material with any particular size of aperture. Some off-cuts from 9.5mm dice, for example, are useful for soup formulations, where the particle shape may not be too critical. For a quality soup, however, the vegetable is usually cut to the appropriate size, initially in the raw state. When screening 9.5mm carrot dice (in the dry state), with a 4.8mm sieve on the top of the screen, about 10 percent will pass through as off-cuts or ’Small cut’, and a rather smaller percentage when sieving potato. With a 6.4mm sieve fitted, up to 20 percent will pass through. The decision on which to use, can only be made in the light of circumstances, taking into account the buyers’ specification for the appearance and size of the main product, and what outlet there may be for the smaller particle fraction. In addition to these two fractions, using a twin deck screen, a 1.2mm screen can be used at the lower level to take out fines which can be milled for vegetable powder in a Turbo Mill.

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SELECTION Manual and visual selection of some dehydrated products is still necessary, as the particle size may not lend itself to electronic colour sorting. The latter method can be adopted for free-flowing material, such as dice, peas and some flaked vegetables, but is unsuitable for strips, rings and leaf products. Manual selection of dehydrates is carried out on PVC-coated inspection belts 7m long and 60cm wide for a medium throughput. Ideally, these belts should be fitted with a feed hopper incorporating a vibrating tray or chute, giving a controlled and metered feed of material across the belt. Bucket and belt elevators, and auger feeds, should be avoided in conveying diced material at any point of the process, as these cause severe abrasion and loss of product, and they are difficult to clean. A well-designed elevator, with moulded rubber flights, or a spiral vibratory elevator are the only satisfactory means of elevating and conveying dry materials. The selection belts should accommodate a team of women on either side and there should be good natural light in day-time, as the inspection is tedious and liable to cause eyestrain in poor light. Whilst white is an hygienic colour for belts, it may be found beneficial to use other colours which will highlight the blemish that has to be removed. There is always a risk of metal abrasion in the plant at some point or another, and it is essential to have a series of powerful permanent magnets fitted on the selection belts. One of these should bridge the belt, across its width, just high enough to allow the material to pass underneath. At the end of the belt, where the material discharges, it is a wise precaution to have a second pair of magnets set at about 45" to each other, over and under which the product cascades into the collecting hopper. These magnets will, of course, only abstract ferrous metal, and most processors install a more sophisticated electronic detector for all types of non ferrous foreign matter which may pass over the belt. These detectors are designed to stop the belt when any extraneous matter is detected, and it is then manually removed. The speed of the selection belts should be from 4 to 5m per minute, according to the capability and availability of the staff and the means of selecting efficiently. The recommended loading rate for onion slices, for example, is 250g per metre of belt length. ELECTRONIC C O L O U R S O R T I N G This method has made tremendous strides in the last five years, and Sortex Ltd of London are specialists in this field, having made an extensive study of the dehydrator's requirements. Their machines are capable of efficient throughputs of vegetable dice, flakes, peas and particles smaller than dice, although in the latter case the

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throughput is obviously restricted, as each particle has to be scanned individually. Some types of optical colour sorters operate by feeding material through an optical box fitted with sixteen photo-electric cells, for each of 10 chutes, which scan the surface colour of the product against automatically adjusted backgrounds. Pieces which are ‘in-balance’ as to colour, pass through an ’accepted’ delivery chute at the bottom of the machine, and those which are ‘foreign’ to the background are blown out of trajectory, by a fine jet of electronically signalled compressed air, through a ‘reject’ spout at the back of the machine. Modern machines may operate from a common feed, and have a throughput capability of 1200kg per hr with some types of vegetable dice cut to 3/8in. by 3/8in. by 3/8in (10mm cubes). . These machines are progressively replacing manual inspection of dehydrated vegetables as they are infinitely cheaper to operate. Some final visual inspection is always advisable, however, after the product leaves the colour sorter but this is mainly a ’policing’ operation, and only makes minimal demands on staff. The use of electronic sorters, however, demand the employment of highly skilled personnel to service them. Air Separation Some products lend themselves to quality grading and selection by aspiration, and very efficient machines are now available for this purpose. It sometimes happens that the fraction of material to be abstracted from a product has a different specific gravity from the acceptable fraction. A finely balanced air separator will deal with this abstraction very adequately, and will save hours of manual selection. Two examples of this are the coarse core pieces present in cabbage, and the green fraction of leeks. Both of these fractions can be eliminated by aspiration and air separation. PACKAGING Both materials and units of packaging must satisfy a specific set of requirements: (1) They must be compatible, costwise, with the value of the product they are designed to carry; (2) They must give protection against the ingress of moisture, light, air and infestation by vermin and insects; (3) They must be sufficiently strong and stable to protect the product from damage by abrasion, and a considerable degree of handling in store and in transit; (4) Materials must be approved for contact with a food product;

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(5) Size and shape must be acceptable from a distribution and storage point of view. BULK PACKAGING Peas, vegetable dice and small cuts, granules and flakes are usually packed in multi-ply paper sacks with a polyethylene liner inside. This packaging is acceptable where the abrasion factor is low but it is not so suitable for such products as onions, green beans and cabbage. A suitable specification for a 5-ply paper sack for dehydrated vegetables is: 1outer ply 361b wet strength kraft; 1inner ply 521b Union kraft (bitumen impregnated); 3 inner plies 361b natural kraft. Above specification is based on UK standards.

Above: Vibratory packing table made by Valley Products Ltd for the consolidation of bulk materials; it is suitable for packing dehydrated products in tins.

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The optimum packing weight is usually about 25kg for this type of sack, which will measure approximately 114cm by 68cm by 9cm (gusset) for diced root vegetables. The polyethylene liner for this sack is normally of 300 gauge, and preferably pigmented to keep out light. Buyers should avoid the acceptance of liners made from regenerated material, as pigmented polyethylene is often made from reprocessed scrap and should be graded accordingly. The liner should be tightly secured at the neck by a non-metallic fastener after filling with product, and then the sack must be stitched along its mouth. The more delicate materials, such as onion, green beans and cabbage, which are all subject to abrasion and handling damage, should be packed in polyethylene-lined fibreboard drums or cartons, the net weights varying between 8 and 10kg.

Above: A Valley Products’ horizontal vibratory feeder equipped with a small bulk feed hopper

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Should larger packs be required, for shipping economy, then the above weights may be exceeded by using fibreboard drums, with metal reinforced ends and a polyethylene liner inside. These drums have the merit of rigidity, and give the product good protection but they are cumbersome to stack in warehouse and in transit. Reference has been made earlier to packing in tinplate containers but the current cost of tinplate almost precludes this, except for high value material, for example, meats, poultry and special vegetable packs for export to the tropics, or for storage in exceptional conditions. The standard dehydrator’s tin is a nominal 18 litre capacity container, 23cm by 23cm by 33cm high, with a 15cm aperture for filling, and a lever lid to fit this aperture. These tins, which are normally nitrogen-flushed after filling, give excellent protection on all counts, and they ensure a shelf life of 12 months or more for the product. Against these factors must be balanced the cost of the container, the fairly high labour cost of filling, gassing and soldering, and the fact that it is not easy for the user to empty the tin of its contents completely. The 15cm aperture never appears large enough to eject the last few ounces of product lodging in the square corners of the tin. Another objection by users is that the soldered tagger plate is difficult to remove. An alternative tinplate container is the nominal 5kg open top can, which can be easily filled, hermetically sealed on a double seamer and nitrogenflushed through a brogue hole in the end. This container is, however, too small for most vegetables, other than potato granules, but it is ideal for meat packs. Packaging for retail and small catering packs may be selected from a wide range of materials, including polypropylene film, cellulose and polyethylene film, and laminates of many types. A dehydrator must take into account the barrier properties he requires, before deciding on a film or laminate, and he must also establish what shelf life a particular form of packaging will provide. The shelf life of retail and catering packs of vegetables is normally guaranteed for nine months, and this requirement must be considered when selecting packaging material. The only satisfactory way to establish suitability is to undertake accelerated storage tests, by incubating products in test packaging and logging the results at prescribed intervals. It is possible to nitrogen-flush small packs, with suitable equipment, where it is found necessary, to inhibit oxidisation. Low moisture content is, in the ultimate, the major requirement for satisfactory storage of all dehydrated foods. Low temperature storage conditions are also important. Ideally, warehouse temperatures should not exceed 10°C and, in hot climates, some cooling equipment is necessary in stores.

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Dry conditions and low relative humidity are essential, and all warehouses should be serviced to prevent rodent and insect infestation. Failure to do this can cause extremely heavy financial losses. Pybuthrin is an effective aerial spray to control most flying insects, and this should be used weekly throughout the whole of the factory and warehouses. It is non-toxic but the application should be given whilst the plant is closed down at weekends, as it can have unpleasant effects on personnel whilst the spray is in suspension. The operator should wear a suitable mask whilst using the spraying equipment. Rodent control should always be carried out by specialist contractors, as this can rarely be done satisfactorily by factory personnel.

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Quality Control In broad terms, the quality control staff, under the supervision of a qualified food chemist, should be responsible for the following: (1) The evaluation of quality of all incoming raw material, supplementary ingredients used in processing, chemicals, packaging material, cellulose and other film, paper and fibreboard containers, and certain consumable stores: (2) All routine laboratory tests on raw material, finished products, lye and blancher liquor, boiler and processing water; (3) Sampling procedures; (4) Recording processing data, ie, drying temperatures, peeling and blanching procedures, cooking records for precooked products, such as meats, etc; (5) Research and development work on new products, packaging and processing methods; (6) Logging of complaints from consumers, and pursuing these to origin and eliminating the cause; (7) Supervision of methods of plant cleaning and sanitation, and establishing firm principles of hygiene for personnel and plant maintenance; (8) Arrangements for and supervision of pest and rodent control by contractors primarily concerned in these duties; (9) Liaison at all times with production management.

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LABORATORY ANALYTICAL TESTS Having received samples representative of a batch of finished product, or incoming raw material, the staff will carry out the following tests:

Moisture For moisture tests, either a vacuum oven, set at 70°C,or a fan assisted air oven, set at 10Oo-103"C,is used. The former is more accurate, albeit slower, on account of the low temperature used, as this prevents the charring and burning of the sample when it is completely dried out, and allows a more exact result to be calculated. Samples of raw vegetable should be grated finely before testing, and dry products should be ground in a small coffee grinder. The sample material is dried down to zero moisture, and the loss in weight expressed as a percentage of the original to the nearest 0.1 percent. Two hours is the average time for drying down most dehydrated vegetables, from 8 percent to zero moisture; raw vegetable samples will take 16 hr. These times apply when using an air oven. A more rapid calculation of moisture in dry products can be made by using an infrared moisture tester. The sample must be finely ground so that it passes through a 10 mesh sieve; a given weight is dried out under an infra red lamp, the loss in weight being recorded by a scale on the tester. Results can be obtained in up to 7min, and in as short a period as 4min for some vegetables. These moisture testers, however, are not as accurate as the oven-type, and results can vary about 0.5 percent when compared with the latter. It is, nevertheless, an indispensable instrument for the shift chargehand to use for rapid tests on material in course of process, particularly for testing products drying in finishing bins, where it is important for the operator to know the drying end-point accurately, before discharging the material to the packing department. Sulphur Dioxide Tests for SO, concentration are carried out by the Monier Williams method, or what was described in the early days of dehydration as the 'Committee' method. The former method is rather more accurate but the latter is more generally used with vegetables, for the sake of speed. Basically, the calculation is made by boiling a 20g sample of the ground product in dilute hydrochloric acid and titrating iodine into the distillate as follows: 250ml of distilled water are placed in a 500ml flask connected by a splash-head to a vertical condenser terminating in a bubbler feeding into a 600ml beaker. 20g of the dried product for analysis are put into the distilled water in

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the flask, with 10ml of concentrated hydrochloric acid. Heat is applied to bring about boiling in 2-3min. The distillate is collected in 200ml of water in the beaker at the bottom of the condenser, and N/100 iodine is titrated from a burette to maintain a slight excess of iodine. A little starch solution indicator is added to the beaker. A marked reduction in the rate of evolution of iodine combining substances is taken as the end-point, or when more than one minute is required to decolorise 0.2ml N/100 iodine. The distillation should be complete in 5-l0min. Calculations: lml N/100 iodine titrated = 0.32mgm sulphur dioxide. Peroxidase Test for Vegetables During blanching, the enzymes present in active form become progressively inactivated by heat. Of these enzymes, the peroxidase complex is readily perceived because of the colour reaction it promotes with a reagent. A suitable reagent is a solution of Guaiacol and hydrogen peroxide made as follows: (1) 1per cent w/v Guaiacol dissolved in distilled water: (2) Mix 25ml of 20 volume hydrogen peroxide in 75ml of water, and add 100ml of 1per cent Guaiacol solution.

The sample for analysis is liberally wetted by the above solution, and the development of a brown colour indicates active, or positive, peroxidase. If the colour is not apparent in one minute, the result is negative, and it can be assumed that blanching is adequate. If the result is positive, it is necessary to adjust the blanching conditions, either by increase of temperature or product immersion time. Blemish Count A limited number of minor blemishes is often permitted, commercially, in dehydrated vegetables but the tolerance must be rigorously controlled. Blemish may arise from disease in the fresh vegetable, skin, root or growth defect, or can stem from a processing fault, such as scorching, under or overblanching, or inefficient peeling. Obvious blemish should not be present, and the only tolerated blemish is what is described as ‘minor’, ie, slight blemish in the dry state, which mainly disappears on reconstitution. The standard will obviously vary from processor to processor but, on average, the permitted tolerance is from 5-7 minor blemishes in a 50g sample of dehydrated vegetable. A similar standard applies to meats.

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Reconstitution Ratio The dried product must be regularly checked for the reconstitution value, in order that correct cooking instructions can be supplied to the ultimate user. A 50g sample is rehydrated and cooked in the prescribed manner and time. The cooking water is drained off, and the drained weight is calculated against the original dry weight, to give a reconstitution ratio. Culinary Report This test is combined with the previous ratio test, and a system of quality marking is implemented and recorded for flavour, texture and colour. The criterion of quality, overall, is that of the freshly cooked fresh vegetable. Bacteriological Tests Dried vegetables must not contain bacteria likely to be harmful to man, and the conditions of manufacture must be such that bacterial toxins cannot be formed. General bacterial counts must be low, and it is the microbiologist’s duty to ensure that factory and personnel hygiene are of a particularly high standard. The use of bactericidal hand creams by operators who handle the raw material - particularly meat and poultry products - is a very essential precaution. Bacteriological equipment required for elementary tests will comprise two incubators (maintained at 37” and 55”C), a good microscope and an adequate supply of Petri dishes for culturing. Meat Product Tests In addition to bacteriological tests, for meat products, there are special tests required to establish free fatty acids, fat content, peroxide value and salt content. Potato Product Tests In addition to the specific tests noted above, for vegetables, tests are made for reducing sugars in raw potatoes and in the dried product in its various forms, and also ‘blue value’ tests to evaluate free starch. Residual Oxygen Test When products are gas packed, tests are made to establish the percentage of residual oxygen in the pack. An Orsat apparatus is required for this, and the commercially accepted standard for residual oxygen in a nitrogen-flushed pack is 2 percent or less.

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Periodical Tests It is necessary that checks should be made at regular intervals for the presence of arsenic, lead and iron in dehydrated products. Metal abrasion is often a source of contamination in a product. This can arise from various items of plant and equipment, hence the necessity for using stainless steel in food handling machinery as far as possible, particularly at the 'wet' end of the process. Galvanized iron is sometimes resorted to for equipment in contact with the dry material, mainly on grounds of cost, but this should be kept to a minimum, in view of the contamination risk. Arsenic contamination can arise from flue gases, where a direct system of heat is used, but, if proper attention is paid to the use of correct fuels, and the hot air supply is kept clean, this should not give rise to serious problems. SPECIFICATIONS Finally, a set of specifications must be established by the technical staff, to cover every product to be handled. It is the duty of the laboratory staff to acquaint production personnel with these specifications,and then evaluate the production samples for compliance. Obviously, it is of paramount importance that there is no undue delay in carrying out quality control tests, and it is vital that these run continuously and concurrently with the 24 hour production schedule. Failure to maintain a round-the-clock check can mean considerable quantities of material being turned down as substandard because they do not meet the specification. This can be very costly to the dehydrator, as a salvage operation is not always easy or practicable. Liaison between quality control and production is, therefore, of paramount importance and this cannot be overstressed. Bacteriological specifications may well vary, according to the demands of the customer, but the following specification would be generally accepted as the norm.

Meat Products: Total Count 5000 per g. Escherichia coli - absent from 0.lg. Salmonella species - absent in 25g Vegetables: Total Count - 50,000 per g. Maximum Yeast and mould count: 200 per g. Bacillus coli - absent from 0.lg. Salmonella species: absent in 25g The complete specification, therefore, will appear under the following headings, against which the Laboratory will report on every batch of material:

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SPECIFICATION Culinary- Colour: Flavour: Texture: Blemish per 50g: S02ppm- Target: Maximum: Minimum: Moisture YO- Target: Maximum: Minimum: Peroxidase: Screening: Fat YO (Meats) Peroxide Value of extracted fat (Meats): Free Fatty Acids (Meats): Bacteria per g: Total Count: Escherichia coli: Bacillus Coli-Salmonella species Moulds/Yeasts per g: Arsenic ppm: Lead ppm: Iron ppm: Packing - Residual Oxygen YO:

Some major buyers of potato granules for use in snack foods require additional tests as under as well as those listed above: Maximum 1%-typically0.6% (1)Level of Glycerol monostearate Maximum 0.5Y0-typically0.3% (2) Tetrasodium pyrophosphate Maximum 25mg/kg-typically (3)Anti-oxidants (BHA and/or BHT) 15-20mg/ kg (4) Reducing sugar 2.0% 0.9 - 1.0 g./cc (uncompacted) (5) Bulk density Brabender Amylograph units (6) Rehydration Characteristics 550-1000 Packaging Specificationfor potato granules intended for use in value added products.

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Packaging (Factory)

All product packed in drums under nitrogen pending calloff. Drums: Gas tight construction with septum allowing head space analysis. Packed under a nitrogen atmosphere containing a maximum of 2% oxygen. Drum to be internally lacquered (Shipping) Sacks: 25kg per sack effectively sealed to prevent spillage. Shelf-life: Drums 12 months. Sacks 4 months. Holding temperature: Maximum 7°C.

Laboratory methods for determining moisture, rehydration viscosity, free fatty acids, and reducing sugars are appended in Tables 12.1,12.2,12.3 and 12.4 and are extracted from buyers’ specifications for bought-in material. Other tests are already outlined in this chapter.

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METHODS O F ANALYSIS

MOISTURE IN POTATO GRANULES BY VACUUM OVEN

I Apparatus 1. Balance accurate to f 0.001g. 2. Vacuum oven. 3. Vacuum pump capable of maintaining vacuum equivalent to 25mm Hg or less. 4. Aluminium moisture dishes, diameter 2-1/2in., height 5/8in., with slip-over cover. 5. Gas drying bottle containing concentrated H,SO,. 6. Desiccator containing drying agent. (Silica Gel self-indicating).

I1 Method 1. Weigh approximately 2g of potato granules into an aluminium dish previously dried at 98"-100"Cto constant weight, and cooled to room temperature in a desiccator. Duplicate test. 2. Place dishes with cocked lids (do not remove lids) in vacuum oven for 6hr at 70°C under vacuum equivalent to 25mm of mercury. When the correct vacuum pressure is obtained, the time interval of 6hr is then begun. At this time, air at the rate of 2 bubbles per second is allowed to enter the vacuum oven through a sulphuric acid drying bottle. 25mm of mercury means that the internal pressure in the vacuum oven will be 5mm of mercury above perfect vacuum. 3. Remove the dishes after tightening their covers. Transfer to the desiccator, and allow to cool to ambient temperature (approximately 10-15min)before weighing. 4. Calculate the moisture. I11 Calculations

Loss in weight x 100 sample weight 2. Duplicate samples should be within 5 0.1% moisture 1. % Moisture =

-

*^

EVALUATION O F POTATO GRANULE REHYDRATION CHARACTERISTICS USING THE BRABENDER VISCOGRAPH (VARIABLE SPEED) (COLD METHOD) I Apparatus 1. Brabender Viscograph, A. Set at 75rpm B. Fitted with a 2000cm per g sensitivity cartridge. 2. 500ml graduated cylinder. 3. Balance capable of weighing f 0.lgram. I1 Calibration and Checkout Procedures 1. Once per day the stirrer and the bowl should be checked with a gauge. A. Insert gauge into bowl. The pins should be so aligned as to go through the holes in the gauge. Note: Mis-alignment is noted by a clicking sound. B. The pins on the stirrer should also be aligned with the gauge. 2. If the sensitivity is changed, zero the instrument as follows: A. Place 500ml cold distilled water into bowl. B. Turn on the machine as noted in 111.1and 111.7. C. Loosen sensitivity cartridge lock nuts and turn the head until the pen reads zero without using any added weights. D. Tighten lock nuts while holding the sensitivity cartridge so that the pen is on zero. E. Run for approximately 5min to ensure the pen is on zero. 111 Procedure 1. Turn water and power on.

2. Set thermoregulator transport in centre position. (Leave in this position). 3. Put the toggle switch under coding heading into the (Fast Uncontrolled) position. 4. Check to make sure pen is working and set at zero. 5. Place the cleaned mixing bowl into position and add 400ml of distilled water at 4°C. 6. Add lOOg of potato granules and stir vigorously to wet all granules. 7. Within 30sec lower stirrer and lock pin in place. Then press red button to start. 8. Timer should be set for 10min. 9. Lower cooling probe. 10. The answer is reported by taking the chart reading after l0min.

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DETERMINATION O F CHLOROFORM EXTRACTABLE FATTY SUBSTANCES IN POTATO GRANULES

Apparatus Whatman Extraction Thimble 30mm by 100mm (41 by 123mm) Analytical Balance Cotton Wool Quickfit Round Bottom Flask 250ml. (500ml). Soxhlet Extractor Soxhlet Condenser Isomantle Drying Oven 100°C Desiccator & Desiccant Reagents Petroleum Spirit (40"- 60°C). Method 1. Weigh accurately, approximately 20g (50g) sample into an extraction thimble 30 by lOOmm (41 by 123mm). 2. Plug with wad of cotton wool (fat-free). 3. Weigh accurately a clean dry 250ml(550ml) Round Bottom Flask. 4. Pour 150ml (300ml) Petroleum Spirit into the flask. 5. Place the thimble containing the sample into a Soxhlet extractor. 6. Connect the Soxhlet extractor to the flask. and a condenser. 7. Place in an Isomantle. 8. Extract for at least 4hr. 9. Distil off Petroleum Spirit. 10. Place the flask in the drying oven for lhr. 11. Remove and place in the desiccator to cool. 12. Reweigh the flask. Calculation % = Extractable Fat =

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Increase in weight of flask x 100 Weight of Sample

REDUCING SUGARS I N POTATO GRANULES USING DINITROSALICYLIC ACID REAGENT Purpose To enable reducing sugar contents of potato granules to be determined. Modifications in weights and dilutions allow its application to other food products: Principle Sugar is extracted from the sample using cold water (thus minimising interference from protein and fat). A filtered aliquot is then heated with dinitrosalicylic acid reagent. A coupling reaction occurs and produces an orange red colour, which can be measured at a wavelength of 580mm using a simple filter colorimeter. Apparatus Boiling water bath Test tubes approx 25 by 150mm 5ml Pipettes Measuring cylinder Magnetic stirrer Colorimeter with appropriate filters Beakers Graduated flasks Funnels Filter papers Test tubes Balance Reagents DinitrosalicylicAcid Reagent l g of Dinitrosalicylic acid is dissolved in 20ml of Sodium Hydroxide solution (1.6gpellets in 20ml water). Reaction is complete when the dinitrosalicylic acid has all changed colour. Then add 50ml water to 20g Potassium Sodium (+) Tartrate. Dissolve by gentle warming if necessary then dilute to 100ml with water. Dilute DNSA Reagent Dilute 2 volumes of DNSA reagent with 3 volumes of water. Standard Glucose Solution Prepare fresh standard solutions containing lOOmgm of dried glucose per 100cm of water. This solution contains lmgm Glucose per ml.

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Method (1) Weigh out 5g (approx.) of potato granules into a clean 400ml beaker. Record the weight of sample. (2) Add the sample to 250ml f 2mls of distilled water in a 400ml beaker. (3) Stir on a magnetic stirrer or a minimum of 15min. (4) Remove beaker from stirrer and allow contents to settle. (5) Decant the upper layer through a No.2 filter paper pouring back the first 10-20ml of filtrate into the filter. If filtrate is not clear pour back until a clear filtrate is obtained. (6) Pipette 5ml of filtrate into a boiling tube. (7) Add 5ml of dilute dinitrosalicylic acid solution. (8) To a second tube add 5ml distilled water and 5ml dilute dinitrosalicylic acid solution. This is the blank solution. (9) Place the tubes in a vigorously boiling water bath for lOmin, making sure the level of the contents in the tube is at least one inch below the surface of the boiling water. (10) Remove the test tubes and cool in cold water. (11)Transfer the cool blank solution to a clean cuvette and using a 580 filter, set the colorimeter to zero. (12) Replace the blank solution with the sample solution and read the optical density (OD) on the absorbance scale. (13) From a standard curve calculate the sugar content of the potato granules. Preparation of standard Curve Into tube (1)pipette 5ml water 4.5ml water and 0.5ml glucose solution 2)pipette (3)pipette 4.0ml water and 1.0ml glucose solution (4)pipette 3.0ml water and 2.0ml glucose solution (5)pipette 2.0ml water and 3.0ml glucose solution Draw a graph of OD against concentration of glucose solution.

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METHODS FOR MICROBIOLOGICAL ASSESSMENTS Specificationsrequire the following to be determined:

Total Viable Count @ 30°C E. Coli Coliforms Yeast and Moulds B. Cereus St. Aureus Salmonella Cl. Perfringens

100,000 per gr. m a (500,000 for onions) 10 per gr. max. 100 per gr. max. 1000 per gr. max. 100 per gr. max. 100 per gr. max. Absent in 25 gr. 100 per gr. (not always)

It is customary to use ready prepared selective Agars, and ’Oxide’ has been suggested throughout. The organisms under examination will have distinctive characteristics and for routine work this should prove satisfactory. Over recent years a piece of equipment called a ‘Stomacher’ has been developed and its use has been widespread for resuscitation of bacteria. However it relies on the use of pre-sterilized plastic bags which cannot be recycled. As these may not always be available overseas, the traditional method of preparation is submitted. It must be stressed that all glassware and media must be sterilized unless stated otherwise in the method. Media to be autoclaved at 121°C(15 p.s.i.) for 15 minutes, and glassware (pipettes and petri dishes) to be dried at 121°C for a minimum of 2 hours. Disposable pre-sterilized petri dishes are available in the U.K normally. This reduces the likelihood of cross-contamination but cost and availability may preclude their use in some overseas locations. Thought will have to be given to sampling frequency - say, every 2 to 4 hours or on a weight basis, say, every 250 to 500kg batch, according to the overall production. Do not ‘bulk’ samples and, say, carry out daily or weekly assessments, since rogue high results may put the product out of specification and give a totally distorted view. More and more emphasis is now being placed on microbiology and regular structured testing will give valuable pointers as to the cleanliness of plant and soundness of raw material. Outbreaks of food contamination in recent years have highlighted the importance of microbiology in the factory. Separate methods for all the above assessments follow.

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SAMPLING A N D SAMPLE PREPARATION

Reagents Peptone Water Powder (CM9 - Oxoid) 0.1% Peptone Water 180ml in 200 ml medical flat bottles 0.1% Peptone Water 9ml in Universal media bottles Reagent Preparation Dissolve lgm of peptone water (CM9) in 1 litre distilled water and dispense either 180ml or 9ml per bottle as given above. Autoclave for 15 minutes at 15psi. Sampling Samples should be taken using clean equipment and cross contamination must be avoided. This is most easily effected by using a polythene bag which is inverted over the hand, the product is grasped by the ‘gloved’ hand and enclosed by re-inverting the bag. Sample Preparation Place part of sample into grinder and mill, reject, repeat operation twice, the third part is retained. Transfer 20gm into 180ml of sterilized peptone water using a flamed spoon/spatula, mix well, allow to stand for at least 20 minutes to resuscitate the bacteria. A 10%homogenate has been produced i.e. lml contains 0.lgm. Further dilutions are obtained by taking lml and adding to 9ml sterilized peptone water as shown below: 20gm + 180ml= 10% lmllO% + 9ml= 1% lml1% + 9ml= 0.1% lml 0.1% + 9ml= 0.01% and so as may be required

lml contains O.lgm or x 10 lml contains 0.01 g m or x 100 lml contains 0.001gm or x 1,000 1ml contains 0.0001gm or x io4

NOTE (1) 10%homogenates can be obtained by using lOgm + 90ml,25gm + 225gm or 5gm + 45ml if desired. (2) When moving from dilution to dilution a fresh clean sterilized pipette must be used.

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TOTAL VIABLE COUNT (TVC)

Media Plate Count Agar (CM463B - Oxoid) Peptone Water (CM9 - Oxoid) Media Preparation Add 23.5gm plate count agar to 1 litre of distilled water, dispense 9ml into universal bottles and sterilize for 15 minutes at 15psi. When cooled the agar will solidify and can be stored in this state for several months. For use the agar should be melted in a boiling waterbath and allowed to COO^ to 45-50°C. Method Take the 0.1% dilution of the sample as prepared under sample preparation and pipette 1.0ml via a sterile petri dish, add 9mls of cooled melted agar and mix by gently swirling the petri dish (or plate). Allow the mixture to set, place upside down in the incubator at 30°C and leave for 2 days. After this time the number of colonies are counted and multiplied by 1,000 to give a count per gm. If counts in excess of 300,000 per gm i.e. 300 per plate are expected then the 0.01% dilution should be used. The dilution should be increased so that the count does not exceed 300 per plate. Initially it may be necessary to carry out several dilutions in order to ascertain the range of results. E. (ESCHERICHIA) COLI Media MacConkey No 3 (Cm115 - Oxoid)

Media Preparation Dissolve 51.5gm of agar in 1 litre distilled water, by bringing to the boil, dispense 10mls into universal bottles, sterilize for 15 minutes at 15psi. When cooled this media will set, prior to use melt in a boiling water bath and allow to cool to 45-50°C. Method Pipette lml of the 10% homogenate onto a sterile petri dish, add lOml of cooled, melted agar, swirl to mix and allow to set. Incubate upside down at 44°C for 24 hours. Count only the red/purple colonies and multiply by 10 to give the number of colonies per gm.

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T O T A L C O L I F O R M BACTERIA Violet Red Bile Agar (Cm107 - Oxoid) Media

Media Preparation Dissolve 38.5gm in 1 litre of distilled water by bringing to the boil. Allow to cool to 45-50°C. The media can be held at this temperature for a maximum of 3 hours. Do not autoclave this material. Method Pipette lml of the 10% homogenate onto a sterile petri dish, add lOmls of freshly prepared cooled agar, swirl to mix and allow to set. Incubate upside down at 37°C for 48 hours. After incubation count the red colonies and multiply by 10 to give count per gm. Y E A S T S AND MOULDS Rose Bengal Agar (CM49 - Oxoid) Media Chloramphenicol Supplement (SRT8 - Oxoid)

Media Preparation Dissolve 16gm of agar in 500ml of distilled water by bringing to the boil. Sterilize at 121°C for 15 minutes and allow to cook to 50°C.Add the contents of 1 vial of supplement which has been dissolved in 2ml of acetone. Pour 10ml of agar onto sterile plates and store at 5°C. Method Pipette 0.2ml of the homogenate onto a prepared plate and spread over the surface of the agar using a sterile glass spreader. The spreader can be sterilized by flaming between use. The plate should be incubated upside down at 22°C -t 2°C for 4-5 days. Inspect the plate daily after 3 days as vigorous mould growth may make counting difficult. Count moulds (rough, hairy, fungal appearance) multiply by 50 to give number of moulds per gm. Count yeasts (smooth surfaced colonies) and similarly multiply by 50.

24%

BACILLUS CEREUS Media Bacillus Cereus Agar-(CM617 - Oxoid) B.C. Supplement-(SR99- Oxoid) Egg Yolk Emulsion-(SR47- Oxoid) Media Preparation Dissolve 20.5gm of agar in 475m1 distilled water by bringing to the boil. Sterilize at 121°C for 15 minutes. Cool to 50°C and asceptically add the contents of 1 vial of B. Cereus supplement which has been rehydrated with 2mls of sterile distilled water and 25ml of Egg Yolk Emulsion. Mix well and pour 100mls onto sterile petri dishes. Store plates at 4". Method Pipette O.lml of 10% homogenate onto a prepared place and spread using a sterile spreader. Incubate at 37°C for 24 hours. Examine plates for peacock blue colonies surrounded by egg precipitate of the same colour. Leave for a further 24 hours at room temperature (16°C) for all colonies to develop. Count colonies and multiply by 100 to give count per gm. STAPHYLOCOCCUS AUREUS Media Baird-Parker Medium (CM275 - Oxoid) Egg Yolk-Tellurite Emulsion (SR54 - Oxoid) Media Preparation Dissolve 63gm of Baird-Parker medium in 1 litre of distilled water, sterilize for 15 minutes at 121°C.Allow to cool to 50°C and asceptically add 50ml of Eggtellurite emulsion, mix well. Pour approximately l.Omls onto sterilized petri dishes and allow to set, store prepared plates at 4°C. Method Pipette 0.1 ml of the 10% homogenate onto a prepared plate and spread over the surface using a glass spreader. Incubate upside down at 37°Cfor 24 hours. Count black shiny convex 1.0-10.5mm diameters st. Aureus colonies, multiply by 100 to give number per gm. If no colonies appear incubate for a further 24 hours.

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SALMONELLA Media Brilliant Green Agar SS Agar Selenite Broth Sodium Biselenite

(CM 263 Oxoid) (CM 99 Oxoid) (CM 395 Oxoid) (LIZ1Oxoid)

Media Preparation (a) Brilliant Green Agar: Dissolve 50gm of agar in 1 litre of distilled water by bringing to the boil, sterilize at 121°Cfor 15 minutes. (b) SS Agar: Dissolve 63gm of agar in 1 litre of distilled water by bringing to the boil. DO NOT STERILIZE. Allow to cool to 50°C and pour into sterile petri dishes. (c) Selenite Broth: Dissolve 4gm of sodium biselenite in 1 litre of distilled water, add 19gm of selenite broth powder, dissolve, fill into containers to 5cm and sterilize for 10 minutes in a boiling water bath. Method Prepare a 10% homogenate of 25gm of sample in 225m1 of peptone water and incubate at 37°C for 24 hours. Take lOmls of the homogenate after incubation and add to Selenite Broth, incubate for 48 hours at 42°C. Streak plates containing Brilliant Green Agar and SS Agar after 24 and 48 hours ex Selenite Broth. Incubate plates at 37°Cfor 24 hours. Salmonella will appear as pink colonies on BG agar and transparent colonies with black centres on SS agar.

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CLOSTRIDIUM PERFRINGENS Media Perfringens Agar Supplement A Supplement B

(O.P.S.P.)-(CM543- Oxoid) (SR76 - Oxoid) (SR77 - Oxoid)

Media Preparation Dissolve 22.8gm of agar in 500mls of distilled water by bringing to the boil. Sterilize for 15 minutes at 121"C,allow to cool to 50°Cand asceptically add the contents of one vial each of supplements A and B which have been rehydrated by the addition of 2ml distilled water. Mix well and pour into sterile plates. Method Pipette lml of the 10% homogenate onto a prepared plate and spread with a sterile spread. Further dilutions may be used if the levels are high. Incubate anaerobically for 18-24 hours at 37°C (a suitable gas jar and gas generating kits are available from Oxoid - HPOllA, BRO38B, BRO42A and BRO55A). Count large black colonies and multiply x 10 to give a count per gm.

25 I

13

The Economics of Dehydration The food manufacturing industry, in general, has always been a highly competitive business but no branch of it is more so than dehydration. Profitability hinges on so many factors, some of which are outside the manufacturer’s control. One of the main hazards in this context is that of climate. Total solids in raw materials are the key to a viable operation, and, if these are low, due to wet growing conditions, the plant throughput is going to be seriously reduced, often with disastrous effects on costs. The evaporative capacity of the dryers, in these circumstances, will be strained to the limit, with perhaps a 20 percent reduction in weight of end-product, after additional labour, fuel and overhead costs have been thrown in to what is inevitably a losing battle. Studies have been made of weather statistics in the UK, over the period from planting to early maturity of potatoes and root vegetables, and total solids appear to be affected by the amount of rainfall and hours of sunshine in this period, ie, from early May to late September. Given low rainfall, and a good record of hours of sunshine in these months, the total solids in these vegetables are usually high and subsequent deterioration of weather conditions in the later part of the year, whilst the crop is still in the ground, does not appear to materially affect the balance of moisture content and solids characteristics.

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Where a wide variety of vegetables is being handled, great care has to be exercised in dovetailing the cropping programme, so that there is no hiatus at any time of the year, which would create costly 'downtime' for the plant. The calling off of tonnage against contract purchases must also be done at a rate of intake which will give the factory a safe margin of stock level if bad weather interferes with harvesting or lifting of crops. With potatoes and root vegetables in silos, a yard stock to keep the plant running for up to four days is a workable and wise precaution, provided that the silos are equipped to give adequate protection against the weather. Where controlled temperature and humidity storage is available, a much larger buffer stock is possible but the cost of operating this, including weight loss and rot wastage, must be taken into account. Onions for example can lose 15-20 percent in weight, even in ideal conditions. From the factors outside the control of the processor, we can now turn to the absolute essentials, which are controllable, for conducting a viable dehydration business. HOURS O F OPERATION It is essential that the plant be operational 24hr per day, six days per week. Eight, or sometimes twelve, hours of the seventh day are required for plant cleaning and maintenance, and four hours are needed to heat up the plant for the ensuing week. In effect, therefore, dehydration becomes a seven day operation. The mechanical and electrical maintenance at the weekend is vital to the profitability, because downtime, arising from any breakdown, is extremely costly. This could amount, with a medium size plant, to perhaps US$700-1000 per hour, according the level of production at the time. LENGTH O F SEASON Any length of shutdown in the year is a cost factor, which must be carefully considered and budgeted for during the months of actual production. This, again, is an insupportable burden if the period of shutdown is long. Normally, it should be possible to process vegetables for about 10-11 months in the year, limiting the shutdown period to 5-8 weeks. Basic wages and salaries, and all standing charges, will have to be covered, in this period, by a weekly contribution in the costing system whilst the factory is in operation, just as, in the same way, annual and statutory holidays are provided for. A major plant overhaul is always undertaken annually and it is essential to have an ample number of fitters and electricians available for a concerted and sustained effort over this period.

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RANGE OF PRODUCTS This should always be as wide as the limitations of the plant and premises will allow. Without a broad-based programme, the dehydrator can never hope to produce economically. It is almost impossible to specialise, as it is in some other parts of the food industry. For example, it is not a viable proposition to specialise only in potato dehydration, although the raw material may be available nearly all the year round unless there is diversification into a large volume of potato-based valueadded products, snack and impulse foods. In the context of our industry, potato is a low priced product, and equally there is a low profit margin on whatever form the dehydrated potato takes. The large potato processors in America solve this problem by diversification in the format of processing. Usually, they buy the potato crop ‘as lifted’ and grade it in their plants. The largest tubers are sometimes foil wrapped and sold as ’bakers’ through the retail chain stores. These are bought by the American housewife for baking in their jackets. They next grade out a top premium grade potato of medium size for prepacking - again selling to the chain stores. The third grade, perhaps not quite bright enough in external appearance to fetch the prepack premium, is diverted to the frozen French Fries line, or to potato crisp production. Eventually, the culls from the foregoing grades go to the dehydration plant for the manufacture of flakes and granules. The exterior imperfections in the raw material, at this stage, are of little consequence in this process, which has built-in facilities for removing them. By intensive diversification of processes and outlets, therefore, it is possible to specialise with potatoes but, where only dehydration is concerned, such specialisation is impossible for purely economic reasons. A rotation of vegetables is required, therefore, to keep the plant operational for 10-11 months of the year, and it is possible that, in some locations, this range may extend to ten different varieties. It is important, however, in the interests of costs, that the production run on any one variety should be unbroken for at least 3-4 weeks. Broken runs, or production runs terminating midweek, are expensive in the context of lost time in cleaning down and running off dryers before another product can be processed. It is impossible to clean down a complete production line properly in less than eight hours, and if this has to be done midweek, the loss of profitability will be obvious. STAFF DEPLOYMENT Economy in manual operations is essential and, wherever the capital cost of a machine, which displaces hand labour, can be seen to be recoverable within a reasonable time - say one to two seasons - then that machine should be

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installed, provided the staff have the requisite skills to operate and maintain such machines. Areas in which automation is becoming more and more essential are those of raw vegetable preparation, and dry material sorting and selection. Electronic equipment is rapidly providing the answer to many of these problems, and a realistic capital plant investment policy must be adopted by the dehydrator to ensure he keeps abreast of all this development. BY-PRODUCTS A N D THEIR OUTLETS It is inevitable that there will be some quantity of downgraded product and by-products arising from the plant in the course of a season, and it is important to find satisfactory outlets for these at an economic price. Some dried vegetables, which are downgraded for reasons of colour, texture or general substandard appearance, usually find ready acceptance in powder form, as this tends to present a more homogeneous product. A Turbo mill is, therefore, a necessary adjunct to the drying plant, for the purpose of dealing with such material. Reject materials from sorting machines and selection belts usually finds outlets in compounding mills for animal foods. Wet vegetable waste should also be disposed of to the best advantage, and this can be converted to animal food if it can be dried cheaply by any waste heat from the plant. A resourceful plant engineer should be able to solve this problem without any great expense on plant or operating cost. By-products and substandard material must at all times be taken into the initial stock at low cost - any writing down of the value being done immediately quality control has designated the product as ’underspecification’. The carrying forward of such stocks at full standard cost until the end of an accounting period, perhaps arising months later, can create severe financial embarrassment when the ultimate stock evaluation comes to be made. Salvage operations are always expensive, therefore it is important to have ready outlets at hand and to dispose of substandard material as it is discovered. COSTING A comprehensive weekly costing system should be established to arrive at a basic factory cost for each product. The standard cost system is undoubtedly best for the dehydrator, and, on the evaluated factory cost, the selling cost can be calculated, and the ability to maintain the factory standard cost will be a measure of the plant’s efficiency. Any profit or loss against standard is brought forward into a reconciliation account and balances set against the company’s annual financial accounts.

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The weekly cost analysis usually takes the following form:

Raw Materials Weekly usage is calculated by evaluating opening and closing stocks, and cost is calculated by establishing a ’cost average’ each week. That is, each week’s intake at a particular price level, is integrated with the carry-forward stock from the preceding week, costed at that week’s price level. Price fluctuations are, therefore, taken into account immediately, and a true cost is established for each week‘s production. The ’cost average‘ system should be applied to all materials used in production. Additives and Process Chemicals These comprise chemicals which remain in the end-product as a constituent, or chemicals used merely in the treatment of vegetables. Sugar, milk powder and glycerol monostearate would come into the former category, and caustic soda, sulphite and sodium carbonate would be designated as process chemicals in the latter category. Hourly usage is invariably logged in the Process Supervisor’s records, therefore this is a simple costing calculation, which is also checked with opening and closing stocks. Fuel Weekly records should be kept for metered fuels, such as gas, and weights of solid fuels and oil, and usage measured from these. A weekly cost average should be calculated, if there are any price fluctuations on fuel purchases. Wages The total factory wages and salaries are computed from the payroll, and their apportionment to the various products made is either the function of the Cost Accountant or the Works Manager. Overheads An estimated weekly sum should be charged to cover rents, rates, depreciation, office administration and expenses, insurance, quality control and general factory expenses. As the actual accounts for these items are received, any excess or deficiency in the estimated weekly provision is corrected through a reconciliation account. Maintenance An arbitrary estimated charge per kilo weight of finished product is brought

into the weekly costing and, again, correction is applied as maintenance accounts are received. It is good policy to charge maintenance at a rate which

256

will accrue an increasing credit balance in the reconciliation account, as the season proceeds, so that at the end of the processing season, an adequate balance has been built up to finance the annual plant overhaul during the shutdown period. Conversely, maintenance may be costed as a fixed percentage of the capital cost of the plant (See Table 13.2) Consumable Stores These items comprise all purchases of materials ancillary to production, such as lubricants, adhesives, paint, cleaning materials, industrial clothing, etc. Again, an allowance related to weight of throughput is made, with reconciliation being made as factual expenditure is known. Water The actual metered quantity is charged to the weekly production. Electricity The cost of power and light is calculated from meter readings, and the apportionment to the various products, or departments, is made as for overheads. Unpacked Cost With the above information, and costs apportioned to the relative products made in the week, an 'unpacked cost' is computed. The main costs are factual, based on known usage and value, and the arbitrary charges per pound of endproduct, such as maintenance, overhead, consumables, etc, are corrected continuously in the reconciliation account, as the true costs become known. Packaging The specific packaging materials are charged to each product in its particular cost column, and after this addition has been made, a 'packed' cost, or 'ex factory' cost is calculated. This can now be evaluated against the previously fixed 'standard' cost, to measure the efficiency of the factory's operation. Selling Cost and Transportation Having established the true factory cost and its relation to the standard cost, the operations of selling, promotion and shipping have to be considered. The dehydrator will have to decide whether, in the main, he is going to sell his production in bulk packs to wholesale, catering and manufacturing buyers, or specifically to retail outlets. Sales budgets will vary widely in accordance with this decision, as will promotion budgets and transport costs, and it is, therefore, not possible to elaborate in this chapter on this area of economic practice.

257

Financial Assumptions for Feasibility Studies for New Projects To illustrate these assumptions for an overseas Study, the following data will have to be collated by a team consisting of a food technology consultant, a consultant horticulturalist, a plant and machinery design engineer, an architect with intimate knowledge of building design in the region of operation, and a corporate finance consultant To arrive at a format for the financial projections a hypothetical project is taken as an example, located in, say, Southern Europe. In this case the farming would be on the 'estate' pattern on irrigated land, mainly controlled by the investors in the project. Fig. 13.1 shows the best cropping time for a range of 6 different types of vegetables, and Fig. 13.2 the possible processing times. Realistically the processing period would be limited to about ten months when the factory is on full stream, to take account of annual shutdown, holidays, etc, but this shut-down period would be integrated with the cropping programme at such times when harvested crops (onions and carrots) could be stored over the period of plant overhaul, in controlled temperature conditions. Also the programme would need to be flexible to meet the market conditions at the time of operation. Onions, for example, could be increased in tonnage, and other vegetables decreased. Fig. 13.1, in fact, indicates what vegetables have already been grown in trials and for commercial fresh markets in the region, and is only a pointer to the range available for processing. The Pre-Production period is assumed to be 9-12 months, during which time construction work could be carried out, indents for machinery and other equipment would be progressed, horticultural programmes would be finalised with the growers, and towards the end of the period supervisory staff would be selected and engaged. The plant would be operated at 60 percent capacity for Year 1,80 percent in Year 2 and 100 percent in the third, fourth and fifth years. In the Financial Assumptions, the farm equipment would be financed by the growers, and these costs are quite separate from the factory capital expenditure. All farm costs, however, must be calculated in the Study to arrive at a factory-gate price for the raw material. Fig. 13.2 also indicates that two multi-stage band dryers are envisaged in order that two vegetables may be processed simultaneously at periods where harvesting times overlap. This level of drying capacity would be needed for an annual putative throughput of 30,000 tonnes of raw vegetables in any case. In the Study all financial calculations would be in local currency but, for the purpose of this example, all calculations have been converted to €Sterling.

258

259

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0

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DRYER 1

DRYER 2

(1) Financial Assumptions and Estimates (a) Cost of Raw Materials per tonne (b) Volume of Raw Materials per season (c) Cost of production - raw materials per annum (d) Wages and Salaries - job description, numbers and remuneration. (e) Factory Overheads - Distribution costs, Fuel, Power, Water, administration, insurance, shut-down provision, consumable stores (f) Repairs and Maintenance: based on 5 percent of cost of plant (g) Depreciation: Buildings 5 percent: Machinery 10 percent: Transport 25 percent (h) Other Related Costs and Contingencies (i) Total cost of Production: Raw Material, Labour, Overheads, Maintenance, Depreciation, Other Costs (j) Sales Pricing Structure, based on current market values. (k) Loan Schedules: Export Credits, Foreign Currency Loans, Local Loans, Bank Overdraft, Repayment Schedules. (2) Projected Cash-Flow Table 13.1 shows this with figures in Esterling, based on the assumption that the project is financed with equity at €3m., an Export Credit Loan* of E3m. and bank overdraft of €789,000. These figures are arbitrary and are purely for a hypothetical project which purports to process 30,000 tomes of raw vegetables per annum at full capacity. ‘ECGD Loan against purchase of plant from UK.

(3) Projected Profit and Loss Projections Table 13.2 shows the profit and loss balances for the production years one to five. The pre-production expenses are amortised over the five productive years, as is interest.

26 I

The table shows a manufacturing loss in years 1and 2 but indicates a profit in years 3,4 and 5. (4) Projected Balance Sheets Table 13.3 shows that in the 5th Year the Term Loans are paid off and a small overdraft remains. Accumulated profits stand at E944,325.

Table 13.1 Projected Cash Flow € 0 0 0 ~ Year

Cash Flow Equity Foreign Loan Local Loan Net Profit + Depn + Amortisation

PreProduction 1 EOOOs 60%

262

4 100%

100%

(441)

(164)

367

494

689

739 243

738 574

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738 1232

683 1372

918 918 (620) (620)

918 918 (344) (964)

918 918 188 (775)

918 918 314 (462)

917 917 455 (7)

5

6194 220 300

450 425 7589

Cash Surplus (deficit) Accumulated Cash

3 100%

3000 3800 789

7589

Cash Outflow Capital cost of Equipment & Buildings Vehicles Pre-Op Expenses Working Capital (Stock of Raw Materials & Debtors) Loan Interest during Construction Repayment of Loan

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Organisation of Project Control Figure 13.3 indicates the chain of command for the complete project incorporating the horticultural management. The latter element is included in this example in view of the involvement of the local directors and shareholders in the estate farming side of the project. Such collaboration is not always feasible with some overseas projects and here the raw material is contracted for with a multiplicity of smaller growers, whose farms are visited throughout the growing and harvesting period by fieldsmen employed by the factory these fieldsmen being under the supervision of the senior horticulturist of the factory. Estate farming and the participation of the growers with the financing of the processing plant sometimes works very satisfactorily but not always. The intending processor must be the final arbiter of the system of raw material procurement which suits the local situation most effectively. Figure 13.4 shows the Management Organisation Chart where the processing factory is independent of the farming operation and management, and where the vegetables are purchased from several sources on contracts which are entered into seasonally. In this instance the contract conditions and supervision of the crops are supervised by the agronomist, assisted by his fieldsmen - all under the overall control of the factory general manager. Several photographs appear in this chapter illustrating the many functions undertaken by the technical consultant and horticulturalist in evaluating the infra-structure, the cropping potential of new regions, availability of labour and services, before Feasibility Studies can be prepared. These Studies have ranged over four Continents - South America, Western and Eastern Europe, India, The Middle East and Africa - but the illustrations indicate only the very early steps in a vastly complicated exercise - that of collaborating with seed breeders, seed merchants, organising field trials, logging fertiliser, herbicide and pesticide treatment, irrigation trials and harvesting yields. In the course of these exercises, the services of the local Horticultural Institutes and their staff are essential, and usually invaluable otherwise the project leaders would have to become permanent expatriates for two or three years, as horticultural problems are not solved in one growing cycle. It is only then that attention has to be focused on the viability, or lack of same, which has to be assessed by an equally convoluted process. Some of the illustrations in this chapter would appear to show less than encouraging horticultural prospects, and whether one is looking at State farming, estate farming, or husbandry more closely related to oxen-power, or irrigation methods centuries old by application of an ancient Archimedes screw made by a village blacksmith from oil cans with hand-fashioned blades

264

turned by a small boy who lifts water to the land by dipping the end of the tube into the waters of the Nile or the Ganges, the task of converting all this into a thriving agro-industrial enterprise is not a job for the faint-hearted. It has a success rate about on a par with panning for gold in the out-back but, when it does come off, as it has been known to do, the satisfaction of beating the odds, not only physical but also bureaucratic, is tremendous. It is perhaps one of the few occupations one rarely retires from. After all, where food is concerned, there is never enough time to look after the World’s needs. There will always be millions who never have sufficient, and the task of turning the desert into a granary will always be a challenge. However perhaps we should learn a lesson from the past. It is not always massive machinery which will achieve this, nor the bull-dozing of forests. A politician once had the idea that this was the only way to produce much wanted groundnuts in East Africa. The buI1-dozers and tractors reversed the agricultural ’miracle’ and turned fruitful green land into a desert dust-bowl. A journey across the African continent would have demonstrated to the ’experts’ that in the tropical rain forests of West Africa, from Gambia down to the Cameroons, the peasant farmer in every village in an area covering a million square miles, produced the greater part of the world’s supply of groundnuts by hand cultivation in small clearings out into the tropical rain forest with a machete. The micro-climate and infra-structure needed for the crop was sacrosanct and nurtured by these small farmers, and the joke was on the bureaucracy who was quite sure it could be ’estate farmed’. Today, one has to keep a sense of balance and approach any new horticultural or agricultural project with a knowledge of history and tradition and not be blinded by today’s availability of high technology, and in the developing countries one has to get the blend of old and new just right to achieve success.

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Conclusion The author has endeavoured to describe the various processes used in the manufacture of a modest range of dehydrated foods, and to bring the operation through to the factory warehouse. At this point, it is hoped that some enthusiasm has been inculcated to promote and further the spread of convenience foods in world markets, which many, who have pioneered in the industry, firmly believe are there for the seeking.

269

Index abrasive peelers, 49 additives and process chemicals, 52 air lift dryers, 83 air separation, 228 apples, 170 cutting, 172 dryers, 174 preparation, 172 ratio, 174 resulphuring, 174 sulphuring, 174 apricots and peaches, 175 cutting and pitting, 175 drying, 176 grading, 176 peeling, 181 processing, 176 ratio, 182 resulphuring, 182 sulphuring, 182 sweating, 182 varieties, 175 beef, mutton, ham, oxtails, kidneys, 216

beetroot, 125 blanching, 125 dicing, 126 dryers, 126 peeling, 126 process, 126 ratio, 126 sizing and selection, 126 trimming and inspection, 126 varieties, 125 bin dryers, 81 blanchers, 51 hot water, 51 steam, 52 boilers, 31 bulk packaging, 229 by-products and their outlets, 255 cabbage, 129 blanching, 129 cutting, 129 dryers, 131 packaging, 132 process, 129 ratio, 130

27 I

272

sizing and selection, 129 trimming, 129 varieties, 130 washing, 129 cabinet dryers, 65 carrots, 134 blanching, 135 dicing, 135 drying, 135 nitrogen packing, 135 packaging, 135 peeling, 135 process, 135 ratio, 136 sizing and selection, 135 starch dip, 135 trimming, 135 varieties for dehydration, 134 celery, 139 blanching, 140 cutting, 140 dryers, 141 process, 141 ratio, 141 sizing and selection, 141 trimming, 140 varieties, 140 chicken granules, 214 cooking, 214 drying, 215 fleshing, 214 mincing, 215 mixing, 215 packing, 216 ratio, 216 consumable stores, 257 contracts, 22 conveyor band dryers, 76 conveyors, 53 costing, 255 cutters, 39

green beans, 123 blanching, 124 dryers, 124 process, 123 ratio, 124 varieties, 124

dehydrated apples, 171 dehydrated soups, 219 basic vegetable soup mix, 221

ham, see beef, mutton, ham, oxtails, kidneys heat rising plant, 31, 32

formulation, 220 ingredients, 220 method, 221 dehydration of fruits, 169 dehydration of meat, raw materials, 213 double tunnel dryers, 67 drum dryers, 112 dryers, 66 air lift, 82, 83, 91 bin, 81 cabinet, 66 conveyor band, 73,80 double tunnel, 67 drum, 90,114 fluidised bed, 84 foam mat, 91 freeze, 87, 88 pneumatic ring, 83 rotary, 84 spray, 192 thermal venturi, 34 three tunnel, 69 tunnel, 67 vacuum, 85 effluent, 35 electricity, 30 electronic colour sorting, 227 fluming, 29 foam mat dryers, 91 freeze dryers, 87 fuel, 32,34,35

combined systems, 34 direct system, 32 indirect systems, 33 hot water blanchers, 51 hours of operation, 253 intake staff, 26 kidneys, see beef, mutton, ham, oxtails, kidneys laboratory analytical tests, 234 bacteriological tests, 236 blemish count, 235 culinary report, 236 meat products tests, 236 moisture, 234 periodical tests, 237 peroxidase test for vegetables, 235 potato product tests, 236 reconstitution ratio, 236 residual oxygen test, 236 sulphur dioxide, 234 laboratory staff, 233 labour requirements, 23 leeks, 143 blanching, 143 cutting, 143 dryers, 143 ratio, 144 sizing and selection, 144 trimming and washing, 144 varieties, 144 length of season, 253 lye peeling, 48 maintenance staff, 23 maintenance, 23 mutton, see beef, mutton, ham, oxtails, kidneys onions, 151 cutting, 160 dryers, 161

packaging, 158 peeling, 155 process, 156 ratio, 156 sizing and selection, 154 topping and tailing, 154 varieties, 152 overheads, 256 oxtails, see beef, mutton, ham, oxtails, kidneys packaging, 257 peaches, see apricots and peaches peas (fresh), 146 additives, 149 air freeze drying, 149 blanching, 150 cooling, 150 drying, 150 inspection and scarifying, 149 packaging, 150 process, 149 quality grading, 148 ratio, 150 sizing and selection, 150 varieties, 147 vining, 148 washing and cleaning, 147 peelers, 45 abrasive, 45 flame, 45 lye, 45 steam, 45 peeling, 45 plant location, 21 pneumatic ring dryer, 83 potato cubes, 115 drying, 115 process, 115 ratio, 115 sizing and selection, 116 varieties, 117 potato flakes, 113 drying, 113 packing, 113

273

process, 113 ratio, 113 varieties, 113 potato granules, 108 drying, 108 process, 108 ratio, 108 varieties, 108 potato starch, 120 powder screens, 110 power, 30 prunes, 187 artificial drying, 187 drying, 187 process, 189 ratio, 191 range of products, 254 raw materials, 256 selection, 225 selling cost and transportation, 257 silos, 29 size grading, 225 specifications, 237 spray dryers, 192 staff deployment, 23 intake, 26 laboratory, 254 maintenance, 27 warehousing, 27 steam blanchers, 52 steam peeling, 45 swede and white turnip, 165

274

blanching, 165 dicing, 165 dryers, 165 packaging, 165 peeling, 165 process, 165 quartering and trimming, 165 ratio, 165 sizing and selection, 165 varieties, 165 washing, 165 thermal venturi dryer, 83 three tunnel dryer, 67 tomato powder, 195 drying, 195 evaporating, 195 packing, 195 process, 195 pulping, 197 ratio, 196 straining, 196 tunnel dryers, 67 turnip, see swede and white turnip unpacked cost, 257 vacuum dryers, 85 wages, 256 warehousing staff, 26 washers, 140 water, 147