Practical Dehydration

274 Pages·1998·26.038 MB·English

by  M. Greensmith (Auth.)

Practical Dehydration
Maurice Greensmith
2nde dition
WOODHEAD PUBLISHING LIMITED
Cambridge England
Published by Woodhead Publishing Limited,
Abington Hall, Abington, Cambridge CB 1 6AH, England
First published 197 1, Food Trade Press
Second edition 1998, Woodhead Publishing Ltd
0 1998, Maurice Greensmith
The author has asserted his moral rights.
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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 1 85573 394 3
Printed by St Edmundsbury Press, Suffolk, England
Preface to the
Second Edition
The first edition of PRACTICALDEHYDRATION,p ublished 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 70-80t onnes 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, prodncing 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 war-
time industry. Production today is centralised 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’ pductsi n 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 up 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.
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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 mono-
culture 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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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 root 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 mently 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
journey 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 fmm the sea coast.
It forms a regular part of the Catholic diet on fast days, in the absence of 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 pmbe 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 Eumpe from the US and, to a
lesser extent, fmm 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 pmgress 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 tobe solved, in that dried vegetables, meats and soups, pmduced
for the Armed Services' use, occupied only a fraction of the space taken up
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.
Experimental work 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
pmduction 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 1942 a pint 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 cumnta nd 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
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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, pduced Potato Flakes by
using the technique of drum drying. The resultant pduct was a mashed
potato almost indistinguishable in taste and texture from that of a hshly
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
1958-59 processing season in the US, 75,000,000lb 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 llelied 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.
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