of
CllEMISTRY TEACBERS
Dehydrated and Compressed Foods' B. E. PROCTOR Director, Subsistence and Packaging Research, Ofice of the Quartermaster General, U . S . Army
T
HE HISTORY of food dehydration over the past 80 years closely parallels the military conflicts of this period, from the standpoint of both time and magnitude. Until shortly before the present conflict, the peacetime intervals were dormant lapses during which the production of dehydrated foods was negligible, with certain exceptions such as the dried fruit industry of our Pacific Coast states. Our participation in World War I, ending in 1918, brought dehydration to heights of production never reached previously, although the quantities which reached foreign shores amounted to only a few million pounds. published within the present The year, indicates the goals which must be reached during the approaching crop season to furnish the requirements set up as necessary for our needs and those of our Allies in the months ahead. 355,627,000 lbr. 60,472,000 lbr.
.................................... ~ 0 t . 1 weight.. ..........................
Vegetables Beets, carrots, cabbage, onions. sweet potatoes, white potatoes-precooked, white potatoes-julienne and dices, mtabagas, hominy. Fruits Cranberries, blueberries, cherries, apricots, peaches, apples, orange juice, lemon juice.
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TABLE 1
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modern food dehydration processes we remove water from foods to preserve them. The practice of dehydration is far from new. The Egyptians dried their wheat in the days of the Pharoahs, and the Indians dried their corn and buffalo meat before the colonization of America. Perhaps your grandparents dried apples on strings, a common New England custom until a few decades ago when cold storage for apples proved a more ideal solution for this area. The following commodities are being dehydrated a t the present time, most of them in considerable quantities:
516,756,000 lbs. 460,129,000 lbs. 120,000,0001br. I . . ~ I O , ~ O ~ ib.. ,OOO
The numerous reasons for this vast production, which involves thousands of farmers, many thousands of fertile acres, and hundreds of dehydrated food manufacturing establishments, rest on the fundamental consideration that we have the problem of feeding millions of soldiers, sailors, and civilians outside the limits of our food production areas. A large number of these consumers are thousands of miles distant. The shift of ordinary food processing to the manufactureof dehydrated foods is due to the advantages which this method of food preservation presentsunder the circumstanceswe now face. =ehydration saves shipping space and weight, ~talso minimizes the "tilization of critical metals in food containers and other important packaging materials, such as paperboard. circumstances we add waterto many under foods in the heat-processing or canning of foods.
Green pea, yellow pea, navy bean, bouillon types, simulated chicken types. Other Products Whole eggs, whole mik, skimmed milk solids, beef, pork. corned beef hash, cocoa beverage powder, coffee, baked beans.
It is immediately apparent that in this list we have a representative cross section of many of the common and some of the favorite foods of the normal American home. There will be others as time goes on. Some of these will be in homes after hostilities have ceased and be be produced in peacetimes in the future. Two Years ago such a prophecy, except for milk and egg powder, which have uses in other manufactured food products, would have been received with
Perfection in all respects has not been attained, nor is i t anticipated. Dehydrated foods will never seriously displace canned and frozen foods in peacetimes, and well-founded canning and food-freezing industries, which have played such an important part in our food picture in the past, will continue to do so in the future. The better dehydrated products, however, which combine convenience and consumer acceptance, will have their place in the postwar period in increasing amounts, ' Presented at the Fifth Summer Conference of the New Engin areas or instances where transportation, land Association of Chemistry Teachers, Andover, Massachustorage, and space are factors. setts. August 28. 1943. 619
It is only because rapid and constructive advances have been made in the underlying sciences which relate to foods that this prophecy is possible now. The chemists, food technologists, and nutritionists have been working hand in hand to make available larger quantities of dehydrated foods which are more acceptable, more attractive, more convenient to use, and capable of longer storage life under adverse conditions. As teachers in the fundamental science of chemistry, you will be interested in knowing that developments in chemistry, perhaps made by some of the students you have trained over the years, have played a major part in these advances. Since 1 9 l S t h e previous high point in food dehydration production-many developments in science have taken place, of which all chemists are aware. More is known about enzymes and their complex chemical systems. Improved devices for temperature and humidity measurement and control have beeu developed. The dynamics of fluid or air mechanics have become more adequately understood. The means of more satisfactory heat transfer have resulted from engineering researches. The chemistry and physiology of vitamins have made spectacular advances. Each of these has been reflected in the new developments in food dehydration. Dehydration, model 1943, is not just drying foods. I t is the removal of water from foods under controlled. and accurately controlled, conditions. The methods involved diier widely. Among the more recent and promising ones is a feasible method of dehydration in the presence of inert gases. Another is the removal of water from frozen material under a pressure of only a few millimeters. Each presents its advantages, but the water removal is only one phase of an integrated series of procedures. The best dehydration plant in the world would produce poor products if any one of the numerous steps, from the proper selection of raw material varieties to the unwise choice of final package, is not properly considered in relation to all the other necessary operations. These operations may be briefly summarized in general as: procurement of raw material; cleaning; blanching; peeling and reduction to standard size; drying; inspection and sorting; compression; packaging. In some instances there may be changes in the order of operations; blanching and peeling may be reversed; inspection and sorting may precede dryiig ; compression is not now conducted except in a limited way, but i t will be quite general in the near future. The knowledge of enzymes has brought about a conspicuous improvement in the quality of many dehydrated vegetables, because the inactivation of enzyme systems by heat, either in the form of steam blanching or hot water blanching, tends to protect the foods against some deteriorative enzymatic changes. The t ~ m r sand trmpenlturcs rlecrs%ry to accomplish this obiective have been determined and are available to :ill dehydrating plant operators. Relatively simple chemical tests which determine the presence of these enzyme
systems enable the plant operator to determine the proper procedures for his products. The enzyme systems present in diierent varieties of the same vegetable determine the adaptability of raw material for the dehydration processes. One of the long-range problems relating to dehydration is the development of new variations which may have characteristics particularly suitable for dehydration methods. Some fine varieties of vegetables suitable for canning and freezing are unsuitable for dehydration. The peeling of vegetables previous to 1942 involved losses in the vicinity of 30 per cent of the raw material. This was purely a method dependent on the utilization of abrasive surfaces. It has since been superseded in many plants by peeling in a lye bath or by flame peeling. Each of these methods now appears likely to become obsolete in the near future due to improved methods of steam-contour peeling which result in trimming losses to about 10 per cent. This will obviate the wasting of thousands of tons of good food material which otherwise could be used only for animal feed or discharge into sewerage systems. The latter frequently causes serious problems of disposal because of subsequent microbiological and chemical decomposition. The improvements that have taken place in the drying operation itself have been largely due to the utilization of control instruments, permitting narrow limits of temperature and humidity. These improvements in turn have made possible the development of two- and three-stage drying processes which have the advantage of more economical operation, while producing superior products. Tunnel dehydrators are the common type used for vegetables, but the utilization of drum driers and spray driers for products such as milk and eggs have also resulted in improved products. Although used to a much lesser extent, the modified process for drying blood plasma has made possible the drying of fruit juices to a powdered form of high acceptability and high vitamin content. Citrus juices are especially suitable for this type of treatment. The increased knowledge of vitamins and apparatus devised for determining vitamin contents have been widely utilized as means of following changes in vitamin content which occur during dehydration. Losses are incurred during drying and also occur later in storage. The use of low temperature storage of all dehydrated products is highly desirable. It has long beeu known that the keeping quality of dried fruit is improved by treatment with sulfur dioxide. It has also been determined that this same type of treatment has definite advantages in the conservation of ascorbic acid. Such treatment may also be applied advantageously to some of our vitamin C in vegetables, such as cabbage and carrots. Regardless of how the products are manufactured, their keeping quality is dependent upon the manner in which they are packaged. The complete removal of oxygen in the final container is also a factor in vitamin retention. This may be accomplished in two ways: either by mechanical evacuation or by the utilization of
inert gases, such as carbon dioxide, which will replace the oxygen present by gravity displacement. In order for this to be effective, however, it is necessary to have hermetically sealed containers. The best containers of this sort are metal cans, hut because they require critical material, they are used for only the most delicate productscarrots and cabbage. Onions are also packed in metal containers because this product is one having extremely hydroscopic qualities. A variety of other types of containers which provide adequate moisture protection-which is essential for overseas shipmentsincludes bags which are comprised of a combination of either fiber or metal, and one of several plastics or asphalts. Fiber containers which are
dipped in wax compounds after the products are packed have also proved satisfactory. The latest innovation in respect to dehydration is the utilization of hydraulic presses for the compression of the various dehydrated products. This method is applicable to dehydrated vegetables, meat, eggs, and numerous other commodities. It results in further economies in space and packaging; i t brings about reductions of approximately 60 per cent in vegetables, and may run as high as 80 per cent for very light substances such as dehydrated cabbage flakes. In addition to compressing the product, this method also permits a minimum of air or oxygen in the container. It will save many thousands of cargo tons of shipping space and tremendous quantities of packaging materials.
