Dried Foods in the Home

by ELSIE H. DAWSON DRYING IS one of the oldest methods of preserving food. It is also one of the cheapest, easiest, and most widely used. Yet there is a great deal still to be learned about it. Especially is there a need for improving the quality of the products to meet present-day standards.

The factors that affect the quality of foods dried at home are pretreatment of the food before it is dehydrated, operation of the dehydrator, storage, and the preparation of the foods for the table. In the laboratories of the Bureau of Human Nutrition and Home Economics and cooperating institutions, we have given special attention to those points and, to meet an urgent wartime need, have developed some practical directions about them. Dehydration has three general steps : Preparation and pretreatment, dehydration, and storage. A fourth could be added: Reconstitution and cooking.

Vegetables and fruits are washed, peeled by hand or by mechanical device, and cut into small pieces for quick drying. With a few exceptions, among them onions, celery, peppers, and herbs, vegetables need partial cooking in boiling water or steam before drying. Cooking destroys the enzymes which, if left active in the dehydrated food, might cause the development of a disagreeable "hay" flavor, change the color, and lower the vitamin content. We chose vitamin C for study because it is the most easily destroyed by heat and oxidation. Vitamin C content is measured by dichlorophenolindophenol titration; color is determined by comparison with Munsell color standards; and flavor is evaluated by expert tasters.

In order to give the homemaker practical directions about precooking, most of our early work was set up on the basis of cooking until tender. We recognized, however, that overcooking is then likely to result when the dehydrated food is prepared for the table. On the other hand, if certain foods are precooked insufficiently, they cannot be properly reconstituted after dehydration. Precooking in steam half the time required to cook tender is enough to inactivate the enzymes in precooked carrots and broccoli, which were selected as typical vegetables, and to keep the enzymes inactive in the stored, dehydrated vegetables. Their keeping quality is as good as those fully cooked before dehydration, and the food is softened sufficiently to insure complete reconstitution without overcooking. Leafy green vegetables must be precooked slightly more than half-time to wilt the leaves, but less than full-time to avoid matting on drier trays.

There are various methods of precooking vegetables. Precooking in steam or in a small amount of water saves time and fuel, retains flavor and food values better, and is preferred to precooking in much water.

Pretreatment of light-colored fruits and vegetables, such as apples and cauliflower, with 1-percent solutions of sodium sulfite or bisulfite improves the quality of the dehydrated product by preventing development of strong flavors and darkening of the color which occurs during dehydration and storage of untreated material. One can hardly taste the small quantity of sulfur dioxide present in the reconstituted samples. The retention of vitamin C, palatability, and color in dehydrated, stored cauliflower is greatly increased by dipping steamed cauliflower in the solution of sodium bisulfite for 15 seconds.

Chemical pretreatment of green vegetables like broccoli and snap beans helps to preserve the bright green color, crisp texture, and natural flavor during drying and storage. Dipping the steamed vegetable in one-fourth teaspoon of sodium bicarbonate per quart of water or one teaspoon of sodium sulfite per quart of water produces good results.

Food may be dried outdoors or indoors. Indoor drying is much faster and much more dependable because it is not affected by the weather. It also saves more vitamins. Artificial dehydration, as distinguished from natural drying in the sun, consists of passing hot air over the vegetable or fruit to remove moisture. The air must circulate freely around and over the food, and there must be sufficient heat to dry the food in the shortest possible time, but not enough to scorch it. The smaller the load on each tray the shorter the drying time. The most satisfactory results are obtained by using one-half to 1 pound per square foot of leafy green vegetables and 1 to 2 pounds per square foot of other vegetables and fruits. The smaller the pieces of food, the shorter the drying time.

Dehydration and Storage

Several designs of home equipment for the indoor dehydration of fruits and vegetables have been developed and adapted. We tested gas and electric ovens for dehydrating, as well as home-built units heated by kerosene heaters, coal and wood stoves, electric heating elements, and light bulbs. In the electrically heated dehydrator, forced circulation of air was used. In all others the circulation of air was brought about by natural convection.

Dehydrated foods must be put into moisture-proof packages to prevent absorption of moisture-and consequent spoilage-during storage. Such containers as tin cans with tight-fitting covers, glass jars fitted with rubber rings, or sealed packages of moisture-proof materials may be used.

Most of the home-dried fruits can be stored at room temperature for several months without becoming inedible. Among the vegetables we tested, home-dehydrated sweetpotatoes, beets, broccoli, and green leaves are the most satisfactory. Their palatability remains high during 6 months of storage at room temperature. The loss of vitamin C parallels the losses of flavor and color. At temperatures above 100 F., most dehydrated foods will keep only a few weeks. The lower the storage temperature, the better are color, palatability, and vitamins retained.

Another way to retard the rate of deterioration is to reduce the moisture content as much as possible. In an experiment with home-dehydrated broccoli, we found that lowering the moisture content from 11 percent to 8 percent increased the storage life from 3 to 9 months at 75 F.

The Use of Home and Commercially Dehydrated Foods

Many foods that are dehydrated commercially because they require elaborate equipment are available to the homemaker.

Whole eggs, yolks, and whites in powder form are among them, and beef or pork as dry shreds or chunks, dehydrated vegetables and fruits in many forms-cubes, slices, flakes, powders, or nuggets-and these may even be compressed into blocks.

Powdered whole eggs of good quality can be used in cooking in much the same way as shell eggs are used except in sponge cakes, fluffy omelets, and similar products that depend on the whipping quality of eggs. For such products one should use a combination of dried egg white and dried egg yolk. When sucrose and lactose are added to the whole eggs before dehydration, even they can be used to make good sponge cake without the use of baking powder to lighten it. Allowance must be made for the sugar in the dry product when measuring the sugar for the recipe. Little time is needed for reconstitution; sugar-dried egg can be used immediately after the water is mixed with it. The presence of the sugar also improves the keeping quality of the dried egg. Untreated dried egg requires temperatures below 60 F. to keep well for longer than 6 months. The addition of sugar makes it possible to store dried egg at higher temperatures for longer periods.

Dehydrated meat for making stews, meat loaves, hamburgers, casserole dishes, and the like was developed during the war for shipping overseas without the danger of spoilage encountered in shipping fresh meat. Whether homemakers will continue using dehydrated meat will depend upon its initial quality and how well it retains high quality during distribution to the consumers. Dehydrated prefrozen raw meat more closely approaches fresh meat in quality than. the cooked dehydrated meat; the former will remain edible for several months at room temperature when packed in vacuum-sealed cans. Refrigerator temperatures retard greatly the physical and chemical changes that are responsible for the changes in flavor and texture.

Dehydrated vegetables are easy to prepare because they are cleaned, trimmed, and cut-all ready to have water added and to be cooked, even without preliminary soaking in some cases. As they are semi-precooked before they are dried, they can be served in a short time. Differences in size of pieces, variety of vegetable used, and length of storage period are some of the factors that determine how much soaking and cooking are needed. It is important to cook dehydrated vegetables in a minimum amount of water if the product is to have maximum palatability and nutritive value.

Compression of dehydrated fruits and vegetables into blocks saves space, lowers the cost of packaging, and helps prevent deterioration by Oxidation and fragmentation due to handling. Compression must not interfere with easy reconstitution of dehydrated foods, however. Compressed food blocks are especially useful where space is scarce, as in the small city apartment or on exploring and camping expeditions.

Dehydrated foods are a long way from being perfect, but they have served well in both local and national emergencies. If they are to be improved, we need to continue research work on the methods of preparing them for dehydration, on new and better dehydration procedures, on improved storage facilities to increase shelf life, and on quicker, easier methods of reconstitution. Only when one is certain of uniform quality will dehydrated foods take their place alongside canned and frozen foods in the homemaker's pantry when all types are equally available.

THE AUTHOR Elsie H. Dawson, a food specialist in the Bureau of Human Nutrition and Home Economics, has done work in the field of dehydrated foods, including research on improvement in quality and use of dehydrated eggs, meat, milk, and many fruits and vegetables. She is a graduate of the University of California and taught food chemistry and experimental cookery there and at Syracuse University and Cornell University before joining the Bureau in 1941.