People have passed down food drying techniques, such as salting and sun-drying, for centuries. Drying, or dehydration, is an ancient food preservation method. Efforts to perfect food drying led to the invention of the first food dehydrator in 1795. Consumers dehydrate foods for personal use and manufacturers offer a wide variety of dehydrated foods for different uses. Dehydration causes some loss of nutrients in foods; however, the processes used in dehydration and rehydration play important roles in how much nutritional value is lost.
Food Dehydration
Dehydration removes moisture from foods. The methods of dehydration include sun-drying, electric dehydrators and regular ovens. Microwave ovens are used to dry herbs. Solar drying collects the sun's rays in a ventilated unit that removes moist air. The benefits of dehydrated foods include convenience, taste and storage. Dehydrated foods lack the moisture needed for bacteria, yeast and molds to grow. Dried fruits and vegetables, which are called leathers, are used for snacks and dehydrated vegetables are used in stews and soups. Hikers and campers value dehydrated foods for the light weight, shelf life and simple preparation.
Calories and Fiber
Dried foods are higher in calories, when compared weight-for-weight, because nutrients are concentrated. For instance, 100 grams of fresh apricots contains 51 calories and 100 grams of dried apricots contains 260 calories. The removal of moisture during dehydration concentrates the nutrients into a smaller mass, but the beginning and ending products are equal in calories, if not weight. Dehydrating 14 lbs. of fresh tomatoes nets ½ lb. of dried tomatoes.
Vitamins and Minerals
Dehydration does not cause any change in fiber or iron content. While the use of heat and air, and blanching, in the dehydration process can destroy vitamins A and C, you can retain much of the vitamin A by using a controlled heat method of dehydration. Blanching results in some loss of vitamins A and C, thiamine, riboflavin and niacin; however, blanching also can reduce the loss of these vitamins during storage and rehydration. Sulfite treatments, which are used to destroy enzymes during vegetable dehydration, prevent the loss of some vitamins, although it causes the loss of water-soluble vitamins and minerals, such as B-complex and C vitamins.
Retaining Nutritional Value
The best way to retain the nutritional value of dehydrated foods is to carefully control the process, which means low heat during dehydration, careful rehydration and low humidity during storage. Rehydration of dried foods without soaking the food in water can cause loss of minerals. You can make good use of remaining nutrients by consuming the water used to rehydrate the food. Follow proper methods for cooking dehydrated foods. For instance, dried vegetables require less cooking time than fresh vegetables. Store dehydrated foods in cool, dark places and use the items within a year of dehydrating. It is best not store rehydrated foods since they spoil quickly.
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