Dehydration, the oldest form of food preservation, is the process of extracting water from food. Because dehydrated food is comparatively light, and usually requires less storage space, it's popular among camping, biking and hiking enthusiasts, as well as people who wish to store food for emergency preparedness. However, dehydrated food does have some disadvantages.
Freeze drying, or lyophilzation, is a vacuum-based process in which the moisture in food is frozen and then evaporated, leaving only about 2 percent of the original water content. According to Emergency Essentials, this type of drying is best for fruits and meat.
Unless the food is packed and maintained at low humidity, the process may not totally inhibit the microorganisms that cause food spoilage, or the toxigenic and infectious organisms that cause food poisoning. In some cases, the end product may crumble easily and lose aroma.
Since this process does not change the shape or size of the food item, the finished product requires more space to store than other types of dehydrated food.
Air-Drying, Sun-Drying and Kiln-Drying
Air-drying, sun-drying and kiln-drying often cause foods to lose some texture and taste. Foods dried by these methods generally require an airtight storage container that includes an oxygen absorber.
If dried too quickly, the outer cell layer of the food product may harden, causing the product to become tough and rubbery.
According to Jeff Schalau of Backyard Gardener, sun-dried foods may lose various nutrients, including vitamin C.
Food Storage Simple cautions that dried foods are raw, and may require preparation time. This may be problematic in certain types of emergencies or living situations.
It also notes that while some foods (e.g., apples, raisins, bananas and other fruits) are edible in dry form, others (e.g., corn, eggs, potatoes, onions and green beans) need water to become edible. In some emergency situations, this may be impractical or impossible.
Dried meats last from a few weeks to a year, depending on the drying method and type of meat. This gives them a short shelf life compared to other dehydrated foods, most of which have a guaranteed shelf life of 25 years or more. For this reason, meat substitutes such as textured vegetable protein (TVP) are used for long-term storage.