Michigan State University Extension
Preserving Food Safely - 01600516
For thousands of years, people have dried many foods to preserve them for leaner times. Preserving seasonal foods by drying is still useful and convenient, and it has the added advantage of conserving storage space.
Successful home food dehydration is dependent on three basic principles:
Heat: controlled temperature high enough to force out moisture, but not hot enough to cook the food.
Dry Air: to absorb the released moisture.
Air Circulation: to carry the moisture away.
When food is dehydrated, 80 to 95 percent of the moisture is removed, inactivating the growth of bacteria and other spoilage microorganisms, making it a useful method of preparation. In hot, dry climates, food will be reduced in a few days to a moisture level that preserves them. In any climate, however, you can create satisfactory drying conditions at a moderate expense by using artificial heat and circulating air over the food. You can do this:
-- in your own kitchen oven (equipment needed: drying trays, an oven thermometer and a small fan)
-- in a homemade or commercial portable vegetable dehydrator (USDA Bulletin 217 has instructions on how to construct a natural-draft dehydrator. Electric food dehydrator can be purchased in most appliance stores.