Dehydrating is the removal of moisture from food to prevent microbial growth and enzymatic spoilage. Drying is the oldest method of food preservation, dating back to prehistoric times. Dehydrated food retains most of its nutritional value, requires no refrigeration, and occupies minimal storage space. The moisture content of dried food is typically 10 to 20 percent, compared to 80 to 95 percent in fresh food.
Sun drying uses direct sunlight and is practical only in hot, dry climates with low humidity. The food is spread on screens or trays and covered with cheesecloth to protect from insects. Sun drying requires 3 to 7 days and is not recommended for meat or low-acid vegetables.
Oven drying uses the lowest oven setting, typically 50 to 65 degrees Celsius (120 to 150 degrees Fahrenheit), with the door propped open to allow moisture to escape. Oven drying is 2 to 3 times faster than sun drying but uses significant energy.
Electric food dehydrators are the most efficient and consistent method. The dehydrator has a heating element and fan that circulate warm air across stacked trays. The temperature is controlled between 40 and 70 degrees Celsius (105 to 160 degrees Fahrenheit), depending on the food type. Dehydrators are available in round or rectangular shapes, with capacities of 4 to 12 trays.
food is washed, trimmed, and cut into uniform pieces for even drying. Fruits are often pretreated with ascorbic acid, citric acid, or lemon juice to prevent browning (enzymatic browning). Vegetables are blanched in boiling water or steam for 2 to 5 minutes to inactivate enzymes that cause off-flavors during storage. Meats are trimmed of fat and sliced thin for jerky.
Dried food is conditioned by storing in a loosely filled container for 7 to 10 days, shaking daily to distribute any remaining moisture. The food is then packaged in airtight containers or vacuum-sealed bags and stored in a cool, dark, dry location. Properly dried food stores for 6 to 12 months at room temperature or 1 to 2 years in the Freezing.