One of the oldest methods of preserving food is dehydration. Water is removed from the food, leaving it lighter in weight and smaller in size. The dehydrated food takes up less storage space than canned goods and does not require any type of refrigeration. Foods can be dried using a variety of appliances and techniques including an electric dehydrator, a conventional oven or the heat from the sun.
Dehydrating food removes water from the food, leaving the microorganisms that promote spoilage without sufficient moisture to live, grow and cause spoilage. A combination of low heat, dry air and air movement forces moisture from food. Most fruits, vegetables and meats are dehydrated at about 60 degrees Celsius. Herbs will keep more of their flavour if dried at a lower temperature between 35 and 46.1 degrees Celsius.
An electric dehydrator is a self-contained appliance with a heat source, a fan for circulation and multiple trays for drying many foods at one time. Less expensive models do not have temperature controls and the heat source and fan are combined into a single unit that resembles a hair dryer. Better quality dehydrators have thermostats, temperature controls and double-walled construction for more efficient energy usage.
A conventional oven may also be used to dehydrate food if the oven can maintain the 140 degree Fahrenheit temperature needed to dehydrate food without cooking it. Many ovens today will not operate at such a low temperature. However, the oven's warmer drawer may be sufficient. Always test the temperature with an accurate thermometer before using the oven or the warmer drawer for drying foods. Dehydrating food also requires good air circulation, which ovens do not provide. Propping open the oven door a couple of inches and placing a fan in the opening will solve this problem.
Food can also be dehydrated using the heat from the sun. Solar drying foods requires a little more attention than drying foods in an oven or a dehydrator. In order to take advantage of the sun's energy for dehydrating foods, air temperatures must be at least 29.4 degrees Celsius by noon; humidity should be below 60 per cent, and food needs to be turned once a day. Food not completely dehydrated should be taken in or covered at night to prevent rehydration. Renee Boyer at the Virginia Cooperative Extension recommends sun drying be used only for drying fruit.
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- Virginia Cooperative Extension; Using Dehydration to Preserve Fruits, Vegetables, and Meats; Renee Boyer, et al.; June 2009
- National Center for Home Food Preservation; Food Dehydrators; Elizabeth L. Andress, et al.; 2006
- National Center for Home Food Preservation; Herbs; Elizabeth L. Andress; 2006
- University of Missouri Extension; Quality for Keeps: Drying Foods; March 2010