Many methods are effective in dehydrating meats, fruits and vegetables. The sun, a microwave, conventional oven or electric dehydrator all dry foods efficiently to preserve them. Dehydrating foods in an oven is a preferred method for beginners since it protects the foods from dust and insects, and is not dependent upon the right weather conditions. If you want to dehydrate foods on a regular basis, electric dehydrators are inexpensive and use less energy than a conventional oven.
Test the temperature in your conventional oven with an oven thermometer. Many ovens cannot maintain a temperature below 200 degrees Fahrenheit; a temperature of 120 to 140 degrees Fahrenheit is optimal for oven drying foods.
Measure your drying trays or wire cooling racks to ensure they fit in your oven. They must be 1 1/2 inch narrower than the width of the oven to ensure proper air circulation. Allow at least 3 inches of space at the top of the oven and 2 1/2 inches between each rack.
Harvest the fruits and vegetables the same day you dehydrate the foods if you have a garden. Select the freshest produce possible. Slice fruits evenly so they dehydrate at the same speed; fruit halves take a long time to dry thoroughly. Wash all produce before dehydrating it. Vegetables take approximately eight hours to dehydrate, fruit leathers approximately four to five hours, and jerky takes around four hours.
Preheat the oven to 150 degrees Fahrenheit. The oven is propped open during the drying time, so this should keep it around 140 degrees Fahrenheit. In a gas oven, a pilot light may be all that is necessary to maintain a temperature of 140 degrees Fahrenheit. Temperatures above 140 degrees Fahrenheit may cause the foods to scorch and have an unappetizing flavor.
Cover the racks or trays with nylon netting or cheesecloth so you can remove the dehydrated foods with ease. Cookie sheets are useful in drying fruit leather since it does not require air circulation.
Place the food on the racks in a single layer.
Prop the oven door open 4 inches, or more to allow for proper air circulation.
Position a fan near the oven door to help circulate the air in the oven and kitchen. Set it to one side of the oven--using a chair if necessary--and switch sides at least once an hour.
Watch the oven temperature carefully during the drying process. For the best results, maintain the temperature at 140 degrees Fahrenheit.
Rearrange the trays approximately every 30 to 45 minutes to keep the dehydration even.
Inspect the foods carefully, particularly near the end of the drying time. Remove foods as they dry. It may be necessary to turn the oven down to 120 degrees Fahrenheit toward the end of the drying time to prevent scorching.