Excerpt from the Popular Kitchen Series magabook Canning & Preserving with permission from its publisher, BowTie magazines, a division of BowTie Inc. Purchase Canning & Preserving here.
There are several approaches to dehydrating foods. To find the one that works best for you, think about what you want to dehydrate and your geographical and climatic situation.
Sun-drying is the oldest and most inexpensive method of food drying. While a great idea in theory, sun-drying can be tricky in practice. Sun-drying depends upon weather, which is often unpredictable, resulting in uneven drying and poor food quality. Ideally, use sun-drying when you experience several consecutive breezy days of high temperatures (a minimum of 86 degrees Fahrenheit) and low humidity. Fruits are better suited for sun-drying, because their high sugar and acid content makes fruits less prone to spoilage risks.
A sun-drying setup is easy to make: Place screens (stainless steel, Teflon-coated, fiberglass or plastic screens are recommended) on blocks to allow air movement around the food. Birds and insects are attracted to dried fruit, so use two screens: one to hold the food and another to protect it.
Bring the fruit in at night, because the cooler night air could add moisture to the food and prolong the drying process. Because the fruit was outdoors where insects might have touched and laid eggs on it, you must pasteurize the dried fruit. To pasteurize, place the food in a single layer in an oven set at 160 degrees for 30 minutes. Let the food cool before storing. Another option is freezing the food at 0 degrees or below for a minimum of 48 hours.
Oven-dehydrating doesn’t depend on the weather and uses equipment already in your kitchen. The downside is that an oven has finite space, limited by the number of oven racks. Additionally, vegetables can take more than 12 hours to dry, during which you can’t use the oven for other cooking. Many people dehydrate overnight in the oven to help manage time.
The key with oven-dehydrating is keeping the temperature at 140 degrees. Use an oven thermometer placed near the food to monitor the temperature. The oven temperature usually is warmest near the heating element such as the pilot light.
Air circulation also is crucial to oven-dehydrating, which can be achieved by propping the door open 2 to 6 inches.
For people who enjoy drying food and want to experiment with various foods and process larger batches, an electric dehydrator makes things much easier. These relatively small appliances have an electric heating element as well as air vents and fans for air circulation. These machines vary in size and price range. They also come with stackable trays, and you can purchase additional trays to increase your batch size.
Electric dehydrators can be more economical than oven-drying, because they run more efficiently and use less energy. With an electric dehydrator, a general principle to keep in mind is that 12 square feet of drying space typically dries about a half-bushel of produce (about 4 gallons).