Dehydration is one of the oldest methods of food preservation with the sun as the original dehydrator. You can purchase a dehydrator for this purpose, but instead of spending the money on yet another appliance, you can just as easily use your conventional oven as a dehydrator. Knowing what temperatures to use, the tools required, air flow requirements and timing makes all the difference in successfully dehydrating foods in a conventional oven.
For proper drying in a conventional oven, stick to the lowest temperatures for your oven. It may have a warm setting or a preselected low temperature. Ideally, use a temperature between 54.4 and 60 degrees Celsius for dehydrating food. Higher temperatures may dry out the food too quickly and give it a tough texture while lower temperatures don't dry out the food quick enough.
You can use a non-stick pan or other oven-safe pan to dry food leathers -- dried puréed fruit -- in the oven. But use a drying tray, wire cooling racks or some other kind of cookware that allows for proper airflow to dry fruits, vegetables and meats. If you use wire cooling racks, cover them with cheesecloth or netting to easily remove food from them after drying. Do not place food directly on oven racks when dehydrating.
A typical dehydrator uses air flow to help dry your foods. Keep the door on your oven slightly ajar when dehydrating. While a conventional oven does not usually have a source of air, you can use a fan in front of the oven to speed up the process. Keep the fan on the lowest setting. Direct the air toward the rack of food and move the fan around occasionally to give a consistent, even supply of air throughout the oven.
Different foods have different drying times, whether you use your oven or a dehydrator. These times vary widely, so it's helpful to just watch for signs of dehydration. The general oven recommendation is that your foods may dehydrate in half the time it would take in a conventional dehydrator. Signs of dehydration include crisp, leathery, brittle food with no moisture pockets.