Distribute the food on trays in a single layer. Different foods can be dried at the same time, but try to choose foods that will dry in about the same amount of time. (Dry similarly sized pieces together.) Onions, peppers, and other strong foods tend to flavor other foods, so dry them separately.
Moisture must be removed from the food as quickly as possible at a temperature that does not seriously impair the flavor, texture, or color of the food. If the temperature is too low at the beginning, the food may spoil before it dries. If the temperature is too high, the surface may harden so that the interior dries much more slowly. Start the dryer at 140° to 150°F, with the exceptions noted in the drying guidelines After 2 to 3 three hours, lower the dryer temperature to 130°F to 140°F. Adequate air flow can reduce drying times.
Monitor the drying process.
If necessary, rotate the trays to ensure even drying. You may need to stir grated, shredded, or finely cut foods.
Many factors affect drying time, including type of food, size and moisture content of the food pieces, pretreatment method, dryer type, dryer temperature, relative humidity of the air, and amount of air movement in the dryer and in the surroundings. With so many factors at work, it’s impossible to give precise drying times.
Generally, you can figure on drying times of 6 to 36 hours for fruit and 3 to 16 hours for vegetables, which take less time due to their lower sugar contents. Check the instructions that come with your dehydrator, and read the general guidelines for drying times for various foods In the end, you need to decide when food is dry.
Vegetables are sufficiently dry when they are brittle or leathery. Leathery vegetables will be pliable and spring back if folded. Brittle vegetables such as corn and peas will shatter when hit with a hammer. Fruits are sufficiently dry when they are pliable and leatherlike and have no pockets of moisture.
Herbs are sufficiently dry when brittle. Their leaves will shatter when rubbed together.
When you think the food is sufficiently dry, remove a piece and allow it to cool completely. Then check for dryness. When you are in doubt about the dryness of a food, continue to dry it. Foods dry more quickly toward the end of the drying period, so check them frequently, and avoid leaving them in the dryer after they are done. Leaving them in will reduce their quality.