Michigan State University Extension
Preserving Food Safely - 01600531
Temperature plays a key role in the drying process. If the temperature is too high, food may case harden; that is cook and harden on the outside while trapping moisture on the inside.
Other variables to consider when timing foods in a dehydrator include: the amount of natural water in the food, the size and thickness of the food, the relative humidity of the air and the efficiency of the dehydrator. Vegetables may take as little as 3 to 4 hours or up to about 14 hours to dry, depending on the above variables. For example, sliced mushrooms will probably dry in an average of 4 hours, while beets may take as long as 12 to 14 hours to dry.