There are several commercial models available, and a homemade model is not difficult to build. The most efficient dehydrators have a heating element and a fan. At the beginning of the drying process, you will keep a vent or door partly open to allow the moisture to escape. Toward the end of the drying process, you will close the vent or door to raise the temperature and drive the moisture from the center of the food. In the food tables mentioned above, the authors describe the appearance of a food when it is dry.
Some foods are leathery.
Others are crisp. The authors give a much simpler way to determine dryness. Dry food can spoil if it is exposed to moisture, so the trick is to keep the atmospheric moisture away from the food. There are several types of vacuum packaging systems available commercially, but the authors don't recommend them for long-term storage. They can lose their seal or develop punctures that will allow moisture to contact the food.