Tray drying refers to dehydrating small pieces of produce by exposing them to a source of hot dry air or to the sun until dry enough to store at ambient temperature with minimal spoilage. Dried foods are lighter and store in a smaller space than canned foods and do not require a constant power supply like frozen foods. Humanitarian organizations have taken up tray drying technology for use in areas of the world without access to easy energy, where food preservation is critical to maintaining communities under threat of social, economic or environmental pressure. When portability is essential, whether out of necessity or for recreational use, dried foods are the obvious choice.
Fabrication and operation of the equipment used for tray drying are simple and the most cost-effective choice for home or small-scale business. Size of the cabinet and heat source for tray drying varies, depending on need and locally available resources. Generally, tray drying equipment entails a cabinet fitted with shelves of perforated trays or screens, a way to heat the air and a usually a fan to circulate moisture away from the product, unless the environment is arid enough to allow convection alone to circulate air. If air circulation is not ideal, trays closer to the heat source will dry first and those farther away will mold before dehydrating. Some dryers are designed to use this problem to advantage for continuous production, where the bottom trays are removed when dry and fresh trays are loaded from the top.
Seasonal harvests create a welcome yet overwhelming glut of one type of food. Commodities such as cereal grains and root crops, while dietary staples, are in large production and are both more available and less perishable; therefore, these types of foods are more efficiently dehydrated with higher throughput, industrial drying processes. Minor, yet important, garden and orchard produce like fruits, vegetables, herbs, and spices are well-suited for tray drying. Even thin slices of meat, a highly perishable food, can be flavored with salt and spices and dried for jerky. In addition to preserving foods, drying concentrates flavors that are signature to many types of cuisine.
Tray drying techniques have been used in homes and by small commercial growers worldwide for millennia. Only the engineering of the basic techniques has changed to increase throughput and minimize spoilage during the process.