Food dryers can be very different from each other in terms of specific processes, yet the basic idea is the same: the temperature is raised (lowered in the case of freeze drying) until the water evaporates or sublimates out of the food, leaving behind the dried product.
Most food dryers have a few features in common, such as a holding tank or container with a door, a heat source and an accessible and convenient way to remove the finished product. Personal food dryers are small enough to fit on a countertop, while commercial or industrial dryers have up to 8,000 square feet of drying capacity.
Food grade stainless steel is often used for the tank or container because of its corrosion resistant and sanitary properties, and fiberglass can be used as insulation for more precise temperature control. Food dryers are used by food and beverage companies to create fruit leather, beef jerky, powdered juice, vegetables for dried soup mixes, spices, fruits for breakfast cereals, powdered milk and more. Militaries and space programs use dried foods as rations, and campers or hikers appreciate their compact and lightweight nature.
Though there are differences, food dryers are often mistakenly called food dehydrators. Dried food loses approximately 75% of its water content and remains soft and pliable, whereas dehydrated food reduces its moisture content by about 98%, resulting in a shriveled and brittle product with a longer shelf life. Industrial food dryers are also frequently interchangeably called dehydrators, in part because dehydration can take place if left in the dryer for longer periods of time at higher temperatures.
There are three main ways of drying food: in the oven, by the sun and through a food dryer machine or appliance. Food dryers themselves use a number of techniques to achieve the final result, including spray, freeze, tray, belt and bin drying. Spray drying uses a jet of hot steam to instantly dry any moisture on a food particle.
Freeze drying lowers the temperature in order to freeze a substance then allows sublimation to occur, consequently drying it. Tray drying usually occurs in dollies, or racks on wheels. Items are placed on trays and slid into shelving units. The door is closed, the temperature raised and, as time passes, the food dries. Depending on the heat flow, some trays may have to be rotated to ensure equal heat penetration.
Belt dryers have a modular design where the humidity, air flow and temperature can be controlled in zones. Bin dryers, however, provide a more consistent product because each bin is separately and individually controlled.