BASIC DRYING SUPPLIES and METHODS
(Content provided by: University of Illinois at Urbana-Champaign College of Agriculture Cooperative Extension Service)
One of the advantages of drying foods rather than canning or freezing them is that you can get by with almost no special equipment. A kitchen oven, drying trays or racks, and storage containers are the only basic equipment needed. If you want to dry large quantities of food, you may decide to buy or make a food dryer, but it is not essential. For sun drying you need only racks and storage containers.
Although the following equipment is not absolutely necessary, it will help you make a more uniformly good product:
Wood slats or stainless steel screen mesh are the best materials to use for the racks. Cake racks or a wooden frame covered with cheesecloth or other loosely-woven cloth can also be used for drying racks.
Do not use solid metal trays or cookie sheets to dry food because air must circulate all around the food so that drying can take place from the bottom and the top at the same time. Pieces of meat for jerky can be placed directly on the metal racks in the oven if the pieces are large enough not to fall through the spaces in the racks.
Do not use racks made of galvanized screen, aluminum, copper, fiberglass, or vinyl. Galvanized screen contains zinc and cadmium. These metals cause an acid reaction that forms harmful compounds and darkens the food. Aluminum becomes discolored and causes an off-flavor in sulfured fruit. Copper materials destroy vitamin C. Fiberglass may leave dangerous splinters in the food, and vinyl melts at temperatures used for drying.
Oven drying is the simplest way to dry food because you need almost no special equipment. It is also faster than sun drying or using a food dryer. But oven drying can be used only on a small scale. An ordinary kitchen oven can hold only 4 to 6 pounds of food at one time.
Set the oven on the lowest possible setting and preheat to 140 degrees F. (60 C.). Do not use the broiler unit of an electric oven because the food on the top tray will dry too quickly' Remove the unit if it has no separate control. Some gas ovens have a pilot light, which may keep the oven warm enough to dry the food.
It is important to keep the oven temperature at 140 to 160 F. (60 to 70 C.). So put an oven thermometer on the top tray about half way back where you can see it easily. Check the temperature about every half hour.
Arrange 1 to 2 pounds of prepared food in a single layer on each tray. Put one tray on each oven rack. Allow 1-1/2 inches of space on the sides, front, and back of the trays so that air can circulate all around them in the oven. To stack more trays in the oven, use blocks of wood in the corners of the racks to hold the trays at least 1 inche apart. Dry no more than four trays of food at a time. A lighter load dries faster than a full load.
Keep the oven door open slightly during drying. A rolled newspaper, a block of wood, or a hot pad will keep the door ajar so that moist air can escape while the heat stays in the oven. Four to six inches for electric ovens or 1 to 2 inches for gas ovens is usually enough space for ventilation, but use a thermometer to check the oven temperature to make sure it stays at 140 F. An electric fan placed in front of the oven door helps to keep the air circulating.
Shifting the trays often is important for even drying because the temperature is not the same everywhere in the oven. Rotate the trays from top to bottom and from front to back every half hour. It helps to number the trays so you can keep track of the order in which you rotate them. Stirring fruit or vegetables every half hour or so also helps the food to dry evenly. Jerky needs to be turned over occasionally to keep it from sticking to the trays.
A commercial or homemade food dryer or convection oven provides automatically controlled heat and ventilation. Most households will not need a dryer unless they dry large quantities of food. A food dryer takes less electricity than drying the same amount of food in an electric oven. However, the temperature is usually lower (about 120 degrees F. or 50 C.), so drying takes a little longer than in an oven.
You can buy a dryer at hardwares, housewares farm supply, or health food stores. The price of commercial dryers varies greatly depending on the size, type of heating element, and other, special features. An old refrigerator or icebox can be converted into a food dryer. Just be sure the temperature is controlled and the ventilation is adequate.
When using a dryer, preheat it to 125 F. (52 C.). Place the food on trays and stack the trays in the dryer. Gradually increase the temperature to 140 F. (60 C.). It takes 4 to 12 hours to dry fruits or vegetables in a dryer.
Do not use space heaters to dry food. These stir up dust and dirt, which contaminate the food. For the same reason, do not try to dry food on a furnace vent or clothes dryer.
Sun drying is the old-fashioned way to dry food because it uses the heat from the sun and the natural movement of the air. But bright sun, low humidity, and temperatures around 100 degrees F. are necessary. This process is slow and requires a good deal of care. The food must be protected from insects and covered at night. Sun drying is not as sanitary as other methods of drying. Don't sun dry food if you live near a busy road or in an area where the air is not clean.
If you decide to sun dry foods, you might want to use a natural-draft dryer. The advantage of this kind of dryer is that it hastens drying by trapping heat from the sun. It also protects the food from insects and birds.
Place pieces of food on drying trays and then cover them with a layer of cheesecloth or netting to keep off dust and insects. Place the dryer in direct sunlight on a roof or high surface away from animals, traffic exhaust, and dust. After the food is almost dry, put it in an airy, shady place to prevent scorching during the final stage of drying.
Be sure to bring the dryer indoors at night if the temperature drops more than 20 degrees F. Dew and sudden temperature change put moisture back into the food and lengthen the drying time. Fruits and vegetables take 3 to 7 days to dry in the sun. The length of time depends on the type of food and the atmospheric conditions. Natural heat is slower and less dependable than controlled drying in an oven or food dryer.
Back to Home Page