Self Sufficiency: September 2008 Archives

SUCCESSFUL DRYING

Don't be surprised to find a variety of suggestions for drying methods, temperatures, and lengths of time. The drying process is simply not as precise as canning and freezing because it involves so many different factors. You may need to use a trial-and-error approach to find what suits you best. Whatever method you use, be sure to remove enough moisture from the final product so that spoilage organisms cannot grow.

When you dry foods, remember the following:

• Cleanliness and sanitation are essential.
• The flavor of dried fruits and vegetables will be somewhat different from that of their fresh, canned, or frozen counterparts.

EQUIPMENT

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:

• a food scale to weigh food before and after drying
• an electric fan to circulate the air
• a thermometer to check the oven temperature
• a blancher for vegetables
• a sulfur box for fruit

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.

METHODS

Oven 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 right, 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 comers of the racks to hold the trays at least I inches 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.

Food Dryer

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 hardware, 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. Directions for making an inexpensive dryer (see illustration above) are given in several of the publications listed at the end of this circular. 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 

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. In Illinois the humidity is usually too high for successful sun drying. 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 (see illustration above). 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. Its construction is described in several of the recommended publications.

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.

 Reprinted from University of Illinois College of Agriculture

DRYING FOOD BASICS

Drying is the oldest method of preserving food. The early American settlers dried foods such as corn, apple slices, currants, grapes, and meat. Compared with other methods, drying is quite simple. In fact, you may already have most of the equipment on hand. Dried foods keep well because the moisture content is so low that spoilage organisms cannot grow.

Drying will never replace canning and freezing because these methods do a better job of retaining the taste, appearance, and nutritive value of fresh food. But drying is an excellent way to preserve foods that can add variety to meals and provide delicious, nutritious snacks. One of the biggest advantages of dried foods is that they take much less storage space than canned or frozen foods.

Recommended methods for canning and freezing have been determined by research and widespread experience. Home drying, however, does not have firmly established procedures. Food can be dried several ways, for example, by the sun if the air is hot and dry enough, or in an oven or dryer if the climate is humid. Drying is not difficult, but it does take time and a lot of attention. Although there are different drying methods, the guidelines remain the same.

SOLAR DRYING, OVEN DRYING  DEHYDRATOR DRYING

Although solar drying is a popular and very inexpensive method, it depends on the climate where you live. It requires 3 to 5 consecutive days when the temperature is 95 degrees F. and the humidity is very low. Drying food in the oven of a kitchen range, on the other hand, can be very expensive. In an electric oven, drying food has been found to be nine to twelve times as costly as canning it. Food dehydrators are less expensive to operate but are only useful for a few months of the year. A convection oven can be the most economical investment if the proper model is chosen. A convection oven that has a controllable temperature starting at 120 degrees F. and a continuous operation feature rather than a timer-controlled one will function quite well as a dehydrator during the gardening months. For the rest of the year it can be used as a tabletop oven. (Details on these will be covered in the next blog post.)

GUIDELINES

Speed

For a good-quality product, vegetables and fruits must be prepared for drying as soon as possible after harvesting. They should be blanched, cooled, and laid out to dry without delay. Foods should be dried rapidly, but not so fast that the outside becomes hard before the moisture inside has a chance to evaporate.

Drying must not be interrupted. Once you start drying the food, don't let it cool down in order to start drying again later. Mold and other spoilage organisms can grow on partly dried food. 

Temperature

During the first part of the drying process, the air temperature can be relatively high, that is, 150 degrees to 160 degrees F. (65 degrees to 70 degrees C.), so that moisture can evaporate quickly from the food. Because food loses heat during rapid evaporation, the air temperature can be high without increasing the temperature of the food. But as soon as surface moisture is lost (the outside begins to feel dry) and the rate of evaporation slows down, the food warms up. The air temperature must then be reduced to about 140 degrees F. (60 degrees C.).

Toward the end of the drying process the food can scorch easily, so you must watch it carefully. Each fruit and vegetable has a critical temperature above which a scorched taste develops. The temperature should be high enough to evaporate moisture from the food, but not high enough to cook the food. Carefully follow directions for regulating temperatures. 

Humidity and Ventilation

Rapid dehydration is desirable. The higher the temperature and the lower the humidity, the more rapid the rate of dehydration will be. Humid air slows down evaporation. Keep this in mind if you plan to dry food on hot, muggy summer days. If drying takes place too fast, however, "case hardening" will occur. This means that the cells on the outside of the pieces of food give up moisture faster than the cells on the inside. The surface becomes hard, preventing the escape of moisture from the inside.

Moisture in the food escapes by evaporating into the air. Trapped air soon takes on as much moisture as it can hold, and then drying can no longer take place. For this reason, be sure the ventilation around your oven or in your food dryer is adequate. 

Uniform Drying

Drying the food evenly takes a little extra effort and attention. Stirring the pieces of food frequently and shifting the racks in the oven or dryer are essential because heat is not the same in all parts of the dryer. For the best results, spread thin layers of uniformly-sized pieces of food on the drying racks.

TYPES OF FOOD TO DRY

Many kinds of fresh fruits, vegetables, herbs, meat, and fish can be dried. If you have never tried drying food before, though, it's a good idea to experiment first by drying a small quantity in the oven. This way you can see if you like the taste and texture of dried food. At the same time, you can become familiar with the drying process.

Fruits are easier to dry than vegetables because moisture evaporates more easily, and not as much moisture must be removed for the product to keep. Ripe apples, berries, cherries, peaches, apricots, and pears are practical to dry.

Vegetables that are also practical to dry include peas, corn, peppers, zucchini, okra, onions, and green beans. Produce from the supermarket is usually more expensive and not as fresh as it should be for drying. It is a waste of time and energy to dry vegetables such as carrots that can be kept for several months in a cool, dry basement or cellar.

Fresh herbs of all types are suitable for drying. The parts of the plant to dry vary, but leaves, seeds, or blossoms usually give the best results.

Lean meats such as beef, lamb, and venison can be dried for jerky. Fish also is excellent when dried. Certain foods are not suitable for drying because of their high moisture content. Lettuce, melons, and cucumbers are a few foods that do not dry well.