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Drying Fruits -- Mississippi State Univ. Extension Service

  Drying Fruits

For thousands of years, people have dried fruits to preserve for leaner times. Preserving foods by drying is still useful, convenient, and inexpensive, and dried fruits need little storage space.

Basically, drying preserves food by removing enough moisture from food to prevent decay. Drying requires a method of heating the food to evaporate the moisture and removing the water vapor formed.

Selection of Produce

Select sound, ripe, firm fruit. Fruits ripened on the tree, vine, or bush have a better flavor and color. Wash fruit thoroughly to remove dirt and insecticides. Discard mushy, decayed, bruised, or molded fruit. Some will need to be peeled or have seeds removed; other fruits can be dried as they are.

Pretreating

Enzymes in fruit are responsible for color and flavor changes during ripening. These changes continue during drying and storage unless the produce is pretreated to slow down enzyme activity. Many fruits, especially apples, peaches, and pears, tend to darken during drying and storage.

Fruits may be pretreated by sulfuring, salt solution, ascorbic acid solution, or steam blanching.

Sulfuring Outdoors (Burning Method)

Sulfuring is the most effective treatment to retard darkening. Use Sulfur Flowers U.S.P. or flowers of sulfur that may be bought at most pharmacies. This sulfur has no impurities and burns readily. Do not use garden-dusting sulfur; it contains impurities.

1. Always burn sulfur outdoors in an open area. Sulfur fumes can be irritating to the eyes and nose and can harm plants, shrubs, and trees.
2. Use wooden trays with ventilated bottoms. Do not use aluminum or galvanized screening materials, because sulfur fumes discolor and corrode most metals.
3. Weigh fruit. Generally, if you use a cardboard box to cover the trays, use 1 tablespoon of sulfur per pound of fruit (weight before drying). If you use a more airtight wooden box, use 1 1/2 teaspoons of sulfur per pound of fruit. Prepare fruit as directed in this publication. Spread fruit in a single layer; pieces should not touch each other.
4. 4. Stack the trays at least 1 1/2 inches apart so sulfur fumes can circulate. Raise the bottom tray with wooden blocks on bricks 8 to 10 inches above the ground. Separate trays with small wooden blocks or spools.
5. Pour sulfur about 1/2 inch deep into a clean metal container that is shallow but deep enough to prevent overflow.
6. Place the container of sulfur beside the stacked trays; ignite the sulfur. If it doesn't burn, put in a small piece of paper. Roll the paper loosely and twist the ends closed. Do not leave burned matches in the container; they may keep the sulfur from burning completely. Because of the flame and heat from the burning sulfur, allow enough space between the container, the trays, and the sides of the cover. The burning time of sulfur varies with the ventilation, shape of sulfur container, weather conditions, and amount of fruit to be sulfured.
7. Cover the stacked trays with a heavy cardboard or wooden box that has no cracks or openings. The box should be several inches higher than the stacked trays and at least 1 to 1 1/2 inches wider on all sides of the trays, including the sulfur container placed beside them.
8. To provide air for the burning sulfur, leave the bottom of the box propped up slightly, or cut an opening at the bottom (about 1 inch by 6 inches), leaving a flap. The opening should be on the side by the sulfur. A slash or small opening may be needed at the upper edge of the opposite side. When sulfur is burning well, after about 15 minutes drop the box or close the openings. Seal the bottom edges to the ground with dirt or rocks.
9. Sulfuring is complete when fruit appears bright and glistening; generally it takes about 1 to 2 hours. Various factors affect sulfuring time, including texture of the fruit, size of pieces, and whether fruit is to be sun-dried or dried under controlled conditions. After sulfuring, remove the trays and begin drying the fruit. Do not dry sulfur-treated fruit in your oven because of the objectionable odor.

Salt Solution

You can pretreat fruit in a salt solution. Prepare a solution of 2 to 4 tablespoons of salt to 1 gallon of water. Soak the fruit 15 to 30 minutes; then drain well. Fruit treated in this way takes longer to dry than fruit that is not soaked.

Ascorbic Acid Solution

Another method of drying fruit is to use pure ascorbic acid, which you can buy at drug stores.

For apples, dissolve 2 1/2 teaspoons of crystalline ascorbic acid in each cup of cold water. For most other fruits, 1 teaspoon of ascorbic acid per cup of water is enough. One cup of this mixture treats about 5 quarts of cut fruit. Sprinkle the solution over the fruit as you prepare it.

Commercial ascorbic acid mixtures do not work as effectively but are easier to find at grocery and drug stores. Use about 4 teaspoons to a quart of water. Soak fruit no longer than 15 to 30 minutes. Remove fruit and drain.

Steam Blanch

Steam blanching can be used for pretreating. Put 1 1/2 to 2 inches of water in a boiler; let it come to a boil. Place fruit loosely, not more than 1 inch deep, into a colander or basket. Put it (basket or colander) into the boiler and place a tight-fitting lid on it. Follow directions in the table for blanching time. Spread fruit on a clean cloth or paper towel to remove extra moisture.

Water blanching gives fruit a cooked flavor, so it is not generally recommenced. Steam blanching does not give a cooked flavor.

Drying

Get the drying process underway as soon as possible. After pretreating, remove any excess moisture by placing the food on paper toweling or clean cloths. Arrange the fruit on drying trays, leaving small spaces between slices or pieces for air circulation. Food should be only one layer deep.

Successful drying depends on:

• Enough heat to draw out moisture, but not so much to cook the food. Hot sunny days are best for sun drying. Low heat, about 140 °F, dries it even faster. Do not let the heat go above 165 °F.
• Dry air to absorb the released moisture. Rainy, humid weather is a bad time to dry food, unless you are using heat.
• Air circulation to carry off the moisture. A light breeze, a fan, or a draft supplies moving air.

Try to interrupt the drying process as little as possible. Sun-drying is slowed at night because the temperature drops or the fruit is brought inside. Prolonged drying at low temperatures or interrupting the drying process may result in fermentation or spoilage.

Sun-Drying

Place trays of fruits in direct sun in a flat or tilted position so that air can circulate underneath them. Cover trays with netting to protect food from insects. Raise trays off the ground or place them on a roof to protect them from dust, dirt, and animals. Stir food gently several times each day so it will dry evenly. Bring trays indoors at night to protect the food from dew or rain. Sun drying may take a few to several days, depending on thickness of fruit, how full the trays are filled, and moisture content of the fruit.

Oven-Drying

Oven-drying is faster than sun-drying. However, oven-drying is done on a smaller scale and is more expensive than sun-drying. Limit oven load to 4 to 6 pounds of fresh prepared fruit. Trays should be at least 1 1/2 inches smaller than the width and depth of the oven. Separate trays by about 2 1/2 inches. Allow a 3-inch clearance from the top and bottom of the oven. An oven temperature of 140 °F is desirable for drying. Disengage the top heating element of an electric oven. Preheat at its lowest setting. Place the trays in the oven. Prop open the door of an electric oven 1 inch, a gas oven 8 inches. This helps control heat and lets out moist air. A fan can help circulate the air and speed the drying. Use a thermometer to check the temperature throughout the drying process. Stir the food occasionally from the outside to the center and shift trays from top to bottom every 1 to 2 hours. Foods dried in the oven must be watched closely. It is easy to scorch food that overheats near the end of the drying time. The drying time will vary according to the fruit, size of pieces, and tray load. Do not dry sulfur-treated fruit in the oven.

Using a Dehydrator

Prepare foods and load trays as for oven-drying. Preheat the dehydrator 160 °F. Reduce the temperature to 140 °F to complete the drying. Do not add fresh, moist pieces of fruit to a dryer filled with partially dried fruit. The increased humidity greatly increases the drying time of the partially dried fruit.

Testing for Dryness

Cool the food before testing for desired dryness. Foods that are warm or hot seem softer, more moist, and more pliable than they will be when cooled. Foods should be dry enough to prevent microbial growth and subsequent spoilage.

When the fruit is cool, squeeze it. Open your hand; if the fruit separates, it is dry enough to store. If it stays in a "ball," it had too much moisture and needs additional drying. Fruit should be leathery and pliable when dry enough for storage.

Conditioning and Pasteurizing

When drying is completed, some pieces will be more moist than others because of the size of the pieces or their location in the dryer. Conditioning equalizes the moisture. Place cooled fruit in a glass or plastic container or crock. Metal containers may give an unpleasant flavor to the fruit. Cover the container tightly and let stand for 3 days to a week. Stir the fruit gently each day.

Pasteurizing is recommended when fruits are sun-dried. Insects that may have gotten on the fruit while it was drying can cause it to spoil during storage. To pasteurize, spread the dried, conditioned fruit on trays in a single layer. Place in a preheated oven, 175 °F for 15 minutes or at 160 °F for 30 minutes. Remove and cool the fruit. You may also pasteurize fruit by sealing it in heavy plastic bags and placing the bags in the freezer at 0 °F for at least 48 hours.

Packaging

Dried foods should be thoroughly cooled before packaging. Pack the fruit as tightly as possible (without crushing) into clean, dry, insect-proof containers. Some good containers are fruit jars, coffee cans with tight lids, and plastic freezer bags you can seal with heat, twist tapes, string, or rubber bands. Package fruits in small amounts that can be used within several days after opening. There will be a slight deterioration in quality every time the fruit is exposed to air.

Storing

Store containers of dried fruit in a dry, cool, and dark place. Low storage temperatures extend the shelf life of the dried product. Check the fruit occasionally to insure that moisture has not been reabsorbed. You can see any moisture that collects on the inside of glass jars or plastic bags. If this happens, rescue the fruit by heating it to 150 °F for 15 minutes and resealing. If there is any sign of spoilage (off-color or mold growth), discard the food. Recommended storage time is 6 to 12 months.

Cooking

One cup of dried fruit reconstitutes to about 1 1/2 cups. Add water just to cover the fruit; you can add more later if needed. It takes 1 to 8 hours to reconstitute most fruits. The time varies with the kind of fruit, size of pieces, and the temperature of the water. Hot water takes less time. Oversoaking will produce a loss of flavor.

To cook reconstituted fruit, cover and simmer in the soak water to retain the nutritive quality and flavor. Add sugar near the end of the cooking process so it will not interfere with the fruit's absorption of water. Adding a few grains of salt helps bring out the natural sweetness of most fruits. Fresh lemon or orange juice added just before serving will help give a fresh fruit flavor.

Drying Fruits

Distributed by Melissa Mixon, Ph.D., R.D., L.D., Leader, Extension Home Economics