How to Dehydrate Foods

quality for keepsDeveloped by Barbara Willenberg

Revised by Susan Mills-Gray
State Nutrition Specialist

Dehydrated foods are a sensible way for busy families to make healthy, portable snacks or store seasonal produce for use. You need to carefully follow directions for preparing and pretreating produce to maintain quality. For dehydration basics, see MU Extension publication GH1562, Introducing Food Dehydration.

Fruits

Select fruit that is just ready to eat for best quality when dried; dehydration does not improve the quality of the fruit. Fruits with high water content, such as citrus fruits, are not suitable for drying. Do not use underripe produce. Fruits to be used in leathers can be overripe as long as they are not spoiled.

Prepare only as much food as you can dry at one time. Wash fruit in cold running water to remove dirt, insect larvae and any surface microorganisms. Trim away bruises or soft spots. Remove stems, cores and pits. In some cases, skins should be removed because they will become tough or brittle when dried. Slice fruits uniformly, about ¼ to ½ inch thick, for even drying, shorter drying time for a quality product. Because fruits contain sugar and are sticky, spray the drying trays with nonstick cooking spray before placing the fruit on the trays. Refer to Table 1 for notes on specific types of fruits.

Pretreatment options to prevent fruit from darkening

Pretreatments prevent fruits from darkening. Many lightcolored fruits, such as apples, darken rapidly when cut and exposed to air. If not pretreated, these fruits will continue to darken after they have dried.

Prepare a holding solution when slicing large amounts of fruit that tends to brown. This step is not necessary if only a small amount of fruit is being prepared.

Solutions for pretreating fruit can be made with ascorbic acid (vitamin C) or a ready made ascorbic acid mix, such a Fruit Fresh (Levi this needs a trademark emblem) or a full strength fruit juice.

  1. Ascorbic acid. Ascorbic acid (vitamin C) mixed with water is a safe way to prevent fruit browning. However, its protection does not last as long as sulfite dip. Use as a holding solution when slicing large amounts of fruits that tend to brown. This step is not necessary if only a small amount of fruit is being prepared. Ascorbic acid is available in the powdered or tablet form, from drugstores or grocery stores. Use 1½ tablespoons (13,500 mg) of pure crystalline ascorbic acid per quart of water. For example, if you purchase 500 mg tablets, you would use 27 tablets. After this solution is used twice, add more ascorbic acid mixture.
  2. Ascorbic acid mixtures. This is a mixture of ascorbic acid and sugar commercially sold for use on fresh fruits and in canning or freezing. It is more expensive and not as effective as using pure ascorbic acid. Follow label directions for cut fruit. Hold fruit in solution no longer than an hour because the fruit will absorb moisture and take longer to dry. After this solution is used twice, add more ascorbic acid mixture.
  3. Fruit juice dip. A fruit juice that is high in vitamin C can also be used as a pretreatment, though it is not as effective as pure ascorbic acid. Juices high in vitamin C include orange, lemon, pineapple, grape and cranberry. Each juice adds its own color and flavor to the fruit. Place enough juice to cover fruit in a bowl. Add cut fruit. Soak 3 to 5 minutes, remove fruit, drain well and place on dryer trays. This solution may be used twice, before being replaced. (The used juice can be consumed.)
  4. Sulfite dips. Only use the food-grade quality of this chemical, which can be purchased where wine-making supplies are sold. You may also purchase at natural food stores or pharmacies (ask for sodium bisulfate, sodium sulfite, or sodium metabisulfite. Soaking times vary with the type of fruit and thickness of slices (Table 1). Dissolve ¾ to 1½ teaspoons sodium bisulfate per quart of water. If using sodium sulfite, use 1½ to 3 teaspoons. If using sodium metabisulfite, use 1 to 2 tablespoons. Place the prepared fruit in the solution, and soak 5 minutes for slices, 15 minutes for halves. Remove fruit, rinse lightly under cold water and place on drying trays. Use the solution once; make a fresh solution for dipping another batch of fruit. Penetration of sulfite may be uneven, resulting in varied color retention. Also, the fruit may absorb water, which will result in a longer drying time.

    Warning: Recent research indicates that certain people with asthma may react adversely to sulfites. People who are sensitive to sulfites should avoid preparing or eating sulfite-treated foods. Sulfite fumes will be given off during the drying process; also, if sodium bisulfite is added to water for steam blanchings, fumes will escape with the steam.

  5. Honey dip. Many store-bought dried fruits have been dipped in a honey solution. A similar dip can be made at home. Honey-dipped fruit is much higher in calories. To make a similar dip at home, mix 1½ cup sugar with 1½ cups boiling water. Cool until lukewarm, and add ½ cup honey. Place fruit in dip, and soak for 3 to 5 minutes. Remove fruit, drain well and place on dryer trays.

Table 1. A guide to home drying fruits for portable dehydrators with temperature set to 140 degrees F.

 

 Pretreatment 
 Blanch 
FruitPreparationSteam (minutes)Syrup (minutes)OtherDehydrator drying time* (hours)Test for dryness (cool before testing)
ApplesPeel and core, cut into slices or rings about 1/8 inch thick.3 to 5, depending on texture10None6 to 12 hoursSoft, pliable, no moist area in center when cut
ApricotsPit and halve. May slice, if desired.3 to 410None24 to 36Soft, pliable, no moist area in center when cut
BananasUse solid yellow or slightly brown-flecked bananas. Avoid bruised or overripe bananas. Peel and slice ¼ inch to 3/8 of an inch thick, crosswise or lengthwise.3 to 410Dip into mixture of lemon juice (1 tablespoon), honey (1 /4 cup), and water (1 /4 cup), or ascorbic acid or pineapple juice; pretreat if a lighter color is desired.8 to 10Pliable to crisp
Firm berries, suitable for snacks or cookingWash and drain berries with waxy coating (blueberries, cranberries, currents, gooseberries, huckleberries).No treatment necessary Plunge into boiling water 15–30 seconds; stop cooking action by placing fruit in ice water; drain on paper towels.24 to 36Dry and leathery or crisp
Soft berries, not a superior productBoysenberries, strawberries. Sort and wash carefully.No treatment necessary  24 to 36Dry and leathery or crisp
CherriesStem, wash, drain and pit fully ripe cherries; cut in half, chop, or leave whole.No treatment necessary 

Whole: Dip in boiling water 30 seconds to crack skin (10 seconds for sour cherries).

Cut and pitted: No treatment is necessary.

24 to 36Shriveled, leathery, dry, no pockets of moisture
Citrus peelPeels of citron, grapefruit, kumquat, lime, lemon, tangelo and tangerine can be dried. Thick-skinned navel orange peel dries better than thinskinned Valencia peel. Wash thoroughly.No treatment necessary Remove outer 1 /8 inch of peel; avoid white bitter pith.8 to 12Crisp
Grapes, seedlesssLeave whole.No treatment necessary Dip in boiling water for 30 seconds or more to check skins; plunge in ice water to stop cooking; drain on paper towels.12 to 20Raisin-like texture, no moist center
Grapes with seedsCut in half and remove seeds.No treatment necessary None.12 to 20Raisin-like texture, no moist center
Nectarines and peachesWhen sulfiting, pit and halve; if desired, remove skins; for steam and syrup blanching, leave whole, and then pit and halve; may also be sliced or quartered.810None36 to 48Soft, pliable, no moist area in center when cut
PearsCut in half and core. Removing peel is preferred.6 (will be soft if peeled)24 to 36 hoursNone Soft, pliable, no moist area in center when cut
PineappleUse fully ripe, fresh pineapple; wash, peel and remove thorny eyes; slice lengthwise and remove core; cut in 1/2-inch slices, crosswise.No treatment necessary None24 to 36Leathery, but not sticky
Plums (prunes)Leave whole.No treatment necessary Dip in boiling water 30 seconds or more to check skin.24 to 36Leathery; pit should not slip when squeezed if prune is not cut
*A dehydrator is suggested rather than an oven because of time needed to dry fruits, especially those in large pieces. Range ovens can be used, but time and fuel expense will be great for the amount dried. Apples are the only fruit practical to dry in large pieces in a home oven.

Blanching

Blanching is the process of heating vegetables to a temperature high enough to destroy enzymes that would otherwise survive the dehydration process and cause the loss of color and flavor over time. It also shortens the drying and rehydration time by relaxing the tissue walls so moisture can escape and later re-enter more rapidly.

Syrup blanching

Combine 1 cup sugar, 1 cup light corn syrup and 2 cups water in a saucepan. Bring to a boil. Add 1 pound of prepared fruit and simmer 10 minutes. Remove from heat; let fruit stand in hot syrup for 30 minutes. Lift fruit out of syrup, rinse lightly in cold water, drain on paper towels and place on dryer racks. See Table 1 for fruits that may be syrup blanched. While syrup blanching adds calories to final product, steam blanching does not.

Steam blanching

Place several inches of water in a large saucepan with a tightfitting lid. Heat to boiling. Place fruit, no more than 2 inches deep, in a steamer pan or wire basket over the boiling water. Cover tightly with lid, and begin timing immediately. See Table 1 for blanching times. Check for even blanching halfway through the blanching time. Gently stir fruit to ensure even blanching. When done, remove excess moisture using paper towels and place on dryer trays.

Checking process for small whole fruits

Cherries, grapes and small, dark plums that are dried whole may require a short heat treatment, called checking, to crack the skins and to remove a naturally occurring waxy coating. Checking speeds up drying by allowing interior moisture to evaporate. If checking is not done, there is a greater chance of case hardening, which is the formation of a hard shell on the outside with moisture trapped within the fruit. Case hardening may occur more readily when fruit is dried in an oven rather than a dehydrator.

Fruit to be checked should be immersed in briskly boiling water for 30 to 60 seconds and then dunked in cold water and drained on paper towels. Treatment time depends on the thickness of skins. Checking can be done in a microwave oven by heating on high about 20 to 30 seconds, and then chilling. Some flavor loss may result from the checking process.

Table 2. A guide to home drying of vegetables.

 

 Blanching time 
VegetablePreparationSteamWaterDehydrator drying time* (hours)Characteristics
Beans, greenWash thoroughly. Cut in short pieces or lengthwise.2 to 2½28 to 14Leathery, brittle
BeetsCook as usual. Cool; peel. Cut into shoestring strips 1/8 inch thick.Already cooked. No further blanching is required.10 to 12Brittle
BroccoliTrim; cut as for serving. Wash thoroughly. Quarter stalks lengthwise.3 to 3½212 to 15Crisp
CabbageRemove outer leaves; quarter and core. Cut into strips 1/8 inch thick.2½ to 3**1½ to 210 to 12Brittle
CarrotsUse only crisp, tender carrots. Wash thoroughly. Cut off roots and tops; peel, cut in slices or strips 1/8 inch thick.3 to 3½10 to 12Tough to brittle
CauliflowerPrepare as for serving.4 to 53 to 412 to 15Crisp
CeleryTrim stalks. Wash stalks and leaves thoroughly. Slice stalks.2210 to 16Very brittle
Corn, cutHusk, trim cobs. Blanch cobs. Cut kernels from the cob after blanching.2 to 2½6 to 8Dry, brittle
EggplantUse the same directions as for summer squash.312 to 14Leathery
HorseradishWash; remove small rootlets and stubs. Peel or scrape roots. Grate.NoneNone6 to 8Brittle
Mushrooms***Scrub thoroughly. Discard any tough, woody stalks. Cut tender stalks into short sections. Do not peel small mushrooms or “buttons.” Peel and slice large mushrooms.NoneNone8 to 10Leathery
OkraWash, trim, slice crosswise in 1/8-inch to ¼-inch disks.NoneNone8 to 10Very brittle
OnionsWash, remove outer "paper shells." Remove tops and root ends, slice 1/8 inch to ¼ inch thick.NoneNone3 to 9Brittle
ParsleyWash thoroughly. Separate clusters. Discard long or tough stems.NoneNone1 to 2Brittle, hard
PeasShell.328 to 10Wrinkled, green
Peppers and pimientosWash, stem, core. Remove "partitions." Cut into strips, slice or dice.NoneNone8 to 12Leathery to brittle
PotatoesWash, peel. Cut into shoestring strips ¼ inch thick, or cut in slices 1/8  inch thick.6 to 85 to 68 to 12Brittle
Spinach and other greens (kale, chard, mustard)Trim, wash thoroughly.2 to 2½18 to 10Crisp
Hubbard squashCut or break into pieces. Remove seeds and cavity pulp. Cut into 1-inch-wide strips. Peel rind. Cut strips crosswise into pieces about 1 /8 inch thick.2½ to 3110 to 16Tough to brittle
Summer squashWash, trim, cut into ¼-inch slices.2½ to 3110 to 12Leathery to brittle
Tomatoes, for stewingSteam or dip in boiling water to loosen skins. chill in cold water. Peel. Cut into sections about ¾ inch wide, or slice. Cut small pear or plum tomatoes in half.3110 to 18Leathery
Tomatoes, slicedWash, remove core, and cut crosswise into 1 /4- to 3 /4-inch slices. No peeling or blanching is necessary. Slices can be lightly sprinkled with crumbled dry oregano or other dry herbs of your choice before drying.NoneNone6 to 12Leathery to brittle
*Drying times depend on initial moisture content of the product and the particular dehydrator being used. Drying times in a conventional oven could be up to twice as long, depending on air circulation.
**Steam until wilted.
***WARNING: The toxins of poisonous varieties of mushrooms are not destroyed by drying or cooking. Only an expert can differentiate between poisonous and edible varieties.

Fruit leathers

A variety of fruits can be used for leathers. Some favorites include apples, apricots, bananas, peaches, pears and plums. They can be used singly or in combinations. Spices such as cinnamon, cloves, ginger, nutmeg and mint add extra flavor. Fruits are naturally sweet, so it is usually unnecessary to add sweetener.

Making fruit leather

Use a blender or food processor to puree about 1 cup of fruit chunks at a time. To keep light-colored fruits from turning dark, add 2 teaspoons lemon juice or 1/8 teaspoon ascorbic acid per 2 cups of fruit. Puree fruit.

Thicken juicy puree to shorten the drying time. Place pureed fruit in a deep, heavy saucepan, and cook over low heat, stirring constantly, until mixture thickens. Remove from heat and cool.

Drying concentrates flavors, making the fruit leather taste sweeter than the puree. If you desire to sweeten, use ¼ to ½ cup corn syrup, honey or sugar for each 2 cups of fruit. Corn syrup or honey is best for longer storage because both prevent crystals. Sugar is fine for immediate use or short storage. Saccharin-based sweeteners could also be used to reduce tartness without adding calories. Keep in mind that heat diminishes sweetness of products made with aspartame sweeteners, and may leave a bitter after taste. For extra flavor, add ¼ teaspoon cinnamon or a dash of nutmeg per quart of puree.

To dry fruit puree in an electric dehydrator, use specially designed solid liners that are included with most electric dehydrators. You may also line the plastic dryer trays with plastic wrap. Be careful to avoid leakage.

For drying in the oven, a 13-by-15-inch cookie pan with short raised edges works well. Line the pan with parchment or plastic wrap, rather than waxed paper or aluminum foil, making sure to smooth out any wrinkles. Silicone nonstick baking mats can also be used to line the cookie pan.

Whether using an electric dehydrator or the oven, spread puree evenly, about 1/8 inch thick, onto the liner in the drying tray. Avoid pouring puree too close to the edge of the tray as the edges could burn before the center is done. Approximate drying times are 6 to 8 hours in an electric dehydrator or up to 18 hours in an oven.

Dry fruit leathers at 140° F. Leather dries from the outside edge toward the center. Test for dryness by touching the center of the leather; no indentation should be evident. While leathers are warm, peel from plastic and roll. Allow to cool, and rewrap the roll in plastic. Cookie cutters can be used to cut out shapes that children will enjoy. Roll, and wrap in plastic.

Chances are the fruit leather will not last long enough for storage. If it does, it will keep up to 1 month at room temperature. For storage up to 1 year, place tightly wrapped rolls in the freezer.

Vegetables

Vegetables do not need pretreatment. Instead, they must be blanched before need to be blanched before drying to stop enzyme activity. If enzymes are not destroyed, they will produce off-flavors and the vegetables will turn brown during the drying process and in storage. Blanching times vary with vegetables and thickness of slices (Table 2.)

To blanch, use 1 gallon water per pound of prepared vegetables. Place vegetables into a wire basket, coarse mesh bag or perforated metal strainer and lower into boiling water. If it takes longer than 1 minute for the water to come back to boiling, too many vegetables were added. Reduce the amount in the next batch.

To steam blanch, add 1 to 2 inches of water to a large pot and bring to a boil. Place a single layer of vegetables in a basket nestled above the boiling water. Cover. Start counting immediately as soon as the water returns to a boil.

Keep heat high for the time given in the directions. Cool immediately in ice water for the same time used in blanching. Stir vegetables several times during cooling. Drain vegetables thoroughly prior to transferring to the dehydrating tray. See Table 2 for specific directions for each food.

Dairy products and eggs

Milk, milk products and eggs are not recommended for home drying because of the high risk of food poisoning. Commercially dried milk and egg products are processed rapidly at temperatures high enough to prevent bacterial contamination. Home dehydrators cannot duplicate this process, and the safety of home-dried milk and egg products cannot be guaranteed.

Meat jerky

Use lean meat such as turkey, venison, elk, beef flank steak or pork tenderloin. The leaner the meat, the better the product. Cut partially frozen meat into slices no thicker than ¼ inch. Uniform slices will shorten drying time and ensure even drying among the pieces.

The thickness of the meat strips will make a difference in the safety of the methods recommended. Trim and discard all fat from meat because it becomes rancid quickly. If a chewy jerky is desired, slice with the grain. Slice across the grain if a tenderer, brittle jerky is preferred. If desired, a tenderizer can be used according to package directions, if desired. The meat can be marinated for flavor and tenderness. Marinade recipes may include oil, salt, spices and acid ingredients such as vinegar, lemon juice, teriyaki or soy sauce, or wine.

Jerky marinade*

  • ¼ cup soy sauce
  • 1 tablespoon Worcestershire sauce
  • ¼ teaspoon black pepper
  • ¼ teaspoon garlic powder
  • ½ teaspoon onion powder
  • 1 teaspoon hickory smoke flavored salt

*Recipe for 1½ to 2 pounds of lean meat. Adjust quantities for the size of your dehydrator or oven trays.

Procedure:

  1. Combine all ingredients. Place strips of meat in a shallow pan, and cover with marinade. Cover and refrigerate 2 to 12 hours.
  2. To decrease the risk of foodborne illness, the meat must be heated either before or after drying. If you choose to heat the meat before drying, do so at the end of the marinating time. To heat, bring strips and marinade to a boil. Boil for 5 minutes, drain and dry. If strips are more than ¼ inch thick, the length of time may need to be increased. Remove meat strips from the marinade, and drain on clean, absorbent towels.
  3. Arrange strips on electric dehydrator trays, or on cake racks placed on baking sheets for oven drying. Place the strips close together, but not touching or overlapping. Place the racks in a dehydrator or oven preheated to 140° F.
  4. Begin checking samples after 3 hours. The jerky is dry if a test piece cracks, but does not break, when it is bent. Samples heated in marinade will dry in about 3-5 hours or longer, depending on thickness.
  5. If the strips were not heated in marinade before drying, they should be heated in an oven after drying as an added safety measure. Place the dried strips on a baking sheet, close together, but not touching or overlapping. For strips originally cut ¼ inch thick or less, heat 10 minutes in an oven preheated to 275° F. Samples heated after drying may take 10 to 24 hours to dry.
  6. Once drying is completed, pat off any beads of oil with clean, absorbent towels, and cool. Remove strips from the racks. Cool. Package in glass jars or heavy-duty plastic food storage bags. Vacuum packaging is also a good option.

References

  • White, Athalie, Ann Ford, Elizabeth L. Andress, and Judy A. Harrison. 2014. So easy to preserve, 6th ed. University of Georgia Cooperative Extension Service.