DRYING FOOD AT HOME

1. Foods Suitable for Drying

• A. Fruits and vegetables should be ripe but firm and at peak maturity.
  • a. Fruits which have a high sugar content (peaches, apricots) dry well. You may need to "rupture" their skins for even drying. If very high sugar foods are dried too rapidly, they may form a "case" of leathery material over the outside which won't allow water to pass through-these fruits must be dried very slowly.
  • b. Ripe vegetables are more flavorful than underripe, and are less tough than overmature. Skins may become very brittle and sharp (tomatoes, green peppers) so you may want to remove them.
  • c. Herbs and spices: pick them when the plant is young before flowering (later they get woody and bitter).
  • d. DO NOT DRY MILK OR EGGS AT HOME BECAUSE OF THEDANGER OF SALMONELLA.
• B. Produce should be undamaged by insects or microorganisms. Any bruised or damaged parts must be removed before drying the produce.
• C. Trim or cut produce to uniform thickness or size (slices of 1/8 to ¼") to facilitate even drying. Pierce skins of thick, sweet and juicy fruits, or those with "tough skins" (eg. grape)
• D. Meats should be low in fat and well-trimmed (jerky).
• E. Dry foods you have a lot of which may not be available year round (green pepper, chili peppers).
• F. Dry what you know you will eat.
• G. Dry foods which have acceptable quality when dried.

2. Preparation of Food for Drying

• A. Wash, sort, pare, peel or otherwise open up to expose the inner tissues to the air. If you want to dry whole, small fruits (grapes, small plums, etc.), blanch to open the skins or prick them with a fork so moisture can get out.
• B. Pretreat-Most fruits and vegetables require pretreatment to stop enzymatic activity which can result in color, flavor and nutrient losses or changes.
• Pretreatments:
  • a. Ascorbic acid mixture (vitamin C) (used for fruits)
    • Ascorbic acid 1 tsp = 3000 mg (8 tsp/25 grams)
    • 1 tsp crystalline = 1500 milligrams
    • Solution: refrigerate up to 2 days prior to use Use ¼ to ½ teaspoon crystalline / qt of water.
  • Crushed tablets: 1 tsp (or 3000 mg) / 1 cup of syrup(tablets are of lower ascorbic acid concentration than crystalline ascorbic acid).
  • Dip fruit in solution for 30-60 seconds.
  • b. Citric acid (dissolve) (used for fruits): sometimes sold as "sour salt" or "lemon salt"-requires 3 times as much, measure-for-measure, as ascorbic acid. Dip fruit in solution for 30-60 seconds.
  • c. Lemon juice (used for fruits): 3 tablespoons / quart of water. Dip fruit in solution for 30-60 seconds.
  • d. Steam blanch (used for vegetables): 1-3 min in live steam.
  • e. Salt water treatment(used for fruits or vegetables): prevents browning but may cause some greying of the color. Dip fruit or vegetables in solution for 60 seconds. 2-4 tbsp/ gallon of water
  • f. Sulfur (used for fruits). See "Sulfuring Fruits for Drying" (EHE-691)
• Sulfuring: can be done by placing food in a semi-closed system and burning rock sulfur to deposit sulfur on the surface of the food, or by dipping the food in a sulfur solution. Sulfur to burn is sold as "flowers of sulfur", "sulfur berries", or"sublimed sulfur" at drugstores and chemical supply companies. Sulfite Dip: Sodium bisulfite (1 ½ tsp / gal.), sodium sulfite (1 tsp / gal.),or sodium metasulfite (2 tbsp / gal.) is used for soaking slices (5 minutes) or fruit halves (15 minutes). Drain well and dry.

3. The Drying Process

• A. Oven: cover racks with food grade material such as stainless steel window screen or cheesecloth in an electric oven (Do not use aluminum or galvanized screening-food acids will degrade them or leave metal residues in the food, and may cause flavor and color changes). Preheat oven to 150 F. Drop drying temperature to 140 F after 1-2 hours. Leave space around the racks for air circulation. Check temperature with a thermometer several times, prop door 2-4" open and place a fan at one side to blow across the open door and remove wet air. Oven drying is not recommended for sulfured fruits because of the odor of sulfur fumes
• Problems: scorching, expensive, danger of getting burned. Oven drying should be done at 140 F. Watch food closely towards the end of the drying period to prevent scorching. You may need to turn the heat down to 120 F for the last ¼ of drying period.
• B. Food dehydrator: a dehydrator should have:
  • a. Some form of temperature control
  • b. A fan to circulate air and remove moisture
  • c. Easily removable, washable trays
  • A dehydrator should be operated where there is a clear flow of air. Some vegetables will release odors in large quantities during the early part of the drying period, so you may want to locate the dehydrator where these odors will not be bothersome. Do not put dehydrators in the garage-gasoline and oil odors will end up in the dried food products.

Procedure:

• 1. Preheat the dryer to 150 F (extra 10 F counteracts the temperature- lowering effect of cool food).
• 2. Place food on racks in a single layer, so that pieces do not touch each other and so there is 1" around the edges.
• 3. After 1-2 hours, set thermostat back to 140 F.
• 4. Put racks in the drier-don't mix strong and mild flavored foods.
• 5. Check progress of food every 2 hours at the beginning, and more often towards the end.
• 6. Rotate trays and turn food to promote even drying.
• 7. Do not interrupt the drying-once you start, finish it. Partially dry food will mold. Do not add fresh food to a dryer containing partially dried food.

4. Drying is done when:

• a. Fruit is tough, leathery, pliable, does not have moist center when cut. Is not brittle. 15% moisture.
• b. Vegetables are brittle, will crack if bent, shatter if hit with a hammer when cool. 4-5% moisture.

5. After Food is Dried

• A. Conditioning dried fruit: allowing the moisture to equalize through all the food so there are no damp spots where mold will grow. Place dried food in large glass or plastic container (fill half way).Cover container tightly. Check every 24 hours for 3 or 4 days for condensation (moisture on the top or sides of the container). If condensate appears, return food to dryer. Dried vegetables do not need conditioning.
• B. Pasteurization: to kill any eggs laid on the food while it was outside.
  • a. Freeze below 0 F for 1-2 weeks. Remove and store at room temperature.
  • b. Dry Heat pasteurize: Place food loosely less than 2"deep in pan and place in preheated oven. Pasteurize at 175 F for 15 min or 160 F for 30 min. Cool, package and store.
• C. Packaging
  • a. Must be moisture proof and impervious to insects.
  • b. Package in useable amounts.
  • c. Squeeze air out of flexible plastic bags.
  • d. Do not store sulfured food in a metal can-fumes will corrode the can and give food off-flavors.
• D. Storage
  • a. Protected from insects.
  • b. Away from light and heat.
  • c. Use of drying agents: in humid areas, you can use silica gel" (find at floral shop-used to dry flowers). Put ½-3/4 cup in a cloth bag for a 3-5 gallon container.
  • d. Cool area-below 60 F. For every 18 F decrease in temperature, the storage time will be increased by 3-4 times.
• E. Rehydration
  • a. Vegetables: rehydrate with ¼ cup water for each Tablespoon of powdered vegetables for cream soup consistency. Once rehydrated, vegetables will support the growth of CLOSTRIDIUM BOTULINUM
  • b. Fruits: place in small amount of water, simmer or steam. Do not leave on the stove overnight-mold may grow.
  • c. Foods which require more than 2 hours to rehydrate should be rehydrated in the refrigerator or in simmering water.

Prepared by Susan Brewer
Foods and Nutrition Specialist
Revised, 1992 EHE-690

Last updated on April 03, 1996