Food dehydration

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Food Dehydration is food preservation method with a very long history. Dehydration generally uses some combination of heat, smoke, and/or air flow to remove moisture from food, making it more stable at room temperatures and is often used as a preparation for some secondary form of storage such as vacuum storage.

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Contents

Why Dehydration

Dehydration makes food smaller, lighter, more stable at room temperatures, and can be accomplished with or without the aid of modern technology. Dehydration also occurs a much lower temperatures than canning, leaving far more nutritional value intact. Dehydration yields much more portable food as the food will be lighter and not require fragile containers.

Supplies & Equipment

Only a dehydrator is necessary to perform dehydration. This can be a modern, electric dehydrator, a conventional oven or a solar dehydrator.

Electric Dehydrators

Popular electric dehydrators include the tray stacking models from Nesco, and the slide-in tray models from Excalibur. The main differences in the two dehydrators are price, and the drying method used. The Nesco models are significantly cheaper ($70-120) than the Excalibur dehydrators ($150-250). The Excalibur dehydrators implement the heating and fan element that blows horizontally across all trays, providing even and consistent drying. The Nesco dehydrator places the fan and heating element on the top of the unit, which blows the heated air downward. In order to provide even drying and concurrent completion of the dehydrated items, the trays may need to be rotated throughout the dehydrating process (take the top tray and move it to the bottom, repeat), or placing the items that need longer drying time at the top of the tray stack.

Conventional Oven

By combining low heat, low humidity, and air flow, a standard kitchen oven can be used as a dehydrator. Oven drying will take up to two times longer since they don't typically have fans to move the air. To use your oven first check that it can be set to as low as 140 F. If the oven will not go that low, then the food will cook instead of dry. For air circulation leave the oven door propped open 2 to 6 inches. Further circulation can be added by placing a fan outside of the propped door. This will cause the temperature to fluctuate so adjustments to the temperature may be necessary. Drying trays should be narrow enough to clear the sides of the oven and 3 to 4 inches shorter than the oven from front to back. Cake cooling racks placed on top of cookie sheets will work sell for some foods. The oven racks holding trays should be 2 to 3 inches apart for air circulation.

Solar Dehydrator

Solar dehydrators can be commercially purchased or you can build them yourself. They offer the benefit of not requiring electricity to perform the dehydration, which works well in an off grid or SHTF situation. A sheet of glass or clear plastic sheeting is placed over a vented box made of wood or other materials that trap the suns heat inside. This heats and helps to dry the food inside. The dehydrator will also contain an absorber plate which will assist in the drying. The plate will indirectly heat the food and create a convectional air current bringing cool air from outside though the bottom vents which will heat up inside the dehydrator and the warm air will exit through the top and side vents. The key to a solar dehydrator is to produce enough air flow to dry the food fast enough before it can spoil. Heat is important, but typically the cause for a solar dehydrator to fail will be with the lack of air movement.

An example of a build your own design can be found here

Dehydration Tips

  • Blanch vegetables prior to dehydration
  • Select the best quality produce at the peak of ripeness and flavor
  • Fruits and vegetables should be dried in the range between 130 to 140 F (55 to 60 C)
  • Meats should be dried at higher temperatures, the highest setting typically if using an appliance dehydrator
  • For solar dehydration you may want to slice your food thinner to speed up the drying process

Fruit Drying Guidelines

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Drying fruit is ideal because they have a naturally high sugar content. They are high in acid, are less prone to spoilage and taste delicious when dried. Obtaining fruit seasonally from your own garden, orchards and farmers markets in bulk will typically offer the benefit of purchasing at lower cost and allow for dehydrating in large batches.

Preparing fruits

Wash fruits and cut away any bruised or spoiled portions. Some fruits are prone to oxidation(browning), by pre-treating them it will give you superior quality, better looking and better tasting dried fruit. Apples, pears, peaches and apricots benefit from being pre-treated.

Natural Pre-Treatment

Fruit Juice Dip: Fruit juices containing absorbic acid may be used as a natural pre-treatment to reduce oxidation. Although there might be some loss of color, the use of pineapple, lemon, lime or orange juice may be used a pre-treatment when mixed with a water solution. Usually a 1 to 1 ratio of juice to water will be adequate, but you might experiment to see what works best. Place cut fruits into the solution for 5 to 10 minutes before dehydrating, then drain well. Do not let fruit sit in the solution for longer than an hour.

Abscorbic Acid: Abscorbic acid (vitamin C) mixed with water is another safe way to prevent oxidation. Abscorbic acid is available in powder and tablet form from drugstores and grocery stores. One teaspoon of powdered abscorbic acid is equal to 3000mg of abscorbic acid in tablet form. Mix 1 teaspoon of powdered abscorbic acid in 2 cups of water and mix well. Place the fruit in the solution for 3 to 5 minutes. Remove fruit, drain well and its ready to be dehydrated.

Drying fruit

Whichever method you decide to use for drying the fruit, place the fruit in a single layer on the drying trays. The fruit should not touch or overlap. Follow the guidelines in the table below and dry until the food tests dry. Food dries much faster at the end of the drying period, so watch it closely. Most fruits should not be dehydrated to the point of brittleness if you plan to eat them without re-hydrating. To test for dryness, cut several cooled pieces in half. There should be no visible moisture, and you should not be able to squeeze any moisture from the fruit. Some fruits will remain pliable but shouldn't be sticky or tacky. After drying, cool fruit for 30 to 60 minutes before packaging. Packaging the food warm can lead to sweating and moisture buildup and should be avoided.

Fruit Drying
Food Preparation Average Drying Time Uses
Apples Core, cut in 3/8" slices, treat with lemon/lime juice 4-10 hrs Applesauce, pies, cobblers, rings, snacks, breads and cookies
Apricots Halve, remove pit then quarter, treat with lemon/lime juice 8-16 hrs Desserts, muesili, meat dishes, pies and sauces
Bananas Peel, cut in 3/8" slices or divide lengthwise 6-12 hrs Snacks, baby food, granola, cookies, banana bread
Blueberries Wash, remove stems, freeze (optional but reduces drying time drastically) 10-18 hrs Breads, baked goods, snacks, ice cream, yogurt
Cherries Wash, remove stems and pit 18-26 hrs Breads, baked goods and snacks
Citrus Peel, if desired. Slice 3/8" thick 6-12 hrs Flavorings when powdered
Cranberries Wash, remove stems, freeze (optional but reduces drying time) 10-18 hrs Breads, baked goods, snacks, yogurts
Coconut Remove dark outer skin, slice 3/8" thick 3-8 hrs Cakes, cookies, desserts and granola
Figs Remove stems and halve 8-15 hrs Fillings, cakes, puddings, breads and cookies
Grapes Remove stems 10-36 hrs (6-10 hrs if blanched) Raisins; use in baked goods, cereals and snacks
Kiwi Peel, slice 3/8" thick 5-12 hrs Snacks
Lemon Powder Zest of rind 8-12 hrs Seasoning
Mangos Peel, slice 3/8" thick from seed 6-16 hrs Snacks, cereals and baked goods
Melons Remove skin and seeds. Slice 1/2" thick. 8-20 hrs Snacks
Nectarines Slice 3/8" thick, treat with lemon or lime juice 6-16 hrs Snacks, desserts and baked goods
Peaches Halve, quarter or 3/8" thick slices 6-16 hrs Snacks, breads, cobblers, cookies and granola
Pears Peel, core and slice 3/8" thick 6-16 hrs Snacks, breads, cookies, fritters and granola
Pineapple Peel, core, slice 1/2" thick 6-12 hrs Snacks, baked goods, baked granola
Plums Halve or quarter, remove pit 8-16 hrs Snacks, cookies, muffins, bread and granola
Rhubard Slice in 1" lengths. Steam until slightly tender. 6-14 hrs Pies, tarts and other desserts
Strawberries Slice 1/2" thick 6-12 hrs Snacks, cereals and baked goods

Vegetable Drying Guidelines

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Some vegetable are quite good when dried. Others will lose their appeal and are better suited to be eaten fresh or preserved by canning or freezing. Vegetables have a lower sugar content and are low in acid, which makes them more susceptible to spoilage, and a reduced shelf life when compared to fruit. Vegetables will need to be dehydrated to the point of being brittle. Packaging and ideal storage conditions are key elements to producing dried vegetables which will taste good all year long.

Preparing Vegetables

Wash vegetables thoroughly and remove any blemishes. Peel, trim, core, and/or slice vegetables.

Pre-treating Vegetables

Blanching is a necessary pre-treatment for most vegetables before dehydrating. Blanching stops the enzyme action that could cause loss of color and flavor during drying and storage. It also will reduce the drying and rehydration time by relaxing the tissue walls of the vegetables.

Water Blanching:

Fill a large pot two-thirds full of water, cover, and bring to a rolling boil. Place the vegetables in a wire basket or a colander, and submerge them in water. Cover and blanch according to directions in the table below. Begin timing the blanch process once the water has returned to a boiling after adding the vegetables. If it takes longer than one minute to return to a boil, then you added too many vegetables. Reduce the amount in the next batch.

Steam Blanching:

Use a commercial steamer or deep pot with a tight fitting lid and a wire basket, colander, or sieve placed so that the steam will circulate freely around the vegetables. Add water to the pot, and bring to a rolling boil. Place the vegetables loosely in the basket and no more than 2 inches deep. Make sure the water does not come in contact with the vegetables. Cover the pot, and steam. Steam until vegetables are heated completely through, but not cooked. This is usually about 1/3 of the time required to cook the vegetable. Vegetables should still be crunchy. Drain in steamer rack and place immediately on dryer trays.

Microwave Blanching: A microwave oven is ideal for blanching vegetables. Prepare them in the same manner as for steam blanching. Place them in microwave-safe dish, cover and cook on high for about 1/2 of the time required to completely cook the fresh vegetable. Depending on the style, and age of your microwave oven, you may want to stop the cooking halfway through and stir the vegetables to achieve a more uniform and even blanching.

Drying Vegetables

After blanching, dip the vegetables briefly in cold water. Drain and arrange them onto drying trays so that air can move freely between the pieces. For vegetables such as corn or peas, that tend to clump together, stir occasionally to allow air to reach all of the pieces. Vegetables need to be dried until they are crisp, brittle, or tough. Package immediately after drying to prevent moisture reabsorption.

Vegetable Drying
Food Preparation Average Drying Time Uses
Artichoke Cut hearts into 1/8" strips. Blanch. 6-12 hrs Marinate or dip in batter and fry
Asparagus Wash and cut into 1" pieces. Blanch. 3-10 hrs Rehydrate, service in cream sauce
Beans Green/Wax Remove ends, cut into 1" pieces. Blanch. 6-12 hrs Stews, soups and casseroles
Beets Steam until tender. Cool and peel. Cut into 1/2" pieces 3-10 hrs Soups and stews
Broccoli Wash, cut as for serving. Blanch. 4-10 hrs Soups, quiche or souffles, cream or cheese sauce
Carrots Peel, cut ends, slice in 3/8" thick slice or shred. Blanch. 6-12 hrs Salads, soups, stews and carrot cake
Cauliflower Wash, cut as for serving. Blanch. 6-14 hrs Soups and Stews
Celery Trim, wash and cut 1/2" slices. Blanch in solution of 1/2t of baking soda to 1 cup water. 3-10 hrs Soups, stews, power for celery salt(add equal parts celery and salt).
Corn Husk, remove silk and blanch. Remove from cob. 6-12 hrs Fritters, soups, stews or grind for cornmeal
Eggplant Peel, slice 1/4" thick. Blanch. 4-14 hrs Cream sauces, casseroles, dip in batter and fry
Garlic Separate and peel cloves. 6-12 hrs Powder for seasoning
Mushrooms* Clean with paper towel, don't wash. 4-10 hrs Rehydrate for soups, meat dishes, omelettes or frying
Onions Remove skins, tops and root ends. Slice 3/8" thick. 6-12 hrs Soups, stews and sauces. Powder for seasoning salt. Package immediately.
Peas Shell, wash and blanch 5-14 hrs Soups, stews and mixed vegetables
Peppers (sweet) Remove stem and seeds. Cut into 1/2" pieces. 5-12 hrs Soups, stews, pizza and seasoning.
Peppers (hot) Wash, slice or cut in half. Remove seeds for milder pepper. 3-20 hrs Soups, stews, pizza and seasoning.
Potatoes** Use white potatoes. Peel and slice 3/8" thick. Blanch, rinse then dry. 6-12 hrs Stews, soups and casseroles.
Tomatoes Wash and slice 3/8" slices or dip in boiling water to loosen skins, half or quarter. 6-12 hrs Soups and stews. Powder in blender and add water for paste or sauce
Squash/Zucchini Wash, remove ends and slice 3/8" thick or grate. Steam if you plan to rehydrate. 5-10 hrs Breads, snacks, soups and casserole

* Dry at 90F for 2 to 3 hrs, then increase temperature to 125F and dry for remaining time.

**Blanch for 5 minutes or until translucent. If not steamed long enough, they will turn black during drying and storage.

Meat Drying Guidelines (Jerky)

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Drying meat, also known as making meat jerky, is another method of preserving meat for your food storage. Homemade meat jerky is also less expensive then jerky slices or sticks purchased from a store. Typically 3 pounds of fresh meat will yield 1 pound of jerky. Jerky can be made from a variety of wild game meats, fish and poultry. Use fillets of fish and breasts of poultry. If you are purchasing meat for making jerky, choose lean meats with minimal fat marbling. Fat tends to get rancid during storage. A lean cut of flank steak, lean ground beef or eye of round make excellent beef jerky. When making jerky from pork, chicken or turkey, use precooked and processed meat. Be sure to dry it at the highest temperature setting (160F). After drying, heat it in your oven at a minimum temperature of 165F for at least 30 minutes as a precaution against the risk of salmonella. When you are jerky game meats, freeze the meats for at least 60 days at 0F before drying as a precaution against any diseases the animal might have been carrying. Then thaw the meat, add seasonings and press into strips or sticks.

Preparing Meat

With a sharp knife remove all fat, gristle, membranes and connective tissue. Cut into strip 1/4" to 3/8" thick and 5" to 6" long. It is easier to slice partially frozen meat for jerky. Cut meat in uniform thickness so it will dry in the same amount of time. Cut strips across the grain to produce jerky that is easier to break apart and chew. Marinate cut meats in store-bought or your own recipe. Marinade for 4 to 8 hours in the refrigerator before drying. The longer the the meat marinates, the more flavorful the jerky. If you use your own recipe, be sure to use a curing spice combination that includes salt, sodium nitrite to prevent bacterial growth during the initial stages of drying.

Drying Meat

Meat should be dried at 160F. Depending on how thick the meat is cut, how heavily the dryer is loaded, and the humidity, jerky takes from 4 to 15 hours to dry. Pat jerky with clean paper towels several times as it dries, to remove the oil that accumulates on top of the jerky. When removing jerky from the dehydrator trays, wrap it in paper towels and let it stand for a couple hours prior to packaging. Excess fat will be absorbed in the paper towels and the shelf life will be extended.

Dried Meat Storage

Beef Jerky that is stored un-refrigerated will start to go rancid at room temperature after 3 to 4 weeks. Refrigerate or freeze for longer storage or until you are ready to use.

Drying Cooked Meats

If you are drying meats for other purposes than jerky, such as for stew, sandwich spreads or stroganoff, the meat should be tender and choice. It must be cooked so it will not be tough and chewy when reconstituted. Using the remainder of a dinner roast or leftover steak saves the step of precooking the meat. Dehydrate those leftovers for snacks, backpacking and camping meals.

The shelf life of dried, cooked meats is 2 to 3 weeks at room temperature. Store in refrigerator or freezer to maintain the best quality before use. They will stay fresh and tasty for up to 6 months in the freezer.

Complications and Concerns

  • Thorough dehydration is critical, food that retains too moisture may still spoil.
  • Oxidation of dehydrated foods, especially fruits and vegetables, damages its nutritional value and makes it less visually appealing. Vacuum storage and/or oxygen absorbers can help prevent this.

See Also

References

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