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August 25, 2009

Quality for Keeps: Drying Foods Part 2

Here is Part 2 of the article written by Karla Vollmar Hughes and Barbara J. Willenberg from the University of Missouri. Great advice and tips! (Part 1 Here)

Procedures for drying

When using the oven-drying method, it is important to control the temperature. Use an oven thermometer to test the temperature of the oven at its lowest setting. Many ovens cannot maintain a temperature below 200 degrees Fahrenheit. This is too hot for successfully drying food, and alternative drying equipment must be used.

Trays upon which the food is placed must be at least 1-1/2 inches narrower than the inside of the oven to allow for air circulation. Allow at least 2-1/2 inches between trays and 3 inches of free space at the top of the oven for good air circulation.

About 4 to 6 pounds of food can be dried in an oven at one time. Place food on drying trays, or wire cooling racks covered with cheesecloth or nylon netting, to allow easy removal of dried food. Pieces of food should be in a single layer. Do not place food directly on oven racks. Cookie sheets are acceptable only for fruit leathers, which do not require good air circulation.

Place an accurate, easy-to-read thermometer on the top rack toward the back. Preheat oven to 150 degrees Fahrenheit. For gas ovens, if temperature cannot be maintained below 200 degrees Fahrenheit, it may be possible to use only the pilot light. For electric ovens, use only the bottom element, disconnecting the broiler element if necessary. Arrange trays in the oven to allow for adequate air circulation. Prop oven door open at least 4 inches.

Place a fan outside the oven door to aid air circulation. Move it from side to side occasionally. The room should be well ventilated, also. Oven drying, particularly if a fan is used, should be done with caution if small children are around.

Maintain the temperature at 140 degrees Fahrenheit. Watch the temperature even more carefully toward the end of the drying process. To prevent scorching, lower temperature to 120 degrees Fahrenheit if possible. Examine the food often and turn trays frequently, removing foods as they dry.

When using a dehydrator, load food on trays in single layers so that pieces do not overlap. This allows air to circulate through the trays. A constant temperature of 140 degrees Fahrenheit is necessary for dehydrator drying. Large pieces, such as apricot halves, should be turned halfway through the drying time. Pieces near the sides of the tray should be moved to the center. Stir small pieces with your fingers (make sure they're clean) every 1 to 2 hours, separating bits that stick together. It may be necessary to rotate the trays within the dryer at least once during the drying period. Vegetables usually take six to 16 hours to dry. Fruits can require up to 48 hours.

Note: Never dry sulfured fruits in an oven or dehydrator, because the sulfur dioxide fumes can be irritating.

Use sulfite dips, steam or water blanching in place of the sulfur treatment.

Different foods requiring similar drying times and temperatures can be dried together. Vegetables with strong odors or flavors (garlic, onion and pepper) should be dried separately. Don't dry strong-smelling vegetables outside in an electric dehydrator, because dehydrators are not screened and insects may invade the food.

Because an electric dehydrator can be an expensive investment, choose a specific brand or model carefully. Refer to the information in Table 1, for features to look for and evaluate before making your investment.

When is it dry?

Judging when food is dry requires experience. It is better to overdry than to underdry. When in doubt, continue drying for an additional 15 to 30 minutes. Check for doneness. Allow the product to cool before testing.

Vegetables are sufficiently dried when they are leathery or brittle. Leathery vegetables will be pliable and spring back if folded. Edges will be sharp. Corn and peas shatter when hit with a hammer.

Fruits are adequately dried when moisture cannot be squeezed from them, and if they are tough and pliable when cut. Fruit leathers may be slightly sticky to the touch, but should separate easily from the plastic wrap.

Meats should be extremely dry unless they are to be refrigerated or frozen for long-term storage. Meat is sufficiently dried when it is dark in color, fibrous, and forms sharp points when broken.

Herbs are dried when brittle. Their leaves shatter when rubbed together.

After drying

Even when a food tests dry, it may not be uniformly dry. Also, there is a chance of contamination of dried foods, especially if racks have been exposed to the open air for any period of time. Therefore, conditioning and pasteurizing should be done before storing.

Conditioning is the process used to equalize (evenly distribute) moisture left in the food after drying. It is usually done to fruits, herbs and seeds to improve storage, because it decreases the chance of spoilage, especially by molds. To condition a food, follow these steps:

-Cool foods on trays.
-Pour into a large, nonporous container of food-grade material, fill to about 2/3 full.
-Cover container and place in a convenient, warm, dry place. Shake container daily or stir contents at least once a day for 10 to 14 days.
-Check for condensation on the lid and any signs of spoilage. If condensation occurs, return food to the dryer to finish the product. Recondition after it is dry.
-Cool thoroughly before packaging.

Note: If any sign of mold growth occurs, destroy the product.

Freshly dried fruit can be added to the conditioning batch within the first five days. Conditioning time will need to be lengthened to accommodate the additional food.

Pasteurizing is recommended for foods that have been contaminated before or during storage. It can be used as a second treatment for vegetables held in storage if the vegetables do not have any mold on them. Keep in mind that this treatment can cause quality changes. To pasteurize, use one of the two following methods:

-Freezer: Seal dried food in a heavy, plastic bag after drying (and conditioning, if necessary. Place in a freezer at 0 degrees Fahrenheit for a minimum of 48 hours and up to two weeks.

-Oven: Preheat oven to 175 degrees Fahrenheit. Spread food loosely on a 2-inch-deep tray, and place in the oven (15 minutes for fruit and 10 minutes for vegetables). Cool and package for storage.

Package dried foods in glass jars, food-grade plastic storage containers, or plastic food-storage bags. Make sure the package has an airtight seal. It is a good idea to package dried foods in small amounts, because after the package is opened, the food can absorb moisture from the air and quality deteriorates.

Store containers of dried foods in a cool, dark, dry area such as a basement or cellar. Exposure to humidity, light or air decreases the shelf life of foods. The lower the temperature, the better: Foods stored at temperatures under 60 degrees Fahrenheit will keep approximately one year, at 80 degrees Fahrenheit to 90 degrees Fahrenheit the food begins to deteriorate within several months. For every 18 degrees Fahrenheit drop in temperature, the shelf life of fruits increases three to four times.