Dehydration
Drying (dehydrating) food is one of the oldest and easiest methods of food preservation. Dehydration is the process of removing water or moisture from a food product. Removing moisture from foods makes them smaller and lighter. Dehydrated foods are ideal for backpacking, hiking, and camping because they weigh much less than their non-dried counterparts and do not require refrigeration. Drying food is also a way of preserving seasonal foods for later use.
How dehydration preserves foods
Foods can be spoiled by food microorganisms or through enzymatic reactions within the food. Bacteria, yeast, and molds must have a sufficient amount of moisture around them to grow and cause spoilage. Reducing the moisture content of food prevents the growth of these spoilage-causing microorganisms and slows down enzymatic reactions that take place within food. The combination of these events helps to prevent spoilage in dried food.
The basics of food dehydration
Three things are needed to successfully dry food at home:
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Heat — hot enough to force out moisture (140°F), but not hot enough to cook the food;
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Dry air — to absorb the released moisture;
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Air movement — to carry the moisture away.
Foods can be dried using four methods:
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In the sun — requires warm days of 85°F or higher, low humidity, and insect control; recommended for dehydrating fruits only;
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In the oven — drying in an oven uses the most energy. It is possible if you can set your oven temperature very low. Some recommend propping the oven door open to let moisture evaporate. A convection oven often does a good job dehydrating food as it uses the fan function to facilitate drying
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Solar dehydrator: a solar dehydrator is an enclosed structure that uses natural convection to move the warm air over the food inside. Sometimes called an Appalachian Dehydrator. Plans are available from many websites.
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Using a food dehydrator — electric dehydrators take less time to dry foods and are more cost efficient than an oven. Look for one with UL Seal of Approval for safety. Older models are not always safe.
Methods
Choose a fruit or vegetable in great condition. Drying will not make a fruit become better than it is. If you do have fruit that is getting too soft, you can make a purée and make fruit leather.
Cut your produce into thin slices. The thinner the slice the faster it will dehydrate. Too thin, though, could make a final product that is so thin in breaks into pieces.
As you cut up certain fruits, such as apples and pears, you will need to drop them into a bowl of acidified water. You can use lemon juice, ascorbic acid (vitamin C), or citric acid to help prevent unwanted browning of the fruit.
Many vegetables benefit from blanching prior to dehydrating. Fill a large pot with water and bring to a boil. Place prepared vegetable in the water. Bring back to a boil. See the USDA guide for timing guidelines for each vegetable.
http://nchfp.uga.edu/how/dry/csu_dry_vegetables.pdf
Place the produce in a single layer on the trays of the dehydrator. Set the temperature to the correct setting for what you are drying. Most fruits and vegetables are dried at 125° to 135° while herbs are dried at a much lower temperature and meats for jerky are at a higher temperature.
After dehydration, check food to see if it is pliable but not moist. Place food in a container and shake daily for several days to condition, which distributes the moisture evenly, and check for condensation. If there is any moisture, return the food to the dehydrator. If you have used a method for dehydration that could have allowed insect access to the food, it is recommended that you freeze the food to kill any bugs or insect eggs.
Store dehydrated food in an airtight container in a cool, dark place for the best quality. Dried foods maintain the best quality and nutritional value if they are used in less than 12 months. Dried foods may still be edible after many months or years in storage, although they may not be as tasty or nutritious.
Fruit Leathers
Fruit leathers can be made by puréeing fruit and pouring the fruit on a special fruit leather tray. Mixing the purée with applesauce or instant pectin makes for a more flexible final product. Follow the directions on the pectin for the amount of pectin to add.
Visit the USDA website for further information and recipes: http://nchfp.uga.edu/how/dry.html