Drying Fruits and Vegetables Theo Thomas and Holly Berry INTRODUCTION Drying is the oldest known method of preserving food. Historically, food was dried in the sun. Nowadays, we can sun dry or dry in an oven or a dehydrator that is especially designed for home drying. Drying has many advantages. It is safe. By removing most of the moisture from a food, microorganisms can't grow in it. Dried food is co mpact so that less storage space is needed. P lus, dried foods keep well , travel well and add variety to our diets. For more information, refer to publication PNW0397, "Drying Fruits and Vegetables." TERMS YOU SHOULD KNOW RECONSTITUTING - restoring moisture to a dried food. Properly dried foods return to approximately their original size, form and appearance. SULFITE SOLUTION - solution of 1 water and sodium sulfite, sodium bisulfite or sodium metabisulfite. Soaking fruit 10 minutes in this solution effectively prevents changes in color, flavor and nutrition. Sulfite-sensitive people should choose another pretreatment. SULFURING FRUIT - pretreating fruits with the fumes of burning sulfur. This method is done outdoors in a partially ventilated container and effectively maintains food quality. Sulfite- sensitive people should choose another pretreatment. WHAT TO DRY Fruits and vegetables selected for drying shou ld be of the highest quali ty -- fresh and ripe. Drying does not improve the qua lity. Immature produce will lack flavor and co lor. Overmature
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produce may be fibrous or mushy. If the food is not perfect for eating, it is not suitable for
drying.
PNW0397, "Drying Fruits and Vegetables" gives directions for the most commonly dried foods.Any fruit or vegetable can be safely dried, but some of them just don't taste good dried.
DRIED VEGETABLES can be used as chips, reconstituted for a cooked side dish, used in soups,
stews, casseroles and stuffings or made into powders. (To powder: use very dry vegetables and
put only one-half cup at a time in a blender.) DRIED FRUITS tend to be chewy and make
delicious snacks. Pieces of dried fruits are good in cookies, muffins, cakes and breads. They can
also be reconstituted and used in sauces, pies or cobblers or added to gelatin salads, cooked
cereals and ice cream.
For information on reconstituting dried fruits and vegetables, see page 26 in PNW0397.
NUTRITIONAL CHANGES DURING DRYING
Fresh fruit and vegetables provide us with bulk, energy, minerals and vitamins. Bulk is provided
by the indigestible fiber and energy is provided by the carbohydrates and protein. Neither bulk
nor energy is lost in the drying process. During blanching, a small portion of the vitamin C may
be lost by leaching. The amount varies depending on the care taken in blanching. To keep
leaching to a minimum, blanch only as long as required. Do not under-blanch, however, because
then the food's enzymes will still be active, reducing the quality. Pretreating light-colored fruits
helps protect against loss of vitamins A and C.
To avoid nutrient losses during drying, follow these guidelines. Use proper pretreatments (see
PNW0397). Dry food quickly at a maximum of 150°F with good air circulation and lowhumidity. Eat the dried food as soon as possible. Store a maximum of 6 months to 1 year in
airtight containers.
Nutrients are concentrated in dried food, compared to fresh on a per pound basis. But you need
to eat an amount equal to the fresh to get the same nutrition (2 fresh apricots = 4 dried halves).
The most effective pretreatment is "sulfuring." Prepared fruit is exposed to fumes of burning
sulfur. This must be done outdoors. Detailed instructions are found in PNW0397.
Indoor pretreatments include dipping the cut fruit in sulfiting solutions, ascorbic acid solution, or syrup blanching. These methods are not as effective as sulfuring, but may be used by people who
are sulfite-sensitive. Check in PNW0397 for instructions.
CAUTION: Sulfur dioxide and sulfiting agents, like sodium sulfite, sodium bisulfite and sodium
metabisulfite, are hazardous to the health of a small group of people. It is estimated that 5% of
asthmatics are sensitive to sulfites, and an unknown number of nonasthmatics. The symptoms are
sudden attacks of asthma, difficult breathing, nausea, diarrhea and even death. Persons who are
sulfite-sensitive should not use any sulfur-containing products to pretreat fruit before drying, and
should not eat food treated with sulfur.
EQUIPMENT AND METHOD
You can satisfactorily dry produce wherever you have a fairly constant temperature (as close to
140°F as possible), low relative humidity and circulating air.
Products dried in controlled heat generally are superior to sun-dried ones in color, flavor,
cooking quality and nutritive value. Oven or dehydrator dried foods will also be free of insects.
However, controlled heat drying requires additional equipment and operating expenses.
Consider the following factors in choosing the method best for you.
SUN DRYING depends on the weather, the temperature and relative humidity outside. If you
live in a hot, dry climate, sun drying may be successful. Its advantage is the cost. The only
investments are drying trays, netting to protect against insects and the food itself. Its main
disadvantage is time. What would take 6 to 10 hours to dry using another method may take 3 to 5
days in the sun. To avoid scorching, move the food into the shade to finish when it is about two-
SOLAR DRYING is like sun drying only better. You are still dependent on the weather but the
sun's rays are concentrated so drying time is shortened. The back window of a car with the
windows open slightly to allow air flow is an example. You may wish to build a solar oven.
OVEN DRYING is small-scale drying. It's a good choice if you want to dry only 4 to 6 pounds
of produce at a time. Disadvantages are the cost of the energy and having the oven on constantly.
Oven drying takes 2 or 3 times longer than a dehydrator. You must rotate and shift trays every
half hour and turn the food occasionally to assure even drying. To avoid scorching food, turn off
the heat when drying is almost completed and open the oven door wide.
DEHYDRATOR DRYING is a more reliable method. Dehydrators should have a heat source,thermostat and some method of air circulation. They can be purchased or made. When selecting
a dehydrator consider:
- Capacity -- drying area in square feet (each square foot holds about 1 pound produce); adequate
size for family needs; easy to handle and move.
- Construction -- sturdy, safe and durable (metal and high-grade plastic are superior to wood for safety, durability and cleaning; wood eventually dries, absorbs odors and warps); double-wall
construction to cut heat loss; convenient to load and unload; adequate venting; easy to clean;
trays slide in and out easily; trays are food-safe plastic, stainless or nylon; trays have durable
mesh and are replaceable.
- Operating parts -- constant heat source; heating element enclosed; parts easy to replace; wattage
adequate and suitable for average circuit; temperature dial easy to read; dial easy to adjust; fan
for even air distribution that is quiet and durable.
- Economy -- cost per square foot of drying area; a model with lowest cost per square foot may
not be economical if it doesn't hold enough; electricity use.
finishes; warranty; repair location; no sharp edges or corners; instructions for use and
maintenance.
OTHER APPLIANCES , such as some forced convection ovens (with drying trays as optional
accessories), may be used for food drying. Foods can be dried in a convection microwave; it's the
convection cycle, not the microwaves, that actually dry the food. Read the directions that come
with those ovens for more information.
Fruits, vegetables and meats should not be dried in a microwave for two reasons: 1. The oven
door must be open for moisture to escape. A microwave can only be operated with the door shut;and 2. Drying times vary. Foods can become so dry they ignite and burn out the magnetron tube.
TRAYS
You can make your own drying trays. They should be made of a food-safe material that allows
Sulfur may be purchased at your local pharmacy. Get a pure form of sulfur. It also may be called
flowers of sulfur or sublimed sulfur. Garden dusting sulfur is not suitable. Do not use it in
solution.
I DID NOT PRETREAT MY PEARS BEFORE DRYING AND NOW THEY ARE DARKER.
ARE THEY DANGEROUS TO EAT?
No, the fruit is still good to eat. Next time try soaking them for 10 minutes in 1 to 2 tablespoons
of sodium sulfite in 1 gallon of water. Drain well. If you're sensitive or allergic to sulfites, you
can use a saline solution or ascorbic acid solution. Directions are available in PNW0397.
However, while these solutions prevent browning during preparation, they do not guarantee
stability of color during drying and storage.
DOES THE CALORIE CONTENT OF FOODS CHANGE DURING DRYING?
The calorie content of foods does not change but is concentrated into a smaller mass as moisture
is removed during drying. Therefore, on a per pound basis, dried foods contain considerably
more calories than do the same foods fresh.
I FOUND SOME WILD MUSHROOMS IN MY BACK YARD. CAN I DRY THEM?
Only if they are edible varieties. The toxins of poisonous mushrooms are not destroyed by dryingor cooking. Make sure you know the difference between poisonous and edible varieties before
you start picking.
PROBLEMS
There aren't many problems in food drying. However, here are some things to watch for.
CASE HARDENING - If the drying temperature is too high or the humidity too low, the food
may harden on the surface. This makes it more difficult for the moisture inside to escape and for