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SUN DRYING
The high sugar and acid content of fruits make
them safe to dry out-of-doors when conditions are
favorable for drying. Vegetables (with the exception
of vine dried beans) and meats are not recommended
for out-of-doors drying. Vegetables are low in sugar
and acid. This increases the risks for food spoilage.
Meats are high in protein making them ideal for
microbial growth when heat and humidity can’t be
controlled. It is best to dry meats and vegetables
indoors using controlled conditions of an oven or
food dehydrator.
Sun-dried raisins are the best known of all dried
foods. California produces much of the world’s
supply of raisins. In the San Joaquin Valley warm
temperatures, low humidity and a constant breeze are
ideal conditions for drying grapes.
To dry fruits out-of-doors hot, dry breezy days are
best. A minimum temperature of 85°F is needed with
higher temperatures being better. It takes several
days to dry foods out-of-doors. Because the weather
is uncontrollable, drying fruits out-of-doors can be
risky If it rains in California while the grapes are
drying, the entire supply of raisins can be destroyed.
High humidity in the South is a problem for
drying fruits out-of-doors. A humidity below 60 percent
is best. Often these ideal conditions are not
available when the fruit ripens and other alternatives
to dry the food are needed.
Fruits dried out-of-doors must be covered or
brought under shelter at night. The cool night air
condenses and could add moisture back to the food,
thus slowing down the drying process.
Equipment
Racks or screens placed on blocks allow for better
air movement around the food. Because the ground
may be moist, it is best to place the racks or screens
on a concrete driveway or if possible over a sheet of
aluminum or tin. The reflection of the sun on the
metal increases the drying temperature.
Screens need to be safe for contact with food.
The best screens are stainless steel, teflon-coated
fiberglass and plastic. Avoid screens made from
"hardware cloth." This is galvanized metal cloth that
is coated with cadmium or zinc. These metals can
oxidize, leaving harmful residues on the food. Also
avoid copper and aluminum screening. Copper
destroys vitamin C and increases oxidation.
Aluminum tends to discolor and corrode.
Because birds and insects are attracted to dried
fruits, two screens are best for drying food. One
screen acts as a shelf and the other as a protective
cover. Cheesecloth could also be used to cover the
food.
SOLAR DRYING
Recent efforts to improve sun drying have led to
solar drying. Solar drying uses the sun as the heat
source, but a specially designed dehydrator increases
the temperature and air current to speed up the
drying time. Shorter drying times reduce the risk of
food spoilage or molding.
Solar dryers use a reflectant such as aluminum
foil or glass to increase the sun’s temperature by 20°
to 30°F. Air current is improved by using air vents at
each end. Cooler air enters the dryer, crosses the
food, removes moisture and escapes. Plastic covers
the frame and prevents rain or condensation from
dampening the food. Screens over the vents keep
insects and birds off the food.
Solar dryers may need turning or tilting
throughout the day to capture the direct, full sun.
Food on the shelves needs to be stirred and turned
several times a day.
There are several models of solar dehydrators.
Directions for making them at home can be obtained
from your county Extension agent.
VINE DRYING
Another method of drying out-of-doors is vine
drying. To dry beans (navy, kidney butter, great
northern, lima, lentils and soybeans) leave bean pods
on the vine in the garden until the beans inside rattle.
When the vines and pods are dry and shriveled, pick
the beans and shell them. No pretreatment is
necessary If beans are still moist, the drying process
is not complete and the beans will mold if not more
thoroughly dried. If needed, drying can be completed
in the sun, oven or a dehydrator.
PASTEURIZATION
Sun dried fruits and vine dried beans need
treatment to kill insects and their eggs.
1. Freezer Method-Seal the food in freezer-type
plastic bags. Place the bags in a freezer set at 0°F
or below and leave them at least 48 hours.
2. Oven Method-Place the food in a single layer on
a tray or in a shallow pan. Place in an oven
preheated to 160°F for 30 minutes.
1. This document is Fact Sheet FCS 8493, a series of the Department of Family, Youth and Community Sciences, Florida Cooperative Extension
Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: June 1998. First published: February 1994.
Reviewed: June 1998.
2. Written by Susan Reynolds, M.S., former Extension Foods Specialist, University of Georgia, College of Agricultural and Environmental
Sciences, Athens. Reviewed for use in Florida by Mark L. Tamplin, associate professor, Food Safety Specialist, Department of Family, Youth
and Community Sciences, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
32611.
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