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      Solar food drying is one of the oldest methods of
preserving food for long-term storage.  Ancient peoples,
particularly those in nomadic cultures knew the value of drying
food to eat between harvests or on the trail.  Solar drying
appears to have been practiced globally.  Just as early Egyptians
placed dried food in the tombs of their dead, evidence of the
same has been found in Latin American burial grounds a half a
world away.  For centuries North American natives dried a variety
of foods for use during the winter or on the long journey between
hunting grounds.

     Food drying served an important function during both World
Wars.  This method of preservation allowed large quantities of
food to be shipped in small spaces.  Dried foods have a weight
1/4 that of fresh foods and require only 1/3 to 1/6 the storage
space.  However, following World War II, food drying lost much of
its popularity.  This was due mainly to advances in canning and
freezing methods and the convenience of pre-packaged foods.

    Today, with more people concerned about chemical food
additives, air pollution and declining fossil fuels, the
ecologically sound, energy-conserving practice of solar food
drying has renewed appeal.  One big advantage of solar drying is
that, with careful temperature monitoring, much of the nutrient
content and flavor lost in other high-energy methods of drying
(as well as canning and freezing) can be maintained.  No
chemicals or processed sugars are added and almost any type of
fresh food can be dried.  In contrast to canning and freezing,
solar food drying requires no energy other than that of the sun,
uses no chemicals or preservatives, and retains much of the
flavor and nutritive value of the foods.  
                                                               
    1. Design
   
    The Appalachian Solar Food Dryer (diagram 1) incorporates a
food dryer into a window box heating system.  The window-box
heater was designed for providing solar heat through a window
during cold months.  Air from the room, is heated by the sun and
circulated back into the room (Diagram 2).  By attaching a food
dryer to the outlet of the unit, warm air passes over the food.
This system can be placed outside in the summer, installed as an
indoor dryer in the fall, or used as a heater in the winter.  It
can be built for as little as $120.
   
            -------------------------------------
              Diagram 1






         -------------------------------------  
              Diagram 2






         -------------------------------------
         
    Solar Drying Goals

    Proper food drying should accomplish two goals:  

 1.  Removing 75-90% of moisture from the food which  
     makes it unsuitable for bacterial growth.

 2.  Causing enzymes to become inactive thus halting the
     ripening process.

 To accomplish these goals three conditions must be maintained:

 1.  HEAT RANGE: The temperature should reach 100-
     160 F to kill bacteria and inactivate enzymes.  

 2.  AIR FLOW:  A steady flow of air out of the dryer
     carries moisture away from the drying food.

 3.  LOW HUMIDITY:  This allows for the moving air to
     carry away more moisture.

   2.  What Foods can be Dried?

    Almost any food can be dried with good results.  The only
limits are experience and imagination.  The methods described in
this paper are suitable for most fruits and vegetables.  Some
sources give instructions for drying meat and fish which can be
done successfully.  However, we strongly caution the novice not
to experiment in drying meats unless instructed by someone with
practical experience in the techniques.  CAUTION:   Mistakes in
drying perishable foods may result in food poisoning.
   
    Various sources suggest pre-treating some foods before
drying to maintain the flavor and texture of fresh food.  These
pre-treatments include blanching (boiling or steaming), treating
with ascorbic acid (vitamin C) or sulfuring.  However, other
experienced dryers have achieved  excellent results without
pretreating.  There is no need to add chemicals to food and
blanching can remove vital nutrients.  While the flavor and
texture of some dried foods may differ from fresh, the taste is
often just as good.  If you feel some sort of pre-treatment is
necessary, fruits or vegetables can be dipped in a mixture of 2
tablespoons of honey and the juice of one lemon.  Pineapple juice
is also effective in retaining the color of some fruits.  Drying
dipped fruit is sticky but it has a good flavor.

    A fairly constant temperature of 95-100 F is best for drying
food quickly.  If possible, the temperature should not exceed 110
F.  A thermometer will be helpful until you develop a feel for
the characteristics of your individual dryer.  If you find that
the temperature is rising too high (on a particularly sunny day)
a white sheet can be draped over the heater box to cool it down.

    Do not overload the drying racks.  Food should be placed in
a single layer with space between the pieces to allow for proper
air flow.   Most foods will be dried directly on the racks, so it
is very important that the racks be cleaned after each drying.
Residue from previously dried foods can give unpleasant flavors
or odors to your product.  Strong smelling foods, such as onions
or garlic, should not be placed directly on the racks.  Instead,
dry them on plastic wrap or baker's parchment paper with
alternate sides of the racks uncovered for ventilation.  This
method is also advised when drying juicy or pureed foods (as when
making "leathers").  

    With proper care, the racks of your solar food dryer should
give you many seasons of successful drying.  After food is
removed, the racks should be wiped with a damp cloth.  If
necessary they can be washed and scrubbed with a brush, then
rinsed and towel dried.  After washing replace the racks in your
dryer and allow them to dry.

     When drying food it is a good practice to rotate the racks.
Keep the racks of food that seem drier on the bottom.  This helps
equalize moisture and speed up drying time.

    3.  Storage

     The main problem associated with storing dried foods is
damage from humidity.  If food has not been dried completely, any
moisture can cause it to mold.  In some areas insects and mice
may also pose problems.  There are three things to remember about
storing dried food:  NO  AIR, NO LIGHT,  and  NO  MOISTURE.  Food
should be placed in clean, air-tight containers and stored in a
cool dark space.  Glass or plastic containers work well, as do
metal cans with tight fitting lids.  Plastic bags can also be
used but these must be placed in other containers, such as paper
bags or glass jars.  Try to store food in portions that are
appropriate to your family's size and eating habits.  This will
help avoid contaminating large quantities of food when removing
small amounts.  Check occasionally for signs of mold or insect
infestation.  If mold is present, remove the damaged pieces and
heat the rest in the oven at 165-175 F for 30 minutes.  Use this
food as soon as possible.                                        
                                                                 
    4.  Weatherization of Solar Dryer

    Since the solar food dryer/heater will probably be kept
outside in various weather conditions, care must be taken to
protect the wood from water damage.  One expert suggests adding
rot proof wooden feet to the parts of the heater box that are in
contact with the ground.  A more convenient alternative would be
to place a rubber or plastic mat beneath the heater box edge and
the legs.  As a further precaution, treated wood can be used for
the legs.

REFERENCES

Clark,Wayne A.  Plans For  an  Appalachian  Solar  Food  Dryer.  
Mount Vernon, Kentucky.   ASPI Publications, 1980.  

Valdez, Arnie and Maria.  A  Cookbook for  Building a Solar Food
Dryer.   Alamosa, CO:  Sangre de Cristo Printing,  1977.  (924
Main Street, Alamosa, CO  81101)