food drying is a very simple

8/3/2019 Food Drying is a Very Simple

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Food drying is a very simple, ancient skill. It requires a safe place to spread the food where dry

air in large quantities can pass over and beside thin pieces. Sun is often used to provide the hot

dry air. Dry, clean air including dry cold air from any source will dehydrate food.

Contents

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Draping food over branches or spreading it on wide shallow baskets on the roof is an old

widespread tradition still in use around the world. Many other arrangements have been used to

support a thin spread of food pieces. Some options that have been used are to thread the

pieces on a cord or a stick and hang it over a fire, wood stove or from the rafters. Or one can

bundle herbs or strawflowers and suspend them from bushes or a door knob or nails in rooms

with good ventilation. Screen doors placed across chairs or sheets hung between clothes lines

or possibly on a quilting frame have also been used. Vans, clean garages, or backseats of cars

can be safe places to spread trays of drying food just as well as specially constructed cabinets.

In the pioneer tradition food might be spread in the attic or in an upstairs room with screened

windows wide open.

Modern variations are to build special enclosed drying racks or cabinets to expose the food to a

flow of dry air heated by electricity, propane or solar radiation are a modern variation. These are

refinements not essential to the basic process but handy, particularly in the humid tropics or

when the rainy season coincides with the harvest.

Natural ventilation may be used in dry areas such as the American southwest or the Arctic. If

necessary, the drying capacity of the air can be increased by heating it, which lowers the

relative humidity. While any source of heat may be used, solar energy is free and usually

plentiful in season. A solar heating panel screened on both ends with air intake on one end and

opening to the food at the other is universally used to solar heat air. Hot dry air may be moved

over the food by use of natural convection or a solar chimney or a fan run on solar electricity.

Trays need not be bulky and in fact lightweight ones with open screening block less airflow and

so are preferable. Screening may be woven out of local materials or may be commercial screen

of non-toxic materials such as nylon and some plastics. Fiberglass window screening is not

recommended as it is coated with vinyl that may contain flame retardants and other chemicals.

Open weave organic fibers and nylon material works fairly well, but can be difficult to clean. The
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usual commercial bridal veil is too fragile to last as screening on the trays but may be spread

over top to control insects. Avoid screen materials that may contain toxic chemicals or additives.

Galvanized metal screens or aluminum or copper screens are not recommended as potentially

toxic salts can migrate into the food. Top quality food drying screens are made from food-safe

plastic screening, such as polypropylene, which is available from Living Food Dehydrators and

Sunworks Technologies. (See Bibliography)

Trays, if used, are sized to comfortable dimensions (24" x 24" or 20" x 30", for instance). Then a

supporting rack is made to that size. Air flow is essential so it is important that trays be

sufficiently far apart to ventilate properly -- 6 to 8 inches if using natural ventilation. Less for

forced ventilation. Tray frames should be light, but strong -- 1 1/4 inch x 1/4 inch or 3/4 inch x

1/2 inch small wood strips are sufficient for most purposes. The wood strips for the tray frames

are cut to the full length and the full width of the tray. They are overlaid at the corners, notched if

they are very thick, glued and screwed. Or they may be nailed with small nails which are bent

over on the under side and pounded flat. Screen is stapled on. It may be secured with silicon

sealant or thin lightweight wood or both.

One or two heavier screens made from 1" x 2" pine and covered with galvanized hardware

cloth, are useful for drying non-food items -- clothing, wool, kindling and so forth. For support of

extra heavy loads, rigid galvanized trays may be used under food safe screen. Galvanized

screens may also be used to make fruit leathers. The sauce is protected from the galvanizedmetal by a sheet of Tedlar or of regular kitchen plastic taped to the frame.

Indoors, it is easy to use screened trays placed around on chairs or saw horses. No further

equipment may be needed. Outside, the food must be protected against insects and animals

and moved or covered in case of rain or blowing dust. Exposed trays also must be carried in at

night and out again in the morning to prevent rehydration from the dew even in the desert.

A single layer of trays outdoors may be covered with sheets of cotton, glass or plastic through

which the sun falls on the food. Sunlight heats the food driving out moisture. The moisture-laden

air falls down from the bottom of the screened trays. In this generic design, the food is usually

exposed to direct sunlight. Direct sunlight destroys some of the more fragile vitamins and

enzymes and the food loses color. The better quality food is produced by flat screen designs

having a dark sheet of cloth or metal that shades the food. This metal shield slows the drying


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but these designs are still very productive. Their disadvantages are they spread out over a

larger area of ground than the cabinets and they tend to blow over in gusty wind.

One simple, open-air dryer design that can be used indoors or outside is called the Kerr-Cole Z-

dryer. This is a rack of trays 6 to 8 inches apart stacked in a frame. The frame of open racks is

braced with a diagonal piece of wood forming a Z. (See the bibliography). The frame can be

sized to fit an available space such as the back of a car, or some place in a well-ventilated

room, etc. Also Z-dryers also can stand in the yard, optionally covered with a light cloth. Or one

can be fitted to go into a solar heated, ventilated cabinet such as a downdraft solar food dryer.

Without increasing drying time very much such an open rack may be covered with a lightweight

cloth to protect from insects. Ants and other crawling insects may be blocked from the trays of

food by placing the feet of a rack in containers of water. Such moats can be used with any of the

stacked designs. If ants and some other insects invade the drying racks, it is difficult to remove

them. However, they will go home at night. Protective measure instituted early the next morning

can block their return.

UPDRAFT SOLAR DRYER designs are the most frequently seen cabinet form. In this design,

the hot air flows upward through a solar heat collection trough and enters the bottom of a

cabinet underneath the food. The dry air rises through the trays and around the food, exiting

through a vent at the top or near the top of the shadowed side. (See the Bibliography -- Valdez)

The theoretical basis for this design is that hot air rises and therefore when heated, the air flowsnaturally upward through the trays of food.

DIRECTLY HEATED SOLAR cabinet dryers allow the sun to directly heat and dry the food

inside an enclosed one-piece cabinet. Direct heating tends to be very efficient and produces fast

drying. Proper air flow is essential to achieve maximum performance.

Solar food dryers can be hybridized so they continue to dry during cloudy weather. Removing a

tray or two from the bottom, a very small flame from a 16 oz. or picnic size propane burner can

be placed on the bottom. Alternately a small electric heating unit may be used. Heat rises and

triggers the same effect as the solar heat. It is important to avoid overheating the food,

maintaining temperatures below 120 degrees Fahrenheit.


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A solar box cooker being used as a solar food dryerFood drying is

not difficult, although some books give considerable details on handling each food differently.

Special guidelines are needed for handling jerky and fish. (Seebibliographyand your own

recipes.) General guidelines for fruits and vegetables follow:

Good quality food cut in thin pieces, not more than about 1/4 to 3/8 inch thick) Spread thinly on trays initially so there is a third to a half of the screen area clear for the

passage of air. Can be more compact after the first moisture is gone.

Label all food on the trays and carry the label along through processing to storage.Thick vegetables need to be blanched or lightly pre-cooked. Leafy vegetables may be wilted

slightly with steam, or dried directly from the garden. Cook potatoes and green beans

completely. Fruit is pretreated by dipping in quite sour lemon water, or Ascorbic Acid (Vit.C)

2000mg/quart. After a short soak, the fruit is drained and spread on trays. This retards

browning. (Later, the sour soak water flavored by the fruit can be used as a concentrate for

making cool drinks.) Sugar, honey or salt are optional. Sulfuring is no longer used in most

homes due to the possibility of breathing the hazardous fumes and allergic reactions to sulfur

compounds. It has been found to be unnecessary anyway.

To test if food is sufficiently dried, remove a piece and let it cool. Vegetables should be brittle.

Fruits because of their sugar content may never get beyond a firm bend or leather quality. If

they do become brittle, it is o.k. They just need a little more soaking or chewing time for full

flavor to develop.

All dried foods may be pasteurized after drying except for the greens and herbs. Spread dried

food no more than an inch thick on a metal tray and cover it with another dark metal tray. A

solar oven is excellent for this. Place it in an oven at temperature between 200 and 220 degrees

F. for 10 minutes. Stir and leave another 10 minutes. Do not overtreat. Cool and package

immediately. Store in a dry location as cool as possible.
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For people on the move or with limited storage space, plastic freezer bags are safe, durable and

easily transported. Food should be put in small clean bags, labeled and dated. The smaller bags

can be grouped into larger freezer bags, giving larvae two layers to penetrate if they attempt to

invade. For those who avoid plastic, glass jars or metal containers with tight lids do well. Pack to

eliminate air.

Indians in the American Southwest sometimes stored dried food in large earthen jars packed

very tightly and covered with leather tied on tightly. These jars were kept on the roof and so

were subject to low temperatures at night. Others stored dried food in hay-lined pits lined with

flat rocks to deter rodents. These pits were so deep a person had to be assisted to get out.

These were covered with leather or boards as a rain protection.

All stored food should be checked periodically for weevils. Weevils are a small, relatively cleaninsect. Infestations come from eggs hatched in your storage area. They grow to about 1/2 inch

long and then go into a small webbed cocoon. The mature form is a thin, gray-brown moth

about 1/2 inch long. Infestation can be controlled by eliminating the adult moths before they lay

their eggs. Once hatched, the larvae feed only on your clean food. The form most prevalent in

the USA is found as white, soft-bodied active "worms" with dark heads. Since they feed only in

the stored food, they do not usually carry disease or toxic contamination. Even if the larvae

themselves are not visible, weevil infestation is easily recognized. Small brown granules in the

bottom of the packages or 1/2 inch bits of white webs indicate infestation. The samepasteurization method can be used to kill adult and immature weevils. Treat and then sift out the

residue. Pasteurized dried goods rarely show infestation if stored in airtight containers. If stored

in bread bags, they almost always will.

Cooked weevil infested food is usually safe to serve and eat if food is scarce. Some cooks on

seeing larva facetiously say "Just a little clean protein ... God's gift to vegetarians." But

prevention is the best policy. Clean, quick handling and good packaging is the key along with

storing at the lowest available room temperature. Below 70 degrees there is little or no weevil

activity.

So drying and storing food is a simple process. Using dried food can be equally simple. Fruits or

vegetables may be eaten out of hand. Or fruit may be rinsed with water, drained briefly, and

placed in a closed jar in the refrigerator to soften. Any of the dried produce may be covered with

boiling water to slightly above the food level. Food should then be tossed to insure all parts of


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the dried bits are in contact with water. Most foods are allowed to stand for 15 minutes (equal

parts packed food and water) before being added to standard recipes. Heavier pieces may

require more time to rehydrate to the center. Easier yet, they may be just thrown in dry by the

handful into soups or casseroles. Crisp dried foods may be pulverized in a blender and added

by the spoonful to recipes for breads, soups, casseroles, sauces, etc.

For instance, greens can be used as a regular dish by pouring boiled water over them and then

continuing steaming for a few additional minutes depending on the type of green. Dried squash

and small pieces of potatoes can be covered with boiling water plus about 1/2 inch depth. They

are then allowed to stand for 20 to 30 minutes to become moistened to the center before

starting to cook. Larger pieces of potatoes require soaking for several hours.

Nutritionally, dried food is ranked by the USDA as better than canning, just under freezing. Thetastes are related to the food, but there is some uniqueness in their flavor and texture. This is

similar to the differences between fresh, frozen, and canned foods...another variation in taste.

In conclusion, select good food, wash, slice, dip or blanch, spread on trays or other drying

arrangement and allow to dry. Pasteurize, package with a label showing the date and anything

special about the food and store in a cool dark dry location as much as possible.. Use in

rotation, oldest packages first. If there is excess, it can be pulverized in a blender and added to

many foods: breads, casseroles, soups, gravies, sauces.

Stored dried food is prepared every growing season. Dried food should be used within the next

months as the nutritional value slowly drops over time. It is customarily eaten the following

winter and then any remainder composed as soon as new foods become available. As you

enjoy solar food drying, you are joining generations who have preserved foods in this manner

over the ages. Please pass this simple basic knowledge long to your children or community.

News and recent developments Edit
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UC Davis team demonstrating the solar dryer.

February 2011: A group from the UC Davis Program for International EnergyTechnologies installed a solar box dryer for drying fruit inNicaragua. They worked with the

local organizationsGrupo Fenixand theSolar Women of Totogalpa. They also connected

with students and faculty at the Alternative Energy Program at Nicaragua's National

Engineering University, and the directors of the new dried fruit export company SolSimple.

They plan to send a follow-up trip the summer of 2011.More Information...

January 2009:Korea and Sri Lanka sign a Memorandum of Understanding for theconstruction of a 500kv solar power plant- Spot.lk

May 2006:John MainaofKenyawins the Energy Globe Award for 2006. Employing solarenergy for drying food & gaining income security In Kenya, 30-40% of vegetables and

fruits are lost due to poor post-harvest handling. The lack of firewood, which is necessary

for drying and treatment of durable goods, is one of the major reasons for the loss. Since

2002 SCODE (Sustainable Community Development Services) has employed a solar

dryer in Kenya for the drying of harvesting produce. The advantages are obvious: solar

energy is free and available virtually everywhere. The fresh produce can be made durable
http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=1http://solarcooking.wikia.com/wiki/Nicaraguahttp://solarcooking.wikia.com/wiki/Nicaraguahttp://solarcooking.wikia.com/wiki/Grupo_Fenixhttp://solarcooking.wikia.com/wiki/Grupo_Fenixhttp://solarcooking.wikia.com/wiki/Grupo_Fenixhttp://solarcooking.wikia.com/wiki/Solar_Women_of_Totogalpahttp://solarcooking.wikia.com/wiki/Solar_Women_of_Totogalpahttp://solarcooking.wikia.com/wiki/Solar_Women_of_Totogalpahttp://dlab-ucdavis.blogspot.com/2011/01/hola-from-nicaragua.htmlhttp://dlab-ucdavis.blogspot.com/2011/01/hola-from-nicaragua.htmlhttp://dlab-ucdavis.blogspot.com/2011/01/hola-from-nicaragua.htmlhttp://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://solarcooking.wikia.com/index.php?title=John_Maina&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=John_Maina&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=John_Maina&action=edit&redlink=1http://solarcooking.wikia.com/wiki/Kenyahttp://solarcooking.wikia.com/wiki/Kenyahttp://solarcooking.wikia.com/wiki/Kenyahttp://images.wikia.com/solarcooking/images/b/be/Energy_Globe_Award_2006_food_drying.jpghttp://images.wikia.com/solarcooking/images/f/f8/20110211_nicaraguadryer_ucdavis.jpghttp://images.wikia.com/solarcooking/images/b/be/Energy_Globe_Award_2006_food_drying.jpghttp://images.wikia.com/solarcooking/images/f/f8/20110211_nicaraguadryer_ucdavis.jpghttp://solarcooking.wikia.com/wiki/Kenyahttp://solarcooking.wikia.com/index.php?title=John_Maina&action=edit&redlink=1http://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://www.spot.lk/article12665-mou-signing-for-solar-park.htmlhttp://dlab-ucdavis.blogspot.com/2011/01/hola-from-nicaragua.htmlhttp://solarcooking.wikia.com/wiki/Solar_Women_of_Totogalpahttp://solarcooking.wikia.com/wiki/Grupo_Fenixhttp://solarcooking.wikia.com/wiki/Nicaragua


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in a cheap way and market value will be increased. Through the fast drying process the

farmers can raise harvesting production and therefore able to generate additional income.

This means up to 50% more productivity. The time needed for collecting firewood before,

can now be used for various other activities and deforestation is reduced as well.

Currently 30 solar dryers have been installed and 920 farmers have been trained in the

use of these. Thirty craftsmen have also been trained in the construction and installation

of these solar dryers. The project contributes to an overall improvement of living

conditions, family nutrition, environment protection and income generation. At the moment

the project is implemented in the Rift Valley in Kenya and has the potential to be

duplicated in other areas.[1]

Documents Edit

March 2011:Analysis of the Drying Kinetics of S. Bartolomeu Pears for Different DryingSystems-Electronic Journal of Environmental, Agricultural and Food Chemistry

January 2009:Practical Application of Solar Tunnel Dryers-Klaus Triebe January 2009:Perspectives of solar food processing in India-C. Palaniappan January 2009:Micro-enterprises in Solar Food Processing Technology - Case Study-M.

Ramakrishna Rao,D.J. Rao,S.L. Kumar

November 1984:Understanding Solar Food Dryers-Roger G. Gregoire, P.E.
http://www.energyglobe.info/geg/frontend_en/view.php?MENUEID=137http://www.energyglobe.info/geg/frontend_en/view.php?MENUEID=137http://www.energyglobe.info/geg/frontend_en/view.php?MENUEID=137http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=2http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=2http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://images2.wikia.nocookie.net/__cb20090324212732/solarcooking/images/a/a2/Practical_Application_of_Solar_Tunnel_Dryers_-_Klaus_Triebe_%28January_2009%29.pdfhttp://images2.wikia.nocookie.net/__cb20090324212732/solarcooking/images/a/a2/Practical_Application_of_Solar_Tunnel_Dryers_-_Klaus_Triebe_%28January_2009%29.pdfhttp://images2.wikia.nocookie.net/__cb20090324212732/solarcooking/images/a/a2/Practical_Application_of_Solar_Tunnel_Dryers_-_Klaus_Triebe_%28January_2009%29.pdfhttp://solarcooking.wikia.com/wiki/Klaus_Triebehttp://solarcooking.wikia.com/wiki/Klaus_Triebehttp://solarcooking.wikia.com/wiki/Klaus_Triebehttp://images4.wikia.nocookie.net/__cb20090324212707/solarcooking/images/3/3a/Perspectives_of_solar_food_processing_in_India_-_C._Palaniappan_%28January_2009%29.pdfhttp://images4.wikia.nocookie.net/__cb20090324212707/solarcooking/images/3/3a/Perspectives_of_solar_food_processing_in_India_-_C._Palaniappan_%28January_2009%29.pdfhttp://images4.wikia.nocookie.net/__cb20090324212707/solarcooking/images/3/3a/Perspectives_of_solar_food_processing_in_India_-_C._Palaniappan_%28January_2009%29.pdfhttp://solarcooking.wikia.com/wiki/C._Palaniappanhttp://solarcooking.wikia.com/wiki/C._Palaniappanhttp://solarcooking.wikia.com/wiki/C._Palaniappanhttp://images3.wikia.nocookie.net/__cb20090327041123/solarcooking/images/5/57/Micro-enterprises_in_Solar_Food_Processing_Technology_-_Case_Study_-_M._Ramakrishana_Rao%2C_D.J._Rao%2C_S.L._Kumar_%28January_2009%29.pdfhttp://images3.wikia.nocookie.net/__cb20090327041123/solarcooking/images/5/57/Micro-enterprises_in_Solar_Food_Processing_Technology_-_Case_Study_-_M._Ramakrishana_Rao%2C_D.J._Rao%2C_S.L._Kumar_%28January_2009%29.pdfhttp://images3.wikia.nocookie.net/__cb20090327041123/solarcooking/images/5/57/Micro-enterprises_in_Solar_Food_Processing_Technology_-_Case_Study_-_M._Ramakrishana_Rao%2C_D.J._Rao%2C_S.L._Kumar_%28January_2009%29.pdfhttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://solarcooking.wikia.com/wiki/D.J._Raohttp://solarcooking.wikia.com/wiki/D.J._Raohttp://solarcooking.wikia.com/wiki/D.J._Raohttp://solarcooking.wikia.com/wiki/S.L._Kumarhttp://solarcooking.wikia.com/wiki/S.L._Kumarhttp://solarcooking.wikia.com/wiki/S.L._Kumarhttp://pdf.usaid.gov/pdf_docs/PNABC941.pdfhttp://pdf.usaid.gov/pdf_docs/PNABC941.pdfhttp://pdf.usaid.gov/pdf_docs/PNABC941.pdfhttp://solarcooking.wikia.com/index.php?title=Roger_G._Gregoire&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Roger_G._Gregoire&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Roger_G._Gregoire&action=edit&redlink=1http://solarcooking.wikia.com/index.php?title=Roger_G._Gregoire&action=edit&redlink=1http://pdf.usaid.gov/pdf_docs/PNABC941.pdfhttp://solarcooking.wikia.com/wiki/S.L._Kumarhttp://solarcooking.wikia.com/wiki/D.J._Raohttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://solarcooking.wikia.com/wiki/M._Ramakrishna_Raohttp://images3.wikia.nocookie.net/__cb20090327041123/solarcooking/images/5/57/Micro-enterprises_in_Solar_Food_Processing_Technology_-_Case_Study_-_M._Ramakrishana_Rao%2C_D.J._Rao%2C_S.L._Kumar_%28January_2009%29.pdfhttp://solarcooking.wikia.com/wiki/C._Palaniappanhttp://images4.wikia.nocookie.net/__cb20090324212707/solarcooking/images/3/3a/Perspectives_of_solar_food_processing_in_India_-_C._Palaniappan_%28January_2009%29.pdfhttp://solarcooking.wikia.com/wiki/Klaus_Triebehttp://images2.wikia.nocookie.net/__cb20090324212732/solarcooking/images/a/a2/Practical_Application_of_Solar_Tunnel_Dryers_-_Klaus_Triebe_%28January_2009%29.pdfhttp://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://ejeafche.uvigo.es/component/option,com_docman/task,doc_view/gid,765/http://solarcooking.wikia.com/index.php?title=Solar_food_drying&action=edit&section=2http://www.energyglobe.info/geg/frontend_en/view.php?MENUEID=137