How to Make and Use A Home Food Dryer
(Page 2 of 3)
July/August 1975
By Peter Murphy
A removable plywood chimney fits into the vent and is held in place by a 1" X 1" strip on each side. Nails are driven partway through these braces to help keep the structure rigid, but can easily be withdrawn and the chimney lifted off when the cabinet is to be stored.
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The seven identical trays each measure 14 1/2" X 23" and can be made of 1/8" or 1/4" galvanized wire mesh, framed on both sides with 1/2" X 1" wood strips. (Ruth Hertzberg, Beatrice Vaughan, and Janet Greene, authors of the excellent book Putting Food By, advise against the use of metal screening — especially galvanized wire, which has been treated with zinc,and cadmium — for tray bottoms because of possible contamination of the food. Suggested alternatives are tightly stretched cloth netting, woven baling twine, wood strips, or hardwood dowels. The last are recommended as especially easy to clean. — Mother.)
The dryer's door is built of 1" X 2" stiles and rails, fitted together with a half lap joint (see the detail drawing above). The framework is covered on the outside with 1/4" plywood or some similar material and on the inside with 1/2" insulation board.
As shown above, a 12" X 18" piece of sheet metal is suspended by wire from the dryer's upper corners and hangs below the racks to act as a spreader for the warmed air. The distance from the top of the heat source to this panel should be at least 2".
We've found that a medium-sized kerosene stove provides sufficient warmth to operate our dryer. Other sources of controlled heat — such as gas or electric heaters or even a battery of light bulbs may also be used. If the unit is to be powered by an oil stove or similar device, fireproof aprons of asbestos or sheet metal should be installed permanently on the cabinet's sides and temporarily on its front and back.
The cabinet is warmed before the filled trays are put in. It's a good idea to have a thermometer inside the dryer to check the temperature which should vary from 125° to 160° F during the drying period and is usually increased during the middle stages. The fruits or vegetables undergoing dehydration should be moist to the touch, and cooler than the air flowing over them. If they feel hot and dry, the processing is being done too rapidly.
The positions of the trays are changed every 30 minutes or so during the drying period. Remove the top shelf, shift the remaining racks up one space, and replace the top tray at the bottom of the stack. Be sure to alternate the racks against the back and front of the cabinet at each change, so that the hot air will always travel back and forth inside the dryer.
The time required to dry food will vary according to the type of produce, the size of the pieces, the type of dryer and even the weather. Fruits are ready to be removed from the cabinet when they're leathery and tough (after six to 24 hours), and vegetables after they've become brittle (three to 15 hours). Whenever you're in doubt about whether or not your unit's contents are done, continue the heating a little longer at a reduced temperature. Even then, some of the pieces may not be completely dried when a batch of food is taken from the dryer. If so, cull out the offenders, since they may mold during storage.
