KX)Di. November Oregon State University, Corvallis. Extension Bulletin 818. Cooperative Extension Service

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1 KX)Di tuswifietikeati.xlafifrielf sippargirrovall Extension Bulletin 818 November 1966 Cooperative Extension Service Oregon State University, Corvallis

2 Contents - Size and Capacity Heating Units and Fan 4 Trays 7 Cabinet Construction Materials for the Dehydrator Unit Doors and Latches Operation 11 List of Parts for Electric Food Dehydrator 14 Full Size Patterns for Door Latches 1 5 3

3 A Home-Built Food Dehydrator Dale E. Kirk Agricultural Engineer Oregon State University Drying fruits, vegetables, meat, and nuts can be done at home in a small build-it-yourself dehydration cabinet. Air flow and recommended drying temperatures differ for various foods, and this type of home dryer allows the necessary adjustments. This plan was developed and tested years ago, and many home dryers have been built from it. The dehydrator shown in Figure 1 contains seven slotted wood trays, each approximately 18 inches by 30 inches, making a total tray area of nearly 25 square feet. This tray capacity should handle from 15 to 50 pounds of fresh food, depending on the product to be dried. A 20-pound load of sliced or shredded vegetables should dry in 7 hours, while a 40- pound load of halved prunes or peaches might require 15 to 20 hours for satisfactory drying. Whole fruit Size and Capacity would take several hours longer. If a smaller dehydrator unit is desired, the total length of the cabinet may be reduced, with a corresponding reduction in the length of the trays. In a smaller cabinet, the size of the heating unit should be reduced in order to maintain the same relative heating capacityabout 60 watts for each square foot of tray area. All other dimensions should be kept as shown on the drawings to avoid operating difficulties. The electric heating unit shown in the drawings consists of nine 150- watt electric lamps, screwed into porcelain sockets. Other types of electric heating units would be equally satisfactory, but others would be no more effective than the bank of electric lamps, provided the total wattage is the same. An ordinary 10-inch home or office electric fan is satisfactory for air cir- Heating Units and Fan culation. The fan circulates the air through the heating unit and over the food on the trays. A somewhat larger or smaller fan would serve satisfactorily, but without a fan this design of dehydrator would not function properly. The fan and heating unit are mounted on a removable base as illustrated on the drawings in Figures 2A and B. The electric cord to the fan and heating unit may be brought through

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5 SCALE TRAY FAN AND HEATING UNIT Figure 2A a notch cut in the bottom edge of the lower door. Number 14 electric wire with asbestos insulation is recommended. This heating unit and fan will make a full load for a residential electric circuit. Do not run other appliances on the same circuit. Locate the fan directly in front of the fresh air vent, as shown on the plan. The holes in the lower sliding door provide some flow of fresh, cool air past the motor for cooling even when the door is closed. An adjustable thermostat may be wired in series with part or all of the lamps for partial temperature control. The operating range of the thermostat should be from 1000 F. to about 175 F. 6

6 _ J j6" 6 VERTICAL SECTION THROUGH CENTER OF DEHYDRATOR Figure 2B Wood-slatted trays are illustrated in the drawings in Figures 2A and B. Place the slats 1/8 inch apart. Wire screen would be satisfactory in this type of drier, but no sulphuring should be done on metal-screen trays. The tray supports on the side of the cabinet are spaced 3 inches on centers. The tray stops (40) should be nailed Trays on the tray supports near the rear of the dehydrator at the exact location shown in Figure 2B of the drawings. When the trays are pushed back against this stop, the top tray should be 101/2 inches from the door and 11/2 inches from the back. The bottom tray should be 6 inches from the front and 6 inches from the back. 7

7 Figure 3 ISOMETRIC VIEWS SHOWING ARRANGEME SCALE ILLIOULLILIULLILL SEE ATTACHED SHEET FOR KEY TO PARTS NUMBERS 0-0 TOP DOOR BOTTOM DOOR 8

8 OF PARTS 9 DRATOR CAB) NET

9 The general construction plan calls for plywood, which is nailed to four 2 inch by 2 inch posts to form the dehydrator cabinet. Two doors at the front end give access to the drying trays and to the heating unit. Ventilation openings are in the door. Insulation board, 1/2 inch thick, is installed on the outer side of the side walls and on the inside of the back, top, bottom, and doors as shown on the drawings. This arrangement is used to simplify and improve construction. A complete list of the parts that go to make up the dehydrator unit is shown on page 14. The part numbers found in the column at the left of the sheet correspond to the circled num- Ca binet Construction bers on the drawings in Figure 3. If the unit is to be built entirely of these materials, the parts may all be cut to the size indicated and then assembled with the use of the drawings. Actual finished-lumber sizes have been taken into consideration when determining the measurements indicated. For instance, a 1 by 2 board is taken as being actually 3/4 inch by 1% inches, a 2 by 2 as being actually 15/s inches by 1% inches. Note that the two plywood sides (1), have a 3/4 inch by 15/s inches notch cut in each upper corner to fit around the 1 by 2 ties at the top, front, and rear. Materials for the Dehydrator Unit 2 sheets of 1/4-inch plywood, 48" x 96" 2 sheets of 1/2-inch insulation board, 48" x 96" 1 piece of 1/4-inch asbestos board, 18" x 30" 24 feet of 2 x 2 in lengths divisible by 4 feet 48 feet of 1 x 2 90 feet of 1 x 1 in lengths divisible by 6 feet (make 1 tray support and 1 tray side from each 6-foot length) 300 feet of lattice (approximately 3/s" x 13/4") in lengths divisible by 3 feet 30-inch wooden dowel 3/8" in diameter 10 lamp receptacles watt lamp bulbs 20 feet of No. 14 or larger asbestos insulated copper wire 1 cord connector cup 1 dairy thermometer 1 thermostat, (if desired) Nails 1 electric fan, 10-inch diameter or larger 10

10 Doors and Latches In place of metal hinges and door latches, which may be used if desired, the self-tightening home-made wooden latches shown in the drawings have been tried and found very satisfactory. The latches should be cut out and shaped before the dowel holes are drilled for mounting them on the dehydrator. Full-size patterns for the wooden latches for both doors are provided on page 15, which can be cut out and used to outline the latches on a piece of 1 by 2. The inner curve of the hook can be shaped easily by drilling, as suggested on the patterns. The dimensions and placement of the latches are illustrated on page 13. In order to operate properly, the top door latch must be heavier on the end opposite the notch, thus causing it to pivot on the dowel and rest against the stop. The stop (37) causes the latch to rest in a horizontal position when the door is removed. This keeps the latch in the most convenient position to receive the door when it is replaced. Locate the dowel holes for the door latches by the following procedures: Hold the door in a closed position, with the top of door level with the top of the cabinet. Hold the latch in a horizontal position at the approximate location shown on the drawing. Mark the two dowel holes required for each latch, one in the door and one in the cabinet, before moving the latch. Remove the latch and drill the holes as marked. Insert the dowels in the holes; place the latches on the dowels; and nail the stops (37) in place. Be sure the latches pivot freely. Hang the top door on the latch hooks and note which hooks grip the door the tightest. File or rasp the tightest hooks until all four corners of the door are held firmly against the cabinet. The bottom door rests on the plywood front stiffener (7) and the hooks merely hold it in place after the door has been put into position. - The dehydrator should be brought up to the desired drying temperature before loading. Loads of sliced fruits or blanched vegetables should never exceed 1 pound per square foot of tray surface. To prevent wet spots, the material should be spread evenly over the trays. Halved fruit should not exceed 11/2 to 2 pounds per square foot of tray surface. Walnuts or fil- Operation berts should be placed only one layer deep on the trays. The fresh air intake door opposite the fan should be kept wide open during the entire dehydration period. The top door then becomes the actual temperature regulator. If, with the top door wide open, the temperature rises too high near the end of the drying period, or, when drying a partial load, 11

11 part of the lamp bulbs can be removed or a thermostat may be used. If all the trays are loaded with fruit or vegetables, normally the top door should be opened about 2 inches for the first 30 minutes. During this time, the temperature in the drying chamber probably will drop, but it will recover soon. The air exhausted during this 30-minute period will be quite saturated with moisture. After this ml- tial period, the top door can be closed gradually until the desired drying temperature is reached. As drying progresses, the top door may need to be opened gradually to hold the temperature down to the desired level. Reversing the trays near the last of the drying period (end-to-end) will result in a more uniform moisture content of the final product. 12

12 A." DOOR LATCH DETAIL 42 SCALE 2" '.!4" Yi" 0 TOP DOOR LATCH 4 ik " BOTTOM DOOR LATCH 13

13 List of Parts for Electric Food Dehydrator' Part Number number required Name of part Sides Back Top Bottom Top door Bottom door Front stiffener Sliding air controls Lamp receptacle base Fan base Sides Back Top Bottom Top door Bottom door Bottom tray baffle Corner baffle Fan diaphragm Legs Top side rails Top end rails Door stop Bottom end rails Bottom side rails Top door framing Top door framing Bottom door framing Bottom door framing Heating unit runners Top door latches Bottom door latches Tray supports Fan diaphragm stops Fan diaphragm stops Tray sides Door latch stops Tray bottoms Tray runners Tray stops Air control guides Top door latch guides Bottom latch guides Door latch pins Type of material 1/4" plywood 40" x 42" 1/4" plywood 213/4" x 411/2" 1/4" plywood 213/4" x 423/4" 1/4" plywood 18" x 421/2" 1/4" plywood 213/4" x 221/2" 1/4" plywood 17" x 213/4" 1/4" plywood 8" x 213/4" 1/4" plywood 6" x 6" 1/4" plywood 12" x 173/4" 1/4" plywood 8" x 173/4" 1/2" insulation board 391/4" x 391/4" 1/2" insulation board 181/2" x 381/8" 1/2" insulation board 18" x 41" 1/2" insulation board 18" x 411/2" 1/2" insulation board 213/4" x 221/2" 1/2" insulation board 16" x 177/8" 1/4" asbestos board 18" x 30" 1/2" insulation board 12" x 18" 1/2" insulation board 151/4" x 171/2" 2 x 2 dressed 2 x 2 dressed 47" long 41" 213/4" long 18" 181/2" 41" 221/2" 181/2" 17" 181/2" 30" 6" 41/2" 1 x 1 dressed 41" long x 1 dressed 13" 1 x 1 dressed 18" 1 x 1 dressed 30" 1 x 1 dressed 3" 1 lattice' 173/4" long lattice' 30" lattice' 20" lattice' 181/2" lattice' 3/4" x 31/2" lattice' 3/4" x 31/4" 3/8" dowel 21/2" long 'Part numbers in first column correspond to circled numbers in plan, Figure 3. 'Approximately 3A3 inch x 13/8 inches. Size or amount - 14

14 DRILL 32 TOP DOOR LATCH BOTTOM DOOR LATCH -DRILLA"