AGRICULflJRL EXFEPI1ENT STATION
Wrn.
Oregon State College
Director
Corvallis
Station Circular of Information rIo. 309
April 1943
CONSTRUCTION AND OFERATICN OF A HOME ELECTRIC FOOD DEHYDRATOR by
F. F. Price, Agricult:ral Erineer and
Dale F. Kirk Assistant Agricultural ngineer
Information on pparation of fruits and vegetables for dricn, recommended temperature for dehydration, and methods of refreshing the products preparatory to cooking are given in Experiment Station Circular 149.
II\TTRQDUCTION:
The electric food dehydrator illustrated in the accompanying drawings has been developed for home dehydration of fruits and vegetables.
The electric heating demand of 1350 watts is such that it can be plugged into the ordinary home electric outlet.
It requires a home or office-type electric fan and. since one probably cannot be purchased from dealers for the duration it will be necessary for anyone planning to build this dehydrator to make certain that he owns or has access to such a fan.
Aside from this the only other critical material required is a few feet of copper wire which probably can be found around most homes.
It is recommended that families iho are prepared to meet their food preservation needs by canning continue that method and that dehydration be used only to suoplement preservation by canning.
SIZE AND CAPACITY:
This size of dehydrator contains seven wooden trays, each approximately
18 inches by 30 inches making a total net tray area of nearly 25 square feet.
This tray capacity should handle from 15 to 50 pounds of fresh food depending upon the type of prcduct be,tn dried and uite adequately serves three or four families for the dehydration of fruits and vegetables by following a rotated use orogram, Shredded or sliced vegetables reauire more tray area per pound than rost fruits.
A load of shredded carrots which would be about 20 pounds will dry in seven hours, while a load of halved prunes or peaches having a weight of 40 pounds may require 15 to 20 hours for satisfactory drying, due to the larger size of each piece and the greater weight.
Acknowledgments: The authors
express appreciation to the staff of the'
Department of Food Industries for valuable suggestions in designing this dehydrator an for assi3tance in conducting operating tests.

2
If a ia1ler-sized dehydrator unit is desired, the total length of the cabinet may be reduced if a corresponding reduction in the length of the trays is made.
The size of the heating unit should be reduced so as to maintain the same relative heating capacity of about 60 watts for each square foot of tray area.
All other dimensions should be kept as shown on the drawings to avoid operting difficulties.
THE HEATING UNITS AND FAN:
The electric heating unit shown in the drawings consists of nine
150-watt electric larDs screwed into standard sockets, making a total of 1350 watts.
This type of heating unit is suggested because more conventional heating units equiring nichrome wire cannot be purchased for civilian use for the duration.
There are other types of electric heating units that would be equally satisfactory, hut none that would be superior to the bank of electric lamps, providing the total wattage is the same.
An ordinary 10-inch home or office electric C an is recommended but it is assumed that nerscns planningto follow these plans in constructing a dehydrator already have a fan which can he used for this purpose as it is very doubtful that such an electric fan can be purchased for the duration.
The fan is required to circulate the air through the beating unit and over the fruit or vegetables on the trays.
A somewhat larger or smaller fan would serve satisfactorily, but without a fan this design of dehydrator would not function uroperly.
The fan and heating unit are mounted on a removable base as illustrated on the drawings.
The electric cord to the fan and heating unit may be brought through a notch cut in the bottom edge of the lower
Number 14 electric wire will be required.
doors
This heating unit and fan will constitute a full load for a residential electric circuit.
Gas Heating Unit:
An inexpensive gas heating unit can be made to serve in place of the electric heating unit although an electric fan would still be required.
Consult your local gas cipar1y office for information on where to buy or how to construct a safe and satisfactory gas heating unit.
MATERIALS:
Aside from the electric I an and a short piece of insulated copper wire the dehydrator is built entirely of non-critical materials.
If 1/4inch plywood cannot be obtained, 3/4-inch tongue and groove material may be used as a satisfactory substitute.
If 3/4-inch material is used instead of l/4inch plywood the proper adjustments must either be made in the overall cabinet measurements or else narrower trays must be used.
A bill of materials for the dehydrator unit is as follows:

Trill of rnatere1s Tsr the dehydrator unit
2 sheets of 1/4-inch nlvvisod, 4' H y
2 sheets of 1/2-inch inoule Tisu hoard, 43" x 96!
54 feet of 2 x 2 in LenC,tTS dL1ri.slhie by 4 feet
4 feet of 1 x 2
10 feet of 1 x 1 in ienunho ci visib1e by 6 feet (make I trmy susnort end 1 Lray side from each (-foot leneth)
300 feet of i-atLLce (auros. 3/3 x 1-3/2") in lengths divisibl.e by
3 feet
30-inch wooden dowel 3/1 i.e diameter
'ID lamp receptacles
')
150-watt; lamu bulbs
20 feet >f lo. 14 or larger insulated copner wire
.1
cord connector cue
1 dairy thermometer hails
3
CCiTSTRTJCTi0TT
The general construction plan is to use ni.00d (or tongue and groove boards) etshch is naild to four S x 2 posts to form the dehydrator cabi net..
fire doors are provided at the front end to give access to the drying trays and ho the heating unit.
Ventilation orasnings are inc'hld3d i.n the door construction.
Insulation board one-half inch in thickness is installed on the outer side of the side walls and on the inside oT the hack, top, bottom, and doors as shorn on the drawrgs.
This arrangement 2s used to simplify and il5rOVe coistructton.
A cou'iehe list of the parts that co to make um the deimrdrator unit is given on pace 6.
The cart numbers found in the cnlurn.n at. the extreme 11 oft of the sheet correseond to the encircled nuobers found on the drawings.
Tf he untt is to he built entirely of these rnat.o.i.o1s, the parts may cli be cut 'ho the size indicated and then as sembled wilh ;be use of the drawings.
Ictual f :Lnisied lumber sies have been taken into consideration when determining the measurements indicated,, For instance, a.
'1, x 2 bc.urd i.s taken as being actually 3/4 x a 2 x 2 as bein, act.uaJ.ly 1_/k x 1-5/0".
Tt should he noted that 'the two p'Lood sides (1), have a 3/4" x 1-5/2" notch cut in cccii upeer corner to fit .round the 1 x 2 ties at the to, front sod. rear.
floors and Latches: In p1.ace of metal hinges and, door latches, which nay he used if available, the soif-tiebtenine homemade wooden latches shown in the di'swings have been tried curl found very satisfactory.
The latches should be cut out and shaped before the "owel holes are drilled for mounting them on the dehydrator.
Pull-size patterns for toe wooden latches for both doors are 7rovided on the last page o.f this circular.T1C1 can he nut out and used to outline the latches en a piece of 1 x 2.
The inner curve of the hook can be easily shaned by drilling as suggested on the patterns.

4
In order to :peat.e 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 stoo.
The ston (37) causes tho latch to rest in a horizontal position when the door 1S remove(I,
This keeps the latch in the most convenient position to rece.ve the door when this replaced.
The dowel rocedure oles for the door latches should be located by the following
1.
Bold the door in the closed position with the too of the door level with the too or the cabinet.
2.
itold the latch in a horizontal position at the aporoximate locetLon shown on the 'travring.
3.
Bark the two dowel holes required ±.or each latch, one in the door and one in the cabinet, before moving t.he latch.
4.
Remove the latch and drill the holes as marked.
5.
6.
Insert the dowels in the holes and. place the latches on the dowels and nail the stops (37) in olace.
rake certain that the latches pivot free:Ly.
Bang the too door on the latch hooks and note which hooks the door tightest.
grip
File or raso the tightest hooks until all four corners o the door are held firmly aTainst the cabinet.
7.
The bottom door rests on the piood front stiffener (7) and the hooks merely hold it in niece after the door has been nut into nosition.
Trays:
Voodsiatted trays are illustrated in the drawings because of the probable contirued. shortage of wire screen for the duration.
It is recommended that the slats be oleced 1/3 inch art.
If wire screen can be secured it would he sathsfactory in thts tyne of arier sc long as no suiphuring is done on the metal screen trays.
The tray suonorts on the side or the cahnet are spaced
3 inches on centers.
The tray stops (40) hou.id he nailed on the tray supports near the rear of the :Iehvdrator at the exact location shown on sheet 2 of the drawings.
when the trays are nushed back against this stop the top tray should be l0 inches from the door and i inches from the hack.
The bottom tray should be 6 inches from the front and 6 inches from the hack.
CPERATItOT
Before anir food is olaced in the de}wrdrathr, the unit should first he broucht un to a tenoerature o C 150° F.
Be careful to avoid higher tenioeratures.
The vent doors can be closed during the warmup neriod.
The trays should he loaded liahtly until experience has demonstrated heariei loads can be dried satisfactorily.
A load of 2 to 3 counds per tray is

5 recommended for shredded or sliced fruits or vegetables.
can be loaded at the rate of 3 to 5 pounds ner tray.
Fruits which are halved
As soon as the temperature in the dehydrator has reached 150 F. the trays of fruit or vegetables can b placed in the cabinet.
The fresh air intake opposite the fan should he kept wide open during the entire dehydration period.
The top door then becomes the actual regulator which is simpler than adjusting two doors.
If all trays are loaded the top door should be opened about 2 inches for the first 30 minutes.
During this time the temperature in the drying chamber will probably drop, but it will soon recover, At the end of 30 minutes reduce the top door opening to one inch and at the end of one hour reduce this opening to onehalf inch.
This latter position of the top vent can be continued until the temperature in the dehydrator approaches the maximum desired drying temperature
(usually 1500 to l55 F., refer to Circular #149).
Then the top door opening must be increased to prevent excessive temperatures in the dehydrator or the heat input must be reduced.
Inexperienced operators will wonder how to determine when the products have been dried sufficiently.
Sliced and shredded vegetables should be dried until ther are hard and brittle.
Fruits should be dried until they are rubbery.
Suiphuring: It is common prsctice to sulphur apples, apricots, peaches and. pears 1/2 to 1-1/2 hours after the fruit is prepared for the dryer alld before drying is started.
If the dehydrator is operated on an open porch or in a room where the doors and windows may be convenientiy opened, the sulphuring of fruits to be dried may he done i.n the dehydrator cabinet.
The cabinet should be warmed up in the usual manner while the fruit is being prepared.
Then the fruit should be placed on the trays ar the trays shoved into position in the cabinet.
The fan and heating element should then he removed and a pot of burning sulphur set on the cabinet floor beneath the trays for the recommended length of time.
The doors and ventilators should then be closed.
A piece of paper or cardboard can be used to prevent the escape of the sulphur fumes, through holes drilled in the ventilator doors.
It is always necessary to remove the fan and heating unit before sulphuring as the strong concentration of fumes inside the cabinet is harmful to the metal parts and rubber insulation.
A number two standard fruit can (not enameled) may be used satisfactorily as a sulphur burning rot.
About 3/i. of an inch of sulphur should be placed in the can and heated on a stove until the sulphur is melted.
The melted sulphur can be set aflame with a match or piece of burning paper.
Then the can f burning sulphur is set on a brick in the bottom of the dehydrator.
If an enameled can is used it should be charged with sulphur and burned outdoors once before using it to sulphur in the dehydrator, All residue remaining in the can after this burning should be removed, after which it is ready for use in the dehydrator.
Lfter the suifhuring has continued the recommended length of time, the pot should be removed and set outside the house to finish burning out.
The fan ad heating unit should then be placed back in the cabinet and the drying procedure carried on as usual.
The sulphur fumes 'i1l all be expelled from the cabinet by the fan long before the fruit is completely dried,

LIST OF PARTS FOR ELECTRIC FD DEHYDRATOR:
Ka:j to Part Numbers () (44) as shown on plan:
Part
Number
1
2
21
22
23
24
25
26
27
28
29
30
31
32
14
15
16
17
18
9
10
11
12
13
19
20
39
40
41
42
33
34
35
36
37
38
43
44
3
4
5
6
7
8
1
14
6
147
14
2
Number ha'd.
Nome of Part
2 sides
1
1
1
1
1
1
2
1
1
2
1
1
1
1
1
1
1
2
2
2
2
4
2
2
1
2
2
2
4
2
14
2
8
4
2
12 bock top bottom
Lop door bottom door front. stiffener s1.Ldin
air controls lamp receotacle base ran base sides back top bottom top door bottom door bottom tray baffle corner baffle ran iaphrogn legs top side rails top end rails do stop bottom end rails bottom side rails top door framing top door framiog bottom door framing botoni door framing heating unit runners top door latches bottom door latches tray pports fan diaphragm stops fan di aphragm stop tray siies 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' plfroocI
H
Size or amount
40" 42"
21-3/4" X
1/2"
2 .x
I x ti
11
21-3/4)' x 42-3/4"
18 x 42"
21-3/4' x 22"
17" x 21-3/4"
8" x 21-3/4)'
"
'I
U
6" x 6"
"
H
12" x 17-3/4"
8' x 17-3/4" insulation board 39k" x
It
18*" X 38-1/8"
H
H
U
1" x 41"
1$' x 41*"
21-3/4" x 22"
16" x 17-7/8"
18" x 30"
H
12" x 18" l5" x
U
2 dressed
11
2 dressed
47" long
41"
21-3/4" long
U
H
"
Il
18"
18H
41"
22"
181"
"
17"
"
"
1 x
H
1 dressed
"
"
U
3O'
6'
4;"
41" lng
13"
18"
30"
H lattice*
"
3"
17-3/4" long
30"
20"
H
U
3/8"
H dowel
3/4" X
3/4" X
2" long
* (appro:. 3/8" x 1-3/8")

.e, -
ISCMETRIC VIEWS
SHOWING
ARRANGEMENT OF PARTS a" Id"
SCALE kkkI
0"
SEE ATT,olEo sET F:: KEY
4/k
N
N
(44
,r e'4 l
L
16
_
6
Top
[)1
5
S
Ci
II
:
C:
I?
/
3
43
7
C
I
CL
H
BOTTOM DOOR
LH/
DEHYDRATOR CABINET
'4
Lii: cOOFERATIVE EXTENSCN WORK IN
AGRICULTURE 6 HOME ECONOMICS
OREGON STATE COLLEGE
CORVALLIS, OREGON
PLANS BY AGRI. ENGINEERING EXP. STATION
F.E.PIICE
DALE KIRK
ELECTRIC FOOD DEHYDRATOR
PLAN NO.
45 I I SHEET
I
OF 2

i_i'- _1i
:T 'i'
H
VERTICAL SECTION
THROUGH
CENTER OF DEHYDRATOR
H.
r
FAN AND HEATING UNIT
.J
6
3;
9
DOOR LATCH DETAIL
SCALE
TOP DOOR LATCH
L
43
L_____I
BOTTOM DOOR LATCH
WORK IN
AGRICULTURE & HOME ECONOMICS
OREGON STATE COLLEGE
CORV&LIS OREGON
PLANS BY AGRI. ENGINEERING EXP. STATION
F. E. PRICE DALE C. KIRK
ELECTRIC FOOD DEHYCRA1DR
PLAN NO. 5.45
4/43 SHEET 2 OF 2

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