122 MISC. PUBLICATION 5 4 0, U. S. DEPT. OF AGRICULTURE 



sible, until they are cooled to 90° F. or lower. A period of several 

 hours may be needed. Temperature of the air is of course a factor. 

 Canners commonly make use of cooling rooms. When dehydrated 

 vegetables are shipped from a cool area through a hot one, close pack- 

 ing will be helpful provided the cases when shipped are close to the 

 air temperature at the point of shipment. 



The heat-diffusing and heat-conducting properties of various de- 

 hydrated foods have been measured recently at the Western Regional 

 Research Laboratory. The measurements on strips of dehydrated 

 white potatoes, which are representative, approach the corresponding 

 properties of sawdust, which is used commercially as a heat insulator. 

 Cooling rates are directly proportional to the diffusivities. When 

 the containers are cans, the average diffusivity is increased to about 

 three times that of dehydrated vegetables in foil-protected cartons. 

 This is because the steel sheets are highly conductive and will aid in 

 the removal of heat from the stack. No such increase in the rate of 

 cooling occurs in unstacked, single cans, since the steel is on the outside 

 and at once comes to room temperature. 



The peaks of storage rooms should be ventilated in summer and cases 

 should not be stored next to the roof. In a warehouse thus venti- 

 lated, a pronounced increase in temperature from the ground level up- 

 ward has been observed. The outside air was 85° F., that at the floor 

 level was also 85°, at a point 8 stacks high it was 93° and 6 feet above 

 it was 98°. 



STANDARD TYPES OF PACKAGES 



Government specifications define several standard types of packages 

 for use in the exportation of dehydrated vegetables and fruits to the 

 armed forces and to lend-lease nations, but for domestic use "commer- 

 cial packages" are specified. Export containers, particularly for mili- 

 tary use, are designed to be used under average temperatures of as 

 high as 90° F. at a relative humidity of 90 percent, and at occasional 

 temperatures as high as 120° and as low as —15°. The package 

 and contents may be exposed to rain or even immersed in water on 

 being landed from ships. Dropping of cases during handling is three 

 to five times as severe during export for military use as in domestic 

 use. The cases must be capable of withstanding 120 to 200 drops 

 of from 1 to 3 feet without damage. The package must not allow 

 the contents to increase more than 2 percent in moisture content per 

 year even when the humidity of the surrounding atmosphere remains 

 constantly at 90 percent. Packages that contain dried vegetables 

 packed in an inert gas must allow no air to enter nor gas to escape; 

 that is, they must be hermetically sealed. 



Ten types of packages are described below and the approximate 

 numbers of containers required for dehydrated vegetables are shown 

 in table 12. Types 1 to 5 are tin or steel cans, of designs that can be 

 hermetically sealed, excluding moisture vapor, water, air, and insects. 

 Types 6 and 7 are laminated lead-foil, heat-sealed packages. In order 

 to free steel for other purposes and to lessen the demand for tin, sub- 

 stitute containers of high moistureproofness have been developed. 

 For the less hygroscopic dehydrated vegetables and fruits, for ex- 

 ample dry, shelled beans and evaporated apples, standard packages 

 for export (type 8) consist of heat-sealable laminated cellophane, or 



