2 CIRCULAR 619, U. S. DEPARTMENT OF AGRICULTURE 



of a suitable medium for their growth. Changes in composition, 

 flavor, and appearance, however, may also be brought about by the 

 action of the enzymes present in practically all foodstuffs. As these 

 natural catalytic bodies are not always inactivated by the treatment 

 which stops mold and bacterial action, they must be considered in 

 working out methods of dehydration. 



The outstanding advantage of drying as a method of preserving 

 foods is that the weight and bulk of the products are greatly reduced, 

 thus making possible economy in storage and transportation (15). z 

 The production cost of dehydration compares favorably with that of 

 canning. Dried fruits and vegetables are almost as convenient for 

 use in the home as the fresh products. They need no peeling or other 

 preliminary treatment, and soaking and cooking can often be combined. 

 Only the quantity required need be used when the package is opened; 

 the rest will keep in good condition for a reasonable time. 



DEHYDRATION INDUSTRY 



"Dried," "sun-dried," "evaporated," and "dehydrated" are the 

 terms most commonly used to describe dried products. Dried indi- 

 cates drying by any means; sun-dried indicates diying without artifi- 

 cial heat; and evaporated implies the use of artificial heat. Evapo- 

 rated refers more particularly to the use of artificial heat in driers 

 depending for their air circulation on natural draft, while dehydrated 

 implies mechanical circulation of artificial heat. 



The commercial dehydration of fruits has reached a more ad- 

 vanced stage of development than has the commercial dehydration 

 of vegetables, owing largely to the fact that the public is familiar with 

 sun-dried and evaporated fruits, whereas it knows comparatively 

 little about dried vegetables. The development of the commercial 

 dried-fruit industry is shown in table 1, which gives production and 

 values of the principal dried fruits for 1933, 1935, and 1937. These 

 data, based on the Biennial Census of Manufacturers (18), do not 

 include products of small local plants whose annual output is valued 

 at lessthan $5,000. 



During the World War 8,905,158 pounds of dehydrated vegetables, 

 divided as follows, were shipped to the United States Army overseas: 

 Potatoes, 6,437,430 pounds; onions, 336,780; carrots, 214,724; turnips, 

 56,224; and soup mixture, 1,860,000. 



Table 2 shows the extent of the dried-vegetable industry in this 

 country in 1919. All the vegetables were either dehydrated or 

 evaporated. In the years immediately following 1919 the drying of 

 vegetables declined rapidly, and for the last 10 years or more produc- 

 tion has been comparatively small (table 1). 



3 Italic numbers in parentheses refer to Literature Cited, p. 41. 



