DEHYDRATION OF VEGETABLES 5 



the air, the greater is its moisture-carrying capacity, and the rate of moisture 

 removal is more rapid at a low humidity than at a high humidity. However, 

 certain limitations are imposed by the nature of the material being dehydrated. 

 Above a certain temperature the product will be injured by excessive heat, par- 

 ticularly during the latter stages of the drying process. The point at which in- 

 jury occurs is called the "critical temperature," and for most vegetables the 

 finishing temperature should not exceed 150^ F. In home dehydration, where 

 control is limited, the temperature throughout the drymg process should never 

 exceed this point. Also, if the humidity is too low, moisture is taken from the 

 surface of the product more rapidly than it can diffuse from the inside, so a median 

 point of temperature and air flow relationship must be employed to prevent the 

 formation of a dry outside layer or "case hardening" as it is called. 



Figure 2. Forced Draff Dehydrator — Type 2. 



