VEGETABLE AND FRUIT DEHYDRATION 



111 



Sources of Heat 



The air supply to bin driers is preferably heated by steam. 

 Direct-fired units are not recommended, because the product may 

 acquire a disagreeable taste from the flue gases. There is also a fire 

 hazard with the open flame, which may cause dust explosions. The 

 amount of heat required by a bin drier is relatively small; hence, 

 the heat wasted by not recirculating it is negligible. The problem 

 of recirculation should be decided on the basis of absolute humidity 

 only. 



OTHER TYPES OF DEHYDRATORS AND THEIR USES 



Patent files and other publications describe numerous designs of 

 food dehydrators. The truck-and-tray tunnels, the truck-and-tray 

 cabinet, and the belt conveyor are described in previous pages of 



Figuee 59. — Truck carrying trays of sliced onions enters a tunnel dehydrator. 



this manual and their operation has been discussed in detail because 

 of their extensive use in the dehydration of vegetables and fruits 

 (fig. 59). Other types of dehydrators and their uses are described 

 below. 



Spray Driers 



Spray drying is based upon the general principle that moisture is 

 removed rapidly from a finely divided substance suspended in an 

 atmosphere capable of absorbing the water vapor and of supplying 



