VEGETABLE AND FRUIT DEHYDRATION 39 



Boiling point Boiling point 



Altitude (feet) of water (° F.) Altitude (feet) of water (° F.) 



212 5,200 202 



1,000 210 6,300 200 



2,000 208 7,400 197 



3,100 206 8,500 196 



4.100 204 9,000 195 



Since blanching is an essential part of the dehydration process, and 

 since the purchase of finished product by the Government is partially 

 dependent upon adequacy of blanching, the processor of dehydrated 

 vegetables must maintain careful control over the blanching operation. 

 This means that he must be certain that the blancher is designed to 

 insure uniform heat distribution throughout. He should be certain 

 that his steam supply is adequate to maintain a constant, uniform 

 temperature, and must provide for uniform loading and spreading of 

 the material. The blancher should be provided with thermometers 

 at various points so that frequent checks can be made on the mainte- 

 nance of temperature and uniformity of heat distribution. As it 

 comes from the blancher the product should be tested at frequent inter- 

 vals for adequate blanching by the use of enzyme tests. If a positive 

 test is obtained, steps should be taken immediately to discover the cause 

 and remedy it. Under ordinary blanching conditions, where the op- 

 eration is carried out under atmospheric pressure, the operator should 

 strive to maintain the temperature in the blancher as close to 212° F. 

 as possible. 



Vegetable Blanchers 



The dip method or tank blanching requires a steam-heated water 

 vessel. If the unit is used for batch blanching, the produce is placed 

 in perforated metal baskets and held submerged in hot water until 

 all of the product has been raised in temperature above 190° F. 

 If dip blanching is to be continuous, the blancher is equipped with a 

 double draper belt similar to that shown in figure 17. The upper belt 



Figure 17. — Dip blancher equipped with double draper belt. 



is used to hold the product submerged in the tank during the blanch- 

 ing process. Another method of adapting the tank blancher for 

 continuous processing is to provide an endless chain fitted with hooks 

 to carry metal mesh baskets through the bath (fig. 18). Naturally. 



3 — 3 — 3 — 3 — 3 — 3 — 3 — 3 — 3 — 3 — J 



□ D P u □ u u 

 Figure 18. — Dip blancher equipped with baskets. 



the retention time will depend upon the speed of the belts and the 

 length of the tank. 



Atmospheric steam blanching can be either a batch or continuous 

 process. The method consists essentially of exposing cut vegetables 

 to steam in a booth or chamber. 



