VEGETABLE AND FRUIT DEHYDRATION 27 



chain belt. This unit is limited to use on products which are light 

 enough to float in the processing solution. The recovery after peeling 

 and hand trimming that can be expected ranges, for potatoes, from 82 

 to 88 percent under normal operating conditions. Pregrading to size 

 is unnecessary. The salt on the surface of the product retards dis- 

 coloration due to oxidation. 



Flame feeling. — Flame peeling has been variously popular over the 

 last 10 years. It has been used with some success on carrots and pota- 

 toes and is particularly adaptable for use in removing the paper skins 

 from onions. Essentially, a flame peeler consists of a device for trans- 



Figure 12. — A unit suitable for scalding in the brine-peeling process. 



porting the washed vegetables through an oven which is kept at a 

 high temperature by use of either gas or liquid fuel. 



It has been found that when a product is subjected to temperatures 

 of 2,000° F. or over for a period ranging from 15 to 30 seconds, the 

 outer surfaces or peel will first be dried and then burned to a char. 

 This carbonaceous layer can be removed by rigorous scrubbing and 

 washing, leaving the product in a peeled condition. The application 

 of intense heat results in carbonizing the outer surfaces before the 

 heat has penetrated to an appreciable depth into the product. It 

 has been found by test that the higher the temperature the shorter the 

 necessary retention period and the smaller the depth of penetration of 

 the heat ring. 



Extensive tests on potatoes indicate that although the major part 

 of the outside peel can be removed by the flame peeler-washer com- 

 bination, deep eyes are not effectively removed. If the eyes are not 

 peeled, considerable manual trimming will be necessary. It is doubtful 

 that much time can be saved over that required for peeling the entire 

 product by hand. • 



Some tests with onions have indicated that the char tended to mix 

 with the natural onion oils to form an oil-smudge which is difficult 

 if not impossible to remove from the surface. It is probable that a 

 much briefer and more superficial treatment is necessary than would 

 be suitable for potatoes or carrots. 



Designers and builders of flame peelers face serious mechanical 

 problems. Principally, these lie in the difficulty of conveying the 

 product through the intense heat of the furnace. Several types of 

 conveying means have been employed with varying degrees of suc- 

 cess. One commercial design uses a large cylindrical rotating drum 

 fitted with a refractory lining which is formed as a helical screw 

 to convey the product through the furnace. Gas flame is used for 

 heating. This flame is caused to impinge upon the refractory so 

 that it becomes incandescent. Since the refractory tends to disin- 



