28 MISC. PUBLICATION 540, U. S. DEFT. OF AGRICULTURE 



tegrate if rapidly heated and cooled, the unit should be kept 

 continuously hot insofar as possible, 



Another device that has been used comprises spool-shaped rolls 

 placed on a conveyor chain. These rolls support the product and 

 rotate it continuously as it is being conveyed through the furnace. 

 Still another device consists of a rotary drum constructed like a 

 squirrel cage. The drum is built entirely of heat-resistant metal 

 and the flame is located on the outside of the drum and is directed 

 against the product. Still another system consists of long water- 

 cooled rolls, and alternate rolls are fitted with helical screws suited 

 to convey the product lengthwise of the rolls. All rolls rotate in the 

 same direction and hence the potatoes are rotated as they are 

 conveyed. 



No matter what device is used for conveying the vegetables, its 

 useful life will be limited by the high temperatures. After a careful 

 study of flame- and radiant-heating devices, one would judge them 

 to be relatively inefficient as compared with other devices available 

 for peeling. The fuel costs are comparatively high considering the 

 amount of work done. 



Lye feeling. — Lye or caustic peeling is suitable for processing 

 practically all root vegetables in either a batch or continuous process. 

 The batch process is usually carried out by dipping the product in a 

 hot caustic bath and is generally limited to small-scale operations. 

 Continuous peeling is not thus limited. 



The drum-type continuous caustic peeler consists of a drum rotat- 

 ing partially submerged in hot caustic solution. An internal helical 

 fence advances the product through the bath at a selected rate. 

 This method may be wasteful of lye and heat and is somewhat cum- 

 bersome for its capacity. It is also a source of personal hazard due 

 to dripping and splashing of the lye unless the unit is well shielded 

 to protect the operator from coming in contact with the lye. 



The continuous tank peeler, equipped with a metal belt for sub- 

 merging and conveying the product through the bath, has been the 

 most successful type in operation. Capacity can be varied by 

 lengthening or widening the draper belt. The belt is equipped with 

 advancing flights of lugs to insure uniform conveyance through 

 the tank. Means are provided for draining excess solution from 

 the product prior to its departure from the tank. The time taken 

 for draining should be considered in computing the retention time, 

 because the lye is active until neutralized or washed from the product. 



The most practical type of continuous tank peeler confines the 

 conveyor belt entirely within the tank. This feature prevents exces- 

 sive loss of heat and prevents dripping of the caustic outside of 

 the tank. The belts are normally of very sturdy design, positively 

 driven, and supported by chains so that frequent servicing is 

 unnecessary. 



The chemical action of the lye causes some surface disintegration 

 of the product, forming a sludge which collects on the bottom of the 

 tank. To facilitate drainage, the bottom of the tank should be sloped 

 to a common low point, at which place a draw-off valve should be 

 located. 



Sufficient clearances must be provided in the tank to accommodate 

 a suitable heating coil. The coil should be designed to heat the solu- 

 tion rapidly to the desired bath temperature and to maintain it there 



