212 PASTEURIZATION 



night, the wear and tear on the vats, is very great and their 

 life is comparatively short. In order to keep them in acceptable 

 condition, frequent retinning and other repairs are necessary and 

 even then the vats have to be replaced by new ones every five 

 to six years. 



The flash pasteurizer, on the other hand, is built to with- 

 stand the heat of pasteurization, it is made, intended and 

 used for heating only, and one flash machine performs the heat- 

 ing of all the cream received, as against an entire row of vats 

 in the case of vat pasteurization in a large creamery. Being 

 constructed and operated for but one purpose, that of heating 

 the cream, the flash pasteurizer is capable of serving that purpose 

 without undue wear and damage. Its chief wear is on the tin 

 coating of the heating surface. This heating surface can readily 

 be retinned when desired, or it can be used with the copper 

 exposed without serious danger of damage to the cream, as 

 the exposure of the cream to it is of very short duration only, 

 provided that the copper surface is kept clean and bright and 

 free from verdigris. Since the heating surface in the flash ma- 

 chine is a simple plain surface, easily accessible, it can be kept 

 in proper condition without difficulty. 



In the case of the vat pasteurizer, both the coil and the vat 

 liner are difficult to clean, some portions are almost inaccessible. 

 Hence, when the tin coating is, worn off it is very difficult to 

 keep the vat in proper sanitary condition and the objectionable 

 effect of this condition is greatly intensified by the fact that 

 the cream often remains in the vat for several hours. If the 

 agitator of the flash machine becomes worn, the defective parts 

 can be replaced readily and at small cost, while the expense of 

 removing and retinning the coil and liner in the vat is relatively 

 great. 



The labor required for cleaning the flash machine is com- 

 paratively small. The proper cleaning of vats in which the cream 

 was pasteurized requires much time and hard labor. 



Expense of Equipment and Operation. The initial expense 

 of the equipment is decidedly in favor of the vat pasteurizer. 

 Since the vat is doing both the heating and the cooling, the 

 equipment for vat pasteurization is confined exclusively to the 



