196 PASTEURIZATION 



with objectionable flavors and odors, such as may be derived 

 from weeds, wild onions, etc., or from undesirable fermentations 

 of the cream prior to pasteurization. 



On the other hand, there are some serious objections to the 

 use of surface coolers. There is a tendency to recontaminate the 

 cream,. This is especially the case in an ill-ventilated factory 

 where the air is teeming with undesirable germ life and odors. 

 Again the exposure of the hot cream to air and light, while run- 

 ning over the copper surface cooler, invites oxidation of some of 

 the components of the cream which may lead to serious butter 

 defects, such as tallowy, metallic or fishy flavor, etc. For this 

 reason this type of cooler cannot be recommended ; coolers which 

 do not expose the hot cream excessively to air and light are 

 preferable. 



VAT PASTEURIZATION 



Vat Pasteurizers. The vat pasteurizers on the market are 

 of two general types, namely jacketed vats with plain agitators 

 and non-jacketed vats with hollow disc or coil agitators. In 

 the jacketed vats and tanks, with plain agitators the inside 

 wall of the jacket surrounding the vat furnishes the heating 

 surface. The jacket is charged with a continuous flow of the 

 heating or cooling medium, or the heating or cooling medium 

 is sprayed against the outside of the heating surface. The cream 



Fig*. 31. Progress vat pasteurizer 



Courtesy Davis- Watkins Dairymen's Mfg. Co. 



