CHAPTER XXXIII 



MECHANICAL AND ENGINEERING ASPECTS 

 OF PASTEURIZATION 



GEORGE W. PUTNAIM 

 Department of Health, Chicago, 111. 



METHODS OF PASTEURIZATION 



Milk is pasteurized commercially by one of the following methods: (i) the hold- 

 ing method, using the vat, pocket, continuous-flow, and in-bottle pasteurizers; (2) 

 the flash method, using steam or electricity. 



HOLDING METHOD 



The holding method of pasteurization is practically universally used for milk in 

 the United States. It consists in heating the milk to the legally defined pasteurizing 



Fig. I. — Vat-type pasteurizer (partial-section view); jacketed type with interior heating coil 



temperature (for example, 142° or 145° F.), maintaining it at this temperature in a 

 suitable holder for a period of at least thirty minutes, followed by immediate cooling 

 to 50° F. or lower. 



The vat-type pasteurizer consists of an insulated or jacketed vat (see Figs, i and 7) 

 in which the foregoing operations are carried out by one of the following methods: 

 (a) The milk is heated to the pasteurizing temperature by a milk-heater and dis- 

 charged into one or more vats, which act merely as holders for the milk for the thirty- 

 minute period. The milk is then pumped or flows by gravity from the vat over a 

 cooler, {b) The milk is heated in the vat to the pasteurizing temperature by means 



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