422 



ENGINEERING ASPECTS OF PASTEURIZATION 



vantage from the public -health point of view is that this system eliminates the pos- 

 sibility of contamination of the milk between pasteurization and bottling, which may 

 occur with other methods. 



FLASH METHOD 



The flash method of pasteurization was extensively used prior to 1914 and con- 

 sists in rapidly heating the milk to a temperature of about 160° F. and immediately 



Fig. 3. — Continuuus-llow pasteurizer, ion^ 

 sections), holder, internal tubular heater. 



-disluiiLe lluw t}'pc; internal tubular cooler (three 



cooling. This method was condemned by many health officials on account of the fact 

 that, as carried out in commercial practice, there were large fluctuations in the temper- 

 ature of the heated milk and the temperatures used in a large percentage of cases were 

 considered too low to be effective.' Several epidemics of disease were traced to milk 

 treated by this method. It was also objected to by many physicians^ on the grounds 

 that practically all the lactic acid or souring bacteria were destroyed and other bacteria 

 left viable with the result that the milk on standing would decompose by putrefac- 

 tion instead of by souring. The occasional uneven and excessive heating of the milk 



1913- 



Ayers, S. H. and Johnson, W. T.: U.S. Dcpt. Agric, Bur. Animal Industry, Bull. 161, p. 58. 

 ■ Ilyg. Lab. Btdl. 56, p. 678. 1909. 



