PASTEURIZATION 103 



milk or cream flows into the machines have direct effect 

 on the temperature of the pasteurized medium. Also, at 

 the beginning and at the end of each run, great care must 

 be used in the continuous method of applying the heat. 

 The temperature should not go below 176° F. because the 

 pasteurization is likely not to be efficient, and it should 

 not be permitted to go above 185° F. for fear of producing 

 a burnt flavor. In actual practice, the vat or " holder " 

 method is likely to be more complete than the continuous 

 system, because the heat is applied for a longer period of 

 time, and there is less opportunity for carelessness. 



Efficiency. — The question as to which is the more efS- 

 cient method of pasteurization is pertinent. Hammer ^ 

 states : " The method of vat pasteurization of sour cream 

 at temperatures of 140° to 145° F. for 20 minutes some- 

 times left large numbers of living bacteria present, al- 

 though the percentage killed was high. After pasteurizing 

 sour cream with the flash method at 180° or 185° F. only 

 small numbers of bacteria were found in a living condi- 

 tion." It should be noted that in the flash method a 

 high temperature was not only used, but so long as this 

 was experimental work, this temperature was undoubtedly 

 maintained, which might account for the continuous 

 method giving better results than the " holder " system. 

 In the same publication Mortensen, Gaessler, and Cooper^ 

 say : " Vat pasteurization seems to be the most eflicient 

 method of sour cream pasteurization for improvement of 

 flavor." This conclusion might be true even though there 



1 Hammer, B. W., The Pasteurization of Cream for Butter- 

 making, Agri. Exp. Sta. Iowa State Col., Bui. 156, 2d part, p. 35, 

 1914. 



2 Mortensen, M., Gaessler, W. G., and Cooper, W. H., The Pas- 

 teurization of Cream for ButtermaMng, Agri. Exp. Sta., Bui. 156, 

 1st part, p. 15, 1914. 



