Apparatus for Pasteurization 123 



remain sweet thirty -six to forty -eight hours longer 

 at ordinary temperatures than milk not pasteurized, 

 from which germs have been excluded with ordinary 

 care. 



The problem of successful pasteurization, then, 

 depends upon the means of raising the milk in a 

 short time to the required temperature, holding it 

 there uniformly for ten or twenty minutes, and then 

 cooling it rapidly to 50 or below. Several forms 

 of apparatus have been devised for this purpose. 

 Some of them are fairly perfect, but most of them 

 are lacking in some important point, v With the pres- 

 ent activity in regard to this subject we shall un- 

 doubtedly soon have much more perfect apparatuses for 

 this purpose than are at present available. The per- 

 fect pasteurizing machine should cover the following 

 points: Quick, perfect and uniform heating of the 

 milk; perfect control of the temperature; quick and 

 uniform cooling; compact form; ease of cleansing; 

 absence of pumping arrangements; security against 

 re -infection during the process. 



Selection of milk for pasteurization. For the best 

 results in pasteurizing, it is also essential that the 

 milk be as fresh and free from fermentations as 

 possible. Russel and Farrington have found* that 

 milk that has developed as much as .2 of 1 per 

 cent of lactic acid is too sour for satisfactory re- 

 sults. Inasmuch as this amount of acid cannot 

 readily be detected by the senses of smell or taste, 



*Wisconsin Agr. Exp. Station, Bulls. 44 and 52. 



