Apparatus for Pasteurization. 81 



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. With the pres- 

 ent activity in regard to this subject we shall un- 

 doubtedly have in the course of a year or two, much 

 more perfect apparatuses for this purpose than are 

 at present available. The perfect pasteurizing ma- 

 chine should cover the following points : Quick, 

 perfect and uniform heating of the milk ; perfect 

 control of the temperature ; quick and uniform cool- 

 ing ; 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 



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

 F 



