Preservation of Milk. 113 



.more expensive than that required for the simpler pasteur- 

 izing process. 



Pasteurization. In this method the degree of heat used 

 ranges from 140 to 185 F. and the application is made for 

 only a limited length of time. The process was first exten- 

 sively used by Pasteur (from whom it derives its name) in 

 combating various maladies of beer and wine. Its import- 

 ance as a means of increasing the keeping quality of milk 

 was not generally recognized until a few years ago; but the 

 method is now growing rapidly in favor as a means of pre- 

 serving milk for commercial purposes. The method does 

 not destroy all germ-life in milk; it affects only those or- 

 ganisms that are in a growing, vegetative condition; but if 

 the same is quickly cooled, it enhances the keeping quality 

 very materially. It is unfortunate that this same term is 

 used in connection with the heating of cream as a prepara- 

 tory step to the use of pure cultures in cream-ripening in 

 butter-making. The objects to be accomplished vary mate- 

 rially and the details of the two processes are dso quite dif- 

 erent. The experiments of Bitter 1 indicate that when stored 

 at 86 F., properly pasteurized milk will remain sweet from 

 six to eight hours longer than raw milk; at 77 F., ten 

 hours; at 73 F., twenty hours; and at 58 F., from fifty to 

 seventy hours. This enhances the keeping quality enough 

 so that it serves all practical purposes. 



While pasteurizing can be performed on a small scale by 

 the individual, the process can also be adapted to the com- 

 mercial treatment of large quantities of milk. The appa- 

 ratus necessary for this purpose is not nearly so expensive 

 as that used in sterilizing, a factor of importance when 

 other advantages are considered. In this country pasteur- 



' Bitter, Zeit. f. Hyg., 1890, 17:272. 

 8 



