CREAM. 291 



Sterilization accomplishes this most successfully, but it 

 changes the proteid compounds so that the milk has an un- 

 desirable " cooked " flavor and odor. 



This defect is not found in pasteurized milk, and if prop- 

 erly handled, milk treated by this process will remain sweet 

 from 4 to 8 days. 



For use in the near future the pasteurized product is, on 

 the whole, the most satisfactory; the sterilized material being 

 best adapted for export purposes. 



The essential condition in pasteurization is that the pas- 

 teurizing temperature shall exceed the thermal death point 

 (the temperature at which growing bacteria are destroyed) 

 of disease-producing as well as fermentative bacteria. This 

 temperature for most forms is about 140" F., but certain dis- 

 ease organisms like the tubeicle germ of tuberculosis is not 

 killed below 149 F. for 30 minutes, or 155° F. for 15 minutes. 

 As this germ is often found in milk from tuberculous cows, 

 prudence dictates the use of this temperature as a standard 

 for the pasteurization of milk and cream. The proteids in 

 the milk are slightly affected at this temperature, but if the 

 milk is thoroughly chilled, the "cooked" flavor disappears. 



The application of this temperature kills only the growing 

 bacteria, and does not affect the latent spores. If after 

 being heated the milk is allowed to cool slowly, and is left 

 at a comparatively warm temperature (exceeding 55" F.), 

 these spores germinate and soon change the character of the 

 milk, so that the value of the heating process is lost. To be 

 efficient, it is necessary to rapidly coo\ the pasteurized prod- 

 uct below the germinating point of the spores, for if they are 

 once allowed to sprout, they will develop slowly at a very 

 low temperature. 



In pasteurizing milk or cream, the apparatus should be 

 constructed so that a definite quantity of the fluid can be 

 held at any desired temperature for any length of time, and 

 during the process protected from infection from the air. 

 The apparatus must also be made so as to be easily cleaned 

 and thoroughly sterilized by steam throughout. The milk 

 must be protected from air infection during its withdrawal 

 from the pasteurizing vat into storage vessels (cans and 



