214 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



find that a temperature of 145 F. (62.8 C.) for 30 to 

 45 minutes, under commercial conditions, will destroy 

 the pathogenic bacteria which are most likely to occur 

 in milk, with the possible exception of tubercle bacilli, 

 and it appears probable that this organism will also be 

 destroyed, although it would be desirable to have more 

 definite information on this point. Exposure to heat 

 to this extent, however, cannot be depended upon to 

 destroy all of the toxins and the decomposition products 

 which may be present in milk as a result of bacterial 

 growth, while, at the same time, it destroys the antiscor- 

 butic properties of milk. Moreover, it is not certain 

 that it does not decrease the digestibility of milk. 



METHODS OF PASTEURIZATION 



There are three methods of pasteurization: 



1. The "flash" or continuous process, in which the 

 milk flows continuously and is exposed to a heated sur- 

 face for a few seconds. 



2. The "holder" process, in which the milk is heated 

 to a certain temperature and is then held at that tem- 

 perature for a certain period. 



3. Pasteurisation in the Final Container. In this 

 method, the raw milk is placed in the bottle in which it 

 is to be delivered, the bottle is capped, and the filled 

 bottle is then exposed to the desired degree of heat. 



The "flash" process is less reliable than the "holder" 

 method, as not all of the milk is certain to be heated to 

 the temperature registered by the thermometer; some 

 may be heated in excess of the temperature intended and 

 thus balance any deficiency of temperature in the milk 

 which may not be heated to the desired temperature. 

 Furthermore, a higher degree of heat is required to de- 



