THE CITY Mn.K PLANT lOI 



It is evident that a temperature sufficiently high to kill 

 the bacteria in the milk that passed through in 15 seconds 

 would cause undesirable effects on the milk that was 

 exposed for 60 seconds. And if the temperature was 

 regulated on the basis of an exposure of from 30 to 60 

 seconds, it is evident that the milk passing through in 15 

 seconds would be inefficiently pasteurized. 



The necessity of a continuous pasteurizer and the faults 

 of the first machines led to the adoption of " holding " 

 devices or " retarders. " In such machines the milk 

 is passed through a continuous pasteurizer into a holding 

 tank in which it is kept at the desired temperature for 

 the desired length of time, then passed on to the cooler. 

 Thus the good qualities of the two classes of pasteurizers 

 are combined in one. These machines may be equipped 

 with a thermo-regulator which automatically regulates 

 the flow of steam to the pasteurizer and insures a uniform 

 heating of the milk. In connection with this a recording 

 device is commonly used, 30 that the sHght variations in 

 temperature are recorded. 



Pasteurization applied to fresh, clean milk, and to old, 

 impure milk may destroy 99 per cent of the bacteria in 

 both cases. Now it is quite evident that the clean milk 

 before and after pasteurization would contain b}' far the 

 smaller number of bacteria, and hence would have the 

 better keeping qualities and be more healthful. 



Immediate cooling to about 40° F. subsequent to heat- 

 ing is necessary for successful pasteurization; also all 

 contamination after pasteurization must be guarded 

 against. 



Pasteurization in the Bottle. — Another method of 

 pasteurizing milk that has been introduced recently is 

 pasteurization in the bottles. This method necessitates 



