STATUS OF PASTEURIZATION OF MILK. 13 



145 F. can not be used because of the marked loss in cream line. 

 Harding (19) has studied the effect of temperature on the cream line 

 in a number of different plants throughout the country, and has come 

 to the following conclusion : 



The data here presented show that the volume of cream on milk begins 

 measurably to decrease when the temperature of pasteurization rises from 142 

 F. to 144 F. As the temperature goes higher, the decrease in the volume of 

 cream becomes rapidly more pronounced ; at 145 F. it amounts to slightly more 

 than 10 per cent by volume; at 146 F. it amounts to 1C.6 per cent; and at 

 148 F., to approximately 40 per cent. 



It may be said, however, that there are plants in this country, in- 

 cluding some of the largest, in which milk is successfully pasteurized 

 at 145 F., and this temperature is maintained for 30 minutes. It is 

 also interesting to note that at the 1921 meeting of the International 

 Dairy and Milk Inspectors' Association, Pease reported experiments 

 carried on by Heulings and him which showed that pasteurization at 

 145 F. for 30 minutes did not decrease the cream line when the milk 

 was properly heated and cooled. 



The method of pasteurization, whether it is the holder or in-the- 

 bottle process, is not so important provided the process is such that 

 the milk is heated to 145 F. and that all of it is held for 30 minutes. 

 The great majority of plants pasteurize by the holder process, and it 

 is gratifying to observe that the flash process is but little used. 

 Replies to a questionnaire sent to numerous cities in this country 

 showed only 33 plants using the flash process in 18 cities out of the 

 266 which supplied information on this subject. Five cities reported 

 that the flash process was not allowed, while one permitted its use 

 but would not allow the milk to be labeled " Pasteurized." 2 



SUPERVISION OF THE PROCESS. 



Intelligent supervision of the pasteurizing process is absolutely 

 necessary and can not be provided unless there is a thorough knowl- 

 edge of the primary object of pasteurization and the bacteriological 

 principles involved. 



The primary object is the destruction of any disease-producing 

 bacteria which may be in the milk and the handling of the pasteurized 

 milk in such manner that it can not be reinfected. When this object 

 is accomplished it is found that a large percentage of the bacteria 

 in the milk are destroyed and its keeping quality greatly unproved. 



The primary object can be accomplished by heating all the milk to 

 145 F. and holding it for a period of 30 minutes. It is then only 

 necessary to cool the milk immediately over thoroughly cleaned and 



2 For information on pasteurizing equipment the reader is referred to United States 

 Department of Agriculture Bulletin No. 890, Milk-Plant Equipment. 



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