Two Methods of Pasteurization 



Pasteuri/aiion is a process ot 

 heating milk to a moderate tem- 

 perature lor a definite period ol 

 lime to kill disease germs. In most 

 states t\vo methods ot pasteuriza- 

 tion are emjjloyed: The "holding" 

 method requires the milk to be 

 heated to at least 143°F (142°F in 

 Mass.) tor not less than 30 minutes, 

 whereas the "short-time" method re- 

 quires a temperature ot 161 °F tor 

 15 seconds. The U. S. Public 

 Health Service Milk Ordinance 

 specifically states, however, that 

 other methods may be used it they 

 have been demonstrated "to be 

 equally efficient and . . . approved 

 by the State health authority." 



Short-Time Method Economical 



The short-time method ot pas- 

 teurization is more economical tor 

 large-volume operations, and tor 

 this reason is employed by most ot 

 die large producers. However, this 

 method is not completely satistac- 

 tory because it is difficult to estab- 

 lish and maintain the 15-second 

 holding period. 



Time-Temperature Relationship 



The time-temperature relation- 

 ship is go\'erned by the rate ot flo^v 

 ot milk through a heating tube. 

 Unfortunately, since the milk How 

 varies as the speed ot the pump 

 varies, the time-temperature rela- 

 tionship necessary for proper pas- 

 teurization may be easily upset. 



Higher Temperatures Established 



Inasmuch as more time is re- 

 quired to kill bacteria at a lower 

 temperature than at a higher 

 temperature, it is logical, then, 



to assume that disease-producing 

 bacteria may be destroyed in an 

 even shorter time by using temper- 

 atines that are higher than cur- 

 rently estal)lished j^asteurization 

 temperatmes. Killing temperatures 

 may now be established by a special 

 apparatus that heats milk in a trac- 

 tion of a second to temperatures 

 between 160° and 211° F. Once 

 the effectiveness of these tempera- 

 tures is determined, the heating 

 time will no longer be ot major 

 importance. 



New Pasteurization Process 

 in Sight 



The data obtained in these sx- 

 periments will provide a basis for 

 continuous pasteurization in which 

 temperature will be the only stand- 

 ard that will require enforcement. 

 Because commercial machines are 

 not able to heat the milk to the re- 

 cpiired temperatures and cool it as 

 rapidly as the experimental appa- 

 ratus, the extended period of 

 heating and cooling will provide 

 additional killing ot bacteria. This 

 will be an added safety factor. A 

 pasteurization process based only 

 on a temjierature standard will re- 

 cjuire leAver controls on the part of 

 the health officer. At present, the 

 holding-time is very difficult to 

 check and requires special equip- 

 ment. With only a temperature 

 standard to enforce, the job of the 

 public health inspector is simpli- 

 fied, and a safer milk supply is 

 guaranteed. 



This is a cooperative study under 

 a grant from the U. S. Public Health 

 Service, Department of Health, Ed- 

 ucation, and Welfare. 



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