DAIRYING 81 



approval of continuous pasteurizers by milk dealers is the rapid- 

 ity with which the cream rises on bottled milk. This is a very 

 important point as it appeals'to the eye of the consumer and when 

 milk will keep sweet twelve to twenty-four hours longer than 

 formerly and also shows a satisfactory layer of cream on the sur- 

 face, there is little to be desired besides this on the part of the 

 iverage milk dealer. 



The physician however may know that even if such milk has 

 been pasteurized, the process used has not necessarily made it 

 germ-free because the milk has not been heated long enough to 

 kill all the germs although it may have destroyed over 90 per 

 cent of them. 



806. The number of bacteria found in milk after it has been 

 pasteurized will be influenced by the number present in the raw 

 milk and the length of time it is heated as well as the temperature 

 to which it is exposed during pasteurization. An increase in the 

 time of exposure to a temperature above 145 degrees F. will have 

 a tendency to reduce the likelihood of a satisfactory raising of 

 the cream on the milk and the two desirable qualities of freedom 

 from bacteria and a good cream line are therefore to a certain 

 extent antagonistic, the longer the exposure to a pasteurizing 

 temperature, the less likely will there be a good cream line on the 

 milk and the shorter the exposure, the fewer the bacteria killed. 

 An exposure of one minute even, will destroy more bacteria than 

 the so-called flash heating, and when the length of time of heating 

 is extended without interfering with the cream-raising properties 

 of the milk or the capacity of the machine, a pasteurizer is ac- 

 complishing an important feature of the work it is designed to do. 



COOLING AFTER HEATING. 



807. A sudden cooling of the milk or cream from the pasteur- 

 izing temperature to near 50 degrees F. is a very essential part of 

 the pasteurizing process. A slow cooling not only diminishes the 

 keeping quality, but it retards the cream raising on the milk. 



The spores which are more or less numerous in nearly all 



