Bacteria and Butter- Making. 135 



temperature. By this method the cream layer is exposed 

 to the air for a longer time than with any other, and conse- 

 quently the contamination from this source is greater. 

 Usually cream obtained by the shallow-pan process will 

 contain a larger number of species and also have a higher 

 acid content. 



2. Modern gravity methods. In the Cooley process, or 

 any of the modern gravity methods where cold water or ice 

 is used to lower the temperature, the conditions do not 

 favor the growth of a large variety of species. The number 

 of bacteria in the cream will depend largely upon the man- 

 ner in which the milk is handled previous to setting. If 

 care is used in milking, and the milk is kept so as to ex- 

 clude outside contamination, the cream will be freer from 

 bacteria than if carelessness prevails in handling the milk. 

 Only those forms will develop in abundance that are able 

 to grow at the low temperature at which the milk is set. 

 Cream raised by this method is less frequently infected with 

 undesirable forms than that which is creamed at a higher 

 temperature. 



3. Centrifugal method. Separator cream should contain 

 less germ-life than that which is secured in the old way. 

 It should contain only those forms that have found their 

 way into the milk during and subsequent to the milking, 

 for the cream is ordinarily separated so soon that there is 

 but little opportunity of infection, if care is taken in the 

 handling. As a consequence, the number of species found 

 therein is smaller. 



Where milk is separated, it is always prudent to cool the 

 cream so as to check growth, as the milk is generally heated 

 before separating in order to skim efficiently. 



Although cream is numerically much richer in bacteria 



