146 Dairy Bacteriology. 



to the freedom of the same from organisms other than 

 the lactic bacteria. This is a factor of as much impor- 

 tance as uniformity, because under modern business con- 

 ditions, the surplus production must be kept in storage, 

 and it is essential that the quality should not deteriorate 

 materially during this time. 



Process of pasteurization for butter making. In the 

 pasteurization of market milk, it is necessary to take into 

 account the effect of heating on the physical and chemi- 

 cal properties of the milk, and the degree of heat that 

 can be employed is limited. In pasteurizing cream for 

 butter, there is no such limitation, and the cream may be 

 heated to any temperature desired. In Denmark where 

 the process of pasteurization has been used most exten- 

 sively, temperatures ranging from 176 F. to 190 F. 

 are used. The machines are of the "continuous flow" 

 type, and the cream rather than the whole milk is 

 treated. To prevent the spread of tuberculosis and 

 other diseases, the Danish government requires that all 

 cream and milk be heated to 176 F., before the skim 

 milk or butter milk is returned to the farms. 



The heating of the butter fat to high temperatures has 

 an injurious effect on the texture of the butter, unless 

 the cream is cooled to 50 F., for a period of at least two 

 hours previous to churning. 



Propagation of starters. As has been previously 

 shown, the quality of butter depends on the kind of bac- 

 teria in the cream or in the starter added. The com- 

 mercial starters contain lactic acid bacteria that have 

 been selected with especial care ; most of the starters now 

 sold contain but a single kind of bacteria; hence, are 

 often called pure-culture starters. The package pur- 

 chased contains but a small quantity, and before the 



