Relation of Bacteria to Butter. 67 



proper amount of acid has been developed in the cream. 

 As the development of acid turns generally on tempera- 

 ture conditions favorable to the growth of bacteria in the 

 cream uniformity in the ripening temperature first came 

 to be practiced. Experience also showed that the addi- 

 tion of already fermented milk could be advantageously 

 employed, so gradually sour milk or butter milk began to 

 be employed. These home-made starters have now long 

 been used with success. 



A recognition of the relation of bacteria to the process 

 of cream ripening is comparatively recent and has re- 

 sulted in much improvement in the preparation of the 

 starters used in the cream. The modern operator uses 

 essentially the following procedure in the preparation of. 

 a home-made starter: a small amount of milk which the 

 butter maker thinks has been handled under clean con- 

 ditions is allowed to sour. If the soured milk has a de- 

 sirable flavor and odor, it is added to a larger quantity 

 of milk which has first been heated to a temperature suf- 

 ficiently high to kill the acid-forming bacteria and which 

 has been cooled to 70-90 F. This mass of milk sours 

 quickly under the influence of bacterial growth. "When 

 it reaches the proper degree of acidity, this natural 

 starter is added to the cream, a small amount being re- 

 served with which to inoculate a fresh quantity of heated 

 and cooled milk. By this process the starter is propa- 

 gated from day to day and the butter maker is able to 

 control in large measure the type of fermentations in the 

 cream. Sooner or later the starter propagated in this 

 manner becomes undesirable in flavor and must be re- 

 jected. A new starter must then be developed and 

 propagated as described. 



The home-made starter has been of great service in .the 



