Bacteria and Butter- Making. 153 



7. The starter should not be thoroughly curdled and solid 

 when it is needed for use, but should be well soured and 

 partially curdled. This point is of importance for the fol- 

 lowing reasons: 



a. It is difficult to thoroughly break up curd particles if 

 the starter is completely curdled. If these curd masses are 

 added to ripening cream, white specks may appear in the 

 butter. 



b. The vigor of the starter is in all probability stronger 

 when the milk is on the point of curdling than it is after 

 the curd has been formed some time. The continued for- 

 mation of lactic acid kills many of the bacteria and thus 

 weakens the fermentative action. It is therefore highly 

 important that the acidity of the starter should be closely 

 watched. 



8. The starter should be propagated from day to day by 

 adding a small quantity to a new lot of freshly prepared 

 milk. For this purpose two propagating cans should be 

 provided so that one starter may be in use while the other 

 is being prepared. 



9. The butter-maker must exercise his judgment as to 

 the condition of his starter. If the same should appear 

 moldy or contain evidence of gas, the skim milk has been 

 imperfectly handled. 



How long should a starter be propagated? No hard-and- 

 fast rule can be given for this, for it depends largely upon 

 how carefully the starter is handled during its propaga- 

 tion. If the starter is grown in sterilized milk kept in 

 steamed vessels and is handled with sterile dippers, it is 

 possible to maintain it in a state of relative purity for a 

 considerable period of time; if, however, no especial care is 

 given, it will soon become infected by the air, and the 



