Bacteria in Butter-Making. 141 



and partially curdled. This point is of importance for 

 the following 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 undoubtedly 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. 



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

 adding a small quantity to a new lot of milk. For this 

 purpose two propagating cans should be provided (fig. 

 32 B) so that one starter may be in use while the other 

 is being prepared. 



9. After the starter has been used for a few days, the 

 same should be emptied, and the can cleaned and steril- 

 ized by steam before being used again. 



141. How long 1 should a starter be propagated? 

 No hard and fast rule can be given for this, for it de- 

 pends largely upon how carefully the starter is handled 

 during its propagation. If the starter is grown in steril- 

 ized 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, how- 

 ever, no especial care is given it, it will soon become in- 

 fected from the air and the retention of its purity will 

 depend more upon the ability of the contained organism 

 to choke out foreign growths than upon any other factor. 

 While it is possible by bacteriological methods to deter- 

 mine with accuracy the actual condition of a starter as to 

 its germ content, still such methods are inapplicable in 

 creamery practice. Here the maker must rely largely 



