Bacteria and Butter Making. 147 



starter can be used in the ripening of cream, it must be 

 increased in amount. It must also be propagated from 

 day to day so that a fresh starter shall be available daily 

 for addition to the cream. The propagation of the 

 starter must be done with especial reference to keeping 

 it in good condition and in as high a state of purity as 

 possible. 



In the past the starter was propagated, by adding the 

 contents of the bottle purchased to a small amount of 

 milk that had been heated and cooled; this, if kept in 

 a warm place, would be curdled in twenty-four hours, 

 and could be used for the inoculation of a large mass of 

 milk, that had been treated in a like manner, and which, 

 when curdled, was added to the cream; a small amount 

 was saved for the purpose of again inoculating a mass 

 of milk that had been heated and cooled. Following 

 this method it was very difficult to keep the culture from 

 becoming contaminated with other forms of bacteria. 

 More recently the most successful butter makers have 

 propagated the so-called "mother starters" in small ves- 

 sels, and have used the larger mass of starter for the 

 inoculation of the cream alone. 



Glass vessels are preferable for the propagation of the 

 mother starters since they are impervious and through 

 the transparent wall the condition of the ripened starter 

 can be more easily determined than in a metal or earth- 

 en-ware vessel. An ordinary milk bottle with an in- 

 verted tumbler for a cover, to protect the starter from 

 contamination from the air, is a most convenient vessel. 



The starters may be propagated either in whole or 

 skim milk ; the former is preferable since, in most cream- 

 eries, it can be more easily selected. The quality of the 

 milk used has much to do with the quality of the starter ; 



