1 88 BACTERIA IN BUTTER AND OLEOMARGARINE. 



of from 65 to 70. After one or two days the milk should show 

 signs of souring; when it ha? become decidedly sour, but not yet 

 curdled, it is to be used as a starter. It requires some skill on the 

 part of the butter-maker to know whether the starter thus obtained 

 is of the best character and whether it should be used or thrown 

 away and another obtained. Starters made in this way are not 

 sure to be uniform, inasmuch as the different samples of milk may 

 contain different types of bacteria, and experience is needed on the 

 part of the butter-maker to know whether the starter is satisfactory. 



Starters from Commercial Cultures. Commercial starters are 

 now a well-known article, and several different brands may be pur- 

 chased. In all cases they are prepared by bacteriologists and 

 consist of a culture of bacteria usually a pure culture, though not 

 always that have been found by experiment to produce favorable 

 results in the ripening. These starters as purchased are sometimes 

 in the form of a powder, sometimes in the form of a liquid, but in 

 all cases contain too small a quantity to add directly to the cream 

 that is to be ripened. The quantity of bacteria must, therefore, 

 be increased before using by a process called building up. The 

 procedure is as follows: 



A quart of skim milk, whole milk, or cream is placed in a glass 

 jar and sterilized, either by boiling or, better, by pasteurizing at 

 1 80 for half an hour, stirring frequently to insure uniform heating. 

 The milk is then cooled, and when it has reached a temperature of 

 80 the commercial culture, from & freshly opened package, is thor- 

 oughly stirred in; the whole is covered to keep out the dust and 

 placed at a temperature of about 65. When the milk has become 

 quite sour, but before it is curdled, it is ready to use as a starter. 

 If a larger amount of starter is needed, this first starter is placed in 

 a large can of pasteurized milk and allowed to grow in it at 65 

 until the whole becomes soured. By this means any desired amount 

 can be prepared. 



The starter thus prepared is added to the cream in varying 

 proportions, the larger the amount the quicker the ripening. Some- 

 times one part of the starter to ten parts of cream is used; in other 

 cases a smaller amount is used and sometimes more. After the 



