r. ACTERIA AND BUTTER-MAKING 2O7 



used, to see that the seal of the package is unbroken. If the 

 seal is broken, there has been an opportunity for contaminating 

 bacteria to enter. The culture, if not used immediately upon 

 receiptfshould be kept in a cool, but not cold place; for example, 

 in a refrigerator, not on the ice but near it. At this temperature 

 they will keep best. Lastly, in most cases, the whole culture 

 should be used at once, and the dairyman should make no at- 

 tempt to use half a culture and reserve the other half for a 

 later date, especially if it be a liquid culture. It is almost im- 

 possible for him to remove half of such a culture from its 

 package without so contaminating the other half that, if pre- 

 served for use at a later date, it is no longer reliable. 



Preparation of a Commercial Culture. To prepare a starter 

 some plan must first be adopted to increase the number of bac- 

 teria, for the package bought in the market does not contain 

 enough of these organisms to furnish a starter for any con- 

 siderable quantity of cream. If only a small amount of starter 

 is needed, for example, a quart for a few gallons of cream, the 

 procedure is as follows: 



A quart of skim-milk is placed in a glass jar and sterilized 

 either by boiling, or better by pasteurizing, by submitting it to 

 a heat of 180 for half an hour, stirring frequently to insure 

 uniform heating. The milk is then cooled by placing it in cold 

 water, and when it has reached a temperature of 80 the com- 

 mercial culture, from a freshly opened package, is stirred in 

 thoroughly ; the whole is covered to keep off the dust, and placed 

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

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

 starter. It is much better to use the starter before curdling 

 takes place, for two reasons: I. While the milk is still liquid it 

 is easy to distribute a starter uniformly through the cream that 

 is to be ripened, so that with a little stirring the whole mass 

 of cream is inoculated with the bacteria. After the milk has 

 curdled it is much more difficult to distribute it uniformlv 



