75°, somewhat higher for the first propagation with the pure culture than for the subsequent transplantings when the bacteria, more or less dormant in the dry powder or tablets, have attained full vitality. Some species of bacteria, as the Bacillus Bulgaricus, require higher temperatures—90° to 100° or even 110°—than others. The culture having been thoroughly incorporated in the milk by vigorous and repeated stirring or shaking, the milk is left at rest in an incubator or a waterbath or wrapped in paper or cloth in a warm room where an even temperature can be maintained, until it is curdled, which may take 18 to 24 hours or even longer for the first propagation.
One part of this curdled milk is now added to 5 or 10 parts of fresh pasteurized milk and set to ripen in the same way as described above, possibly at a little lower temperature, and this is repeated every day, thus maintaining the "Mother Starter." After the second or third propagation the bulk of each batch is used as a starter in the larger lot of material to be ripened, be it cream for butter or milk for cheese or for commercial buttermilk, while a little is taken for maintenance of the mother starter as described above.
The amount of starter to prepare every day depends upon the amount of milk or cream to be ripened and the per cent of starter used in same. For instance, if you have ten gallons of cream to ripen every day in which you wish to use about 10% or 12% starter, or one gallon, take a little less than one pint of the first or second propagation for one gallon of milk; the next day use one pint of this to add to a gallon of fresh starter milk, and the remaining gallon to add to the ten gallons of cream, and so on every day.
