Starters.—Beginning with a commercial dry culture in the form of a powder as generally used in the creamery or the cheese factory as well as for the preparation of commercial buttermilk, or with buttermilk tablets as used in the ordinary household or the hospital, such culture is added to a small quantity of thoroughly pasteurized milk. If fresh, sweet skim milk is available it is preferable to whole milk as the butter-fat in the latter only interferes with the process; but either can be used.

Milk for starters should be strongly pasteurized by being kept at a temperature near the boiling point—at least 180°—for 40 to 60 minutes, then cooled to the degree at which it is to be set, usually between 65° and 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.

If you have 4,000 lbs. of milk in the cheese vat to ripen with 2% or 80 lbs. starter, prepare 88 lbs. of mother starter. If, on the other hand, you wish to make only a quart of buttermilk every day, take, say, two buttermilk tablets, crush them thoroughly in a spoonful of pasteurized milk and stir this into a tumblerful of the same milk; let stand till it is thickened the next day and use a tablespoonful of this thickened milk in a quart of fresh pasteurized milk which when ripened is your buttermilk, from which you take out a tablespoonful for starter in the next batch, and so on. In this case there is no “mother starter” except that perhaps the first tumblerful prepared with the tablets may be called so, but afterwards the starter is taken right out of the finished product every day.

The process may be modified to suit special purposes and local conditions, but the following precautions should be strictly observed: (1) to interrupt the ripening immediately by quick and intense cooling as soon as it has reached the proper point in case the ripened product is not used at once, and (2) to keep it ice-cold until it is used. If this is done, it may be kept for two or three days without deterioration if it is not convenient to make it fresh every day which, however, should be the rule.

CHAPTER II
Milk Supply and Creamery Products

In the first chapter the composition of cow’s milk and the nature of its constituents have been considered, the most important tests for its richness and purity have been described, and the ferments have been mentioned which instigate changes for good or for bad, together with the means at disposal for regulating their activity. To use these means intelligently in handling milk and its products is the key to the dairyman’s success.

We shall now briefly consider the various steps that are of importance in modern dairy industry.