Outlines of dairy bacteriology, 10th edition / A concise manual for the use of students in dairying

by H. L. Russell; E. G. Hastings

In order to accomplish this, the maker must be able to maintain constant conditions from day to day, especially with reference to the amount of the ripened starter that is transferred to the fresh bottle of milk, and the temperature at which the bottles are kept. A spoon, arranged as shown in Fig. 31, enables one to carry a definite amount of the ripened starter to the bottle of milk to be inoculated and a constant temperature box (Fig. 32) permits of the maintenance of the same temperature from day to day. Through careful supervision of these points, and by taking care at every step to avoid the introduction of contaminating organisms, the purity of the culture can be maintained, and the bacteria kept in a healthy condition.

The starter is used because of the acid-forming bacteria it contains; it is said to be ripe and in the best condition for use at the time it contains the greatest number of living bacteria. It has been found by experiment that this is at the time the milk curdles at ordinary temperature, or when the acidity is about 0.6-0.7 per cent. If the acidity is allowed to increase to 0.8 or 0.9 per cent, the number of bacteria will be less and a larger amount of the starter must be used in order to ripen a definite amount of cream in the desired time. The use of an overripe starter may also have an injurious effect on the flavor.

Fig. 31.—Bottle for Mother Starters.
A milk bottle with a tumbler for a cover and a spoon for inoculating the other bottles enables the butter maker to propagate the starters without contamination.

The ripened starter should be perfectly homogeneous, showing no bubbles of gas or free whey; the odor should be agreeable and the acid taste mild; on shaking, the curd should break up into a smooth, creamy liquid free from lumps. This is especially important in the starter that is to be added to the cream, since otherwise the starter cannot be uniformly mixed with it and white specks of curdled casein will be noted in the butter.

Fig. 32.—An Incubating Chamber for Starters.
The inner compartment will hold a pail of water and the bottles for the mother starters. The temperature can be kept at any desired point by the use of warm or cold water. The four-inch space between the walls is filled with hay or mineral wool.

The firmness of the curd is not so dependent on the amount of acid formed as upon other factors. If the curd shrinks to any extent and the whey is expressed, it is certain to produce a starter that will contain lumps that cannot be broken up. With a pure culture of lactic bacteria, there is little difficulty in this regard, but as soon as gas-forming bacteria are introduced, trouble is likely to result.

In the propagation of starters, it is always to be remembered that the bacteria, although invisible to the eye, are living things, and unless conditions are favorable in every particular, it is impossible to keep them in a healthy condition, so that growth in the cream is rapid, producing the acid demanded for churning, and imparting to the butter the desired flavor, both as to degree and kind. No part of the daily routine of the butter maker should be performed with more care than the preparation of the starters, both the mother starters, and the larger one for addition to the cream. The latter can best be made in one of the many forms of starter cans now on the market, since by their use, the maker can heat and cool the milk with little trouble, and can maintain the starter at any desired temperature. Better starters cannot be made in them than by the use of simple and improvised apparatus, but better results can be obtained with the same expenditure of time and labor.

In the handling of the large starter, care should be used not to overripen, since the larger quantity is more likely to "whey off" than is the smaller starter. Skim milk rather than whole should be used for this. It should be selected with care and heated to 200° F. for thirty minutes. When it is impossible to secure fresh milk for starter making purposes, either condensed skim milk or milk powder may be used. The condensed milk is diluted with water until its volume is about the same as the milk before concentration; the mixture is then treated the same as fresh milk, being heated and cooled before inoculation. In the case of milk powder, one part of the powder is added to ten or twelve parts of water, allowed to dissolve as far as possible, and the mixture heated and cooled. Either of these liquids will give satisfactory starters; the cost however is high, and in most places milk can be obtained more cheaply. The inoculation and the temperature should be so controlled, as to ripen the starter at the time it is to be needed. These conditions must be determined by the maker for himself. It should be remembered that the bacteria grow much more rapidly, as the temperature is increased; and hence, the amount of inoculation is dependent on the temperature at which the starter is to be kept.