71. Qualities.—The starter, when ready to use, may or may not be coagulated; a good idea of the quality of the starter may be gained by the condition of the coagulation. The coagulation should be jelly- or custard-like, close and smooth, entirely free from gas pockets and should not be wheyed off.
When broken up, the starter should be of a smooth creamy texture and entirely free from lumpiness or wateriness. It should have a slightly pronounced acid aroma. The starter should be free from taints and all undesirable flavors; the flavor should be a clean, mild acid taste.
72. How to carry the mother starter.—Some mother starter must be carried from day to day to inoculate the large starter. This may be carried or made in several ways:
1. Independently: By this method a mother starter is made and carried entirely separately from the large starter. It requires more time and work, but is by far the best method. With a good mother starter, there is not so much danger of the larger starter becoming poor in quality.
2. Mother starter may be made by dipping pasteurized milk from that prepared for the large starter with sterile jars and then inoculating these jars separately. By this method, if the milk selected for the large starter is poor, the mother starter for the next day will be the same. It is very difficult by this method to carry a uniform, high quality mother starter.
There is danger that the container used for the mother starter may not be sterile, and there is also danger of contamination in transferring the milk.
3. Another practice is to hold over some of the large starter used to-day for mother starter. This is by far the easiest method. By this practice, there is no certainty of the quality of the starter, because there is little or no control of the mother starter. If the large starter is for some reason not good, there is no separate reserve of mother starter on which to rely.
73. Starter score-cards.—The use of a score-card tends to analyze the observations in such a way as to emphasize all the characteristics desired in the starter. Such an analysis seeks to minimize the personal factor and produce a standardization of the quality. The score-card finally reduces the qualities of the starter to a numerical basis for ease of comparison. Many score-cards have been proposed but the one preferred by the authors is that used by the Dairy Department of the New York State College of Agriculture, which is as follows:
| Cornell Score-card | ||
| Flavor | 50 | Clean, desirable acid. |
| Aroma | 20 | Clean, agreeable acid. No undesirable aroma. |
| Acidity | 20 | 0.6 per cent-0.8 per cent. |
| Body | 10 | Before breaking up: jelly-like, close,absence of gas holes. No freewhey. After breaking up:smooth, creamy, free from granulesor flakes. |
The qualities mentioned in this score-card can be quickly and easily determined by examining and tasting the starter and by making an acid test of a sample. The acid test is conducted as with milk (see [Chapter II]) except the starter must be rinsed out of the pipette with pure water. Some starter score-cards call for a bacterial examination and counting of the starter organisms. This takes a considerable period of time and is not entirely necessary. The physical properties and acid test are closely correlated with the presence of the desired organisms.