+65. Cleanliness.+--To produce a good starter, great care should be exercised that all utensils coming in contact with the milk are sterile.

After the milk is in the container in which the starter is made, it should be kept covered as continuously as possible. Thermometers should not be put into it to ascertain the temperature. When examining the starter, do not dip into it, but pour out, as this prevents contamination. The cover, when removed from the container, should be put in a sterile place in such way that the dirt will not stick to it and later get into the starter.

+66. "Mother" starter or startoline.+--The thickened sour milk obtained by inoculating the sweet pasteurized milk with pure culture of lactic acid-forming bacteria is known as "mother starter" or "startoline."

+67. Examining starter.+--This starter should be examined carefully as to physical properties, odor and taste. The coagulation should be smooth, free from whey and ga.s.sy pockets or bubbles. Sometimes the first few inoculations from a new culture will show signs of gas, but, usually, this will quickly disappear, and not injure the starter. It should have a clean sour cream odor and clean, mild, acid flavor. After breaking up it should be thick and creamy, entirely free from lumps.

This starter may have an objectionable flavor, due to the media in which the organisms were growing when shipped. In such cases it is necessary to carry the starter one or two propagations to overcome the flavor, to enliven the micro-organisms and to secure the quant.i.ty desired.

+68. Second day's propagation.+--For the second day, the milk for the starter is selected as on the first day. It is pasteurized, and this time cooled to 70 F. The milk is cooled a trifle colder the second day than the first, because the organisms have become more active and hence do not require as high a temperature to grow. Instead of inoculating with powder, as was done the first day, the mother starter prepared the first day is used. This requires only a very small amount, perhaps a tablespoonful to a quart bottle. It should be thoroughly mixed with the milk. This starter may have the flavor of the media used in the laboratory culture, therefore may need to be carried one or two days more to eliminate it. After the flavor has become normal, the mother starter is ready for commercial use.

[Ill.u.s.tration: FIG. 6.--An improved starter-can.]

+69. Preparation of larger amount of starter.+--The first thing to determine is the quant.i.ty of starter required. As much milk should be carefully chosen as the amount of starter desired. This milk should then be pasteurized. An improved starter-can (Fig. 6) may be used in the pasteurization of the milk and the making of starter, or a milk-can (Fig. 7) placed in a tub of water in which there is a steam pipe. The former requires mechanical power to operate the agitator, but the latter can be used where mechanical power is not available. In the latter the milk and starter are stirred by hand. This is the kind of apparatus more often found in cheese factories.

[Ill.u.s.tration: FIG. 7.--A simple device for the preparation of starter.]

If possible, this milk should be pasteurized to 180 F. for thirty minutes; this kills most of the bacteria and spores. The milk should be cooled to 60-65 F., the temperature of incubation. This temperature may be varied with conditions, so that the starter will be ready for use at the desired time. The higher the temperature, the less time is required to ripen the starter.

+70. Amount of mother starter to use.+--The mother starter prepared the day before is now used to inoculate the starter milk. The amount to use will depend on:

1. Temperature of milk when mother starter is added;

2. Average temperature at which the milk will be kept during the ripening period;

3. Time allowed for starter to ripen before it is to be used;

4. Vigor and acidity of the mother starter added. There is a very wide range as to the amount of mother starter required, from 0.5 of one per cent to 10 per cent being used under different conditions.

Some operators prefer to add the mother starter while the milk is at a temperature of about 90 F., before it has been cooled to the incubating temperature. This reduces the amount of mother starter necessary.

If an even incubating temperature can be maintained, it will require less mother starter than if the temperature goes down.

If the ripening period is short, it will require a larger amount of mother starter, than if the ripening period is longer. If the starter has a low acidity or weak body indicating that organisms are of low vitality, it will require more mother starter.

+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 p.r.o.nounced 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 a.n.a.lyze the observations in such a way as to emphasize all the characteristics desired in the starter. Such an a.n.a.lysis 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 free whey. After breaking up: smooth, creamy, free from granules or 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.

+74. Use of starter.+--If all milk could be clean and sweet and the only fermentation from it were the clean acid type, a starter would be useless. Such milk is hard to obtain; therefore, a starter is used to overcome the bad fermentation. This improves the flavor, body and texture of the cheese. The common contaminations which the starter will tend to correct are:

1. Gas-producing bacteria.

2. Yeasts.

3. Bad flavors or taints.

The length of time a starter may be carried depends on the accuracy and carefulness of the maker. This calls for scrupulous attention to the temperature, the selection of milk and keeping out contaminations. The maker must remember that a starter is not merely milk, but milk full of a mult.i.tude of tiny plants, very sensitive to food, temperature, clean surroundings and the quant.i.ty of their own acid.

NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY

+STARTER LOT-CARD+ +Department of Dairy Industry.+ ================================================================== Day and Date_____________________

+MILK:+

Kind________________ % fat_____% solids not fat_____

Flavor__________________________________

Amount of milk____________ Hours old______________

+PASTEURIZATION:+

Method______________________________________________

Milk when received: Temperature_____

Acidity_____ %

Heating: Turning on heat__________ APM.

Desired temp. reached__________ APM.

Turning off heat__________ APM.

Length of time at desired temp.__________