Fig. 7.—A simple device for the preparation of starter. often found in cheese factories.
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.