244 MANUAL OF MILK PRODUCTS 



fit to use ; in other cases it remains good for many months. The 

 maintenance of its good quality depends upon the skill of the 

 maker and the bacteriological quality of the milk. 



"A starter is in the best condition to use when it contains 

 the greatest number of the desirable bacteria. This occurs 

 about the time that it coagulates. It then contains from five 

 million to two billion bacteria per cubic centimeter. For 

 several days after this the bacteria do not decrease very much 

 and it would not be unfit on this point. If it is kept at a ripen- 

 ing temperature after it has coagulated, bad flavors appear in 

 the course of time. This is called over-ripening. It is not due 

 to an excess of lactic acid, but to the development of other 

 bacteria that produce bad flavors. Oidium lactis is also asso- 

 ciated with the bacteria in the production of ill flavors. Over- 

 ripening occurs much more slowly at low temperatures. If the 

 starter cannot be used soon after it is ripe, it is best to cool it 

 as low as possible. 



"There are conditions where milk is received only every other 

 day. In such cases it has been recommended to make up only a 

 small quantity of starter the first day, save some pasteurized 

 milk, re-pasteurize, and inoculate it the next day. This is 

 hardly necessary. The ripening can be managed so as to take 

 two days or the starter can be allowed to ripen and then cooled. 

 The latter method is best because the combined effect of the low 

 temperature and large amount of lactic acid retards the action 

 of undesirable bacteria. Stirring the starter during ripening 

 keeps the temperature more uniform, but it has little value and 

 is not practiced much. Some stir at the time of coagulation to 

 prevent clotting. Stirring after it has coagulated will not cause 

 wheying off unless the temperature is high or the flavor is bad. 



"A starter has the best opportunity for exerting its effect 

 when it is put in the vat before the cream is put in. Some pour 

 the starter into the vat through a strainer to break up the clots 

 of curd which have a tendency to settle to the bottom of the vat. 



