l8 SCIENCE AND PRACTICE OF CHEESE-MAKING 



milk should be strained through two layers of clean 

 cheese-cloth to remove all insoluble dirt (p. 434). 

 While the milk is accumulating in the vat, it should 

 be stirred frequently up to the time of coagulating 

 with rennet in order to keep the cream from separ- 

 ating. When the vat is full enough, the amount of 

 milk present is figured, and the acidity of the milk 

 is determined or a rennet-test made. 



RIPENING MILK 



This consists in the formation of a certain amount 

 of lactic acid (p. 292). Its object is to control more 

 completely the various operations of cheese-making; 

 this is accomplished especially (i) by the repression 

 of abnormal ferments; (2) by assistance in shrinking 

 curd, expelling whey, and maturing the curd in body 

 and texture. Lactic acid may be formed by allowing 

 milk to stand a while at a temperature of about 86 F. 

 When lactic acid bacteria are not present in abundance 

 or are kept back in growth by injurious organisms, it 

 is necessary to use a starter or culture. 



Preparation of starter. A starter is a material 

 (usually milk), containing large numbers of lactic 

 acid organisms, which is added to milk or cream 

 for the purpose of causing lactic fermentation. Start- 

 ers are of two kinds: (i) Natural and (2) com- 

 mercial, (i) Natural starters. A natural starter 

 may be prepared as follows : Milk of the best possible 

 character, taken under precautions necessary to insure 

 cleanliness, is heated to 90 F. for one hour, aerated in 

 a pure atmosphere, and immediately cooled to 65 F. 

 In 24 hours the milk should be sufficiently sour to be 

 ready for use, Some of this starter may be used in 



