166 Dairy Bacteriology. 



tough and firm, the particles showing no tendency to 

 adhere to each other. As the acid increases in amount, 

 the curd becomes plastic, the outer surface of the par- 

 ticles adhering or ' i matting, ' ' as the maker expresses it. 

 The result is a solid coalescent mass of curd, which is cut 

 into small pieces, i. e., "milled," before it is put to press. 

 The acid allows the blending of the pieces under the in- 

 fluence of the pressure so that a cheese is one single mass. 

 Under certain abnormal conditions, the development of 

 acid may be interfered with and the particles of curd 

 fail to mat, in which case, the cheese will be crumbly 

 when it is cut. The determination of the proper time 

 for pressing is made by the application of what is known 

 as the hot iron test. This is made by determining the 

 length of the "strings" or "threads" which can be 

 drawn from a mass of curd when it is brought in contact 

 with a hot iron at a cherry red heat, the length of the 

 curd threads being a measure of the amounib of acid that 

 has been formed in the curd. 



The rate of acid formation within the curd particles is 

 also measured by determining the acidity of the whey 

 as it comes from the curd at different stages in the mak- 

 ing. This test, which is often used in place of the ' ' hot 

 iron", test is carried out in the same manner, as in de- 

 termining the acidity of milk or cream. The quality of 

 the cheese, both as to texture and flavor, is dependent 

 to a great degree upon the amount of acid that is formed 

 during the various stages in making ; hence, the success- 

 ful maker must follow closely by some means the acid 

 formation in the curd until it is put to press. 



It is very necessary that the milk shall contain a suf- 

 ficient number of acid-forming bacteria to produce the 

 required amount of acid. If a sufficient number of bac- 

 teria are not present in the milk as it is received, as is 



