CHEESE 361 



are not very clearly understood. The milk-sugar which 

 can be detected in freshly made cheese generally dis- 

 appears in a few days, and a watery extract of a ripe 

 one contains none of it. The fat undergoes very little 

 alteration. Various acids which are not found in the 

 fresh cheese appear in the ripened product. Lactic acid 

 and its salts are met with, and small amounts of acetic, 

 formic, propionic, butyric, caproic, valeric, and other 

 acids are frequently present either in the free state or 

 united with ammonia or other bases. Ripe cheese 

 always contains a certain amount of free non-volatile 

 fatty acids, such as oleic, palmitic, and stearic acids. 

 The most important changes occurring during the ripen- 

 ing process are those which are concerned with the 

 cleavage or breaking down of the casein. This protein 

 undergoes gradual hydrolysis as ripening proceeds, 

 simpler compounds arising at each stage of the process. 

 At first the casein is changed into caseogluten, a sub- 

 stance closely resembling casein, but differing from it in 

 being soluble in a solution of salt. Later the more 

 soluble and non-crystalline proteoses (caseoses) are 

 formed ; from these less complex peptones (caseones) 

 are produced, and later the peptones give rise to the 

 simpler soluble crystalline amino-acids, the chief of 

 which are glycocoll, alanine, leucine, tyrosine, phenyl- 

 alanine, and tryptophane. From the amino-acids origin- 

 ate small amounts of various amines, such as putrescine 

 and cadaverine, to which may be attributed some of the 

 objectionable flavours and odours of old cheese. Eventu- 

 ally ammonia is formed, and in some instances may be 

 set free in very small amounts, as in the soft cheeses, 

 but it is more frequently present in combination with 

 various acid compounds. 



