CHEESE 363 



cheeses develop a characteristic aroma or odour, which 

 is well-marked and quite distinct from that of fresh 

 curd. The pleasant, sourish smell of a ripening cheese 

 is probably due, to some extent, to minute traces of 

 formic, acetic, and similar free volatile fatty acids present 

 in it. Propionic and butyric acids, which are generally 

 found in greater amount, have a penetrating and some- 

 what rancid smell. Isovaleric acid has a characteristic 

 old-cheesy odour, and the unpleasant smell of the rind 

 of certain overripened cheeses has been traced to the 

 presence of caproic and caprylic acids. The peculiar 

 odours of cheeses are not entirely due to free, fatty 

 acids ; nitrogenous compounds, such as amines and 

 ammonia, contribute their share. Putrescine and cad- 

 averine, both of which have a sharp, objectionable odour, 

 have also been isolated from cheese. The flavour or 

 taste of a good nutty cheese appears to be connected with 

 the amino-acids, most of which have a mild, sweetish 

 taste. According to Jensen, the delicate, nut-like flavour 

 of the best Emmenthal cheese increases with an increase 

 in the amount of those soluble nitrogenous compounds 

 which cannot be precipitated from their solutions by 

 phosphotungstic acid, a class which includes the amino- 

 acids. Many of the more complex protein substances 

 have each a characteristic taste and smell, but nothing 

 definite is known about their influence in the production 

 of good flavour and aroma in ripe cheese. In some 

 instances considerable amounts of bitter substances are 

 produced, but little is known of their nature or origin : 

 they only arise in cheeses undergoing putrefaction or 

 abnormal decomposition, or where little or no salt has 

 been used in the manufacture. Many of the peptones 

 have a bitter taste, but in normally ripened cheese they 



