134 DAIRY BACTERIOLOGY 



in the hard cheeses usually only one-third of the casein becomes 

 converted into water soluble proteins, whereas in the soft cheeses 

 nearly all the casein undergoes conversion. This explains the 

 apparent richness in fat of the soft cheeses, for when anything 

 gives the sensation of melting in the mouth distinction is as a rule 

 not to be made between melting proper, as in the case of butter, 

 and a solvent action. Further examination of the soluble sub- 

 stances in hard cheeses shows that a larger proportion of these 

 have been converted into amino acids than in the soft cheeses ; 

 these conditions may be summed up by saying that in hard 

 cheeses the ripening is less extensive but more thorough., while in the 

 soft cheeses it is extensive but not so thorough. This definition, 

 however, cannot be regarded as a rigid one, for when the hard 

 cheeses are not much older than the soft ones (see, for example, 

 Edam cheese), the proportion of Dec. N. to Sol. N. is not large, 

 and if the soft cheeses do only contain small amounts of amino 

 acids, this is because these are quickly broken down into ammonia 

 on the surface l . Now as ammonia readily combines with the 

 lime free casein to form soluble salts, the high proportion of 

 Sol. N. in the soft cheeses is partly attributable to the thorough- 

 ness of the ripening process. The most important factor in the 

 ripening of the rennet cheeses, besides the various microorganisms, 

 is the rennet. It is the rennet which produces the perceptibly 

 soluble proteins and the microorganisms carry the degradation 

 further. Further, as the action of the most important of the 

 enzymes of the cheese ripening bacteria is inhibited, while that of 

 rennet is promoted by the presence of acid, it will easily be under- 

 stood why the practically neutral hard cheeses contain larger 

 proportions of amino acids than the soft cheeses. 



In the ripening of cheese, not only is the casein converted into 

 easily digestible and palatable products, but the fat and the 

 lactose also undergo changes. As might be expected, the fat is 

 hydrolysed most rapidly in cheeses like Roquefort which are 

 permeated with moulds. Rapid fat hydrolysis also takes place 

 in cheeses made from separated milk, for here the fat globules are 

 very minute and thus expose, a large surface for attack. On the 

 other hand, fat hydrolysis proceeds with extreme slowness in the 

 common hard rich cheeses. As, however, butyric, caproic and 

 capric acids have a very persistent taste, they contribute very 

 largely to the aroma of the cheese even though they may only be 

 present in small amounts. The reason why the choicer cheeses 

 must pass through a long period of ripening in order to attain 

 their characteristic piquant taste to the full, is that the processes 



1 Orla Jensen, " Centralblatt f. Bakt.," 2 Abt., 1900, Bd. VI., p. 773. 



