EXPERIMENT STATION RECORD. 



Vol. XII. No. 9. 



The ph3\sical and chemieul processes involved in the ripening or 

 curing of cheese are extreme!}' complex, and exact knowledge relating 

 to them has been sadly wanting until ver}- recent years. As a cheese 

 matures or becomes lit for consumption not only is there produced 

 the characteristic flavor that is peculiar to the type of cheese made, 

 but with all kinds, regardless of the quality of flavors formed, a pro- 

 found physical transformation of the casein occurs. In this change 

 the tirm elastic curd " breaks down;" i. e.^ becomes plastic, and, from 

 a chemical point of view, the insoluble casein is converted into various 

 soluble decomposition products. 



In discussing these ripening phenomena, the production of flavor 

 and the breaking down of the casein — /. e. , the formation of proper 

 texture — have been'regarded as diflerent phases of the same process. 

 But, as later shown, these changes are not necessarily so closely 

 correlated. 



The theories that have been advanced in the past as explanatory of 

 the ripening changes in cheese have been suggestive rather than 

 founded on experimental data, and it is only within the last five years 

 that carefully controlled scientific studies of this problem have been 

 made. 



At the present time two theories have been advanced whicli purport 

 to account for the changes involved. One of these, which is essentially 

 European, ascribes the ripening changes wholly to the action of living- 

 organisms — the bacteria present in the cheese. The other originated 

 in this country, and asserts that there are digestive enzyms inherent 

 in the milk itself that render soluble the casein of the milk. 



The adherents of the bacterial theory are divided into two classes. 

 One, led by Duclaux, considers that the breaking down of the casein is 

 due to the action of liquef3'ing l^acteria (Tyrothrix forms). On the 

 other hand, von Freudenreich has ascribed these changes to the lactic- 

 acid type of bacteria, which develop so luxuriantly in hard cheese. 



Within the limits of this article it will be impossible to give a crit- 

 ical review of these theories that would do justice to the question at 

 issue. But in view of important practical results recently obtained by 

 Babcock and Russell, of the Wisconsin Experiment Station, it is 



sui 



