802 EXPERIMENT STATION RECORD. 



deemed advisable to review the theory proumlg-ated by them and show 

 its relation to their later work. 



In 1897 they announced the discovery of an inherent enzym in milk 

 which they termed galmtase^ and which has the power of digesting 

 casein of milk and producing chemical decomposition products similar 

 to those that normally occur in ripened cheese. The theory has been 

 advanced by them that this enzym is an important factor in the ripen- 

 ing changes, and, as in their experiments bacterial action was excluded 

 by the Use of anaesthetic agents, they conclude that so far as the break- 

 ing down of the casein is concerned bacteria are not essential to this 

 process. 



In formulating a theory of cheese ripening, they have further 

 pointed out the necessity of considering the action of rennet extract 

 as a factor that is concerned in the curing changes. They have shown 

 that the addition of increased quantities of rennet extract materiallj'^ 

 hastens the rate of ripening, and that this is due to the pepsin which is 

 present in all commercial rennet extracts. They tind it easily possible 

 to differentiate between the proteolytic action of pepsin and galactase, 

 in that the first-mentioned enzj^m is incapable of producing decompo- 

 sition products lower than the peptones precipitated by tannin. They 

 have shown that the increased solubility (ripening changes) of the 

 casein in cheese made with rennet is attributable solely to the products 

 peculiar to peptic digestion. The addition of rennet extractor pepsin 

 to fresh milk does not produce this change unless the acidity of the 

 milk is allowed to develop to a point which experience has shown to 

 be the best adapted for the making of Cheddar cheese. The rationale 

 of the empirical process of ripening the milk before the addition of 

 the rennet extract is for the first time thus explained. 



In stud3ang the properties of galactase these investigators further 

 found that this enzym, as well as those present in rennet extract, is 

 operative at very low temperatures, even below the freezing point. 

 These results have not yet been published, but were presented at a 

 recent convention of the Wisconsin Cheese Makers' Association. When 

 cheese made in the normal manner was kept at temperatures ranging 

 from 25 to 45° F. for periods averaging from 8 to 18 months, it was 

 found that the texture of the product simulated that of a perfectly 

 ripened cheese, but that such cheese developed a very miid flavor in 

 comparison with the normally cured product. Subsequent storage at 

 somewhat higher temperatures gives to such cheese a flavor the 

 intensity of which is determined by the period of .storage. This indi- 

 cates that the breaking down of the casein and the production of the 

 flavor peculiar to cheese are in a way independent of each other and 

 may be independently controlled, a point which is of great economic 

 value in commercial practice. 



Although it is generally believed that cheese ripened at low temper- 

 atures is apt to develop a more or less bitter flavor, the flavors in these 



