CHEESE-RIPENING 211 
upon the amount of water present, and, in the soft cheese, with 
their large amount of water, a slimy and almost liquid con- 
sistency may finally be reached. This softening is due to a 
change in the chemical nature of the casein by which it changes 
from an insoluble into more or less soluble products. The 
changes in the casein during the ripening are, in general, similar 
to those that occur when the casein is digested under the action 
of digestive juices, so that they are frequently spoken of as a 
digestion of the curd. During the ripening the insoluble casein 
is converted into a series of simpler chemical bodies, pepiones, 
proteoses, etc., and as these become partly dissolved the hard 
texture of the cheese becomes softer. Not only are the changes 
similar to those of digestion, but they are produced by enzymes 
similar to, though probably not identical with, the enzymes 
in the digestive juices. The ripening of a cheese is thus a pre- 
digestion which renders the cheese more easily digested when eaten. 
The enzymes that produce this ripening of the cheese come 
from three quite different sources. One enzyme with this power 
of digesting curd is in the original milk itself. This is the galactase 
already mentioned. Another is added to the milk with the 
rennet, for rennet is made from the stomach of a mammal, and 
will always contain some of the pepsin from the stomach. The 
latter is an enzyme with strong digestive power and is sure to be 
present in some quantity in the rennet, and hence in the cheese 
after the addition of rennet. These two enzymes doubtless 
continue to act upon the casein during the ripening, and are 
responsible for a certain portion of the digestive changes that are 
taking place. But there is also a third source of enzyme that, 
in some cheeses, is more important than the others. As already 
noticed, certain microdrganisms have the power of secreting 
enzymes, and some of them, growing in or on. the ripening cheese, 
develop enzymes which contribute largely to the ripening. In 
some of the soft cheeses this is certainly the chief source of the 
enzymes. 
