210 BUTTER-MAKING. 
CHEMICAL, PHYSICAL, AND BIOLOGICAL CHANGES. 
Physical Changes.—All the changes in cream during ripening 
are very complex, and the causes of them are not well under- 
stood. The chief cause of the ripening process, as it normally 
occurs, is the action of micro-organisms. As has been stated 
before, the germs producing lactic acid are the most numerous. 
These germs continue to gain the ascendency in the cream 
during the ripening until cream is almost a pure culture of 
lactic-acid-producing germs. Accompanying this growth, the 
sugar present in the cream is broken up into lactic acid and 
several other by-products which will be mentioned later. 
These different by-products have certain physical effects 
upon the body of the cream. The acid developed causes 
the cream to coagulate and become thick. As the ripening 
process is carried on the appearance of the cream changes some- 
what. It becomes thick, granular, and glistening in appear- 
ance. Undoubtedly the film of casein, or whatever the envelop- 
ment may be, surrounding the fat-globules, is loosened or cut. 
Biological Changes.—Cream when put into the ripening-vat 
usually contains a very large variety of bacteria. Which 
species predominates at that time depends upon the care and 
treatment of the cream previous to the ripening stage. In 
pasteurized cream practically all the germs present are of the 
spore-producing kind, and unless conditions are favorable for 
the development of the spores, these will be suppressed by the 
germs added with the starter. During the first few hours of 
the ripening process there is a gradual growth of all the germs 
present. It is said that in sweet cream the lactic acid germs 
are comparatively few in number, but under favorable conditions 
these grow so much more rapidly in number than any of the 
others, that in a short time they become more numerous than 
all the other germs. The by-product lactic acid is unfavorable 
for the growth of nearly all the undesirable varieties of germs. 
Practically all these germs are suppressed in their development, 
