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, 



