192 BUTTER-MAKING. 
lessening viscosity of the cream. The ripening process causes 
the cream to become thicker but less viscous. Undoubtedly 
the acid developed during the ripening process tends to cut 
the membrane supposed to surround the fat-globules. The 
reduced viscosity of the cream renders it easier for the globules 
to move and unite in the serum when exposed to agitation in 
the churn. It is possible to churn ripened cream in a thinner 
state and at a lower temperature than unripened cream. 
Cream which has been ripened to a normal degree of acidity, 
also allows of a more complete churning than unripened cream. 
Fic. 126—The Boyd cream-ripening vat. 
If cream is properly ripened, and churned at a medium low 
temperature, it is possible to churn so that the buttermilk con- 
tains only about .1% of fat by the Babcock test; while if sweet 
cream is being churned under the same conditions, the butter- 
milk will contain more than this. This is undoubtedly due to 
the fact that in sweet cream the viscosity is so great that it 
prevents the minute fat-globules from uniting when agitated 
in the churn, while in sour milk the viscosity has been largely 
removed. Sour cream is thicker than ripe cream, but less 
viscous. This facilitates the coalescence of the fat-globules 
when exposed to agitation. 
(3) To Increase the Keeping Quality of Butter.—It has been 
demonstrated by several investigators that the keeping quality 
of butter depends chiefly upon the number and kinds of germs 
present in the butter after its manufacture. In order, there- 
