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. 



FIG. 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- 



