CHAPTER IX. 



CHURNING. 



Theory. Under the physical properties of butter fat 

 it was mentioned that this fat existed in milk in the form 

 of extremely minute globules, numbering about 100,000,- 

 ooo per drop of milk. In rich cream this number is in- 

 creased at least a dozen times owing to the concentration 

 of the fat globules during the separation of the milk. 



So long as milk and cream remain undisturbed, the fat 

 remains in this finely divided state without any tendency 

 whatever to flow together. This tendency of the globules 

 to remain separate was formerly ascribed to the supposed 

 presence of a membrane around each globule. Later re- 

 searches, however, have proven the falsity of this theory 

 and we know now that this condition of the fat is due 

 to the surface tension of the globules and to the dense 

 layer of casein that surrounds them. 



Any disturbance great enough to cause the globules to 

 break through this caseous layer and overcome their sur- 

 face tension will cause them to unite or coalesce, a process 

 which we call churning. In the churning of cream this 

 process of coalescing continues until the fat globules 

 have united into masses visible in the churn as butter 

 "granules. 



CONDITIONS THAT INFLUENCE CHURNING. 



There are a number of conditions that have an impor- 

 tant bearing upon the process of churning. These may 

 be enumerated as follows: 



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