CHURNING 269 



units of fat, therefore, retain their identity and individuality and, 

 because of the surface tension, they are present in the form of 

 round globules. 



Adsorption and Viscosity. The ability of the fat globules 

 in milk and cream, to retain their individuality is further assisted 

 by the law of adsorption and by the viscosity of the milk. 



By adsorption, in the sense here used, is meant the some- 

 what greater concentration in the surface layer of the fat 

 globules of the skim milk ; than the concentration of the 're- 

 mainder of the surrounding skim milk. This concentration of 

 the skim milk on the surface layer of the fat globules assists 

 in maintaining their internal cohesion and in diminishing the 

 power of adhesion between fat globules. It tends to convey 

 to the individual fat globules greater stability. 



Finally, the permanency of the emulsion of the fat globules 

 in milk is enhanced by the natural viscosity of the skim milk, 

 caused by the presence of such colloids as albumen and casein, 

 and of milk sugar. 



Effect of Cream Separation. When cream is separated 

 these phenomena do not materially change, they remain funda- 

 mentally the same. Cream still represents an emulsion of fat- 

 in-skim milk. The composition of the non-fatty serum in cream 

 is similar to that of milk and the difference in the surface ten- 

 sion between the fat globules and the cream serum remains 

 the same. There is merely a larger aggregation of fat globules 

 in a smaller volume of skim milk. 



Effect of Cooling of Cream. When cream is cooled, pre- 

 paratory to churning, the fat in the fat globules wholly or partly 

 solidifies. This enhances the internal power of cohesion in the 

 fat globules and increases the power of adhesion between fat, 

 globules, offsetting and completely overcoming the effect of 

 the surface tension of the fat globules. If cream were not cooled 

 sufficiently to partly or wholly solidify the fat, the churning 

 would result in a finer division of the fat globules. 



Effect of Agitation in Churn. When this cooled cream, 

 with the partly, or wholly solidified fat globules is subsequently 

 subjected to the agitation and concussion generated in the re- 



