588 ANNUAL REPORT OF THE Off. Doc. 



32. Eichucss of Cream for Butter-Making. 



How rich in fat should cream be made for butter-makiug? By the 

 gravity method of creaming, we obtain cream containing 15 to 20 

 per cent, of fat, and by the separator we produce cream of any fat 

 content desired. Good results in every respect may be obtained 

 by the use of cream varying greatly in fat content. The tendency 

 has been to use rather rich cream containing 35 to 40 per cent, of 

 fat, in which case a lower temperature is used in churning, usually 

 with loss of less fat in buttermilk. In order to ripen rich cream 

 in the same length of time as poorer cream, somewhat more starter 

 needs to be used, as the richer cream ripens more slowly than poorer 

 cream under the same conditions. 



33. Conditions Affecting Churning. 



Churning is the term applied to the process by which the fat- 

 globules of milk or cream are made to unite into visible aggrega- 

 tions, and to separate from the milk-serum or buttermilk. This 

 massing together of fat-golbules is usually produced by the vigorous 

 agitation of cream in vessels especially constructed for the pur- 

 pose, called churns. When milk or cream is agitated at a tempera- 

 ture somewhat below 85 degrees F., the average melting-point of 

 milk-fat, the fat-globules gradually attach themselves together, 

 each of the small masses first formed continuing to increase in size 

 by uniting with others, until finally the whole of the fat, thus sepa- 

 rated, can be collected in one mass. The readiness with which fat- 

 globules separate from cream in churning is influenced by several 

 conditions, among which we may mention, as the most important, 

 (1) the composition and size of the fat-globules, (2) the composition 

 of the milk-serum, (3) the degree of ripeness of the cream, (4) the tem- 

 perature used in churning, and (5) the kind of agitation or churn. 



(1.) Composition and Size of Fat-Globules. — The readiness of fat- 

 globules to separate from milk-serum and unite in visible masses 

 during the process of churning, is influenced by the composition and 

 size of the fat-globules. As pointed out in section 3, p. 13, milk-fat 

 varies in its composition, and this variation in composition afifeets 

 the hardness or softness of the fat. This quality is influenced by the 

 character of the cow's food. Thus, succulent feeds and feeds rich 

 in starch and sugar make the fat softer. Cottonseed-meal makes 

 the fat harder. Now, it is known that the fat-globules unite more 

 easily in churning when they are composed of softer fat. and less 

 readily when they have larger proportions of hard fat. 



In respect to the influence of the size of fat-globules upon ease of 

 <hurning, the larger the fat-globules the more easily and quickly 



