No. 6. DEPARTMENT OF AGRICULTURE. 689 



they unite. Owing to their size, the larger oues come iuto contact 

 more quicl^ly and more often than do the smaller ones. 



(2.) Composition of Milk-Serum. — The albumin, casein and milk- 

 sugar contained iu milk or cream tend to keep the fat-globules from 

 coming together easily. The larger the amounts of these consti- 

 tuents, the less readily will the fat-globules come together. This is 

 one of the reasons why churning is ofteo so slow and difficult in the 

 case of cream from the milk of cows far along in lactation, since 

 at that time milk contains larger proportions of these constituents 

 than earlier in lactation. 



(3.) Degree of Ripeness of Cream. — The fat-globules of ripened 

 cream churn more readily and completelj^ than those of sweet cream 

 under like conditions, especially in the case of cream raised by 

 gravity. The lactic acid coagulates the casein and thus greatly de- 

 creases the strong influence it has in its usual condition to keep the 

 fat-globules from coming into contact with one another. 



(4.) Temperature Used in Churning. — The condition that exercises 

 most influence upon the ease with which the fat.globules unite in 

 churning is the temperature of the cream. This determines, more 

 than any other factor connected with churning, the hardness or soft- 

 ness of the fat-globules. When the temperature is too low, the fat- 

 globules are so hard that they do not stick together when they 

 come into contact, and, consequently, no butter results. When the 

 temperature is too high, the agitation of the fat-globules in churn- 

 ing tends to break them up into smaller globules rather than to 

 unite them into larger masses, thus forming a more complete emul- 

 sion, more difficult to churn than the original cream. Fat-globules 

 may be made to unite at temperatures as low as 46 degrees F., and as 

 high as 80 degrees F. Thus, the range of possible churning tempera- 

 tures is very considerable, but the quality of butter produced at differ- 

 ent temperatures is very different, particularly in texture. The butter 

 is in the most satisfactory condition at the end of churning, when the 

 temperature of the cream during churning has been such that the 

 fat-globules have united readily into firm, solid granules of butter, 

 with a minimum content of buttermilk. No particular temperature 

 can be prescribed for churning, as other conditions enter in to modify 

 the temperature of churning, such as (a) the individuality of cows, 

 (b) the stage of the lactation period, (c) the character of the food 

 eaten by the cows, (d) the season of the year, (e) the thickness of 

 the cream, and (f) the degree of its ripeness. The conditions men- 

 tioned that are immediately connected with the cow, influence the 

 composition of the milk-fat, making it harder or softer, as stated 

 above. The harder the milk-fat, the higher the temperature at 

 which churning should be done, and the softer the milk-fat, the 



