58 CLEAN MILK 



The cream from set-milk contains 90 to 99 per cent, of the 

 germs which were present in the whole milk, because in rising the 

 fat globules entangle the germs and carry them along to the surface. 

 These germs are chiefly made up of the varieties which cause the 

 souring of milk or cream (lactic acid bacilli), and these increase 

 for forty-eight hours at favorable temperatures — 6o u to 70 F. — 

 in cream, and then gradually die out, owing to the unfavorable in- 

 fluence of the acid formed in souring, so that in a week few remain. 

 During the first few hours there are to be found a great variety of 

 germs in milk and cream, but the lactic acid bacilli crowd these out, 

 because they grow so much more readily than do the other kinds of 

 germs, and at the end of forty-eight hours there may be as many 

 as 500,000,000 lactic acid germs to the quarter teaspoonful. Butter 

 is commonly made from cream which has " ripened." By ripening 

 is meant the changes which occur in cream owing to the growth of 

 germs in it during the process of souring. 



The ripening of cream may be compared to the change which 

 takes place in grape juice when it turns to wine. Both changes — 

 in the grape juice and cream — are brought about by fermentation, 

 and fermentation is simply a term for describing the changes — 

 chemical and physical — which occur in a substance owing to the 

 action of germs * and their products upon it. 



In the ripening or fermentation of cream the germs alter the 

 character of the cream and supply bodies which give to the butter 

 its peculiar flavor and improve its keeping qualities. Butter made 

 from fresh cream has less flavor and does not keep well. The 

 sour milk germs give butter part of its flavor, but the miscellaneous 

 germs which are crowded out by the former also are responsible 

 for much of the flavor. In this country the popular palate requires, 

 a much stronger flavored butter than the European taste, which 

 regards our butter as rank in flavor. Therefore abroad it is often 

 customary to pasteurize fresh cream to kill the miscellaneous germs 



* Or, rarely, to the action of ferments or enzymes. 



