PREPARATION OF THE MILK FOR CHURNING. 167 



and in the case of ripening more slowly, the cream or the milk is 

 exposed longer to all possible accidental sources of injury than is 

 desirable in the interests of the keeping quality of the butter. 



In order to effect ripening in from 18 to 24 hours, the liquid 

 should be placed in large vessels of wood or of white-metal, in a 

 warm and easily ventilated room with a northern exposure. The 

 lactic ferment should be added in sufficient quantity to produce the 

 necessary sourness. The milk should be gently stirred from time 

 to time with a suitable stick made of good wood, and the vessel 

 may either be slightly covered or be open as desired. The milk is 

 to be maintained at as uniform a temperature as possible, which 

 may vary between 15 and 20 C. 



Formerly butter-milk from the previous churning was almost univer- 

 sally used as a sourer. This is still often done, and such a method is all 

 right, provided the butter-milk contains fairly pure lactic ferment, which 

 is capable of producing a rapid development of lactic acid. As soon, 

 however, as other ferments crowd out the lactic ferment in the butter- 

 milk, a state of matters which may easily occur in summer, the milk 

 may become seriously affected. The cream may become caseous or the 

 butter may become oily, a state of matters which may last for months, 

 since the sourer is always obtained from the butter-milk of the previous 

 churning. This may be avoided if, as is now generally done in all well- 

 conducted dairies, the sourer be prepared fresh every day. This may be 

 effected in the following way: 



A small quantity of milk or skim-milk is allowed to sour. This should 

 not be more in amount than 6 per cent of the total quantity to be sub- 

 sequently soured. After lactic fermentation has become well developed 

 in this portion, it is used as a sourer. For this purpose small metal bowls 

 are used, similar to the Swartz bowl. They are covered with felt, placed 

 in a wooden box in clean dry straw, and after they have been filled they 

 are covered with a close cloth. In the bowls the milk or skim -milk, 

 which, according to circumstances, has been heated to a temperature of 

 from 20 to 30 C., before being poured out, is allowed to stand for 24 

 hours in some place with a pure atmosphere. Sweet skim-milk, obtained 

 by the Swartz or separator method, is more suitable than milk, because 

 no cream is formed upon it, and there is no fear, therefore, that the 

 susceptible milk-fat on the surface of the liquid will become tainted 

 during souring, and impart a bad flavour to the liquid to be soured. 

 Since skim -milk sours more slowly than whole -milk, on the surface of 

 which a dense layer of cream quickly forms, the sourer is generally 

 produced from whole-milk. In this case no time should be lost in tasting 



