312 AGRICULTURE FOR COMMON SCHOOLS 



dosirable flavor and odor to the butter. These are known as 

 the lactic acid bacteria or ferments, for souring is a process of 

 fermentation. 



There are two methods of souring cream; namely, natural 

 and artificial. The natural method is the one commonly in use 

 on the farm. It consists in letting the cream stand in a large 

 jar or can at a suitable temperature, usually 60° to 70° F., un- 

 til sour. The cream has a good many kinds of bacteria in it 

 even when care has been taken to keep it clean. The lactic 

 acid ferments are always present, and under favorable condi- 

 tions they will develop and give to the cream that kind of 

 sourness or acidity which will make butter of good flavor. 

 But it often happens that conditions are not favorable for 

 them, and this is especially true jn the winter and early spring. 

 This largely accounts for the poor quality of country butter 

 at that time of the year. During the winter season milk and 

 cream are often kept in the kitchen or pantry. In winter 

 there is a lack of succulent feed and the period of lactation is 

 usually far advanced. Under such conditions it is not easy 

 to make butter of good quality. 



Cream may be ripened artificially in two ways: (1) By 

 adding to the raw cream a starter; (2) by adding a starter to 

 pasteurized cream. A starter is a specially prepared lot of 

 whole milk, skim-milk, or buttermilk that contains the desired 

 lactic-acid bacteria. A whole-milk starter is made by taking 

 a quart of milk just as it comes from the cow (care being taken 

 to have it absolutely clean), putting it in a quart fruit-jar, and 

 letting it stand on a ^elf at a temperature of 70° F. for twenty- 

 four hours. A skim-milk starter is made in the same way, 

 but fresh skim-milk from the separator is used instead of the 

 whole milk. A buttermilk starter is made by taking some of 



