BUTTER 347 



precipitated, calcium citrate is deposited, and other changes 

 also take place which affect the quality of the milk. 



It is unfortunately easier to stop the action of bacteria 

 by the addition of chemical preservatives, and the ones which 

 are most effective in killing bacteria are also the ones which 

 harm the consumer. Formaldehyde, boric acid, salicylic 

 acid, and benzoic acid, are compounds which have been 

 used, but the law in most states prevents their use at all, 

 so that at the present time the consumer is safe from such a 

 dangerous practice. 



247. Cream. — Cream consists merely of the greater part 

 of the milk fat separated from the remainder of the milk, 

 and is obtained by allowing the milk to stand quietly when 

 the fat globules, being lighter than the rest of the milk, rise 

 to the surface and can be skimmed off. Another way to 

 obtain cream is by use of the separator, which is a machine 

 where the fresh drawn milk can be subjected to centrifugal 

 force, the heavier part being thrown to the outside and the 

 lighter part rising in the centre. By appropriate devices 

 the two parts of the milk can be drawn off in separate streams 

 and by regulating the cream discharge pipe, cream of different 

 fat content can be obtained. The fat can be withdrawn 

 more completely from milk in this way than it can by the 

 old-fashioned skimming process, the former removing from 

 97 to 98 per cent, of the butter fat under the best conditions, 

 and the latter not more than 90 to 95 per cent. 



248. Butter. — Both butter and cream consist of milk fat, 

 but cream is mixed with more or less of the other con- 

 stituents of milk, whereas butter consists practically of milk 

 fat only. It is made by agitating cream in a churn whereby 

 the globules of milk fat coalesce into a mass. This is removed 

 and worked over to remove the last trace of buttermilk, which 

 consists of milk minus butter. Buttermilk usually contains 

 about 4 per cent, of lactic acid, giving it a sour taste. This 

 is because the best quality of butter is obtained from cream 

 which has been properly "ripened," or, to put it plainly, 

 which is somewhat sour. The souring, however, is not 

 permitted to take place spontaneously, because of the 

 danger of introducing harmful bacteria, but is accomplished 



