122 THE CHEMISTRY OF THE FARM. 



time occupied in churning, and the amount and character 

 of the produce ; when this is done the temperature for 

 each day can be regulated from the experience of the 

 preceding working. The temperature will rise several 

 degrees during churning. 



Churning must always be stopped as soon as the butter 

 comes, any over churning spoils the texture of the butter. 

 The butter is then separated from the buttermilk, washed 

 with cold water, and after standing to solidify is carefully 

 worked and pressed to expel all watery' matter ; over- 

 working in this stage will also spoil the grain, and make 

 the butter greasy. Butter made from perfectly sweet 

 cream keeps far better than butter made from sour cream, 

 as the latter always contains curd, a substance very prone 

 to change. Salt is generally added to improve the 

 keeping quality of butter. 



First-class butter will contain about 10 per cent, of water, 

 and not more than 0*5 per cent, of casein, but in ordinary 

 butter these proportions are greatly exceeded. Of the 

 fatty acids in butter about 6 per cent, are soluble in 

 water when separated from the glycerol with which they 

 are combined ; this fact serves to distinguish butter from 

 other animal fats in which soluble fatty acids are absent. 

 When butter becomes rancid the glycerides of the fatty 

 acids are partly decomposed, and the fatty acids liberated; 

 the odour and flavour of rancid butter are largely due to 

 free butyric acid. 



Buttermilk. — The liquid remaining in the churn after 

 the separation of the butter from the cream has been but 

 little investigated ; it must vary a good deal in composi- 

 tion. Danish experimenters found that when churning the 



