236 THE CHEMISTRY OF THE FARM 



churning may be ascertained by recording every day 

 the temperature employed, with the length of time 

 occupied in churning, and the amount and character 

 of the product ; when this is done the temperature 

 for each day can be regulated by the experience gained 

 in the last working. In the recently introduced high- 

 speed churns, the work is done by centrifugal action, 

 and is accomplished in a very short time, and with 

 little regard for temperature. 



The temperature will rise several degrees during 

 churning, work being converted into heat. The rise 

 in temperature causes an expansion of the air in the 

 churn, and it is popularly supposed that gas is given 

 off by the cream. The agitation with air displaces 

 a little carbonic acid held by the cream, but no new 

 gas is produced. 



Churning must always be stopped as soon as the 

 butter appears in fine grains ; 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. Batter made from perfectly 

 sweet cream keeps better than butter made from 

 sour cream; the latter always contains somewhat 

 more albuminoids, and the process of change which 

 leads to rancidity has already commenced. Salt is 

 generally added to improve the keeping quality of 

 butter. 



Good churning should result in 96 per cent, of the 

 cream fat being obtained as butter fat. The loss of 

 fat in the buttermilk is least when the cream contains 



