40 DAIRYING 



Ice broken in small pieces and added to cream in a vat or to the 

 churn is less objectionable and this is sometimes done with good 

 results in an emergency. If continued as a constant practice, how- 

 ever, there is danger of injuring the churn, as broken lumps of ice 

 will deface the wood somewhat by scratching it during the churn- 

 ing. 



CREAM RIPENING 



464. The principal reasons for ripening cream before it is 

 churned are: (1) To give flavor to the butter; (2) to aid in 

 churning within a reasonable time and (3), to improve the keeping 

 quality of the butter. 



465. When cream sours a certain part of the milk sugar 

 (lactose) is changed to lactic acid. This and other changes that 

 take place are caused by the growth of bacteria, which are sup- 

 posed to be responsible for much of the flavor in butter. A great 

 deal has been learned about these microscopic plants, but there 

 still remains so much to be found out concerning the part they 

 play in the development of butter flavor that their relation to it 

 will not be extensively discussed at this time. 



466. In a general way it may be said that the milk and cream 

 bacteria may be divided into two classes: (1) Lactic acid bacteria 

 which sour milk and cream by the production of lactic acid, and 

 (2), putrefactive bacteria which change the nitrogenous consti- 

 tuents, such as the casein and curd of milk and cream, into products 

 having an offensive odor and a disagreeable taste. 



467. Both classes are usually present in large numbers in the 

 milk which comes from many herds. The putrefactive bacteria, 

 however, are usually more numerous in the winter season than 

 in the summer, because of the stable milking and the house care 

 of the milk and cream. 



468. The lactic acid bacteria are the ones which the butter- 

 maker should try to cultivate in the cream ripening, and the 

 putrefactive bacteria are not so easily destroyed as many of the 

 other germs in milk and cream. They will survive a temperature 



