70 Agricultural Bacteriology. 



The poor quality of dairy butter is generally due to the 

 fact that no control is maintained over the ripening of 

 the cream, too much acid usually being developed in the 

 cream. 



Deterioration of butter. Butter is in its best condi- 

 tion as soon as it is churned and prepared for the mar- 

 ket. Its best flavor is retained for several days; the 

 period being lengthened by storage at lower tempera- 

 tures. At summer temperatures, the flavor becomes im- 

 paired in the course of a week or so. The nature of these 

 changes is very obscure and they are designated usually 

 as " off "flavors. 



It has been noted that sweet-cream butter has very 

 poor keeping quality at ordinary temperatures when 

 compared with the sour-cream product. This undoubt- 

 edly is due to the fact that many kinds of bacteria are 

 present in sweet-cream butter. In sour-cream butter the 

 majority of the bacteria are acid-forming, most of which 

 have no injurious effect on the butter. The greater care 

 used in making the butter, the better its keeping quality. 

 If it is made from very clean milk, and the cream soured 

 by pure cultures, the keeping quality will be excellent. 

 It may be further enhanced by pasteurization of th& 

 cream. 



The causes of the deterioration of the butter are not 

 well known. It is certain from what has been said that 

 the bacteria must play an important role, for in no other 

 way can the influence of souring the cream and of pas- 

 teurization be explained. The same is also indicated by 

 the influence which the water used" to wash the butter 

 has on its keeping quality. If the water is pure, as from 

 a deep well, its influence will be small, but if surface 

 water from shallow wells is used, which contains many 



