

BACTERIA AND BUTTER-MAKING 215 



true of sour milk, which is also frequently recommended for 

 this purpose. 



BACTERIA IN BUTTER 



The relation of bacteria to butter after it is made is of less 

 practical importance than their relation to the other milk 

 products. Butter when first made contains large numbers of 

 bacteria, for a considerable proportion of those in the ripened 

 cream will get tangled with the fat. In butter, however, the 

 bacteria do not find a medium very favorable to growth, and 

 instead of increasing in this medium they soon begin to decrease 

 in numbers. Their development in the first few hours is not 

 always the same. Sometimes they will increase for a few hours 

 after the butter is made; and sometimes they will begin to de- 

 crease in numbers at the very start. The difference is apparently 

 due in part, if not wholly, to the amount of washing given the but- 

 ter. If the butter is washed until all of the albuminous material 

 is washed out, less food is furnished to the bacteria, the environ- 

 ment is unfavorable to them, and they begin to decline in num- 

 bers at once. If less thoroughly washed, the conditions are 

 more favorable, and they may increase for a day or two. But 

 in either case they soon begin to decline in numbers. In a single 

 experiment, for example, the following numbers were found: 



Butter, 2 hours old . . 50,000,000 bacteria. 



Butter, i day old ... 26,000,000 bacteria. 



Butter, 2 days old . . 2,000,000 bacteria. 



Butter, 30 days old . . 300,000 bacteria. 



In this reduction of bacteria the lactic germs are the first to 

 disappear; and the spore-bearing bacteria are those likely to 

 remain in the end. In old butter the number of bacteria is al- 

 ways small, but they never disappear, and spore-bearing organ- 

 isms are sure to be found. The common dairy organism, Oidium 

 lactis, is almost certain to be present in considerable numbers 



