Relation of Bacteria to Butter. 71 



bacteria coming from the soil, the keeping quality will be 

 greatly injured. This has led to the heating of the wash 

 water in creameries when the supply is not above ques- 

 tion. 



The changes which butter undergoes are usually ex- 

 pressed by the word "rancid." At least two different 

 changes can be distinguished. The butter may develop 

 a flavor or odor resembling that of tallow. This is due,, 

 at least in part, to the action of light and air on the fat. 

 Butter in tubs keeps better than in small packages. The 

 true rancidity, a change in which the butter acquires the 

 odor and taste of spoiled cocoanut milk is due largely to 

 bacteria. 



The number of bacteria in fresh butter is very large 

 but diminishes rapidly after churning on account of the 

 lack of food and the injurious action of the salt, which is 

 usually present in such quantities as to form a saturated 

 brine with the water in the butter. The lactic acid bac- 

 teria decrease with especial rapidity while undoubtedly 

 some other forms of bacteria and molds are able to grow 

 in spite of the salt. 



The role of the bacteria in the spoiling of butter is 

 further emphasized by the effect of cold storage on the 

 butter. In order to preserve* it, modern butter storage- 

 rooms are kept below zero Fahrenheit. After months of 

 storage, the butter is unchanged. It does, however, spoil 

 very quickly on being removed from the cold room ; much 

 more quickly than before storage. Preservatives are 

 widely used in butter, not in our own country, but in 

 Australia and NewZealand in the butter to be shipped 

 to England. 



Undesirable flavors in butter. As has been previ- 

 ously mentioned, the kind of feed may influence the 



