422 STATE BOARD OF AGRICULTURE. 



is to trace them back to their origin and to determine the factors which 

 caused their production. These will probably be some micro-organisms. 

 To be certain that these organisms are the immediate cause, sterile cream 

 must be churned with, pure cultures of them and the resulting butter tested 

 for decomposition. The micro-organisms which cause the off flavor must be 

 found frequently in butter and increase in number at least for a short time. 

 Our investigations show that in our cold storage samples there was "but one 

 species of wild yeast very frequent and Micrococcus lactis varians often present 

 in butter besides the lactic acid bacteria. 



As soon as the problem of the cause of rancidity is solved the ciuestion 

 arises of how to keep these organisms from the butter, or, if this should 

 prove to be practically impossible, how to avoid their development in butter. 

 At first, the origin of the specific micro-organisms has to be discovered, 

 whether they come from the cows, the stable, the milker, or the creamery 

 and its utensils. We must then learn how to avoid these dangerous con- 

 taminations. 



On the other hand, we must try to make the conditions of development 

 in butter as unfavorable as possible. The only two means we have are salt 

 and the effect of temperature. The safest way is certainly the application 

 of high temperature, that is, sterilization; but the consistency of the butter 

 as well as the flavor suffer too much by this treatment. The low temper- 

 ature entirely checks the growth of many organisms, and other species, 

 develop only very slowly. In the same way salt decreases the rapidity of 

 multiplication very much and may kill many cells b}' continuous plasmolysis ; 

 whereas, others are able to multiply even in concentrated brine. It is, 

 however, questionable whether or not the combined action of both would 

 be advisable, since the salt in a certain way prevents the action of the cold. 

 The water in butter without salt will probably solidify a few degrees below 

 the freezing point, but the addition of salt lowers the freezing point con- 

 sidei'ably. In some of our butter samples we have saturated salt solution 

 with a freezing point of about — 22°C. (— 7°F.). 



