CAUSE OF RANCIDITY. 



215 



is an indication that the trouble is due to bacteria which 

 grow in the butter near the surface, where there is the 

 greatest contact with oxygen. The details of these experi- 

 ments we cannot consider here, but the evidence is quite con- 

 clusive that the rancidity is actually due to the development 

 of bacteria or other allied mi- FIG. 26. 



croorganisms, and Jensen has 

 even pointed out the probable 

 species which produce the ran- 

 cidity. The three most promi- 

 nently associated with the 

 phenomena are O'idium lactis 

 (Fig. 26) , Cladosporium butyri 

 and B. ftuorescens liquefaciens. 

 Jensen believes that these 

 come from external localities, 

 and he regards the air and the 

 water as the chief sources of 

 the organisms that produce 

 the rancidity of butter. His 

 experiments indicate that if 

 butter can be made without 

 contact with water or air and 

 without the presence of bac- 

 teria the phenomenon of ran- 

 cidity will not occur. 



The practical results of these facts are not very great at 

 the present time, for it is probably quite impossible to devise 

 any system of butter-making which shall protect the butter 

 from contamination with these rancidity-producing bacteria. 

 A few practical suggestions are possible. Butter in small 

 masses becomes rancid more readily than butter in large 

 masses, because a larger surface is exposed to the air, and if 

 preserved in large tubs the interior of the butter is, for a long 

 time, protected from the changes which affect its surface. 



a, O'idiutn lactis, a common milk organ 

 ism frequently causing the rancidity of but- 

 ter; l> and c, other bacteria associated with 

 rancidity. 



