Bacteria in Cheese. 183 



after it is made. It must be borne in mind, in considering 

 the more important of these changes, that not all defective 

 conditions in cheese are attributable to the influence of 

 living organisms. Troubles frequently arise from errors in 

 manufacturing details, as too prolonged cooking of curds, 

 too high heating, or the development of insufficient or too 

 much acid. Then again, the production of undesirable 

 flavors or impairment in texture may arise from imperfect 

 curing conditions. 



Our knowledge regarding the exact nature of these indefi- 

 nite faults is as yet too inadequate to enable many of these 

 undesirable conditions to be traced to their proper source; 

 but in many cases the taints observed in a factory are due 

 to the abnormal development of certain bacteria, capable 

 of evolving unpleasant or even putrid odors. Most of them 

 are seeded in the milk before it comes to the factory and 

 are due to careless manipulation of the milk while it is still 

 on the farm. Others gain access to the milk in the fac- 

 tory, owing to unclean conditions of one sort or another. 

 Sometimes the cheese-maker is able to overcome these 

 taints by vigorous treatment, but often they pass on into 

 the cheese, only to detract from the market value of the 

 product. Most frequently these "off" flavors appear in 

 cheese that are cured at too high temperatures, say above 

 65 F. 



"Gassy" fermentations in cheese. One of the worst and 

 at the same time most common troubles in cheese-making 

 is where the cheese undergoes a fermentation marked by 

 the evolution of gas. The presence of gas is recognized by 

 the appearance either of spherical or lens-shaped holes of 

 various sizes in the green cheese; often they appear in 

 the curd before it is put to press. Usually in this condi- 



