70 Kansas Academy of Science. 



3. The action of microorganisms after production. 



All of these sources are more or less important, but the 

 most important flavors and odors originating in cream result 

 from microbial activity. 



The different groups of organisms common to milk can be 

 classed into desirable and undesirable types, depending almost 

 entirely upon their fermentation processes as related to their 

 usefulness in dairy products. Those organisms producing 

 agreeable flavors and odors must necessarily be considered 

 desirable types, w^hile those that produce disagreeable flavors, 

 odors or changes are undesirable. The type of fermentation 

 needed for the manufacture of each dairy product will govern 

 the desirability of microorganisms, and on account of the large 

 number of dairy products, the usefulness of these respective 

 types v^ill vary. 



The microbial flora of cream consist of practically the same 

 organisms as found in milk, and may be classified into the fol- 

 lowing groups, based upon their types of fermentation : 



1. The acid group, represented by the common milk-souring bac- 



teria, Bad. lactis acidi. 



2. The gas-producing group, consisting primarily of the colon- 



serogenes group, and yeasts. 



3. Gelatin liquefying group, which is not represented by any spe- 



cific organism, but usually consisting of a miscellaneous 

 group of spore- and nonspore-producing organisms. 



4. Neutral group, consisting of those organisms exerting no 



marked effect in milk. 



Of these four groups only the acid group is desirable from a 

 butter-making standpoint, all others being undesirable. If the 

 flavors and odors common to cream result from the action of 

 microorganisms, it seems logical to assume that a larger per- 

 centage of the desirable organisms would exist in first-grade 

 cream than in second-grade. On the other hand, a higher per- 

 centage of undesirable organisms would probably be found in 

 second-grade cream. 



In the following classification of the types of microorganisms 

 found in the different cream samples the lactic-acid group will 

 always be considered the desirable type, while the yeasts, colon 

 group, gelatin liquefiers and the neutral type will be referred 

 to as the undesirable type. 



