CREAM-RIPENING. 215 



Or do certain species of bacteria cease to act, and are other 

 species, which produce less lactic acid and more gaseous prod- 

 ucts, able to perpetuate their growth and bring about the 

 results observed? The results are probably due to a com- 

 bination of the different actions just mentioned, but the most 

 likely theory is that conditions for the growth of other species 

 of bacteria become more favorable, and other by-products 

 than lactic acid are formed, products that cause the undesirable 

 rancid flavors in over-ripened cream. 



Butyric acid also results from the decomposition of cream 

 constituents during ripening. The origin of the butyric acid 

 formed during ripening is, however, not well known. Freuden- 

 reich says it is the residue resulting from the breaking down of 

 casein and milk-sugar in various ways, and therefore he classes 

 the butyric ferments in the same group as the casein ferments. 



Butyric acid in overripened cream is by some authorities 

 considered to be a direct product from an excessive amount of 

 lactic acid. Each molecule of lactic acid breaks up into butyric 

 acid, carbonic-acid gas, and hydrogen, according to the follow- 

 ing equation: 



Lactic acid. Butyric acid. [. "f" Hydrogen. 



2C3H6O3 = C3H7CO2H + 2CO2 + H4. 



It is questionable whether this reaction ever occurs in the 

 ripening of cream. 



Butyric acid also results from the decomposition of butyrin, 

 through the action of bacteria, and causes the molecules of fat 

 to split up into butyric acid and glycerine, according to the 

 following equation : 



Butyrin (fat). Water. Glycerine. Butyric acid. 



CaHs 



C3H7CO2 



C3H7CO2 + 3H2O = C3H5 



C3H7CO2 



OH 



OH + 3C3H7CO2H 



OH 



