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 cascin ferments. 
Butyric acid in overripened crcam 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: 
Carbonic- 
acid gas, 
2C3H.60s —s C3H7CO2H + 2CO2 + Ha. 
Lactic acid. Butyric acid. Hydrogen. 
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, 
C3H7CO2 OH 
C3Hs ; CsH7COg + 3H20 = CsH; ;}OH + 38C3;H;CO.H 
| CsH7CO2 | OH 
