June is, 1914 
Ripening of Cheddar Cheese 
195 
volatile and probably can influence the aroma of cheese. The other 
nitrogenous end-products undoubtedly are factors in the flavor production, 
and influence taste. 
It is known that proteolysis gives rise also to volatile fatty acids, 
particularly butyric acid. In addition, milk fat, which is present to a 
large extent in the cheese, is a source of caproic and butyric acids through 
bacterial and enzymic action. The glycerin of the fat after hydrolysis by 
biological agencies is a source of acetic and propionic acids under the in¬ 
fluence of further fermentation (Suzuki, Hastings, and Hart, 1910). That 
decomposition of fat occurs during cheese ripening, giving rise to caproic 
and butyric acids, has been shown by a number of workers. Duclaux 
(1894, p. 286) found that this occurred to quite an extent, giving rise to 
free volatile fatty acids. Weigmann and Backe (1898) point to the pres¬ 
ence in ripe cheese of free nonvolatile acids, such as oleic, palmitic, and 
stearic, as an indication of fat decomposition in the cheese-ripening 
process. Kirsten (1898, p. 1), however, thought these higher acids 
could arise from paracasein and claimed that fat decomposition in 
ripening cheese is almost imperceptible. Jensen (1904, p. 319) has 
shown that very probably fat decomposition does take place with pro¬ 
duction of fatty acids during cheese ripening. The lactose fermentation 
produces, besides lactic acid, formic and propionic acids, and under 
certain conditions butyric and caproic acids also are formed (Suzuki, 
Hastings, and Hart, 1910). Calcium lactate, according to Fitz (1878, p. 51; 
1879, p. 479; 1880, p. 1309; 1881, p. 1084), is a source of acetic and 
propionic acids, and under certain conditions also of caproic and valeric 
acids. Jensen (Von Freudenreich and Jensen, 1906, p. 320) and Troili- 
Petersson (1909, p. 333) have shown that the lactates in Emmenthaler 
cheese are fermented by organisms with the production of propionic and 
acetic acids and C 0 3 . Troili-Petersson has also shown that glycerin may 
be a source of propionic acid. 
In an extended investigation (Evans, Hastings, and Hart, 1914) of the 
flora of American Cheddar cheese it has been shown that the organisms 
fall into four groups, the Bacterium lactis acidic the B . casei , and two 
coccus groups. 
The substances produced by the coccus groups form the principal 
theme of this paper. In addition, data are given on the substances formed 
from two representatives of the Bacterium casei group. In the following 
work pure cultures of several of the coccus forms known to occur in 
American Cheddar cheese were inoculated into flasks containing 300 c. c. 
of sterile separated milk and kept at a temperature of 35 0 C. for at least 
two months before being examined. No alkali whatever was added to 
the milk. The high-acid-producing organisms (£. casei group) were 
also inoculated into flasks of milk similarly prepared and incubated. 
Each culture was put up in duplicate flasks. The methods of analysis 
used were those described by Suzuki, Hastings, and Hart (1910). All 
