June is, 191 * 
Ripening of Cheddar Cheese 
213 
Bacterium lactis acidi produced levo zinc lactate, as has already been 
shown, and B . casei 1 gave dextro zinc lactate. The mixture of the two 
gave racemic acid, as shown in section XI. It may be that in curing 
cheese after pressing, factors similar to those used in these experiments 
are operative in the production of the racemic variety of lactic acid. 
The data in section III, which were obtained from the mixed culture 
of Bacterium lactis acidi and B. casei containing calcium carbonate, show 
racemic zinc salt and also active acid, the latter being produced, no doubt, 
by B. casei 1, the activity of which continues after that of Bacterium 
lactis acidi . 
Another experiment, with Bacterium casei cultures 1, 2, and 3, the 
last-named being a pure culture supposedly of a different type from 1 
and 2, was carried out as in the previous experiments. The results are 
given in Table XXIII. 
Table XXIII .—Analysis of medium consisting of 200 c. c. of sterile milk and 6 grams of 
calcium carbonate , showing the production of lactic acid from Bacterium casei j, 2 , 
and 3 
Cultures. , Cultures i and 2. Cultures. 
Fraction No. 
Zinc lactate. 
Water of 
crystalliza¬ 
tion. 
i Zinc lactate. 
Water of 
| crystalliza¬ 
tion. 
Zinc lactate. 
Water of 
crystalliza¬ 
tion. 
I . 
Grams. 
3*40 
•32 
.28 
. OO 
Per cent. 
12. 91 
i 3 * 03 
13.00 
Grams. 
13. 42 
• 71 
. 64 
. OO 
Per cent. 
18. OO 
16. 14 
14.09 
Grams. 
2 . 12 
4. 19 
. OO 
Per cent. 
12. 94 
15. 12 
2. 
7 . 
4 . 
Levo-salt. 
i Dextro- S 
salt. 
Dextro- 
salt. 
The data show that the mixture of Bacterium casei i and 2, which in 
pure cultures produce the two different active lactic acids, gives racemic 
acid with a slight excess of levo-acid produced by culture 1. This phe¬ 
nomenon might also take place in cheese ripening, producing racemic acid. 
Bacterium casei 3 produces dextro zinc lactate just as culture 1 does, and 
it also produces the same kinds of volatile fatty acids. Therefore, cul¬ 
ture 3 may have been identical with culture 1. 
From the foregoing experiments it may at least be concluded tenta¬ 
tively that the formation of racemic lactic acid in Cheddar cheese soon 
after going to press is due to the later development of organisms of the 
Bacterium casei group principally, together with the possibility that cer¬ 
tain forms of the coccus groups can likewise produce racemic lactic acid. 
SUMMARY 
(1) Representatives of the coccus groups of organisms isolated from 
Cheddar cheese when grown in milk produced large quantities of the 
volatile acids, particularly acetic acid. These acids were produced from 
