THE ALCOHOL TEST IN RELATION TO MILK. 

the acidity had increased from 1.98 to 2.14, and the bacteria from 
from 82,000 to 15,100,000 per cubic centimeter. It is interesting to 
note that an extensive multiplication of lactic-acid-forming bacteria 
may occur without causing a positive alcohol test. In the second 
experiment, also shown in Table 4, a heavier inoculation was used, and 
it will be seen that the milk at the beginning of the incubation period 
contained 480,000 bacteria per cubic centimeter. The 68 per cent 
alcohol test was not positive until the bacteria had increased to 
31,400,000 per cubic centimeter. 
These figures show that when a pure culture of lactic-acid-forming 
bacteria is grown in skim milk there must be a very great increase in 
order to produce acidity enough to cause a positive alcohol test. In 
these experiments there were no positive alcohol tests until the bac- 
teria had increased from less than 500,000 to over 16,000,000 per cubic 
centimeter. From these results it is apparent that the growth of 
acid-forming bacteria in milk may, through the formation of acid, 
cause a positive alcohol test. However, when there is sufficient acid 
produced to cause a coagulation with 68 per cent alcohol the number 
of acid-forming bacteria would be very high. 
Table 4. — Influence on the alcohol test of acid -produced by the growth of a pure culture of 
lactic-acid bacteria. 
Experi- 
ment No. 
Age of 
culture 
in hours. 
Bacteria 
per cubic 
centimeter. 
Acidity. 
Alcohol test. 
75 per cent. 
68 per cent. 
44 per cent. 
I 
II 

2 
4 
5 
6 
7 

2 
4 
5 
6 
7 
82,000 
113,000 
1,510,000 
4,300,000 
11,700,000 
15,100,000 
480,000 
1,060,000 
7,500,000 
16, 100, 000 
31,400,000 
46,000,000 
1.98 
X + S 
+ L 
+L 
+M 
+ L 
- 
2.06 
2.08 
2.09 
2.14 
1.94 
2.08 
2.08 
2.30 
2.47 
See footnote under Table 1. 
EFFECT OF PHOSPHATES. 
We have so far discussed in a general way the effect of increasing 
the acidity of milk by the addition of lactic acid and by the generation 
of the acid in milk. Since the acidity of milk when titrated with 
phenolphthalein is due partly to acid phosphates, it will be of interest 
to show the effect on the alcohol test of the increase in acidity by 
acid phosphates. In Table 5 are shown the results of a few tests, 
using sodium and potassium acid phosphate. Various amounts of 
a 5 per cent solution of these salts were added to 50 c. c. of milk. It 
will be seen from the table that when the acidity was increased by 
sodium acid phosphate from 2.15 to 3.33 the alcohol test with 75 
82832°— Bull. 202—15- 
