12 
BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 
RESULT OF MIXING SOUR AND NORMAL MILK. 
Since a positive alcohol test may -be produced by increasing the 
acidity, several investigators have pointed out that a mixture of sour 
and normal milks will give a positive test. The amount of sour milk 
which can be added to fresh milk without causing a positive alcohol 
test will, of course, depend upon the acidity of the sour milk. In 
one experiment, the results of which are shown in Table 7, various 
percentages of sour, raw, and pasteurized milk were added to fresh 
milk. The addition of 1 per cent of sour milk caused a positive test 
with 75 per cent alcohol, 2.5 per cent caused a positive test with 68 
per cent alcohol, and the addition of 10 per cent of sour milk was 
necessary to cause a positive test with 44 per cent alcohol. 
It must be taken into consideration in this experiment that the 
sour milk had a high acidity. If the acidity had been low a much 
higher per cent could undoubtedly have been added to the fresh 
milk without increasing the acidity sufficiently to cause a positive 
alcohol test. 
Table 7. — The alcohol test with a mixture of normal and sour milk. 
Addition of sour raw milk. Acidity 10.23. 
Addition of sour pasteurized milk. 
Acidity 9.87. 
Per 
cent of 
sour 
milk 
added. 
Acid- 
ity. 
A lcohol test. 
Per 
cent of 
sour 
milk 
added. 
Acid- 
ity. 
Alcohol test. 
75 per 
cent. 
68 per 
cent. 
44 per 
cent. 
75 per 
cent. 
68 per 
cent. 
44 per 
cent. 
0.0 
1.0 
2.5 
5.0 
10.0 
1.84 
1.93 
2.06 
2.30 
2.70 
+M 
+ L 
+ L 
+M 
+L 
+ L 
+M 
+S 
+ M 
+ L 
+ L 
+M 
+ L 
+ L 
+VS 
1.0 
2.5 
5.0 
10.0 
1.88 
2.00 
2.29 
2.68 
1 See footnote under Table 1. 
In connection with the relation of acidity to the alcohol test the 
question arises as to whether or not the acidity of a sour milk can be 
neutralized so that the alcohol test will be negative. Some investi- 
gators have shown that the neutralization of the acidity does not 
cause a positive test to become negative, although the size of the 
flakes in the coagulation is somewhat reduced. We have tried one 
experiment in which various amounts of normal lactic acid were 
added to fresh milk, after which the acidity was reduced to the original 
acidity by the addition of sodium hydrate. From the results which 
are shown in Table 8 it will be seen that when the acidity was in- 
creased to 4.3, then neutralized to 1.90, the 68 per cent alcohol test 
was positive. The positive alcohol tests with 68 per cent alcohol 
could be made negative at acidities below 4.30 by reducing to about 
the original acidity of the normal milk. 
