14 
BULLETIN 202, U. S. DEPARTMENT OF AGRICULTURE. 
INFLUENCE OF THE ACTION OF RENNET. 
The relation of the alcohol test to the acidity of milk shows that 
acidity is one factor which may cause a positive alcohol reaction, 
but from the work of other investigators it is evident that it is not 
the sole cause. Morres throughout his papers points out that the 
alcohol test may be caused by an acid fermentation or by a rennet 
fermentation or by a mixture of both fermentations. 
In order to determine the effect of rennet action in relation to the 
test, we first tried the effect of prepared rennet. Four flasks of fresh 
milk were used and to each a different percentage of rennet was 
added. The milk in each flask was tested by the alcohol test at 
intervals of one hour. It will be seen from Table 10 that four 
different percentages of rennet were used, ranging from 0.00005 per 
cent to 0.0015 per cent. The acidity of the milk increased during 
the four hours from 1.64 to 1.70; therefore the influence of acidity 
can be neglected, since it is only a slight change. 
The results show that the action of rennet in milk may produce 
changes which cause a positive alcohol test and that two main factors 
are of importance, namely, the amount of rennet and the length of 
time the rennet has to act. Undoubtedly a third factor must be 
taken into consideration; that is, the temperature at which the milk 
is held. In our experiments the milk was held at room temperature. 
These results confirm those obtained by other investigators and 
indicate that the action of the rennet-forming bacteria might cause 
a positive alcohol reaction. 
Table 10. — Influence of rennet on the alcohol test. 
Alcohol test. 
Hours. 
Rennet 
added. 
75 per 
68 per 
44 per 
cent. 
cent. 
cent. 
Per cent. 

.00005 
— 
— 
— 
.00025 
— 
— 
— 
.0005 
— 
— 
— 
.0015 
— 
— 
— 
1 
.00005 
— 
— 
— 
. 00025 
— 
— 
— 
.0005 
— 
— 
— 
.0015 
i +M 
+ M 
— 
2 
.00005 
— 
— 
— 
.00025 
_ 
— 
— 
.0005 
+ M 
+ M 
— 
.0015 
+ L 
+ L 
+ M 
3 
.00005 
— 
— 
— 
. 00025 
+M 
+ M 
— 
.0005 
+M 
+M 
— 
.0015 
+L 
+ L 
+M 
4 
.00005 
— 
— 
— 
. 00025 
+L 
+L 
L 
.0005 
+ L 
+ L 
+VS 
.0015 
( 2 ) 
( 2 ) 
( 2 ) 
i See footnote under Table 1. 
2 Milk curdled by rennet. 
