148 REPORT OF THE CHEMIST OF THE 
rapid formation of alcohol. The time of the alcohol fermenta- 
tion can readily be reduced one-half or more by the addition of 
yeast, especially when the cider is kept at a temperature of 65° 
to 70° F. The use of any form of commercial yeast, if sufficiently 
fresh, will probably be found to give good results. 
THE ACETIC FERMENTATION OF CIDER. 
The object of the maker of cider vinegar is the production of 
acetic acid, and this is accomplished by means of the fermenta- 
tion of alcohol that has been formed from sugar. The organisms 
that change alcohol into acetic acid are different from those that 
change sugar into alcohol. There are several varieties of acetic 
bacteria capable of causing the acetic fermentation of alcohol. 
For the effective conversion of cider into vinegar, there are 
needed, (1) the acetic bacteria, (2) an abundant supply of air, 
(3) a temperature between 65° and 85° F. There is commonly 
noticed in vinegar a very elastic, slimy, tough, transparent skin 
of a yellowish-white color; this skin is commonly known as 
“mother” of vinegar. This appears to be formed by the growth 
of the acetic bacteria on the surface of the liquid. When one 
skin has formed, it settles sooner or later and in its place another 
is formed and this formation and replacement continue as long 
as air is supplied under favorable temperature conditions. 
The chief chemical change that takes place in the acetic fer- 
mentation of alcohol is the combination of oxygen with alcohol, 
which may be represented thus, though the real change is more 
complicated :— 
Aleohol Oxygen Acetic acid Water 
C. H.O + 0. =C, H, O; + HzO 
Theoretically, we should obtain from 100 parts of alcohol 
about 130 parts of acetic acid, but for various reasons the actual 
yield is probably nearer 120 or lower. 
MANAGEMENT OF ACETIC FERMENTATION. 
In our work, we allowed the cider to remain in the casks and 
bottles in which the alcoholic fermentation had taken place. We 
will first give the general averages of the results obtained with 
the first 10 ciders given in Table I. We shall consider the 
