234 TWENTY-FIFTH ANNIVERSARY REPORT. 
2. ALCOHOLIC FERMENTATION OF APPLE JUICE. 
Apple juice left exposed to the air is acted upon by yeast cells 
everywhere present, the sugar being changed into alcohol and car- 
bon dioxide gas. Theoretically, 100 parts of sugar should yield 
about 51 parts of alcohol, but in actual practice losses are experi- 
enced, reducing the actual yield to 45 to 47 parts of alcohol. The 
fresh apple juice in sound apples contains no alcohol. When 
apple juice has undergone partial or complete alcoholic fermenta- 
tion, it is commercially known as “cider.” Under the ordinary 
conditions of a cellar temperature, most of the sugar is changed 
into alcohol in five or six months. In studying the alcoholic fermen- 
tation at temperatures ranging from 45° F. to 85° F., it was 
found that the change takes place more rapidly at the higher tem- 
peratures. Adding yeast to apple juice tends to hasten the alco- 
holic fermentation. 
3. ACETIC FERMENTATION OF CIDER. 
Certain forms of bacteria act upon the alcohol of cider and con- 
vert it into acetic acid, the presence of which in sufficient quantity 
is the object of the maker of vinegar. The conditions most neces- 
sary for the acetic fermentation of cider are (a) acetic bacteria, 
(b) an abundant supply of air, and (c) a temperature between 
65° F. and 85° F. Theoretically, 100 parts of alcohol yield about 
130 parts of acetic acid, but the actual yield is usually below 120. 
At cellar temperatures, the acetic fermentation takes place slowly, 
requiring about eighteen months. Under the conditions of our work 
the formation of acetic acid took place most satisfactorily at tem- 
peratures between 65° F. and 75° F. The addition of vinegar con- 
taining “mother” to cider after the completion of the alcoholic 
fermentation increases the rapidity of the formation of acetic acid. 
When the clear portion of cider was separated from the sediment, 
the acetic fermentation appeared to be favored, especially at lower 
temperatures. It is possible that different barrels of apple juice, 
placed side by side, may show quite different behavior in fermen- 
tation. 
4. LOSS OF ACETIC ACID IN VINEGAR ON STANDING. 
Several different organisms have the power of decomposing 
dilute acetic acid and thus destroying the value of vinegar. These 
organisms work only in the presence of air. Accordingly, this 
destructive change in vinegar can be prevented by excluding air, 
