4 BULLETIN 656, U. S. DEPARTMENT OF AGRICULTURE. 
is self-evident, since yeasts can not penetrate the sound normal 
skin of the grape. Only in cases where the juice has been exposed 
through injury to the berry, as in the case of crushed or detached 
berries, is it possible for alcohol to form. Under such conditions the 
alcohol content may be as high as 0.3 gram per 100 cubic centimeters 
of juice. To prove this point the alcohol content of two samples of 
the poorest grapes obtainable was determined. The berries were 
badly crushed and covered with mold. These juices showed 0.22 and 
0.27 gram of alcohol per 100 cubic centimeters. 
To ascertain the effect of standing on the development of alcohol 
in grapes, a box of fruit was allowed to stand at room temperature, 
and the fruit analyzed for alcohol from time to time. The fruit was 
of good quality, only slightly damaged. 
Table 2. — Alcohol content of Concord grapes. 
Grams per 100 cc. 
Fresh grapes - 0. 02 
After standing: 
48 hours 08 
72 hours 09 
96 hours 10 
After standing 96 hours the grapes had a dead, dull appearance, 
and had begun to shrivel. 
These experiments are of more than average interest because 
they show that with careful handling grapes do not develop alcohol 
to any extent, and that only in cases of great damage is the alcohol 
content as high as 0.30 gram per 100 cubic centimeters. This fact 
is of importance to the juice manufacturer because grapes must often 
stand several days before they can be pressed. 
It is evident, therefore, that damage from alcoholic fermentation is 
highly improbable with grapes of good quality, and that even the! 
poorest fruit seldom contains more than appreciable amounts of 
alcohol. Far more serious is the presence of mold in grapes, because 
the juice made from fruit so infested may acquire an unpleasant, 
musty odor. In order to avoid such a condition, the producer is 
warned against filling the crates too full, and, wherever it is necessary 
to hold the grapes any length of time, to store them in such a manner 
that air can circulate freely throughout the stacks. 
MANUFACTURE OF COMMERCIAL CONCORD GRAPE JUICE. 
The grapes should be well matured and of the best quality obtain- 
able. Immature fruit or green grapes yield juices of inferior quality 
because of high acidity, lack of sufficient sugar and color, and the 
presence of large amounts of green coloring matter. The well- 
matured grapes are gathered in wooden crates of about 25 pounds 
capacity, and are either crushed immediately or air-ripened. Some 
