4 BULLETIN 6.56, 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 



