16 BULLETIN 335, U. S- DEPARTMENT OP AGRICULTURE. 



Particular attention is called to the data on sugar and acids. 

 The Catawba crop studied in 1911 was harvested October 1 to 4, 

 and though certain plants were held and sampling was continued 

 25 days longer, the results show only a gain of 1.22 grams of sugar 

 and the loss of 0.24 gram of acid in 100 cc of juice. The apparent 

 increase of sugar was doubtless due to evaporation of water from 

 the berries and the loss of acid is possibly accounted for in the loss 

 of malic acid. This would probably have disappeared in wine 

 fermentation, 1 giving practically the same or a lower result than that 

 recorded for the last sample. It is certain that nothing would have 

 been gained for commercial purposes by holding this particular 

 crop on the vine after the date it was harvested. 



It is not to be understood that the dates of full-crop ripeness 

 given in the tables apply to all the vineyards of the Sandusky dis- 

 trict. On the contrary, these dates apply only to the crops sampled. 

 The season for Catawba in the Sandusky district lasts fully 3 weeks 

 and the ripening of other varieties extends over a considerable 

 period, varying with location. 



Clinton was sampled for 21 days after the crop was picked, but 

 shows only an increase of 1.43 grams of sugar and a loss of 0.18 

 gram of acid. This variety lost most of its foliage before the fruit 

 was picked on October 7 and 8 and the later samples were picked 

 from vines practically bare of leaves. This undoubtedly had an 

 influence on the high acid shown. In fact, this crop of Clinton 

 shows the maximum acid at ripening of all the crops of this variety 

 examined at Sandusky during the season of 1911. The fact that 

 this variety showed such high content of both malic acid and cream 

 of tartar at ripening should be noted in this connection, because the 

 presence of those elements greatly assists in the reduction of the 

 acid of the finished products from this variety. This occurs by 

 precipitation of the crude tartar both in grape juices and wines and 

 by destruction of malic acid with the formation of lactic acid through 

 bacterial fermentation 2 in case of wines. 



The Delaware samples at Sandusky show the most notable increase 

 of sugar after the date the crop was marked wine-ripe. However 

 important it might appear to be to secure this increase of nearly 

 3 grams of sugar in 100 cc of juice, it is not practicable to hold this 

 crop so late because of the injury to the fruit from birds, insects, 

 and various other causes. The acid reduction was inappreciable, 

 but as a matter of fact this variety has scarcely enough acid when 

 it is fully ripe for the best results in dry-wine making. Note the 

 unusually wide total acid-sugar ratio in Table 2. 



Ives, though held on the vine 14 days after marked fully ripe, 

 showed very slight changes in sugar and acid. 



1 Kulisch, Weinverbesserung, 3d ed., 1909, p. 19. 2 Ibid. 



