1918] Bioletti-Cruess-Daiy : Chemical Composition of Grapes 129 



Summary of Changes in Must of Grapes During Growth and 



Ripening of Berries 



1. Total Solids. — The total solids remain fairly constant during 

 the period of growth, corresponding to the period between setting of 

 the berries and the time at which the berries have reached almost 

 full size but are still hard and green. From this point on, there is a 

 rapid increase in total solids due to increase in sugar. 



After the period usually considered as full maturity is reached, 

 the increase in total solids is slow. The question may "be raised as to 

 whether this last increase is due to an actual synthesis and secretion 

 of sugar or other solids, or simply to evaporation of water. The fact 

 that there is no change in the curve of the acid decrease at this time 

 indicates that the same processes are continuing and that the increased 

 Balling degree represents an actual increase of solids. This view is 

 fortified by observations regarding the increase of weight of solids 

 during the ripening of raisin grapes. It has been shown that the 

 weight of dried grapes shows a continuous increase up to the highest 

 degree observed, 28.75 Balling. 7 



2. Sugar. — The total sugar during the growth period comprises 

 only a small amount of the total solids. During ripening, the sugar 

 rapidly increases and then constitutes a much greater proportion. 

 During ripening, the sugar curve follows the total solids curve closely. 

 It is more or less the mirror image of the total acid curve multiplied 

 by five, i.e., increases as the acid decreases. 



3. Total Acid and Free Acid. — During the early stages of the 

 growth of the berries, the acidity increases owing to an increase of 

 free acid. This is a fact that the authors have not found mentioned 

 in the literature. During ripening, the total and free acid rapidly 

 decrease. After maturity is reached, the decrease is very slow. 



4. Cream of Tartar. — There is a very slow, but usually fairly defi- 

 nite, increase in cream of tartar during ripening. This increase is 

 very much less than the decrease in free acid, and therefore can not 

 account for any great part of this decrease. 



~ Bioletti, Frederic T., Relation of the maturity of the grapes to the quantity and 

 quality of the raisins. Proe. Inter. Cong, of Viticulture, San Francisco, M»15, 

 pp. 307-314. 



