Sugars grape maturation

Houtman, A. C., Morais, J., Du Plessis, C. S. (1980) Factors affecting the reproducibflity of fermentation of grape juice and of the aroma composition of wines. I Grape maturity, sugar, inoculation concentration, aeration, juice turbidity and ergosterol. Vitis, 19, 37-54. 

As part of their metabolism, all yeasts are known to produce a wide range of esters such as ethyl acetate, isoamyl acetate, isobutyl acetate, ethyl butyrate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, and 2-phenylethyl acetate (Nykanen and Nykanen, 1977 Soles et al., 1982 Edwards et al., 1990 Webster et al., 1993 Rojas et al., 2001 2003 Plata et al., 2003 Lee et al., 2004). Esters are synthesized through reaction of alcohols (commonly, ethanol) and carboxylic acids by different acyltransferases or ester synthases (Mason and Dufour, 2000). Factors that affect ester synthesis include grape maturity, sugar content, fermentation temperature, and juice clarity (Houtman et al., 1980a 1980b Edwards etal., 1990). 

In general, grape maturation results from several biochemical transformations that are not necessarily related to each other. To simplify matters, the increase in sugar concentration and the decrease in acidity are monitored. The accumulation and refinement of white grape aromas and phenolic compounds in red grapes should also be taken into account. The essential property of a quality wine-producing area is to permit a favorable maturation. This corresponds with a harmonious evolution of the various transformations to reach the optimum point simultaneously at the time of the harvest. 

Glucose and fructose are the predominant natural sugars in V. vini-fera grapes. A number of investigators have reported the proportions of these sugars, and generally at maturity the ratio is close to 1 1 although wide variation has been noted (19, 20). 

---