Grape Composition

Given that the two major constituents of wine, water and ethanol, have no flavor, color, or aroma, it is not surprising that the other grape components contribute so much to the organ-oleptic properties of wine. Some of these substances can be problematic, causing a variety of defects. In addition, the composition of grapes changes during growth and maturation on the vine, such that the time of harvest influences the chemical constituents of the grape as well as the wine.For example, the sugar concentration increases as the grape ripens on the vine, due to increased biosynthesis, and to a lesser extent, to water evaporation and subsequent concentration of solutes. In contrast, acid concentrations decrease during maturation. Finally, in discussing the composition of wine, it is often more useful to consider the liquid juice just after the grapes have been crushed as the starting material, rather than the intact grape. As listed in Table 10-2, the juice, or "must," consists of several major constituents and many other minor components that are important, but which are present at relatively low concentrations.

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