Figure 10-2. Representative phenolic compounds in wine. Examples include: a. cinnamic acid, a phenolic acid; b. resveratrol, a derivative of cinnamic acid; c. catechin, a flavan-3-ol; d. gallic acid, a tannin; e. quercetin, a flavonol; and f. malvidin, an anthocyanin.
means that the concentrations of sugars and acids (and the sugar/acid ratio), pH, the total soluble solids, and even the phenolic constituents must be at just the right level for the particular cultivar and the type of wine being made. In addition, berry size and weight also influence the time at which grapes are harvested. In general, grapes should be sampled sometime before their expected harvest time and their composition assessed (at minimum °Brix and pH should be measured) to make sure that over-ripening does not occur.
Unfortunately, there is no exact or objective set of rules to ensure or predict the optimum time for harvesting grapes. Rather, grapes are frequently harvested based on more subjective criteria. As grapes ripen on the vine, the sugar concentration, as well as flavor and color components, increase, and acids usually decrease, so identifying the correct moment for harvesting can be a real challenge. It is possible, moreover, for grapes to over-ripen, such that the harvested grapes contain too much sugar or too little acid or be too heavily contaminated with f.
Figure 10-3. Flow chart of wine manufacture. The main difference between the manufacture of red and white wine is that the grapes for red wines are fermented in the presence of skins and seeds (maceration), whereas for white wines, these materials are removed after crushing. Although optional, sulfiting agents are added to most U.S. wines. Whether the malolactic reaction is induced or encouraged depends on the grape composition, the style of wine, and the manufacturer's preferences.
yeast fermentation and maceration
yeast fermentation yeast fermentation and maceration
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