Quality of material grape for winemaking

Abstract

The way of use of grape is divided into two types, i.e. table grape (eat in raw) and wine grape. In Japan, table grape left unsold are used to process to wine in history. But the quality required for table grape and wine grape is completely different. To make good quality of wine, many attentions are paid in recent grape growing. Sugar content is very important because it is converted to ethanol by fermentation. Malic and tartaric acid content is also important for sourness of resultant wine. But these compounds can easily adjust in its concentration by adding to grape juice/must. Besides these compounds, aroma compounds affect greatly to the wine quality. Aroma compounds have volatility and easily escape from liquid phase during wine-making. This effect partially causes the difference between smell of grape and wine. From this point of view, aroma-precursors considered to be more important. Aroma precursor is converted to aroma compounds during fermentation. For example, glucosidic aroma compounds have weak in smell and difficult to evaporate because of its solubility to aqueous phase by the effect of glucose attached. Once the glucose moiety is hydrolyzed with glucosidase during fermentation, it is changed to aroma compounds and is smell. Amino acids in grape berry are assimilated by yeast, and produce higher alcohol. Amino acids have no smell in grape, but their amount and composition will affect wine quality. Other aroma compounds precursors are also taken account of their concentration in grape at harvest for good quality winemaking.