Phenolic content in wine the ellagic and gallic acid found in the wood. In the vineyards, there is also a growing distinction being made between "ripe" and "unripe" tannins present in the grape. This "physiological ripeness", which is roughly determined by tasting the grapes off the vines, is being used along with sugar levels as a determination of when to harvest. The idea is that "riper" tannins will taste softer but still impart some of the texture components found favorable in wine. In winemaking, the amount of the time that the must spends in contact with the grape skins, stems and seeds will influence
Wine in China "materia medica" compiled in the late Han, states that grapes could be used to produce wine. In the Three Kingdoms era (220–280 AD), Wei emperor Cao Pi noted that grape wine "is sweeter than the wine made [from cereals] using ferments and sprouted grain. One recovers from it more easily when one has taken too much." Grapes continued to be grown in the following centuries, notably in the northwestern region of Gansu, but were not used to produce wine on a large scale. Wine thus remained an exotic product known by few people. Not until the Tang dynasty (618–907) did