Using oak barrels for fermentation is its basic function. Occasionally, we can still see red wine being made in traditional giant oak fermentation tanks. Oak barrels used for white wine fermentation are mostly 225 liters. The fermented white wine is cultured together with dead yeast to make the wine more mellow and sweet. Oak wood is breathable, and a small amount of air can pass through the barrel wall, so the wine can be moderately oxidized. As a small amount of oxygen slowly penetrates into the barrel, the tannins can be softened, and the fruity aroma gradually brews into a rich and varied wine aroma, making the wine more mellow. .Red wine becomes lighter in color after passing through oak barrels; white wine becomes darker in color after passing through oak barrels. When wine is in oak barrels, the aroma contained in the oak barrels will be integrated into the wine. In addition to the oak flavor itself, the degree of smoking of the barrels can make the wine have aromas such as cream, vanilla, toast, roasted almonds, smoke and cloves.