Oak barrels are used as a means of transportation for many goods. After the Gaul period was introduced to France, it began to be widely used in all parts of Europe. In addition to transporting goods, oak barrels are also used to transport and store wine. All kinds of wood in oak barrels have been used to make wine storage barrels, such as chestnut, Chinese fir and mahogany. But it is no longer used now because the tannin contained in wood is too coarse or the fiber is too coarse, and the sealing effect is not good. Nowadays, almost all barrels used for wine brewing are made of oak. Almost all famous high-quality red wines in the world must be stored in oak barrels for one or two years. Oak barrels are usually made of French and American oak. Chardonnay is a particularly popular grape variety in recent years, and it is also popular to ferment in oak barrels. Although today's wine-making technology is very advanced, people's impression of wine is always inseparable from oak barrels, which have existed for thousands of years. 1. Moderate oxidation: The biggest effect of oxidized oak barrels on wine is to stabilize the structure of wine through moderate oxidation, and to integrate the fragrance in the barrel into wine. The wooden cells in the barrel wall of oak barrel have the function of air permeability, which can allow a very small amount of air to penetrate into the barrel through the barrel wall and cause moderate oxidation of wine. Excessive oxidation will deteriorate the wine, but a small amount of oxygen can slowly penetrate into the barrel to soften tannins, make the wine more mellow, and at the same time make the fresh fruit aroma in the wine gradually brew into rich and varied mature wine aroma. Pasteur once said that "oxygen makes wine", which shows the importance of oxygen to wine ripening and cultivation. Because of oxidation, the color of red wine cultured in oak barrels will be lighter than before storage, and the color tone will be orange; On the contrary, after storage, the color of the wine becomes darker and the color becomes golden. The air in the barrel can pass through the barrel wall, and the wine in the barrel will also evaporate into the air through the barrel wall. So after a period of storage, the wine in the barrel will be reduced, leaving a gap in the barrel. In this way, the oxidation speed of wine will become too fast to improve the quality. So every once in a while, the winemaker will "add barrels" and fill the oak barrels with wine. After a year or two, the wine became stronger due to evaporation. However, Spanish fino sherry will not be oxidized without adding barrels during oak barrel culture. This is because there is a layer of white yeast floating on the surface of wine, which can protect Fino from air contact. 3. Aroma and tannin from oak barrels: In addition to providing a moderate oxidation environment for wine, the original aroma of oak barrels will also be integrated into wine. In addition to the smell of wood, according to the degree of smoking in wooden barrels, cream, vanilla, toast, roasted almonds, cigarettes and cloves can be brought into the wine. The aroma of oak itself is not the original natural flavor of wine, but it makes the wine more rich and should not overshadow the original natural aroma of wine. Oak also contains tannins, which are usually rough and astringent. When it is mixed into wine, it will make the wine very astringent and difficult to swallow. Therefore, in the manufacturing process, oak blocks must be naturally dried for a long time (more than three years) to soften tannins slightly, so as not to affect the quality of wine. Fermented oak barrels can also be used as fermented wine jars, and occasionally red wine can be brewed from traditional giant oak fermented wine jars. Most white wines are fermented in 225-liter oak barrels. In addition to the advantages of natural temperature control, fermented liquor can also be directly cultured with yeast that died in the same barrel, which can make the liquor more mellow and sweeter. In order to make the dead yeast fully contact with the wine, the winemaker must always stir in oak barrels with wooden sticks according to the ancient method to mix the sediment with the wine. The size of oak barrel will affect the effect of moderate oxidation, because the larger the volume, the smaller the oxidation effect per unit of wine. In addition, the influence of old and new oak barrels on wine is also different. The newer the barrel, the better the sealing, and the stronger the wood texture brought to the wine. Brewers can choose suitable oak barrels according to their own needs. For example, to keep red wine fresh and fragrant, they can choose big oak barrels, which will not mature too fast and there will be no redundant woody plants. Disadvantages Oak barrels are not only good for wine. For example, if oak barrels are not cleaned or are too old, they will not only bring bad smells to wine, such as musty smell and rotten wood smell, but even cause excessive oxidation to make wine deteriorate. In addition, inferior oak will bring inferior tannins into wine, making it dry and unpalatable. Not all wines are suitable for cultivation in oak barrels. For example, wine suitable for young people will lose its original pleasant fresh fruit aroma after being cultured in oak barrels, and may also destroy the sense of balance in taste.