Tannins are polyphenols, a widely distributed compound found in many plants. Tannins are known to create a drying mouthfeel. Tannins are commonly found in the skins, stems and seeds of grapes. Among them, the most important source is grape skins, and tannins are mainly found in cells that are relatively tough compared to grape skins.

If the grape skins are treated roughly or are pressed excessively, many of the tannin-containing cells will burst, releasing more tannins. Tannins are bitter and astringent compounds that occur in large amounts in nature. They are found in the wood, bark, leaves and fruits of plants such as oak, rhubarb, tea, walnuts, cranberries, cocoa and grapes. The presence of tannins makes the plant unpalatable. Their purpose in nature is to prevent animals from eating the fruit or seeds of the plant before they are ripe. Although tannins taste bitter, when processed correctly, they can also become delicious! These include tea, coffee, dark chocolate and of course wine. Tannins in grapes are mainly found in the skins, seeds and stems of the grapes, as well as in the wooden barrels used in the aging process. They provide texture and mouthfeel, as well as weight and structure to the wine. The tannins in wine depend on how long the grape juice, grape skins, and grape seeds stay together. Therefore, winemakers will ferment grape skins and seeds together with the juice. This will not only get more beautiful flavor from the grape skins. color, and also to get more tannins. This explains why red wine has stronger tannins than white wine. At the same time, oak barrels can also bring some tannins to the wine, increasing the complexity and aging ability of the wine. The stems are rich in tannins, so the contact of the stems with the must during the maceration stage results in a tannin-rich must.

In addition, if the grape skins and grape juice already contain sufficient tannins, people will remove all or part of the stems. The seeds also contain tannins, which account for 20%-55% of the total phenolic content in the grape berries, so the ripeness of the fruit is very important. As temperature rises and ripeness increases, the chemical composition of the polyphenols in the grape skins changes, causing the bitter, green tannins in immature grapes to become softer. Greatly affects the tasting characteristics of red wines from different climates. Wines from cool regions, such as the Loire Valley and Bordeaux, have typically hard tannins, while wines from hot regions, such as Australia and California, have milder and more mature tannins.