During fermentation, the juice macerates with the skin, the seeds and part of the stems. This process releases the tannins into the wine, giving red wine its texture, solidity, character, and colour. The darker the wine, the more tannic it is. Tannins in wine come primarily from the skin, and their concentration varies based on the skin thickness. They can also be found in the oil coming out of the seeds, called polyphenol, and in the wood of the oak barrels in which the wine is aged.