When red wine is made, the skins, seeds and sometimes even the stems are fermented together with the juice. As fermentation proceeds, pigment and tannins are extracted from the skins, seeds and stems, resulting in a wine that is red to purple in color and contains tannins. If the amount of extract is considerable, the wine will be intensely-colored, even opaque, and full of tannins.
When making white wine, the vintner presses the white grapes, separating the skins, stems and seeds from the pulp. This leaves only the juice to be fermented. The resulting wine is pale, transparent, and straw to gold in color, with little or no tannins.
Tannins can also be extracted from the wood used to make barrels.