Do white wine grapes have tannins?

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Dear Dr. Vinny,
Do white grapes have as many tannins as red grapes?
—Patrick, Percy, Ill.
Dear Patrick,
All grapes have tannins. In fact, lots of foods have tannins, including cherries, persimmons, pomegranate seeds, chocolate, beans and most berries. But white wines have lower levels of tannins than red wines because in grapes, tannins come primarily from the skins, seeds and stems. To make a white wine, the juice is separated from the grape skins and seeds immediately after the grapes are crushed. Red-wine production, on the other hand, includes a great deal more contact between the juice and the crushed grape skins and seeds (through a process called maceration), causing the wine to absorb more tannins.
Tannins can also be absorbed from oak barrels, but barrel tannins tend to be less intense, so even a barrel-aged white wine won't be tannic. It’s probably a good thing that white wines usually aren't tannic, because tannins can come across as bitter, and that would stick out in a white wine more than a red.
—Dr. Vinny