The tea plant (Camellia sinensis) is an example of a plant with a naturally high tannin content, though in the case of green tea the leaf does not release its tannin into the infusion.
Tannin has a calming effect on the human central nervous system, countering the stimulating effect of the caffeine in tea. New varieties of tea have been specifically bred for a lower tannin content.
Tannin is also found in wine, particularly red wine. Tannin in wine can come from many sources and the tactile properties differ depending on the source. Tannins in grape skins and seeds (the latter being especially harsh) tend to be more noticeable in red wines, which are fermented while in contact with the skins and seeds.
Modern winemakers take great care to minimize undesirable tannins from seeds by crushing grapes gently to extract their juice. Pressing the grapes results in press wine[?] which is more tannic and might be kept separately. Wines can also take on tannin if matured in oak or wood casks[?] with a high tannin content. Tannins play an important role in preventing oxidation in aging wine and appear to polymerize and make up a major portion of the sediment in wine.