All wines have tannins, but some have a lot more than others. Tannins are naturally occurring polyphenols that are found in plants and trees. The tannins in wine come from the skins and seeds of grapes, as well as from exposure to wood barrels.
Tannins don’t have a taste as much as they have a feel, although if a wine has a lot of tannins, it can come across as bitter. Tannins are an important part of a wine’s structure —they’re largely responsible for that puckery sensation that tugs on your cheeks like a cup of strong black tea. Tannins can make a wine seem chewy, dusty or even drying.
Red wines tend to have more tannins than white wines, since making red wines involves the juice having a longer exposure to the grape skins and seeds (that process is called maceration). Certain grape varieties, climates, yeasts and other winemaking choices will affect how tannic a wine ends up. Winemakers can also add powdered tannins if they feel a wine needs an adjustment, usually to balance out sweetness or add some structure.
There are many different styles of wine, some more dense and rustic, others more velvety and elegant. I like all kinds of styles of wines, so it’s not as if tannic wines always taste better or worse than less-tannic wines. It comes down to balance — the intensity of the flavours should match the intensity of the tannins. But I’ll notice the tannins in a negative way if the tannins overpower or overwhelm the flavours, or if the wine is really big in flavours but lacking in structure.
(Source: Wine Spectator)