Tannins can affect the color, aging ability, texture and taste of the wine.
These prickly babies are the bitter quality in some red wines—a quality that is similar to the tight feeling you get on the side of your mouth when sucking on tea bags. Classic wines with lots of tannin are Bordeaux and Cabernet Sauvignon, though most serious red wines have some amount of tannin to keep them in balance.
Tannins are basically the structure, the flying buttresses and supports to the wine that help them age and stand up to fatty or rich foods. These and other wines may need to be opened early, prior to serving, often decanted, perhaps left in the cellar while a more forward, fruity wine is sacrificed.