Tannin (or tannic acid) and oak are usually present together. It is detected primarily in red wines since it is an acid found in the pigment of grape skins and new oak. Tannin can be felt in the middle of the tongue, the roof of the mouth and the film covering your teeth and gums, creating an astringent or a drying sensation on the top of your mouth causing your mouth to dry out and pucker. It is actually experienced by the sense of touch rather than by the sense of taste, although excessive tannin can cause a wine to taste bitter. The effect of tannin is best compared to the sensation you feel when drinking strong, unsweetened tea.
Tannin is a natural preservative, and a critical component in wine that allows it to age. As wine ages in the bottle, tannin begins to break down and dissipate, “softening” the wine as it matures. It is common for wines of varying ages to display greater or lesser amounts of tannic qualities throughout the life span of a wine, phasing from one level of discernment to another. Tannin is generally present in full-flavored, heavy-bodied red wines such as Bordeaux, Barolo, Cabernet Sauvignon and Burgundy.
Highly tannic wines are balanced by full-flavored, hearty meals. The high protein content of red meat, cheese and duck pair nicely with wines that have a high degree of tannin. The wine and food interact with each other, softening the wine and encouraging the flavors from the meal to be fully appreciated. This is similar to adding milk to a hot cup of tea, which allows the protein of the milk to soften and smooth the tannins of the tea. Highly tannic wines are best enjoyed when selected to accompany a hearty meal.