This is the forth post of the series: Introduction to Wine
Introduction to Wine: Basic Types
Introduction to Wine: Basic Style I
Introduction to Wine: Basic Style 2
Introduction to Wine: Basic Style 3
In a wine, tannin is felt on the teeth, gum and the tongue and makes the mouth feel dry. If you find yourself unconsciously licking your teeth or gums, the wine has at least medium level tannin. Tannin can make a young red wine seems harsh. Although it doesn't sound good to have tannin in wines, they do bring some positive qualities. Tannin can help a wine mature by giving structure and complexity and the cay improve a wine's balance.
For an experiment, try eating a grape without the skin and compare it with another one with skin on. Grape flesh is sweet, but lacks flavours and texture of the skin.
Tannin is a substance found in grape skins or the oak barrels. For red wine, the crushed grapes are often fermented with their skins, and the red color and tannin are exacted from the skin into the wine. All red wines have some level of tannin and, in most cases, the level of tannin can be determine just by the color of the wine. The darker the wine, the more tannin there will be. White wine usually have no tannin, since the crushed grapes are pressed and the juice are fermented without any skin contact. (Yes, white wines can be made from black grapes).
Another source of tannin is from the oak barrels in which the wine ferment and/or matured in. A white wine that has been fermented or matured in an oak barrel, such as Fumé Blanc, will have a low level of tannin. Wines gain flavours, tannin, and texture from contact with the wood. Because the barrel is naturally porous, the wine often gains darker color and a trace of lovely oxidative flavours. In white wine, the wine can become buttery and have vanilla flavours. Red wines can become smoother with added spicy character.
Does "Oaked" on the wine label means the wine have spent time in an oak vat or barrel? No. Oak barrels cost a couple thousand dollars each (they don't hold that much wine either), and lots of wine styles demand new oak barrels each year. For lower margin wines, wine makers cheat by putting in staves or chips of oak into the wine. In order to add more tannin to the wine, some wine makers can even put bags of powdered artificial tannin into the wine.
In a wine tasting, you can detect oak by its vanilla or coconut aroma.