What are tannins? Why does wine contain them and what is their purpose? All you need to know about tannins in wine is explained here
Tannins are a group of beneficial compounds mainly from the grape's skins and seeds. Tannin gives wine structure and because it acts as a natural preservative, allows the wine to age. Normally, tannin is not so much tasted as it is sensed. However, in a young wine, especially if the grapes have been picked underripe, the tannin can cause wine to taste excessively dry and astringent.
Tannins are present in the bark of many trees and fruits, including oak trees. Oak tannins and grape tannins are substantially different, but wine that is aged in oak barrels, especially new oak barrels, is effected by oak tannins. Exactly to what extent oak tannins affect wine differently than grape tannins is not precisely known, and there is a great deal of scientific study going on in that area. Nonetheless, any wine aged in oak, or with oak chips is effected by oak tannins.
Tannins are one of the four main aspects of a wine's balance. The other three are sweetness, acidity, and alcohol. For red wines we want a balance of tannins, acid, sugar, and alcohol. For white wine we want a balance of acid, sugar, and alcohol.
Note the absence of tannins in white wine. Why?
Because Tannins are mainly in the grape's skin and seeds. Red wines are fermented for a period of time with the skin and seeds, thereby making tannins a substantial element in red wine. White wine is made by separating the juice from the skin. Blush wine is made by using red grapes, and leaving the skin in contact with the juice for a very short period of time.
From a structural point of view, Tannins are the backbone of red wine, while acidity is the backbone of white wine.
Tannins have color, too. They are orange, amber, and yellow. If you'll notice in an old bottle of red wine, it sometimes has a brown, red-brick and orange hue to it. What you're seeing are tannins. With age, the first color to go in red wine is purple. A chemical compound known as anthocyanins is responsible for the purple color in a red wine. With age anthocyanins and tannins polymerize (combine with other molecules to form bigger molecules), then precipitate and form sediment at the bottom of the bottle. The anthocyanins polymerize first, taking the purple color with them to the bottom of the bottle, leaving the tannins behind. Hence the brick/orange hue of an older wine.
Does that mean the only thing left is tannins?
No, because it all doesn't happen at once. It happens slowly, over time. Time softens wine, because the tannins polymerize, i.e. become sediment. A wine is ready when enough of the tannins have softened, but not so many of the tannins have become sediment that the wine has lost its structure.
The terms used to define tannins are astringent, firm, or soft. Tannins create a sensation, rather than a taste or smell. The sensation is akin to over-steeped tea, and leaves your mouth feeling dry, sometimes leaving a bitter taste, depending on how it hits the back of your tongue, where you taste bitterness.
Some people like more tannins than others. Just like some people like sweet wine, and others don't. There's not an absolute proper amount of any of those elements for any given wine, because each winemaker has a goal, and his or her goal is to create a wine that for them is perfectly balanced. For you it might be too firm (too many tannins), or too soft (not enough tannins).
Winemaking is all a matter of balance. Any element, such as tannin or acidity on its own is unpleasant. In balance with each other, and with the other elements in a wine, they become the reason we drink wine to begin with.
By Dennis Manuel