The term tannin is commonly used while describing wine. But exactly what is it?
Tannin is the naturally occurring Polyphenol present in plant. They get in to wine by way of stems, seeds and grape skin. They also come from contact with oak barrel during aging.
Tannins add both bitterness and astringency to the wine. Also it gives complexity and sense of structure and hence enhance flavor. It creates drying sensation in mouth. Depending on how dry your mouth feels, you can determine whether the wine is high or low in tannins. Generally the bitterness or firmness of wine is sensed at the rear side of the mouth. But if the wine is more tannic it can be sensed on inside of cheeks and on gums.
The two possible sources of tannins are grapes and wood. Grape tannins come from grape skin, seeds and stems. And wood tannins come from contact with wooden (oak) barrel. Instead of using oak barrels, sometimes oak chips, tannin powders and oak staves are also added in wine, because they are more affordable.
Tannins are commonly found in red wines because of extended contact of seeds and skin with juice during fermentation. But some oak aged white wines also contain tannins.
Some red grapes contain more tannin then others. Cabernet sauvignon and Nebbiolo are the example of more tannic grapes. Tempranillo and Sangiovese are moderately tannic. While Gamay and Pinot noir are tend to have very soft tannins.
Tannins also act as Antioxidants to preserve wine. This is the reason why some red wines are age-worthy. They not only help to age wine but have much health benefits for us.
The only drawback of tannin is that they can cause headaches in some people, but this is rare.