Tannin in Grape Skins, Seeds & Stems
Tannins are not a flavor. Rather, they are polyphenols (astringent chemical compounds) found in grape skins, seeds and stems. They are also found in fruits, veggies, wood, leaves, bark, and a plethora of other livings plants. The compounds result in a cottony mouthfeel when we eat grapes or drink wine.
The best way to understand how tannin influences grapes or wine is to peel the skin off of a black table grape and put it in your mouth, without the juicy pulp. When you chew the skin, you should be able to feel the cottony effect of tannin on your teeth and around your mouth.
Most black grapes are fermented with their skins, allowing the tannin to soak into the wine. However, a winemaker may also choose to add the grape seeds and stems to the must to further extract tannin and flavor compounds. This method may be more common for red wine, but some winemakers also choose to ferment white grapes along with skins, seeds and stems for more complexity.
Black grapes have higher levels of skin tannin than white grapes. And even within the black-grape category, all tannin levels are not the same. Cabernet Sauvignon, Nebbiolo, Syrah and Tannat have some of highest tannin levels. Whereas Pinot Noir and Grenache have relatively lower levels. In addition, smaller berries, i.e. Syrah, may contribute even more tannins to a wine due to it’s high skin/pulp ratio.
Here are a few common grapes and their tannin levels:
Any time grapes are fermented with their skins or aged in oak, the tannins make their way into the final product of wine.
Tannin From Oak
As mentioned earlier, tannins are also found in wood and bark. When any wine is aged in an oak vessel, it extracts the natural tannins found in that particular barrel and increases that cottony feel and flavor complexity of the final wine. Keep in mind, barrels lose their impact and impart lower tannin levels each time they are used.
Softening Tannins for Easy Drinking
Even though tannin is present in wood, extended periods of oak-aging helps to soften the natural tannins found in the grapes themselves. If you were to taste a Tannat wine before barrel-aging, the tannins may be so astringent that your lips pucker and the wine isn’t very drinkable. This is why many red wines need to age a bit.
Although barrels are tightly sealed, they are not 100% air-proof. Placing wine in barrels is a form of deliberate oxidation. As the oxygen seeps in the tiny barrel openings and crevices over time, it will slowly interact with wine and begin to soften the tannin astringency. When the tannins are softer and balanced the wine is more enjoyable.
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