Why would a winemaker add tannins to wine?

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Dear Dr. Vinny,

I saw your answer to a question about how tannins in wine are naturally occurring. I was told by a European winemaker that they have to add tannins to wine before exporting it to the United States. Why would that be?

—Jenny, Mass.

Dear Jenny,

You’re correct that tannins are a class of naturally occurring phenolic molecules found in some trees (including tea) and other plants. In wine, tannins can come from grape skins, seeds and stems, as well as from oak barrels used for aging.

Tannins are an important part of a wine’s structure, and along with alcohol, acidity and sugar, they’re a crucial component in helping a wine age gracefully. While tannins can taste bitter to some people, they’re typically experienced as a tugging or drying sensation in your mouth.

Some winemakers may decide to add powdered tannins to adjust their wine. Adding tannins can help stave off oxidation and even stabilize color. But mostly they improve a wine’s texture and counteract the perception of sweetness. While it’s hard to tell how widespread adding tannins is, it’s not very common among fine wine producers.

Adding tannins is absolutely not a requirement for selling wines in the United States. It’s true that wine labeling laws vary by country, and some countries may allow certain additives that others prohibit. Perhaps the vintner was jokingly referring to a stereotype that American wine lovers prefer big, bold, tannic wines.

—Dr. Vinny

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