Where does sediment come from?

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Dear Dr. Vinny,

Why do older wines have sediment when they age but the same wine has no sediment when it is younger? Where does the sediment come from?

—Matt, New York

Dear Matt,

First off, let me say that sediment is harmless. Many winemakers try to eliminate any solid materials from their wines, whether it's bits of grape pulp, dead yeast cells or harmless tartrates. But if a clear wine magically has some sediment after years of cellaring, where does it come from? Why, from phenolic polymerization, of course!

A red wine gets its color from pigmented components known as phenolic compounds, which are originally found in the skins of grapes. Over time—usually it takes several years in the bottle—these compounds link together (polymerize), the color shifts from purple to brick red, and the phenolics drop out of suspension and become sediment.

—Dr. Vinny

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