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Dear Dr. Vinny,
As wine ages for a very long time, red and white wines tend to end up almost the same color. I've learned that the tannins in reds can bond with pigments in such a way that they lose color and brightness. What happens to whites, in the physical or chemical point of view?
—Alexandre, Rio de Janeiro, Brazil
That’s a good observation, and you’re right that over decades, both red and white wines will head toward brownish tones. Since red and white wines are made differently, the explanation varies.
Red wines get their color from the pigments of phenolic compounds found in the skins of grapes. Over time, those phenols link together (polymerize, for my high-school chemistry teacher) and drop out of suspension. That both accounts for sediment in an older wine, and the reason why the red color fades. White wines don’t have as much contact with the grape skins, so they have less color, phenolic compounds and sediment.
But something else is also happening over time to all wines, regardless of color: oxidation. There’s oxygen trapped inside the bottle (and corks, especially faulty ones, can let even more oxygen inside). Simply put, phenolics turn brown when exposed to oxygen. I like to talk about bananas or apples when bringing up oxidation: Most people understand that when you cut an apple, its flesh starts to turn brown when it comes into contact with air. Same thing happens to wine, but more slowly. I notice it starting around the 10-year mark. Reds turn slightly orange or brown, and white wines can get darker and turn a golden brown. Oxidation is the same reaction responsible for black tea leaves, which come from the same plant as oolong, green and white tea leaves.
Wines can vary with how much color they have to begin with, so the color evolution will also vary. Just as lemon juice or sugar can help prevent an apple from turning brown, acid and high levels of sugar can slow down the process in wines as well. You might not notice a lot of color change with a highly acidic, pale white wine.
As with browning fruit, oxidation causes wine’s flavors to fade. I find that wines that look brown tend to taste kind of nutty, too. You might like that flavor, and it won’t make you sick. But oxidized wines tend to be simple and one-dimensional, their charm long since faded.
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