How does bottle aging affect the acidity of wine?
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Dear Dr. Vinny,
How does bottle aging affect the acidity of wine?
—Amy, Chicago
After a wine has gone through fermentation (when the sugar in the grapes is converted into alcohol) and is botted, the chemical composition doesn’t change very much.
At least at first. We know that as wine ages, some things will slowly change. Depending on the wine, these changes may start to become evident after several years, and certainly around the 10-year mark and beyond. The exact reactions that occur in wine as it ages—and how those are responsible for the aroma, taste and texture of aged wine—all remain something of a mystery, and an area of ongoing research.
But we do know a few things for certain. As wine ages, some tannins and pigment molecules polymerize and fall out of solution as sediment. The color will often start to fade and turn brown. There may also be some reduction of acidity as the alcohols and acids combine to form esters in a process called esterification. Tartaric acid can also fall out of solution as potassium bitartrate crystals.
In terms of pH, the drop in acidity over time will be very small, if it occurs at all. That said, acidity may seem less conspicuous as wine ages. Just as tannins soften and feel rounder, a wine’s acidity is likely to feel more in balance and part of a coherent whole rather than an aspect of the wine that sticks out on its own.
—Dr. Vinny
