Do dessert wines lose their sweetness with age?

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Dear Dr. Vinny,
I tasted a 100-year-old bottle of Sauternes and it didn’t taste sweet at all. Why is that?
—Alex, Taipei, Taiwan
Dear Alex,
The amount of sugar in a wine doesn’t change as it ages. But the way a wine tastes changes a great deal. Aged dessert wines from Sauternes do seem to taste more like drier wines over time. Wine Spectator senior editor James Molesworth, our lead taster for the wines of Bordeaux, describes older Sauternes as having a “waxy, dry, marzipan-type impression.”
I also checked in with Jean-Jacques Dubourdieu of Bordeaux’s Denis Dubourdieu Domaines, which includes a half-dozen estates including Château Doïsy Daëne in Barsac, a subregion of Sauternes. He told me they have a saying: “With time, the Sauternes of Barsac eats its sugar.” But he acknowledged that the sugar content does not actually decrease. “Oxidation, little by little, lowers the perception of sugar,” Dubourdieu said. “There’s no evidence, but we feel that, with time, the oxidation of some phenolic content gives more bitterness, and mitigates the perception of sugar.”
—Dr. Vinny