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Dear Dr. Vinny,

Can a dry red wine have higher sugar content than a sweet wine? Does the amount of residual sugar indicate the alcohol content of a wine?

—Pat B., Huntington Beach, Calif.

Dear Pat,

Let’s start by noting that the fermentation process converts the sugar in the grapes to alcohol. It’s not unusual for at least a little bit of sugar to be left at the end of fermentation. Technically a wine is considered “dry” if there are less than 10 grams per liter left, while a “sweet” or dessert wine has more than 30 grams per liter. Stuff in between is considered “off-dry.”

Of course, most people don’t sip a wine and think, “Boy, this tastes like it has 13 or 14 grams per liter of residual sugar!” Our perception of the sugar is based on our own sensitivity to sweetness (some of us like cotton candy more than others) as well as on the interplay of the other factors in a wine: alcohol, acidity, tannins and glycerin. Two wines might have the same exact amount of residual sugar and alcohol, but one’s fruit flavors could taste more jammy and ripe (and therefore sweet) than the other’s.

Since we’ve noted that fermentation converts grape sugars to alcohol, there’s definitely a relationship between a wine’s residual or unconverted sugar and its alcohol level. The more residual sugar, the lower the potential alcohol that wine could have. But it’s not a simple relationship—there are other factors at play, particularly how much sugar the grapes had to begin with. Two wines could have widely different alcohol percentages but the same amount of residual sugar—or vice versa—depending on how ripe the grapes were.

—Dr. Vinny

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