Q: What kind of sugar is in wine?—Sal, Winner, S.D.
A: We wouldn’t have wine without sugar, and yet the sweet stuff remains a topic of some confusion, for nascent enophiles and seasoned experts alike.
First things first: Most wines are dry, meaning that almost all the sugar in the ripe grapes has been converted to alcohol by yeasts during fermentation. Often, when people describe a dry table wine as “sweet,” they’re referring to ripe fruit flavors that give the impression of sweetness, but usually aren’t the result of actual sugar in the wine.
It’s true that most wines do contain a small amount of residual sugar, typically less than 10 grams per liter and often as low as 1–2 grams per liter. It’s difficult for yeasts to ferment every last bit of sugar in the grapes, but the amount of sugar remaining in the wine is usually so small that humans can’t taste it. Of course, sugar is a crucial component of many off-dry, sweet and fortified wines, which can contain 200 grams per liter or more.
But what kind of sugar are we talking about? Like most plants, grapes convert sunlight and carbon dioxide into sugar during photosynthesis. That sugar mainly takes the form of sucrose—the same molecule that makes up table sugar—a disaccharide resulting from the chemical linkage of glucose and fructose. As grapes ripen, an enzyme splits sucrose into those two monosaccharide constituents. Early during ripening, grapes contain higher amounts of glucose, but typically, grapes contain roughly equal parts of glucose and fructose at harvest.
Glucose and fructose are similar molecules. Both are natural sugars that contain six carbon atoms, and their chemical structures are closely related. However, fructose tastes much sweeter to humans than glucose. During fermentation, when yeasts are converting the sugars in grapes to alcohol, they prefer to consume glucose. Since yeasts “eat” glucose first, the majority of any residual sugar remaining in wine is typically fructose. So, the next time you’re appreciating the balanced sweetness of a glass of Port or Sauternes, thank fructose. Many Champagnes and other sparkling wines get a touch of sweetness, called the dosage, added at bottling. This sweet liquor is usually a mixture of wine and sucrose.
If you’re concerned about sugar for health reasons, it’s worth remembering that even though most wine doesn’t contain appreciable amounts of sugar, wine does contain calories. Alcohol contains 7 calories per gram, which makes for around 120 calories in a typical glass of dry wine. By comparison, sugar (a carbohydrate) contains just 4 calories per gram.
As always, talk to your healthcare provider about incorporating wine into a healthy lifestyle.—Kenny Martin
