Q: Does red wine or white wine have more alcohol? And how does that correlate to calories?—Paula, Colorado Springs, Colo.
A: There are exceptions but, in general, red wines have more alcohol by volume (ABV) than white wines, though the difference is small enough that the National Institute of Health does not differentiate between red and white when defining what constitutes a "standard" drink of wine. (Higher alcohol generally means they have more calories, too.) Keep in mind that the alcohol is mostly (but not entirely) a result of the amount of sugar in the grapes when they were harvested. The riper the grapes, the higher the sugar content, and the more sugar there is for yeast to convert into alcohol during fermentation. Red wine grapes tend to be harvested later—and riper—than white wine grapes. In part that's because of the physiology of various grapes, but also because, broadly speaking, it's reflective of the predominant styles of red wines vs. whites.
There are a lot of variables that go into the ripeness, and thus alcohol and calorie content, of wines—the grapes themselves (some are easier to ripen than others), the climate they're grown in, and the weather conditions of that vintage. But the biggest variable is when the grapes are picked.
Winemakers aren't just trying to get the grapes as ripe as possible; the goal is usually to achieve balance, even if for some winemakers that might mean riper grapes. There's been a movement around the wine world lately to tone down ripeness, and to find fresher expressions of wines that might pair better with food. If you're curious about alcohol content, just look at the label—the law requires the ABV to be listed. (But also keep in mind that the number listed has a range of accuracy.)