What is the purpose of legs on wine after swirling?

• A. Indicate wine's age directly.
• B. They reflect alcohol and glycerol content and can indicate body and alcohol level, though not a direct measure of quality.
• C. Show sugar content levels only.
• D. Indicate viscosity and color.

Answer: (B)

The legs you see after swirling come from the physics of a thin liquid film on the glass: evaporation, surface tension, and viscosity. When you spin the wine, ethanol begins to evaporate from the film more quickly than water. This change in the liquid’s surface tension causes the liquid to pull into droplets that cling to the glass and then run downward under gravity. How pronounced and persistent those droplets are depends mainly on the wine’s viscosity, which is influenced by glycerol (and to some extent sugar). A wine with more glycerol and a bit higher alcohol tends to form thicker, longer-lasting legs, signaling more body and higher alcohol, even though that doesn’t directly measure quality.

These legs don’t reliably indicate age, nor do they provide a precise measure of sugar content or color. Age affects many wine traits such as aroma and tannins, which aren’t reflected by leg patterns, and sugar content isn’t what primarily drives leg formation—the combination of alcohol-driven evaporation and glycerol-driven viscosity is.