What could color staining on the glass from red wine indicate?

Color staining on the glass from red wine is primarily associated with increased alcohol levels. This phenomenon occurs due to the viscosity of the wine, which can be affected by the concentration of various components, including alcohol and residual sugars.

When a red wine has a higher alcohol content, it tends to feel thicker and more viscous. This viscosity causes the wine to cling to the sides of the glass more than wines with lower alcohol levels, resulting in more pronounced color staining as the wine is swirled. The staining can also relate to certain organic compounds present in the wine, which become more pronounced as the alcohol level increases.

Understanding this characteristic allows wine professionals and enthusiasts to make educated guesses about the wine's composition and balance based on how it behaves in the glass.