She's got "legs" and knows how to use them

This is an area fraught with misunderstanding. For a long time, many of us thought that legs on a wine glass (or "cathedral windows" or "baby's tears") were a favorable indication of something. We would hold up the glass and pronounce "it's got good legs," as if that meant something special. Some of us also thought that wine legs were an indication of glycerine, which is naturally-occurring in grapes and contributes to a feeling of greater body in the wine (thicker wine).

Um, sorry, but no on all counts. One of the great things about being human is that, very occasionally, we can learn why our earlier positions were wrong ;)

Thanks to winepros.org for this:

Wine legs originate from high ethanol, and are no indication whatsoever of quality.

The phenomenon, called the Gibbs-Marangoni effect after the two scientists who first explained it, occurs because of four properties of chemical physics. First, if the molecular attraction between solids and liquids called interfacial tension is slightly greater than thesurface tension which holds the liquid molecules together, the liquid "crawls" up the glass (assuming the glass is clean). Of wine's two primary components, alcohol evaporates faster than water. As the ethanol evaporates, gravity takes over, the surface tension is broken and the water runs back down into the glass in rivulets. These "legs" or "tears" are observable because of the difference in the way alcohol and water each refract light. The phenomenon occurs most readily in wines above 12% alcohol. Although ethanol, wine's primary alcohol, is a major contributor to the "body" of a wine, a high content does not alone guarantee fullness or texture in wine.

APPLICATION: Legs are the Lava Lamps of wine tasting; they provide contemplative amusement, but shed precious little illumination on the subject at hand. Next time someone showily remarks that a wine "has great legs," explain the principal and enlighten them. Or don't. In fact, you may get more satisfaction from chiming-in that you think "the wine also displays a great ass" and let it go at that. For a good parlor trick, cover a "weeping" glass with a card. The effect stops (no evaporation). Remove the card, the glass soon returns to "tears".

(photo credits to ShutterStop and The Bottle Stop)