Tears of wine are the viscous drops that run down the glass when the wine is swirled. This phenomenon is called the Gibbs-Marangoni effect (or Marangoni effect in short), and is caused by the evaporation of alcohol and the resulting gradient in the surface tension of the wine. The thickness of these ‘legs’ and the speed at which they run down says something about the amount of alcohol and the viscosity (syrupiness) of the wine. More legs along the glass can indicate a higher alcohol percentage and / or more sugar in the wine. The speed at which the legs form depends on the temperature and the humidity of the room where you drink the wine, so it is a difficult phenomenon to compare.
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