What are "Tears of Wine"?

Have you noticed: every time after pouring wine, near the top of a wine glass there's always a ring of liquid, where droplets form and continue to fall back into the wine? The phenomenon is commonly known as wine tears, wine legs, or wine fingers. 

This happens because alcohol and water have different surface tension. At the meniscus where wine, the mixture of water and alcohol, becomes inhomogeneous, the upper wall of the glass (an area with a lower alcohol concentration) pulls on the wine more strongly than the surface (an area with a higher alcohol concentration), resulting in a ring. 

From there, due to a gradient of the surface tension between the wall of the glass and wine surface, stable droplets or bubbles form (called "beading" in the liquor industry), and fall back to the meniscus due to gravity. This entire phenomenon can explained by the Marangoni effect, named after Italian physicist Carlo Marangoni.

Besides being commonly observed and utilized in the alcohol industry, the Marangoni effect is also crucial for welding metals, manufacturing integrated circuits, and growing crystals.

Source: Physics Girl via Youtube