From the
Wikipedia entry:
The phenomenon called tears of wine is manifested as a ring of clear liquid, near the top of a glass of wine, from which droplets continuously form and drop back into the wine. It is most readily observed in a wine which has a high alcohol content. It is also referred to as wine legs, curtains, or church windows...
Where the surface of the wine meets the side of the glass, capillary action makes the liquid climb the side of the glass. As it does so, both alcohol and water evaporate from the rising film, but the alcohol evaporates faster, due to its higher vapor pressure. The resulting decrease in the concentration of alcohol causes the surface tension of the liquid to increase, and this causes more liquid to be drawn up from the bulk of the wine, which has a lower surface tension because of its higher alcohol content. The wine which moves up the side of the glass and forms droplets that fall back under their own weight...
It is sometimes claimed incorrectly that wine with "lots of legs" is sweeter or of a better quality. In fact the intensity of this phenomenon depends only on alcohol content, and it can be eliminated completely by covering the wine glass (which stops the evaporation of the alcohol). British physicist C. V. Boys argues[4] that the biblical injunction
“Look not thou upon the wine when it is red, when it giveth his colour in the cup, when it moveth itself aright.” —Proverbs, 23:31
refers to this effect. Since the "tears of wine" are most noticeable in wine which has a high alcohol content, the author may be suggesting this as a way to identify wines which should be avoided in the interest of sobriety.
Followed by this interesting notation:
Beading refers to the formation of stable bubbles when liquor is shaken. This occurs only in liquor that contains more than 46% alcohol. It is an example of the Marangoni effect. Shaking a whisky bottle to form bubbles is referred to as “beating [beading] the whisky”.
I've added "bourbon" to the title this post after discovering that a video is available of the phenomenon using my favorite recreational beverage:
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