Tears of wine

Tears of wine

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The phenomenon called tears of wine is manifested as a ring of clear liquid, near the top of a glass of wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

, from which droplets continuously form and drop back into the wine. It is most readily observed in a wine which has a high alcohol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 content. It is also referred to as wine legs, curtains, or church windows.

Cause


The effect is a consequence of the fact that alcohol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 has a lower surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 than water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

. If alcohol is mixed with water inhomogeneously, a region with a lower concentration of alcohol will pull on the surrounding fluid more strongly than a region with a higher alcohol concentration. The result is that the liquid tends to flow away from regions with higher alcohol concentration. This can be easily and strikingly demonstrated by spreading a thin film of water on a smooth surface and then allowing a drop of alcohol to fall on the center of the film. The liquid will rush out of the region where the drop of alcohol fell.

Wine is mostly a mixture of alcohol and water, with dissolved sugars, acids, colourants and flavourants. Where the surface of the wine meets the side of the glass, capillary action
Capillary action
Capillary action, or capilarity, is the ability of a liquid to flow against gravity where liquid spontanously rise in a narrow space such as between the hair of a paint-brush, in a thin tube, or in porous material such as paper or in some non-porous material such as liquified carbon fiber, or in a...

 makes the liquid climb the side of the glass. As it does so, both alcohol and water evaporate
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

 from the rising film, but the alcohol evaporates faster, due to its higher vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

. 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 moves up the side of the glass and forms droplets that fall back under their own weight.

The phenomenon was first correctly explained by physicist James Thomson
James Thomson (engineer)
right|300px|James Thomson was an engineer and physicist whose reputation is substantial though it is overshadowed by that of his younger brother William Thomson .-Biography:Born in Belfast, he grew up mostly in Glasgow...

, the elder brother of Lord Kelvin
William Thomson, 1st Baron Kelvin
William Thomson, 1st Baron Kelvin OM, GCVO, PC, PRS, PRSE, was a mathematical physicist and engineer. At the University of Glasgow he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging...

, in 1855. It is an instance of what is today called the Marangoni effect
Marangoni effect
The Marangoni effect is the mass transfer along an interface between two fluids due to surface tension gradient...

 (or the Gibbs-Marangoni effect): the flow of liquid caused by surface tension gradients.

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 that the biblical
Bible
The Bible refers to any one of the collections of the primary religious texts of Judaism and Christianity. There is no common version of the Bible, as the individual books , their contents and their order vary among denominations...

 injunction
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.

Related phenomena


Other fluid phenomena that arise in alcohol-water mixtures are beading and viscimetry
Viscimetry
Viscimation is the turbulence when liquids of different viscosities mix,particularly the formation of vortices and visible separate threads of the different liquids.The term is archaic and idiosyncratic to whisky tasting;...

. These are more pronounced in liquor than in wine, and both phenomena are more pronounced in stronger liquor.

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
Marangoni effect
The Marangoni effect is the mass transfer along an interface between two fluids due to surface tension gradient...

. Shaking a whisky bottle to form bubbles is referred to as “beating [beading] the whisky”.

Viscimetry is the formation of whorls when water is added to a high-alcohol mixture.

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