The phenomenon called tears of wine is manifested as a ring of clear liquid, near the top of a glass of
wine
Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...
, 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, fingers, curtains, church windows, or feet.
Cause
The effect is a consequence of the fact that
alcohol has a lower
surface tension than
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. If alcohol is mixed with water
inhomogeneous
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
ly, 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 (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces li ...
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
Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phas ...
. 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, the elder brother of
Lord Kelvin
William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy at the University of Glasgow for 53 years, he did important ...
, in 1855. It is an instance of what is today called the
Marangoni effect
The Marangoni effect (also called the Gibbs–Marangoni effect) is the mass transfer along an interface between two phases due to a gradient of the surface tension. In the case of temperature dependence, this phenomenon may be called thermo-capill ...
(or the Gibbs-Marangoni effect): the flow of liquid caused by surface tension gradients.
The
evaporation of alcohol also creates a temperature variation along the film of wine due to
evaporative cooling
An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning s ...
. Since surface tension increases with decreasing temperature, this leads to an enhancement of the Marangoni effect that, until recently, had been overlooked.
The effect can be used to move water droplets around in technical applications.
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
Sir Charles Vernon Boys, FRS (15 March 1855 – 30 March 1944) was a British physicist, known for his careful and innovative experimental work in the fields of thermodynamics and high-speed photography, and as a popular science communicator th ...
argues 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
A proverb (from la, proverbium) is a simple and insightful, traditional saying that expresses a perceived truth based on common sense or experience. Proverbs are often metaphorical and use formulaic language. A proverbial phrase or a proverbia ...
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 that should be avoided in the interest of sobriety.
In 2019 a paper indicated that
shock-wave dynamics may play a part in the phenomenon.
[{{Cite web, url=https://arstechnica.com/science/2019/03/why-is-your-wine-crying-scientists-say-shock-waves-likely-play-a-role/, title=Why is your wine crying? Scientists say shock waves likely play a role, last=Ouellette, first=Jennifer, date=2019-03-05, website=Ars Technica, language=en-us, access-date=2020-03-18]
Related phenomena
Other fluid phenomena that arise in alcohol-water mixtures are ''beading'' and ''
viscimetry
Viscimation is the turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel la ...
''. 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
The Marangoni effect (also called the Gibbs–Marangoni effect) is the mass transfer along an interface between two phases due to a gradient of the surface tension. In the case of temperature dependence, this phenomenon may be called thermo-capill ...
. Shaking a whisky bottle to form bubbles is referred to as “beating
eadingthe whisky”.
Viscimetry is the formation of whorls when water is added to a high-alcohol mixture.
See also
*
Surface tension
*
Marangoni effect
The Marangoni effect (also called the Gibbs–Marangoni effect) is the mass transfer along an interface between two phases due to a gradient of the surface tension. In the case of temperature dependence, this phenomenon may be called thermo-capill ...
References
{{reflist
External links
Wine 'Legs', from ''KitchenSavvy''A video of tears of bourbonWhy Does Wine Cry?
Fluid mechanics
Oenology
Wine tasting