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, from which droplets form and flow back into the wine. It is most readily observed in a wine that has a high alcohol content. It is also referred to as wine legs.
IN the past certain wine connoisseurs held the belief that wines with lots of "legs" indicated a better quality wine - which has proven false. It is a matter of physics. There also is a misconception that abounds in some circles that a Wine's "Legs" are an indication of sugar levels in the wine.
The effect is a consequence of the fact that alcohol has a lower surface tension than water. If alcohol is mixed with water heterogeneously, 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, colours and flavours. Where the surface of the wine meets the side of the glass, 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, on account of its higher vapor pressure and lower boiling point. This change in the composition of the film causes its surface tension to increase - this in turn 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 that moves up the side of the glass then forms droplets which fall back under their weight.
The phenomenon was first correctly explained by physicist James Thomson, the elder brother of Lord Kelvin, in 1855. It is an instance of what is today called the Marangoni effect (or the Gibbs-Marangoni effect): the flow of liquid caused by surface tension gradients.
British physicist C.V. Boys argues that Proverbs 23:31 is probably a reference to this effect:
- Look not thou upon the wine when it is red, when it giveth his colour in the cup, when it moveth itself aright.
Since the "tears of wine" are most noticeable in wine that has a high alcohol content, the author of the Biblical injunction may be using it to identify wines that should be avoided in the interest of sobriety.
[edit] See also
[edit] References
- James Thomson, "On certain curious motions observable on the surfaces of wine and other alcoholic liquours," Philosophical Magazine, 10, 330 (1855).
- Carlo Marangoni, "On the expansion of a drop of liquid floating in the surface of another liquid," (1865).
- C.V. Boys, Soap Bubbles: Their Colours and the Forces the Mould Them, 2nd ed., Ch. 2, (1911).
- Wine 'Legs', from KitchenSavvy
