‘In all the tastings I host, I get more questions about wine legs than any other topic,’ says Matt Walls, Decanter World Wine Awards’ Regional Chair for the Rhône. ‘It’s surely one of the most mythologised aspects of wine drinking.’
Believed by many to be a sign of quality, wine legs are in fact the innocent outcome of a physical phenomenon, determined by the wine’s chemical composition and affected by external factors such as temperature, humidity and pouring vessel.
What are wine legs?
Wine legs, also sometimes called ‘wine tears’ and ‘cathedral arches’ are droplets that form on the inside of a glass after you’ve swirled and liquid resettles to the bottom. A thin film of liquid is attached to the inside surface of the glass once swirled; when the alcohol in this liquid veil starts to evaporate, water and other molecules (such as tannins and sugar) form drops that then fall back into the glass forming the trail described as wine legs.
In a previous article in Decanter magazine, Jane Anson, said, ‘When you swirl wine in your glass, alcohol will first gather at the sides, then start to evaporate, while the water (and other molecules in the wine) will turn into droplets that will crawl back to the glass, like raindrops on a window.’
This is known as the Chris-Marangoni effect, named after the 19th-century physicists Carlo Marangoni and Josiah Willard Gibbs, who first observed and studied the phenomenon.
Scientists describe it as ‘the mass transfer along an interface between two fluids due to a gradient of the surface tension’. Walls explains that ‘tears are formed due to a combination of different forces – surface tension forces and intermolecular forces’.
Sounds complicated but it simply means that there are opposing forces between the evaporating molecules of alcohol and the heavier molecules of water, sugar and other components in wine which, pushed against the glass’s surface by the evaporating alcohol, bind with each other to form drops.
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What do wine legs tell us about the quality of the wine?
‘The reality is that ‘legs tell you relatively little about the wine, and nothing about the quality of what’s in the glass’, says Walls. ‘The only information that legs offer to the wine lover is that your wine contains alcohol. But you don’t need legs to tell you that’.
Because of the nature of the phenomenon, wines with higher alcohol content will form tears more easily. As will wines that contain a larger number of heavier molecules – such as tannins and sugar – which explains why tears are more likely to be seen in heavy reds and/or sweet wines. But none of this correlates with quality.
Moreover, there are many external factors that condition whether and how the tears will form. Temperature and humidity are the most obvious influencing factors, given that they directly affect the alcohol’s evaporation rate.
The shape and texture of the glass also play a key role, changing the evaporation/condensation surface area and the way particles interact with each other. Therefore, the same wine might show legs or not depending on environmental conditions and vessel.
You can see ‘wine legs’ as an indicator of some of the wine’s structural characteristics, but never of its quality. The only way to access how good a wine is to smell, taste and discover if all its different characteristics – aromas, acidity, alcohol level… – are in balance.