| They usually occur in high alcohol wines and you'll | | | | of a wine glass is by mixing alcohol and water on |
| see the link between alcohol and wine legs shortly. | | | | a flat surface. Put some water on a flat surface |
| Some people say you can pick wine quality by | | | | and then add a few drops of alcohol. Watch how |
| the legs. This is just not true. | | | | the water races away from the alcohol drops. |
| The legs occur due to the Marangoni effect. It | | | | This is the lower surface tension of the alcohol |
| comes from the fact that alcohol has a lower | | | | interacting with the water. |
| surface tension than water. Wine is mostly a mix | | | | Physicist James Thomson (Lord Kelvins brother) |
| of water and alcohol plus a few other parts such | | | | first identified this behaviour in 1855. The effect is |
| as sugars, tannins etc. As you swirl your wine | | | | named after an Italian physicist called Carlo |
| around the glass and leave some on the side it | | | | Marangoni from the University of Pavia. Marangoni |
| starts to evaporate. Alcohol evaporates faster | | | | published his doctoral thesis on this phenomenon in |
| than water due to its lower boiling point and higher | | | | 1865. |
| vapour pressure. The changed alcohol to water | | | | As you can see the legs don't have nothing to do |
| mix now has different surface tension areas. The | | | | with wine quality. They're nice to look at and |
| wine forms droplets in the areas of least / most | | | | they're a pretty good conversation starter. But as |
| resistance which fall back down the glass under | | | | a wine quality indicator, I'm afraid they miss out |
| their own weight. | | | | altogether. |
| The quickest way to see this for yourself outside | | | | |