Valerie and I were talking recently, and she mentioned that many people ask her what causes the “legs” in a wine glass and she did not have an answer.  The question made me curious which is always a dangerous thing, so I did some research.

You can easily see the "legs" of wine in the shadow of this glass.

If you swirl some wines in the glass and then hold the glass up to the light the liquid will appear to run down the insides at different speeds and form rivulets.  These are called the “legs”.  You will also sometimes hear them called the “tears of wine” or “church windows”.  Some wines have much longer, more easily seen legs than others.  I have heard people say that the more legs a wine has the richer or more full-bodied the wine is, or maybe the higher quality the wine is.  Do legs really indicated body or quality?  What is the scientific answer?

The effect was first explained by a physicist named James Thompson in 1855.  What he found is today called the Marangoni Effect, and has to do with the flow of a liquid being affected by surface tension.

Wine is basically a mixture of water, alcohol, and all the other good stuff that makes wine so tasty.  The important things in this context are the water and the alcohol.  Alcohol has a lower surface tension that water does, and where there is a lower concentration of alcohol the water’s surface tension will pull the surrounding liquid more strongly than a region with a higher alcohol concentration.  This can be seen really easily if you take a surface that is wet and place a drop of water in the middle of the wet area.  Alcohol also evaporates much more quickly than water which means that when the alcohol evaporates the water takes its place and flows into that space.

So, when you swirl the wine in the glass the edges of the glass get coated in wine.  The alcohol does not evaporate at the same rate in all areas of the glass which causes surface tension to vary across the surface.  Where more alcohol evaporates the surface tension of the water increases which pushes the legs up the glass until gravity finally wins and pulls the liquid back down.  Don’t believe it?  Here is an experiment for you.  Find a wine that looks like it has really good legs.  Cover the glass with your hand, or put a piece of plastic wrap over the top of the glass, and swirl the wine again.  It may not happen the first time, but after several attempts you should see that the legs no longer appear.  That is because when the glass is covered the alcohol does not evaporate as readily which means the surface tension does not vary around the glass and the wine sheets down the surface evenly.

So what do legs really indicate?  Well, the higher the alcohol in the wine, the more likely the wine will have legs.  Alcohol content does affect the body of the wine in the mouth, so to some extent legs can indicate something about the body of the wine.  But other factors like the temperature of the glass or drafts in the room can also effect how quickly the alcohol evaporates, and those factors really have nothing to do with the wine itself.  Legs are definately not an indicator of wine quality.  A wine that shows no legs may be just as good as one that has great legs.

Next time someone says, “Man, this wine really has great legs!” you will be able to explain what that really means.

As always, drink what you like!