Why is your wine crying? Scientists say shock waves likely play a role
Alcohol content, the pour, and shape of the glass are also factors in wine tears.
They probably aren’t, just that the path length (thickness of the legs on the glass) is so small that you don’t notice much if any coloration. Beer’s Law.
In the last couple of weeks, I heard someone say that the legs say more about the glass than the wine. I think that was in a tweet that Jamie Goode retweeted.
It is related to alcohol concentration, but because of the surface tension difference between the wine coating the sides of the glass and the wine at the meniscus, not because of viscosity. Alcohol evaporates faster than water, creating a higher surface tension in the liquid coating the side of the glass. That difference draws more wine upward via capillary action until there is enough for gravity to overcome the upward force.
Which is why you should discount a lot of what winemakers tell you Unless you are very confident they know what they’re talking about.
David G has it right, the legs are an indicator of alcohol. But other factors can enhance them, or make them more noticeable, such as higher sugar content, higher temperature, wine color, etc. A good way to see them in a lighter bodied, lighter color wine is to look at the shadows cast through the glass from an overhead light, particularly in a somewhat darkened room.
Greg, there’s not enough glycerol in any (good) wine to be noticeable in changing the viscosity. And it would lower the surface tension anyway, reducing the effect.
It would be interesting to know the effect of the glass. Water beads quite differently on different glasses, and I have to think that would affect wine legs as well.