Have you ever wondered why wine has “legs” when it’s swirled? What makes the delicious elixir stick to the sides of the glass and run down in lines? Is it because of its consistency? The molecular composition?
If you’re interested in impressing your friends or a date with this interesting but useless piece of trivia, keep reading.
A group of scientists at UCLA set out on a noble quest to get to the bottom of this boozy mystery, but before we get into the science of it, let’s have a little refresher on what wine legs are.
When you swirl wine in a glass, you’re left with a thin film of liquid on the sides of the glass. This is caused by the water in the wine evaporating much faster than the alcohol, and the change in surface tension is what sends the wine up the glass. What’s unknown, however, is why that thin film runs down in “legs.”
The study, led by Hangjie Ji of UCLA and published in the scientific journal Physical Review Fluids, was a theoretical analysis conducted by looking at previous studies on gravitational phenomena. All in all, the researchers concluded that the legs — very simply put — are caused by a shock wave that interrupts the ring of wine stuck to the glass.
To elaborate, when the upward flow of the liquid as it’s being swirled meets the downward force of gravity, it creates an unstable shock wave called an undercompressive shock that breaks up the uniform ring of wine causing it to run back down in separate streams.
This very same shock wave is also what’s responsible for the similar way water runs down windows on a car or airplane.
“Wine tears have been studied for over a century and it is remarkable that this is the first time that they have been connected to the instability of an undercompressive shock,” Anette Hosoi of the Massachusetts Institute of Technology told New Scientist. “This study is a beautiful example of such shocks in a familiar setting.”
Well, that was exciting. The more you know!