Scientists explain why peanuts “dance” when put in beer

When peanuts are dropped into a pint of beer, they initially sink to the bottom before floating and “dancing” in the glass.

Scientists dug deep trying to investigate the phenomenon in a new study published Wednesday, saying it has implications for understanding mineral extraction, or magma bubbles in the Earth’s crust.

Brazilian researcher Luiz Pereira, lead author of the study, told AFP that he first had the idea when he passed through the Argentine capital, Buenos Aires, to learn Spanish.

Pereira said it was a “bartender” in town to take a few peanuts and put them in the beer.

Since the peanut is denser than the beer, it sinks first to the bottom of the glass.

Then each peanut becomes what is called a “nucleation site”. Hundreds of tiny bubbles of carbon dioxide form on its surface, acting as buoys to pull it up.

“Bubbles prefer to form on peanuts rather than on glass walls,” explained Pereira, a researcher at Germany’s Ludwig Maximilian University in Munich.

When the bubbles reach the surface, they burst.

The peanuts then sink to the bottom before being pushed back by newly formed bubbles, in a dance that continues until they run out of carbon dioxide—or someone interrupts them with a beer.

In a series of experiments, a team of researchers in Germany, Britain, and France examined how roasted, shelled peanuts are served in lager-style beer.

Next: more beer

The study published in the journal Royal Society for Open Sciencedescribes two key factors in what the researchers dub the “beer, gas and peanut system”.

They found that the greater the “contact angle” between the curve of an individual bubble and the surface of the peanut, the more likely it was to form and grow.

But it can’t grow too much — a radius of less than 1.3 millimeters is ideal, the study says.

Pereira said he hopes that “by digging deep into this simple system, which everyone can understand, we can understand a system” that is useful to industry or to explain natural phenomena.

For example, he said, the flotation process was similar to that used to separate iron from ore.

Air is injected, in a controlled way, into a mixture in which a metal — such as iron — rises because bubbles stick to it more easily, while other (metals) sink to the bottom, he said.

The same process could also explain why volcanologists have found that the mineral magnetite rises to higher layers in the crystallized magma of the Earth’s crust than expected.

Like peanuts, magnetite is denser, so it should sit on the bottom. But due to the high contact angle, the researchers theorize, the metal rises through the magma with the help of gas bubbles.

Of course, the science is never settled—especially when it comes to beer.

In hopes of creating a better model for the dancing peanut phenomenon, Pereira said scientists will continue to “play with the characteristics of different peanuts and different beers.”