What’s with bizarrely moving legumes in Central and South America? Mexico has its jumping beans and Argentina has dancing peanuts. This is the name of a curious phenomenon that happens when you drop peanuts into a pint of lager, something that some people do in the country of Tango (to remain on the topic of dance).

The peanuts dance has no fabulous movement but it is nevertheless striking. When the nuts are dropped into beer, they should sink and stay down – they are after all denser than the liquid that surrounds them. Archimedes' principle teaches us that this is a sure-enough trip to the bottom.

But peanuts have never heard of Archimedes and once they reach the bottom, they rise again like the proverbial phoenix. The proposed solution is all about bubbles. The new work suggests that bubbles form around the peanuts and more importantly stick to their surface.

This makes them buoyant, lifting them up, back to the top of the beer. And what happens there? Once in contact with the foam, the bubbles more easily separate. Without their support, the peanuts are once again dealing with gravity, sinking back down, where the dance will start anew.

The length of the dance depends on the type of beer and peanut. In the research, the team used roasted, shelled, and unbroken peanuts and lager beer, the most common dancing peanuts setup. 

They draw analogies between this work and previous findings about the motion of objects and bubbles in a variety of fluids, some natural like magma (previously also compared to Guinness), and industrial processes. 

This is more than just a bar trick.

The study is published in Royal Society Open Science.