The reason peanuts 'dance' in beer (we know you want to know)
Beer and peanuts have been a match made in heaven for so long it’s hard to pinpoint just when the holy union came about. It was made commercially official in the US in 1937, with the rather ingenious branding of Beer Nuts, and for almost as long scientists have enjoyed conducting human trials in an effort to explain this cherished coupling.
The latest study examines the peanut’s temporary ability to defy physics – specifically, Archimedes principle of buoyancy – when dropped in a glass of beer. Because the density of a peanut is greater than the beer, it should sink and stay down, but instead it rises back up, then sinks, and rises again, performing a bubble-fueled ‘dance’ until it runs out of gas.
Why drop peanuts (Arachis hypogaea) in beer? That’s also a good question. But it was something Brazilian researcher Luiz Pereira observed being demonstrated in bars in Argentina, and his study into the science behind it may help us understand other ways the laws of density are skewed in nature.
When a peanut is dropped into a beer, it’ll sink towards the bottom of the glass. But quickly, tiny carbon dioxide bubbles cover the surface of the nut and act like floatation devices, dragging the nut up before bursting as it hits the surface.
As the nut sinks, Pereira noted that it becomes a nucleation site. Beer vessels can also create nucleation sites to encourage the gathering of carbon dioxide bubbles to amass and rise through the liquid, sustaining carbonation.
The peanut dance isn’t complete, at this point, as it rolls around at the surface, popping all attached bubbles. It sinks again, then gathers new bubbles and repeats. And the longevity and intensity depends on the contact angle interaction between the bubble of gas and the peanut, and will eventually stop when the carbon dioxide runs out (or, more likely, you grow tired of watching a nut bobbing around in liquid and drink the beer instead).
Through a series of experiments with roasted peanuts dropped in lager-style beers, conducted by researchers in Germany, Britain and France, the team dubbed the ‘dance’ the “beer-gas-peanut” system and say it can be used to understand similar phenomena in nature and industry.
For example, they suggest, it could help explain why dense magnetite rises to higher layers under the Earth’s surface, despite being surrounded by crystallized magma, and a similar contact angle could be at play.
The researchers hope to broaden the study to examine the phenomenon in other types of vessels and beer brews, in the process proving that science data gathering isn’t always tedious work.
“This study has heritage and that the observation of bubble dynamics in beer is a rich topic, worth repeated investigation,” they noted.
The study was published in the journal Royal Society Open Science.