Time in the pub can be useful (Image: Didier Ruef/LUZphoto/eyevine)

Video: Beer physics: How foam affects sloshing

Just a thin layer of foamy head is enough to stop your beer from spilling. That’s according to researchers who were inspired to investigate after spending time in the pub. The findings are more than just a boozy curiosity, they say – the results could help safely transport hazardous fluids.

While carrying drinks from the bar, Alban Sauret at Princeton University and his colleagues noticed that beer rarely sloshed out of a glass, provided it wasn’t full to the brim. The same was true of a latte, as opposed to a regular coffee. To study why, they mixed water with glycerol and surfactants and blew bubbles in the resulting liquid, creating a stable foam. The mix gave them control over the size of the bubbles and the thickness of the foam, allowing them to investigate which aspects prevented sloshing.


It turns out just 0.3 centimetres of foam is enough to dampen much of the sloshing motion, and 3 centimetres stops it almost completely.

“A lot of coffee and beer drinkers have experienced that the presence of foam reduces the sloshing and spilling of their beverage,” says Sauret, who presented the work at the American Physical Society fluid dynamics meeting in San Francisco on 24 November. “Our study has shown that you only need a few layers of bubbles to damp sloshing significantly.”

The study started as pub talk, but may have serious applications. “Sloshing results in large pressure forces on the walls of the container that can damage the structure or disturb the motion of the vessel,” says Sauret. Covering fluids with a layer of liquid foam could solve the problem, he says.