Hard and soft on the heels of the announcement about beer foam’s anti-spillage property comes other news about beer foam research:
“Physics of Beer Tapping,” Javier Rodríguez-Rodríguez, Almudena Casado-Chacón, and Daniel Fuster, Physical Review Letters, 113, 214501, 20 November 2014. The authors report:
“The popular bar prank known in colloquial English as beer tapping consists in hitting the top of a beer bottle with a solid object, usually another bottle, to trigger the foaming over of the former within a few seconds. Despite the trick being known for a long time, to the best of our knowledge, the phenomenon still lacks scientific explanation. Although it seems natural to think that shock-induced cavitation enhances the diffusion of CO2 from the supersaturated bulk liquid into the bubbles by breaking them up, the subtle mechanism by which this happens remains unknown. Here, we show that the overall foaming-over process can be divided into three stages where different physical phenomena take place in different time scales: namely, the bubble-collapse (or cavitation) stage, the diffusion-driven stage, and the buoyancy-driven stage…. The physics behind this explosive process sheds insight into the dynamics of geological phenomena such as limnic eruptions.”
(Thanks to investigator Andrew Garner for bringing this to our attention.)
Lauren Davis wrote about this, earlier in the year, in Io9: “Why does beer overflow when you tap one bottle on top of another?“
Olivia Castellini made a video in which she demonstrates and explains the phenomenon: