Why beer overflows when a one bottle is bumped against another

images (4)Scientists at Universidad Carlos III de Madrid (UC3M) reveal the physical phenomenon that explains beer’s rapid transformation from a liquid to a foamy state as the result of an impact. This research has applications in the area of naval engineering or in studies related to the prediction of gases in volcanic eruptions.

The idea for this research came about at the bar of a tavern when it was observed that the foam of one beer spilled over when somebody jokingly hit the neck of one bottle against the base of another, the researchers confess.

“We all began to propose hypotheses and theories about the cause of the phenomenon, but none of them convinced us, so we decided to take it to the laboratory to do research using controlled experiments in well-defined conditions to analyze which physical phenomena are behind the appearance of that foam,” comments Javier Rodríguez, a professor in UC3M’s Department of Thermal and Fluids Engineering, who has presented a preliminary report on the study’s results at the American Physics Society’s most recent annual conference on fluid mechanics, the most prestigious conference on  in the world.

This study, carried out in collaboration with the Institute Jean le Rond D’Alembert and the Université Pierre et Marie Curie, in France, explains in detail what happens after a bottle receives an impact. It is a process with three well-defined phases. First, expansion and compression waves appear. These advance inside the liquid and cause the gas cavities (bubbles) to burst at the bottom of the bottle. Afterwards, small balls of foam are formed because the bubbles break into even smaller ones. Finally, given that they weigh less than the liquid surrounding them, these bubbles move to the surface so rapidly that the final result is similar to an explosion. “In fact,” comments Rodríguez, “those clouds of foam are very much like the mushroom cloud caused by a nuclear explosion.” In one second, almost all of the beer shoots out of the bottle.

The foam appears because, in carbonated beverages, there is more carbon dioxide (CO2) than the water (the main component) is able to maintain in the solution. “Usually, the CO2 escapes very slowly. But the chain of events set off by the blow to the bottle multiplies the escape of gas by a very high factor: a bottle may lose in seconds the same amount of gas that it would normally lose in hours if we simply left the bottle open on the table,” explains Javier Rodríguez.
Read more at: http://phys.org/news/2014-01-scientific-explanation-beer-bottle.html#jCp