LONDON (TIP): Spanish scientists have discovered why beer transforms from liquid to foam when one bottle is bumped against another. Scientists at Universidad Carlos III de Madrid ( UC3M) and colleagues got the idea for the research when they observed that the foam of one beer spilled over when somebody jokingly hit the neck of one bottle against the base of another.

“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 analyse which physical phenomena are behind the appearance of that foam,” said Javier Rodriguez, a professor in UC3M’s department of thermal and fluids engineering. The study explained in detail what happens after a bottle receives an impact.

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. 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.