A group of European scientists have finally found the answer to the age-old question; why does beer come foaming out when the top of your bottle is taped by the bottom of another. The answer it seems is quite complex and involves fluid dynamics and a process called cavitation.
“We wanted to explain the extremely high efficiency of the degasification process that occurs in a beer bottle within the first few seconds after the impact,” Javier Rodriguez-Rodriguez, lead researcher from Carlos III University in Madrid, Spain said.
Rodriquez, along with researchers from the Universite Pierre et Marie Curie, Institut Jean le Rond d’Alembert, France found that cavitation, a phenomena that is of concern to engineers when exploring the reason for propeller breakdown, is the culprit.
When your prankster friend “crashes heads” with you by tapping your bottle with the bottom of his, he sets off expansion waves that causes the bottle to compress and expand. The rapid back and forth movement of the waves cause bubbles to form and quickly collapse. As the larger, mother bubbles breakdown they form tiny clouds of carbonic gas that form daughter bubbles. These smaller bubbles expand at a faster rate than the larger ones and become boyant.
“Buoyancy leads to the formation of plumes full of bubbles, whose shape resembles very much the mushrooms seen after powerful explosions,” Rodriguez-Rodriguez said in a statement. “And here is what really makes the formation of foam so explosive: the larger the bubbles get, the faster they rise…”
What follows is the characteristic gusher of beer.
The scientist’s presentation, entitled “Why does a beer bottle foam up after a sudden impact on its mouth?” was presented on Sunday at the annual meeting of the American Physical Society Division of Fluid Dynamics. The presentation provided findings that will have wider application beyond the tavern. Certain to benefit will be other engineering systems.
In some circles, such as fraternity houses, locker rooms and anywhere there is an abundance of juvenile-minded guys around, crashing heads is an acceptable and hilarious prank to pull on an unsuspecting bottled beer drinker. But, be warned, there can be consequences. Crash heads too hard and you could chip or even shatter the bottle creating a cut hazard. And, for heaven’s sake, if you do find yourself compelled to crash heads with a buddy, be sure he is drinking one of the mass-produced mega lagers rather than a fine craft beer!
- Beer bottle prank is like nuclear blast (thetimes.co.uk)
- Scientists solve the mystery of why tapping a beer bottle foams it up (dailymail.co.uk)