Germans solve science of sound of swing-top beer bottles opening

By Stephen Beech

The science behind the distinct "pop and slosh" sound when opening a swing-top bottle of beer has been revealed.

German researchers used a high-speed camera to capture exactly what occurs when one of the distinct bottles is opened.

They found that the sound emitted by opening a pressurized bottle with a swing-top lid isn’t a single shockwave, but rather a very quick “ah” sound.

Their high-speed video recordings captured condensation within the bottleneck that vibrated up and down in a standing wave.

The footage, along with high-fidelity audio recordings and computational fluid dynamics simulations, confirmed that the wave is the origin of the “ah” sound.

Dr. Max Koch, a researcher at the University of Göttingen who is also passionate about homebrewing, came up with the idea of using a high-speed camera to capture what happens while opening a swing-top bottle.

When Dr. Robert Mettin, leader of the University's Ultrasound and Cavitation group, suggested that Dr. Koch should submit the findings to the special “kitchen flows” issue of the journal Physics of Fluids, Dr. Koch and his colleagues chose to expand on the home experiment and delve into the acoustics and physics at play.

Dr. Koch said: “The pop’s frequency is much lower than the resonation if you blow on the full bottle like a whistle.

“This is caused by the sudden expansion of the carbon dioxide and air mixture in the bottle, as well as a strong cooling effect to about minus 50 degrees Celsius, which reduces sound speed.

"The decibels it emits are high - inside the bottleneck, it’s as loud, or even louder, than a turbine of an airplane within one meter, but it doesn’t last long.”

After opening the bottle, he explained that the dissolved carbon dioxide starts to form inside the beer and triggers the liquid level to rise.

Dr. Koch says the motion of the bottle also causes the liquid to slosh, and the group’s high-speed recordings captured this wave within the bottleneck.

The researchers also noticed that the momentum transfer of the lid hitting the glass with its sharp edge after popping might also trigger gushing, due to the enhanced formation of bubbles.

Dr. Koch added: “It was a challenge to explain the low frequency of the ‘ah’ sound emitted by the opening and find a simple model to explain the values.

“One thing we didn’t resolve is that our numerical simulations showed an initial strong peak in the acoustic emission before the short ‘ah’ resonance, but this peak was absent in the experimentation.”