Scientists Reveal What’s Behind the “Pop and Slosh” When Opening a Swing-Top Beer

Researchers analyze the acoustics and physics behind the sloshing and popping sounds that occur when opening a swing-top beer bottle.

In a fun experiment, Max Koch, a researcher at the University of Göttingen in Germany, and an avid homebrewer, used a high-speed camera to capture what happens when opening a swing-top bottle of homebrew.

When Robert Mettin, head of the Ultrasound and Cavitation Group at the university’s Third Institute of Physics, Biophysics, suggested submitting the findings to the special “kitchen flows” issue of Physics of Fluids from AIP Publishing, Koch and his colleagues decided to expand on the home experiment and explore the novel acoustics and physics involved.

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

The Physics Behind the Pop

“The pop’s frequency is much lower than the resonation if you blow on the full bottle like a whistle,” said Koch. “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 1 meter, but it doesn’t last long.”

After opening the bottle, the dissolved carbon dioxide starts to form inside the beer and triggers the liquid level to rise. The motion of the bottle also causes the liquid to slosh, and the group’s high-speed recordings captured this wave within the bottleneck.

Additionally, they 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.

“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,” Koch said. “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.”

Simulations aside, Koch joked that another great challenge was drinking the homebrewed beverages and still maintaining clarity during the experiment.

Reference: “On the popping sound and liquid sloshing when opening a beer bottle” by M. Koch, M. Tervo, R. Manso Sainz, C. Lechner and R. Mettin, 18 March 2025, Physics of Fluids.
DOI: 10.1063/5.0248739

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