On the popping sound and liquid sloshing when opening a beer bottle

The opening of transparent 0.33 l swing-top bottles, containing home-brewed ginger beer under 2–5 bars of pressure, was recorded with a high-speed camera at frame rates between 3000 fps and 16 800 fps. Simultaneously, the sound was registered with a microphone of a nominal frequency range up to 100 kHz and a sampling rate between 200 and 500 kS/s. The exhaust condensation cloud could be captured, and the main source of the popping sound, the resonating gas pocket in the bottleneck, was identified by image and sound recordings. It is shown that the sound is actually tonal rather than shock-like. Since the bottles were transparent, the interior fluid flows with sloshing and bubble nucleation were visible as well. The videos, acoustic traces, and spectra are compared to computational fluid dynamics simulations using a solver for two-phase, compressible flow from the OpenFOAM package, yielding detailed explanations on the phenomena involved. Simple resonator models can fairly reproduce the observed frequencies if adiabatic expansion cooling of the gas is taken into account.