There is seldom time to write about all the interesting science stories that come our way. So this year we are releasing a special series of Twelve Days of Christmas publications again this year, highlighting a scientific story that fell through in 2020, every day from December 25 to January 5. Today: researchers have discovered the specific physical mechanism that links the characteristic crackle of champagne to the bursting of its small bubbles.
There is nothing quite like the distinctive crackle and sparkle of a glass of freshly served champagne. It is well established that bursting bubbles produce this sound, but the specific physical mechanism is not entirely clear. For example, physicists at the Sorbonne University in Paris, France, decided to study the link between the fluid dynamics of bursting bubbles and sparkling, crackling sounds. They described their work in a published article in January in the journal Physical Review Fluids.
As we previously reported, the first mention of a sparkling wine dates back to 1535 in the Languedoc region of France. The classic brand Dom Perignon takes its name from a 17e-th century monk who had the task of getting rid of the bubbles that developed in the bottled wine of his abbey, lest the pressure build up so much that they explode. The legend has it that while sipping such sparkling wine, the monk realized that bubbles might not be such a bad thing after all, declaring: “Come quickly, brethren, I drink stars!” “
In the 18th century, British chemist Joseph Priestley invented an artificial carbonation process while living next to a brewery in Leeds. Still the scientist, he started experimenting with CO2 used by the brewery and found that a bowl of water placed over a fermenting liquor became slightly acidic to taste, just like natural mineral waters. He included his simple instructions for artificial carbonation in a 1772 treatise, Water impregnation with fixed air.
Carbonation is a particularly fascinating subject in the sub-field of fluid dynamics. For example, a article 2018 in Physics Today reported that carbonation triggers the same pain receptors in our deep brains that are activated when we eat spicy foods. Other fun facts from champagne science over the years: when champagne bubbles burst, they produce droplets that release aromatic compounds that are supposed to further enhance the flavor.
In addition, the size of the bubbles plays an essential role in a very good glass of champagne. Larger bubbles improve the release of aerosols into the air above the glass – bubbles in the order of 1.7 mm in diameter at the surface. And the champagne bubbles “ringing” at specific resonant frequencies, depending on their size. Thus, it is possible to “hear” the particle size distribution of the bubbles when they rise to the surface of a glass of champagne.
The latter is the only study to date specifically examining the acoustic emissions (crackling and sparkling) of champagne specifically, according to the authors of this latest article. But there were two earlier studies in 1992 and 2013 focusing on the acoustic emission of bubbles collapsing on the water surface more generally, revealing that smaller bubbles emit more chirping sounds.
The effervescence of champagne arises from the nucleation of bubbles on the walls of the glass. Once they break away from their nucleation sites, the bubbles begin to grow as they rise to the surface of the liquid, bursting and collapsing on the surface. This usually happens within a few milliseconds and the distinctive crackling sound is emitted as the bubbles rupture.
French physicists used a glass tank containing tap water and a tank containing a water / surfactant solution for their experiments, as champagne also contains a small volume of surfactant molecules. They injected air bubbles into the reservoirs using submerged needles connected to an air-filled syringe pump. The bubbles would rise to the surface and float briefly before bursting. All of this was captured on video with two high-speed digital cameras, while the acoustic emissions (sounds) were recorded by a microphone placed just above the surface of the liquid. Finally, they filtered the acoustic data to eliminate any ambient noise.
As Katherine Wright written to APS Physics:
Analyzing the data, Pierre and his colleagues find, as expected, that the production of sound coincides with the bursting of the bubble. As the bubble gets closer to the surface, the pressure of the gas inside increases. This pressure is released violently when the bubble bursts.
The bubble, however, does not immediately disappear. The part of the bubble still submerged generates acoustic vibrations of the liquid-gas interface. The frequency of this vibration depends on the volume of gas in the bubble and the diameter of the bubble hole. As a result, the frequency changes as the rupture grows and the bubble narrows, increasing in height until the bubble dies. For small micrometric champagne bubbles, only the onset of rupture is audible to humans, while for larger millimeter bubbles, the entire burst is audible.
This process is markedly different from the way bubbles below the surface emit sound, and the team believes that the search for acoustic signatures could shed light on other hydrodynamic phenomena that elude conventional imaging techniques. “We believe this [our] a quantitative description could be used to synthesize artificial acoustic signals from digital animated films, ”the authors wrote. “More generally, this work is a step in understanding the acoustic signature of violent hydrodynamic events, which adds to previous studies on volcanic eruptions … breaking waves and bursting soap bubbles.”
DOI: Physical Examination Fluids, 2021. 10.1103 / PhysRevFluids.6.013604 (About DOIs).
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