A popping champagne cork produces freezing jets of carbon dioxide and, unexpectedly, shock waves like the ones released by fighter jets, according to a new study published in Science Advances. The study’s participants comprised six bottles of Vranken Pommery pink champagne.
Before a bottle of champagne has been opened, a mixture of pressurized carbon dioxide and water in gaseous form lie trapped beneath the cork in the bottle’s “headspace”, or neck. When the cork flies off, the gas is released, cooling down and condensing in the process, which forms a jet of dry ice that whooshes out of the bottle faster than the speed of sound.
Meanwhile, the process creates something known as a Mach disk, the kind of shock wave you’d see in the exhaust streams whizzing out of rockets and jets. The Mach disk exits the bottle in the plume of CO2 and water vapor and vanishes in a mere millisecond. The presence of these shock waves shows that the gas bursting from the bottle is moving faster than the speed of sound. They were spotted thanks to high-speed videos of popping corks collected by a team at Equipe Effervescence at the University of Reims Champagne-Ardenne in France.
The speedy jet released by freshly opened champagne is visible as a whitish plume. However, as the researchers note, this plume can also be blue. It all depends on the temperature the bottle has been stored at. The team assessed the outbursts from bottles stored at both 20°C (68°F) and 30°C (86°F) and spotted a difference; the gas in the warmer bottles burst out into a white-gray cloud, while colder bottles emitted a blue hue.
This odd effect is due to differences in pressure. At 30°C, the gas is more pressurized than it is at 20°C, so when released it experiences a bigger drop in pressure, turning into dry ice crystals that reflect visible light. For the cooler gas in the 20°C bottles, the change is less significant, so smaller ice crystals are formed that reflect light at shorter wavelengths, producing a blue color. At 30°C, the gas inside the bottle is 10.2 times that of the air outside; at 20°C, this drops to 7.5 times greater.
The team note that it is safer to uncork a bottle gently with a “subdued sigh” to avoid eye-related incidents, but concede that a dramatic pop is more fun. “Uncorking a bottle with a bang has become a festive and iconic action preceding champagne tasting,” they write.
If you’re wondering what the implications of this research might be, the researchers conclude that using such high-speed camera technology “could be used in a near future to better understand the cork popping process of champagne and sparkling wines.” Essential information for all bubbly connoisseurs and fans of fizz.
"Champagne is one of the most important symbols of France and French glamour," first author Professor Gérard Liger-Belair told IFLScience. "Champagne making is a three centuries-old tradition, but also an ever-evolving know-how which requires constant up-to-date technical knowledge. Our team contributes to this by looking at this emblematic product of France through the angle of science."