Why Champagne Produces a Powerful Shock Wave When Uncapped

In recent years, there have been dizzying advances in rapid imaging, especially with the advent of digital sensors and the miniaturization of electronic circuits. Today there are ultra-fast cameras capable of detecting phenomena of extreme transience. We used this type of camera to study in detail the mechanisms involved in opening a bottle of champagne.

Opening a bottle of champagne stored at 20°C with an ultra-fast camera © Gerard Liger-Béler / The Conversation

During the second fermentation (the so-called mousse prize), champagnes emit carbon dioxide (CO2) – the equivalent of almost 5 liters per 750 ml bottle – which remains under pressure in the closed bottle. The pressure that prevails in a still stoppered bottle depends strongly on its temperature. So, at 20°C, the pressure reaches almost 8 bar, which is equivalent to 8 times atmospheric pressure, that is, the pressure that prevails at a depth of 70 m under water! The video in the image above illustrates the phenomena that occur after the cork pops out of the bottle under an initial pressure of 8 bar.

When the cork bursts, the volume of carbon dioxide under pressure in the neck of the bottle increases dramatically. Then its pressure is increased from 8 bar to atmospheric pressure of 1 bar. This is accompanied by a drop in its temperature: physicists talk about adiabatic expansion. However, depending on temperature and pressure, a pure substance can exist in three phases: gaseous, liquid and solid. So, under a pressure of 1 bar, water at 20 ° C is in a liquid state, below 0 ° C it turns into ice, and at 100 ° C it boils, turning into steam. But what about CO2? At a pressure of 1 bar, CO2 remains in a gaseous state at temperatures above -78.5°C; below this critical temperature, it exists in solid form: dry ice.

When opening a bottle at room temperature, be careful with pressure! © Team Effervescence / CNRS / University of Reims

When cleaning dry ice and shock waves

For this bottle, at an initial pressure of 8 bar, the temperature of the suddenly expanding carbon dioxide drops to almost -90°C. The CO2 vapor then turns into tiny dry ice crystals that can scatter ambient light. The azure blue plume is a sign of the very small size of these crystals. Indeed, particles or molecules that are smaller than the wavelength of the ambient light spectrum (centered at about 0.6 µm) scatter the small wavelengths of the spectrum (in particular blue) much more efficiently than long wavelengths (eg red). ): this is called Rayleigh scattering. This is the same phenomenon that explains why the sky appears blue to us: the molecules that make up our planet’s atmosphere are much smaller than the wavelength of sunlight, so the blue color scatters much more efficiently than other colors in the spectrum.

Did you notice a small horizontal line crossing the blue plume? This is the characteristic shock wave of supersonic jets known as Mach disks. It appears about 500 µs after unlocking, progresses after blocking, and then disappears after about 500 µs. We find similar shock waves in the supersonic plume blown out by the nozzles of the reactors of a fighter or rocket. Thus, for the very first millisecond after the cork is popped, the neck of the champagne bottle behaves like the nozzle of a rocket reactor. Who would have believed it!

This analysis was written by Gérard Liger-Béler, Professor of Physics in the Laboratory of Oenology at the University of Reims Champagne-Ardenne (URCA).
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