The flight of the cork

A supersonic jet

Inside a closed bottle at 20 °C the CO2 pressure is about 7.5 bar; at 30 °C about 10.2 bar.¹ For gaseous CO2, a jet becomes supersonic (under-expanded) when the ratio of bottle pressure to room pressure is above 1.83. Both bottles in the 2019 study were far above that.¹

High-speed imaging in Reims captured the result. A Mach disk, a standing shock wave in the jet, appeared about 580 µs after the cork left and vanished about 1 ms after popping. The jet became subsonic after about 750 µs for bottles at 20 °C and about 920 µs at 30 °C.¹ The cork is much slower than the gas behind it, at about 15 m/s.¹

Cold fog and blue haze

The escaping gas expands so fast that it cools sharply: to about -89 °C for a bottle at 20 °C and about -95 °C for one at 30 °C.¹ An earlier study measured the gas in the bottleneck at between about -76 °C (bottle at 6 °C) and -89 °C (bottle at 20 °C).³

This cold creates the grey-white fog seen above the neck. In bottles at 12 °C and 20 °C a blue haze of freezing CO2 also appeared inside the bottleneck, about 0.8 ms after popping at 20 °C. It was never seen in bottles stored at 6 °C.³

Cork speed and temperature

A 2013 study filmed corks with infrared cameras. It cites cork speeds of 10-15 m/s and found that speed rose with the temperature of the wine, across bottles from about 4 to 18 °C.² The volume of gas escaping at popping also grew with temperature.² Only a small share of the released energy, about 5%, went into moving the 10 g cork.²

For scale, 10-15 m/s is about 36-54 km/h.²

Why it matters

Pressure and cork speed both rise with temperature, so a well-chilled bottle opens more calmly. This is the physical basis for the advice on opening a bottle: cool it first, point it away from people and ease the cork out by hand. For the cork and cage themselves, see cork and wire cage.