The story of a bubble
Psss!
Before the bottle is opened, there are around 12 grams of carbon gas per litre of champagne. When the bottle is opened, the carbon gas pressure falls sharply: there is only 0.035% volume in the air. The champagne therefore has to establish a new pressure balance where the carbon gas is only present in trace condition in the champagne.
Releasing the carbon gas
The liquid must release the 12 grams of carbon gas it contains. A 10 centilitre flute therefore contains 0.7 litres of CO2. So, for bubbles with an average diameter of 0.5 millimetres we get around 11 million bubbles! However, most of the carbon gas (80%) does not escape as bubbles, but directly to the surface of the glass.
Little bubbles rise to become big bubbles
Bubbles that are tiny to begin with swell as they rise to the surface. During this journey, the bubbles are filled with carbon gas until their volume is multiplied by a factor of one million within 10 cm. Bubbles in beer are a third of the size as their CO2 concentration is half that
It all happens in less than 3 milliseconds
A bubble bursts in several stages. When the bubble reaches the surface, it forms a liquid film that gives way under the Archimedes principle. For a short period it remains a "hole" that corresponds to the submerged part of the bubble which, when it closes, projects a thin sliver of liquid to the top: the champagne slops into this hold from the edges of the cavity to the centre. The surface becomes completely flat in less than 3 milliseconds.
Bubbles carry aromatic compounds
Bubbles provide mini-escalators for aromatic molecules. When the bubbles burst they are suspended above the glass in a cloud of very fine drops full of aroma. This is what magnifies their taste. Thanks to convection movements, the surface of the champagne is constantly renewed as aromatic molecules and odour carrying volatile compounds.
A layered structure
Just after the champagne is poured, we see a short phase where the bubbles that are forming and the bubbles that are bursting form a sort of “raft” on the surface. Each bubble is generally surrounded by six of these. When a bubble bursts, it leaves an open space where the adjacent bubbles are literally sucked in. Unfortunately these "bubble flowers" are too transient to be visible to the naked eye.
The bubbles shrink
Thanks to the tensioactive molecules that solidify the bubbles, these will not all burst on the surface. The carbon gas can escape through the thin liquid film that covers their submerged part. They "shrink" and remain on the surface for a few seconds. If we can avoid shaking the glass, they organise themselves in spirals like galaxies due to the circular form of the flute that obliges them to exist within the limits of its walls.
Extract from Effervescence ! La science du champagne - Gerard Liger-Belair, Odile Jacob Text and photos © Gérard Liger-Belair
