How a bubble is born, rises and bursts

Birth: gas pockets in fibres

A bubble cannot appear on its own in champagne. At the supersaturation found after uncorking, a new bubble would need a radius of about 0.25 µm to survive, and such bubbles do not form spontaneously; a pre-existing pocket of gas is needed.⁴ These pockets sit inside hollow, roughly cylindrical cellulose fibres, about 100 µm long, that fall from the air or are left by the cloth used to wipe the glass.^1,4

CO2 diffuses into the trapped gas, a bubble swells at the mouth of the fibre and detaches at a radius close to that of the fibre, about 10 µm.⁴ In a study described in a physics society magazine, the rhythm three minutes after pouring ranged from less than 1 to almost 30 bubbles per second per site.¹ One fibre can release several tens of thousands of bubbles before the dissolved CO2 drops too low.⁵

Engraved glasses

Some glasses have laser-etched spots at the bottom of the bowl. They act as permanent nucleation sites, and a review calls this artificial effervescence.⁴ In a symposium paper from Reims, a single impact in a tasting glass produced one bubble train that did not mix the wine, while a ring of 50 impacts mixed the whole glass, with liquid speeds up to about 9 cm/s.⁶

Rise and growth

A bubble of about 10 µm starts slowly, at about 50 µm/s.⁵ Dissolved CO2 keeps entering it, so it grows as it rises: the review gives growth rates around 400 µm/s in champagne against about 150 µm/s in beer.⁴ Champagne holds about twice as much dissolved CO2 as beer, so its bubbles end up larger.⁴ Champagne also has only about 5 mg/L of surface-active compounds, against several hundred mg/L in beer, so its bubbles behave more like fluid spheres.²

How many bubbles

A 2017 review estimates that about a million bubbles form and rise in a flute under standard tasting conditions if it is not drunk.³ A separate model links this number to the wine and the glass.⁷

Bursting

The film of a bubble at the surface breaks in 10 to 100 µs, and hundreds of bubbles burst every second in the first minutes.¹ Each burst throws up a small jet that breaks into droplets, suggested to carry more surface-active and possibly aromatic material than the wine below.² According to a review (a preprint), the droplets evaporate above the glass and release their own aroma fingerprint.⁴