Foam and collar

Foam and collar

When champagne is poured it forms a head of foam that collapses within seconds. What remains is the collar (collerette): the ring of bubbles that gathers against the wall of the glass.³ Both depend on molecules that sit at the boundary between wine and gas and slow down the draining of the thin films around each bubble.

What makes the foam

Champagne holds only about 5 mg/L of surface-active compounds, mostly proteins and glycoproteins. Beer holds several hundred mg/L.¹ This is the main reason a champagne head is short-lived and a beer head is not. It also changes how bubbles rise: see how a bubble is born.

A 1991 study of champagne base wines looked for the compounds that drive foam. Proteins, polysaccharides and iron were important contributors. Organic acids, total acidity, total nitrogen, calcium, potassium, magnesium and sodium had no significant effect. Proteins came out preferentially in the first fractions of foam.²

The collar is held by an adsorbed layer at the wine surface. A preprint that isolated these molecules reports, citing earlier work, that the layer is made of macromolecules with molecular weights in the 10^4 to 10^5 range.⁵ This result has not been peer reviewed.

With so few of these molecules, champagne bubbles behave closer to fluid spheres, while beer bubbles behave closer to rigid ones.¹

The glass matters

Foam and collar also depend on the glass. Most bubbles start in cellulose fibres left by the drying cloth or fallen from the air.^6,1 A glass without such fibres produces fewer bubbles.

The Comité Champagne advises washing glasses in hot water without detergent, then letting them air-dry or drying them with a cotton cloth, to avoid problems with bubble formation.^3,4

No peer-reviewed study on detergent residue in glasses was found for this page. The washing advice above is the Comité Champagne's recommendation, not a measured result.

Foam is also linked to the pour: a vertical pour into a flute, which builds a tall head, lost more CO2 than a pour down the side of a tilted glass.⁷

More on glass choice: glasses. On how foam forms at the pour: pouring and CO2 loss.