Foam

A foam is a preparation in which gas, usually air or another gas, is dispersed as bubbles throughout a liquid or semi-solid mixture. In cooking, foams create a light texture and can deliver flavour in a different form. They may be stabilized by proteins, gelatin, starch, fats or emulsifiers such as lecithin.

Common culinary foams

• Milk foam: air is incorporated into milk proteins to create a stable foam for cappuccino and other drinks.
• Sabayon: egg yolks are whisked with sugar and liquid over gentle heat to create a light, aerated preparation.
• Mousse: air is incorporated into a base and stabilized by ingredients such as whipped cream, egg whites or gelatin.
• Espuma: a light foam dispensed from a siphon, often using a flavoured liquid and a suitable stabilizer.
• Lecithin foam: a light, often less persistent foam created by incorporating air into a liquid containing lecithin.

How foams are stabilized

Proteins and emulsifiers can help form films around bubbles, while gelatin and other hydrocolloids can increase viscosity and slow bubble collapse. The correct stabilizer depends on the liquid, temperature, acidity and desired bubble size.

Foam versus mousse

Foam is a broad term for a gas dispersed in a liquid or semi-solid. Mousse is a specific aerated preparation with a defined structure and often a richer or more set texture. Not every foam is a mousse.

Chef’s tip: Use a stabilizer appropriate to the recipe and serve delicate foams promptly. Temperature, fat content and acidity can affect stability and bubble size.

Key distinction: A culinary foam is a gas-in-liquid or gas-in-semi-solid dispersion; it is not simply any light or whipped food.