On food and cooking the science and lore of the kitchen ( PDFDrive ) 1210

typically just 0.1% of the liquid weight (1 gram per quart or liter) Stabilizing Foams A liquid that is even modestly supplied with proteins or yolk phospholipids will form an impressive mass of bubbles, solid enough to stand up without flowing or even slumping However, the foam may still collapse within a minute or two Air and water have very different densities, so when the foam is left to stand on its own, the air bubbles rise while gravity pulls the liquid in their walls in the opposite direction This means that liquid drains from the bubble walls, which also lose water to evaporation Eventually, the foam at the surface becomes dry, around 95% air and just 5% liquid, the bubble walls become too thin, fail, and the bubbles pop This instability of the foam as a whole can be prevented by the same materials that stabilize the emulsified sauces: namely materials that interfere with the free movement of water molecules, and thereby slow the drainage and thinning of the bubble walls Foam stabilizers include the microscopic particles in purees, proteins, thickening carbohydrates like starch, pectin, and gums — and even emulsified fat Free fat or oil is a foam killer, because the fat spreads at the interface with the air — it’s chemically more compatible with air than with water — and prevents emulsifiers from settling at the interface and stabilizing it However, if the fat is emulsified — for example in an egg yolk or yolk-based sauce — then it remains dispersed in the water phase, and its droplets only interfere with the flow of liquid from the bubble walls Heat-Stabilized Foams: Sabayons Both the method and the name of the French sabayon derive from the Italian zabaglione, a sweet, winy foam of egg yolks (p 113) Though rich ... interfere with the flow of liquid from the bubble walls Heat-Stabilized Foams: Sabayons Both the method and the name of the French sabayon derive from the Italian zabaglione, a sweet, winy foam of egg yolks (p...materials that interfere with the free movement of water molecules, and thereby slow the drainage and thinning of the bubble walls Foam stabilizers include the microscopic particles in purees, proteins,... and prevents emulsifiers from settling at the interface and stabilizing it However, if the fat is emulsified — for example in an egg yolk or yolk-based sauce — then it remains dispersed in the water phase, and its droplets only