kinds of water-based liquids and semisolids that contain dissolved or suspended or structure-stabilizing molecules of some kind The Catalan chef Ferran Adrià pioneered this development, with foams of — among other ingredients — cod, shellfish, foie gras, asparagus, potatoes, raspberries, and cheese Cooking broths and their reductions, proteinand starch-thickened sauces, juices, purees, and emulsified sauces can all be lightened by incorporating bubbles into them And it’s a quick last-minute preparation: just agitate some of the liquid until it froths, then scoop off the bubble-rich portion, add it to the food, and serve Making and Stabilizing Foams There are several different ways of getting bubbles into a liquid and stabilizing them Whipping with a whisk or hand-heldblender introduces air by agitating the liquid surface; the foaming wands on espresso machines shoot steam, a mixture of water vapor and air; and foaming devices for whipped cream and seltzer water mix a stream of pressurized carbon dioxide or nitrous oxide with the liquid Any dissolved or suspended molecules in the liquid collect at the interface of the air and liquid and give the bubble wall some solid reinforcement However, the reinforcement will be momentary and the bubbles short-lived unless the molecules can form a stable layer at the interface This is exactly what emulsifiers like lecithin and proteins do, and for the same reason that they stabilize oil droplets in emulsions: they have a water-soluble portion that rests in the bubble wall, and a waterinsoluble portion that rests in the air Because the bubbles in a typical foam are between 0.1 and 1 millimeter across, much larger than most emulsion droplets, they require very little emulsifier to cover their surface area, .. .the foaming wands on espresso machines shoot steam, a mixture of water vapor and air; and foaming devices for whipped cream and seltzer water mix a stream of pressurized carbon dioxide or nitrous oxide with the. .. carbon dioxide or nitrous oxide with the liquid Any dissolved or suspended molecules in the liquid collect at the interface of the air and liquid and give the bubble wall some solid reinforcement However, the reinforcement will be... momentary and the bubbles short-lived unless the molecules can form a stable layer at the interface This is exactly what emulsifiers like lecithin and proteins do, and for the same reason that they stabilize oil droplets in