By Harold McGee
A gentle simmer is usually preferred to a rolling boil so as to avoid breaking up delicate morsels. A partial exception to this rule is the bouillabaisse of southern France, whose name includes the idea of boiling, and whose unique character depends on the vigorous agitation that boiling provides. A bouillabaisse starts with a stock made from scraps and small bony fish to provide gelatin and flavor, tomatoes and aromatics for flavor and color, and a large dollop of olive oil—perhaps a third of a cup/75 ml per quart/liter of liquid—which a fierce 10-minute boil emulsifies into fine droplets throughout the soup. The dissolved fish gelatin and suspended proteins coat the oil droplets and slow their coalescence. The other pieces of fish are added last and simmered to cook through, and the soup is served immediately, before the oil has a chance to separate.