other plant tissues. Milk, cream, and egg
yolks are natural emulsions, while sauce
emulsions include mayonnaise, hollandaise
sauce, beurre blanc, and oil-and-vinegar salad
dressings. Modern chefs have applied the
basic idea to the thickening of all kinds of
liquids, and often actually describe the result
on the menu as an emulsion, a word that
lingers on the tongue longer than sauce does.
Emulsified sauces offer a special challenge
to the cook: unlike sauces thickened with
solids, emulsions are basically unstable.
Whisk oil and a little vinegar together in a
bowl, and the vinegar forms droplets in the
oil: but they soon sink and coalesce, and in a
few minutes the two liquids have separated
again. Cooks not only have to form the
emulsion, they also have to prevent the
emulsion from being undone by the basic
incompatibility of the two liquids.
The Nature of Emulsions