On Food and Cooking

salsa verde, “green sauce,” emulsify olive
oil with a hard-boiled yolk and bread. The
Provençal aïoli and Greek skorthaliá are
emulsified with a combination of pounded
garlic and cooked potato; garlic and bread
are also used, as are fresh cheeses. None of
these ingredients is as effective at
emulsifying and stabilizing as a raw egg
yolk, so they will emulsify less oil and the
sauces will tend to leak some free oil.
Holding and Salvaging Hot Egg Sauces
Butter sauces need to be kept warm to prevent
the butter from solidifying, and are best held
at around 145ºF/63ºC to discourage the growth
of bacteria. Because the egg proteins slowly
continue to bond to each other at this
temperature, the cook should stir the sauce
occasionally to keep it from thickening. The
container should be covered to prevent the
sauce’s moisture from evaporating and
overcrowding the fat droplets, and to prevent
the formation of a protein skin on the surface.