Using Eggs to Emulsify Sauces

As emulsifiers, egg yolks are most effective when they’re raw, and when they’re warm. Fresh out of the refrigerator, the various yolk particles move only sluggishly and don’t coat the fat droplets as quickly and completely. When yolks are cooked, the proteins unfold and coagulate, thus ending their usefulness as flexible surface coatings. Hard-cooked yolks are sometimes used instead of raw yolks to make emulsified sauces; their disadvantage is that the proteins have been coagulated in place and phospholipids probably trapped in the coagulated particles, so they have far less emulsifying power, and the yolk texture can give a subtle graininess.