Cook until knife inserted near center comes out clean: Baked custard mixtures are done when a metal knife inserted off-center comes out clean. The very center still may not be quite done, but the heat retained in the mixture will continue to cook it after removal from the oven. Cooking longer may result in a curdled and/or "weeping" custard. Cooking a shorter period may result in a thickened but not set custard.
Cook until just coats a metal spoon: For stirred custard mixtures, the eggs are cooked to the proper doneness when a thin film adheres to a metal spoon dipped into the custard. This coating point is 20 to 30 degrees below boiling. Stirred custards should not boil. The finished product should be soft and thickened but not set. They will thicken slightly after refrigeration.
Slightly beaten: Use a fork or whisk to beat eggs just until the yolks and whites are blended.
Well beaten: Use a mixer, blender, beater or whisk to beat eggs until they are light, frothy and evenly colored.
Thick and lemon-colored: Beat yolks at high speed with an electric mixer until they become a pastel yellow and form ribbons when the beater is lifted or they are dropped from a spoon, about 3 to 5 minutes. Although yolks can't incorporate as much air as whites, this beating does create a foam and is important to airy concoctions such as sponge cakes.
Add a small amount of hot mixture to eggs/egg yolks: When eggs or egg yolks are added to a hot mixture all at once, they may begin to coagulate too rapidly and form lumps. So, stir a small amount of the hot mixture into the yolks to warm them and then stir the warmed egg yolk mixture into the remaining hot mixture. This is called tempering.
Room temperature: Some recipes call for eggs to be room temperature before eggs are to be combined with a fat and sugar. Cold eggs could harden the fat in such a recipe and the batter might become curdled. Remove eggs from the refrigerator about 30 minutes before using them or put them in a bowl of warm water while assembling other ingredients. However, for all other recipes that don't specify "room temperature," use eggs straight from the refrigerator.
Separate: The fat in egg yolks keeps the egg whites from foaming, so the yolks are often separated from the whites and the whites beaten separately so they can reach their fullest possible volume. Eggs are easiest to separate when cold, but whites reach their fullest volume if allowed to stand at room temperature for about 30 minutes before beating.
To use an egg separator, tap the midpoint of the egg sharply against a hard surface. Holding the egg over the bowl in which you want the whites, pull the halves apart gently. Let the yolk nestle into the cuplike center of the separator and the white will drop through the slots into the bowl beneath. Drop one egg white at a time into a cup or small bowl and then transfer it to the mixing bowl before separating another egg. This avoids the possibility of yolk getting into several whites.
Add cream of tartar: Egg whites beat to greater volume than most other foods including whipping cream, but the air beaten into them can be lost quite easily. A stabilizing agent such as cream of tartar is added to the whites to make the foam more stable. Lemon juice works much the same way.
Add sugar, 1 to 2 tablespoons at a time: When making meringues and some cakes, sugar is slowly added to beaten egg whites. This serves to increase the stability of the foam. Sugar, however, can retard the foaming of the whites and must be added slowly so as not to decrease the volume. Beat the whites until foamy, then slowly beat in the sugar.
Stiff but not dry (or until stiff peaks form): Beat whites with a mixer, beater or whisk just until they no longer slip when the bowl is tilted. If underbeaten, the finished product may be heavier and less puffy than desired. If overbeaten, they may form clumps which are difficult to blend into other foods in the mixture and the finished product may lack volume.
Soft peaks or piles softly: Whites that have been beaten until high in volume but not beaten to the stiff peak stage. When beater is lifted, peaks will form and curl over slightly.
Gently fold: When combining beaten egg whites with other heavier mixtures, handle carefully so that the air beaten into the whites is not lost. Then gradually combine the ingredients with a downward stroke into the bowl, across, up and over the mixture motion, using a spoon or rubber spatula. Fold just until there are no streaks remaining in the mixture. Don't stir because this will force air out of the egg whites.
Curdling: Also known as syneresis or weeping. When egg mixtures such as custards or sauces are cooked too rapidly, the protein becomes overregulated and separates from the liquid leaving a mixture resembling fine curds and whey. If curdling has not progressed too far, it may sometimes be reversed by removing the mixture from the heat and stirring or beating vigorously.To prevent curdling, use a low temperature and cool quickly by setting the pan in a bowl of ice or cold water and stirring for a few minutes.
Source: American Egg Board