Separating eggs is a process, generally used in cooking, in which the egg yolk is removed from the egg white. This allows one part of the egg to be used without the other part, or each part to be treated in different ways. Recipes for custard call for egg yolks, for example. The most common reason for separating eggs is so the whites can be whipped.
All methods for separating eggs make use of the fact that the yolk can hold itself together while the white is more runny. Since the yolks of older eggs are more watery, which makes separation difficult, it is best to begin with the freshest eggs available.
Although many recipes require eggs to be at room temperature, it is easiest to separate eggs that are cold. Eggs that are at room temperature can be separated, but this requires greater caution to avoid breaking the yolk. One solution is to separate the eggs, cover them, and then allow them to come to room temperature. In this method eggs should not be allowed to sit too long because of the risk of bacteria growth. An alternate solution is to bring the bowl of egg whites (or yolks) up to temperature by placing it in another bowl of hot water.