Leftover egg whites can be stored in a tightly sealed container in the refrigerator for 7-10 days or frozen for a month. A good way to freeze egg whites is to place them in individual plastic ice cube trays. Once frozen, transfer the whites to a plastic freezer bag. To thaw, simply place in refrigerator overnight. After freezing, the whites tend to be watery and are best used in recipes where the whites are not the sole leavening agent.
Eggs contain a yolk and a white.
The egg yolk is rich in fat and a source of vitamin and minerals. A fresh egg yolk will be rich in color and will stand upright with little spread. Blood spots are not harmful and will disappear with age. Egg yolks add tenderness and color to baked goods. Some recipes call for beating egg yolks and sugar until thick, light, and forms a ribbon.