An egg foam begins with the eggs. Old eggs at room temperature are often recommended on the grounds that the whites are thinner and therefore foam more rapidly. This is true, and very fresh eggs are said to be almost impossible to foam by hand. But fresh eggs are less alkaline and so make a more stable foam; the older thin white also drains from the foam more easily, and old eggs are more likely to leave traces of yolk in the white. Cold yolks are less likely to break as you separate them from the whites, and the whipping process quickly warms cold eggs anyway. Fresh eggs right out of the refrigerator will work fine, especially if you’re using an electric mixer. Egg foams can also be made with dried egg whites. Powdered egg whites are pure, pasteurized, freeze-dried egg whites. “Meringue powder” contains more sugar than egg, and includes gums to stabilize the foam.