Whipping egg whites is much like blowing air into a balloon. Beating causes the protein in the egg whites to unfold, forming a film that traps the air bubbles; and the sugar stiffens the foam. Meringue is really nothing but foam, and foam is a big collection of bubbles. Three- to four-day old eggs yield best results for meringue. Thin older whites whip to a higher volume than fresh eggs but the foam is less stable.
Cold eggs separate more easily than those at room temperature. When separating the yolks from the whites, do not allow even the tiniest bit of yolk to fall into the whites. If it does it will wreck a meringue. Once separated, leave whites to reach room temperature before they are whipped. Egg whites right out of the refrigerator will not whip well. A beaten egg white can foam 6 to 8 times its original volume if the egg whites have been at room temperature for 30 minutes before whipping. Avoid using plastic bowls for whipping the egg whites, as they can often harbor traces of grease or fat. Make sure all utensils are immaculately clean and absolutely dry.
Set your mixer to medium-high speed and begin mixing the egg whites. Add vanilla and cream of tartar, if being used, to egg whites before you begin the whipping. Do not add sugar before whipping the whites. Gradually add the sugar (superfine sugar is great for this), a few spoonfuls at a time and beating the whole time. A general rule is to add ¼ cup of sugar for each egg white. Never use less than 2 tablespoons of sugar per egg white. Meringue is done when you can hold a spoonful of it upside down and none of it drops off.