Egg whites have the amazing ability to hold voluminous amounts of air when whipped. This makes them a key ingredient for leavening baked goods and essential for making meringues. Egg whites (known as the egg's albumen) also help bind ingredients together. And they can clarify cloudy stocks, broths, or coffee when added to the hot liquid by attracting minute particles like a magnet. An egg white contains no fat and is composed of mostly protein, water, and water-soluble vitamins such as riboflavin.
Raw egg whites can be refrigerated in a tightly sealed container for up to 5 days. Or you can freeze egg whites in an ice cube tray, adding 1 egg white (about 2 tablespoons) to each section. When frozen, transfer to a zipper-lock plastic bag. Thaw overnight in a bowl in the refrigerator or in a tightly sealed zipper-lock plastic bag set into a bowl of cool tap water.
Choosing a bowl for beating egg whites
An unlined copper bowl is ideal because it will make the whites stronger so that they can rise for a longer period of time in the oven before they dry out and set. If you don't have a copper bowl, use a glass or metal bowl. Avoid using plastic bowls, which are more porous and tend to retain a greasy film that can prevent egg whites from achieving full volume. Aluminum bowls should also be avoided because they will react with any acid added to the whites and turn them gray.
Preparing equipment for beating egg whites
Make sure that any of the equipment that might come in contact with the egg whites is absolutely grease-free, including the bowl, whisk, beaters, and scraper or spatula. Just a speck of fat can cause the whites to rise to only one-third of their potential volume, because the fat intervenes in the formation of protein bonds in the egg foam. Just to be sure, wipe everything down with a paper towel dampened with lemon juice or vinegar, then rinse and dry thoroughly. If you regularly use a whisk to beat egg whites, store it away from your stove top so that it does not collect grease.
Preparing egg whites for beating
Bring the egg whites to room temperature before beating. Warm eggs have a lower surface tension, allowing bubbles to form more easily. Most recipes call for egg whites to be beaten last, but separate the eggs first, which will give the whites time to reach room temperature as you prepare the rest of the recipe. Or course, you can beat cold egg whites; it just takes longer.
Choosing eggs for beating
Any type of eggs can be beaten, but farm-fresh eggs take longer because they have thicker whites. However, they will have more structural stability. Thin, runny whites (usually found in supermarkets) beat up faster than fresh, thick whites.
Choosing a beater for egg whites
If beating by hand, choose a large, well-rounded balloon whisk with many thin, flexible tines. You can also use a clean, old-fashioned rotary beater. Or use an electric mixer, making sure that the beaters move continuously around the edge of the bowl.
Beating egg whites that won't deflate
Begin by beating slowly. Beating too quickly makes large air cells, which breaks easily. Once an even foam forms, you can beat more vigorously until the egg whites are firm enough to hold the desired shape (soft peaks or stiff peaks). A soon as they do, stop. Over-beaten egg whites can become brittle and deflate rapidly.
To stabilize beaten egg whites
Add an acid, such as cream of tartar, lemon juice, or vinegar. The acid helps bond the protein cells together, so they beat up faster and become more stable and smooth. When beating 6 egg whites, add a pinch of cream of tartar or 1/2 teaspoon lemon juice after the egg whites form a foam, but before they hold a shape.
Keeping beaten egg whites moist and elastic
Add sugar just when the whites reach soft peaks. If added sooner, the sugar may impede foam development. If added later, it may cause the whites to dry out and lose elasticity. To help the sweetener disperse quickly and evenly, use superfine sugar, sometimes called bar sugar, instead of granulated sugar. It also helps to add the sugar gradually, 1 to 2 tablespoons at a time, so that it doesn't decrease the foam volume. To make sure that the sugar has dissolved, rub the egg whites between your fingers. They should feel smooth. If you feel any grit, continue beating.
Folding beaten egg whites into a batter with a spatula
Use the largest rubber spatula you can find, which will cover more area in less time. Folding should be done gently but quickly, using as few strokes as possible to prevent breaking the air bubbles. Lighten the batter first by folding in about one-quarter of the beaten whites. Once they have been incorporated, add the remaining whites and fold in gently. Avoid stirring egg whites, which causes them to deflate. Instead, use a lifting and rolling motion to fold the whites into the batter.
To save time when folding in beaten egg whites
Use the beater used to beat the egg whites rather than a spatula. Because a beater has many more surfaces than a spatula, it will break up the batter more easily, making more spaces into which the egg whites can flow and incorporate.