Whether you fold the egg white foam into a cake batter or spread over a pie as a meringue ,the way you whip it into a foam is crucial. In a nutshell, put the egg whites into a bowl and whip with an electric or hand beater until a proper foam forms in a few minutes. But with poor whipping technique you achieve poor volume. With even poorer technique, you may have no volume at all. The egg whites may even stubbornly refuse to turn into foam.
To get the maximum foam possible, however, takes more than this simple step. First, start with egg whites at room temperature. Cold egg whites don’t produce maximum volume and neither do very fresh eggs. (Unless you have egg-laying hens, today you don’t have to worry about too-fresh eggs.)
Second, both bowl and beaters must be clean and completely free of fat or oil. Even a minute amount in the egg whites reduces, or may prevent, foam development. And since egg yolk is made up of 31 percent fat, you must be careful that no a trace of yolk sneaks into the whites when separating.
Plastic bowls are not ideal for beating egg whites because they may retain traces of fat or oil no matter how well you clean them. Avoid aluminum, too, which tends to discolor the foam, that leaves stainless steel, glass, ceramic or copper bowl. A copper bowl produces the best, most stable, highest volume foam with a slight yellowish tinge. If you happened to have one, clean it first with a little vinegar and hand beat egg whites in it.
Egg whites quickly turn into foam with ease. Food scientists have explained the complex chemistry of interaction of egg whites and copper, but that is far beyond the interest to most of us.
Hand beating egg whites? Nearly all of us consider this chore as something of the distant past, that our small appliances have eliminated, and good riddance. Yet, any accomplished cook should know the technique of hand beating for those times when you need only one egg white or cup cream whipped. Few machines do a good job on small quantities. With a wire whip and a small bowl you can whip egg white or cream easily in a few minutes.But for now let’s just whip egg whites with a mixer.
You have the egg whites in a clean, oil free bowl at room temperature. What else do you need to know? It helps to start off beating slowly for a minute, then gradually increase the speed to high. Small bubbles are more stable than large bubbles. Starting slowly tends to produce small bubbles, and as you increase the mixer speed to high, small bubbles continue to dominate the foam building it into a more stable foam. Should you turn the mixer to high right away, larger bubbles form early, and the resulting foam will be somewhat less stable.
Sugar also stabilizes the foam, gives it more power to rise and additional structural strength to the baking cake. Slowly add sugar as peaks barely begin to form. If you add the sugar too soon, it interferes with the beating process. If you add it too late, the foam may become too stiff by the time you incorporate and dissolve all the sugar.
Beating intersperses air in the egg whites and that is what foam is, a semi-stable material. Don’t let it stand too long, or the air bubbles pop, the volume decreases. When baking with egg whites, plan on a continuous action from whipping to baking.
How long to beat the egg whites is crucial. If you stop beating them too soon, not only you get less volume, but some of the partially beaten liquid drains away, dragging and collapsing bubbles along. It may even partially liquify the foam. If that happens, start beating again, you can still rescue the egg whites.
Overbeating causes the proteins in the egg whites to coagulate and clump up, also resulting in less volume. You cannot rescue overbeaten egg whites. They have high, dry peaks that are so stiff that they don’t fold easily into the batter. You lose volume and the cake doesn’t rise much.
How can you tell when to stop beating egg whites? As beating, watch for five stages they go through:
1. You reach the first stage when the egg whites begin to hold their shape slightly.
2. At the next stage, you already have soft peaks but they don’t hold well, still fall over.
3. The third stage is the point at which the peaks hold their shape but are still quite soft.
This is the ideal stage for folding into cake batters.
4. The egg whites are stiff but not dry in the fourth stage. This stage is perfect for
meringues
5. In the final phase, the whites are both stiff and dry. This is one step beyond any culinary purpose but great for tossing around at wild parties.
To stabilize the foam you want to have a slightly acid environment. Adding a small amount of cream of tartar at the beginning stage (¼ teaspoon for every 4 eggs) acidifies the egg whites. The cream of tartar also has a bleaching effect, resulting in a whiter cake. A small amount of salt also stabilizes the egg white foam, but it interferes with the flavor.