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TASTINGS Egg white foam chemistry
Four different types of proteins in egg whites interact to produce the cake structure.
Two (globulins and ovomucin) give stability owing to their viscosities to the still
liquid foam, the third (conalbumin) helps to stabilize it temporarily at room
temperature, and the fourth (ovalbumin) gives it a permanent stability after you heat
the structure in the oven. Once the foam with the other ingredients are in the hot
oven, the trapped air expands as a result of heating, and the cake rises.
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 ¼
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
2
3
. You reach the first stage when the egg whites begin to hold their shape slightly.
. At the next stage, you already have soft peaks but they don't hold well, still fall over.
. 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
5
. The egg whites are stiff but not dry in the fourth stage. This stage is perfect for
meringues.
. 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
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