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Why do egg whites act so weird?

Light, puffy whipped egg whites are an important ingredient in many dishes--and essential for souffles, tender meringue--topped pies, and crisp meringue shells. How egg whites are whipped affects the volume and texture of these foods; the secret is all in the air bubbles.

When egg whites are beaten briskly with a whisk, a rotary beater, or even a fork, the whites stretch and trap air as bubbles. The smaller and more even-size the bubbles, the more stable (long-lasting) the foam. Large bubbles are inclined to break faster. The tools you use and what you add to whites give you considerable control over the size and strength of the bubbles.

A large whisk with many fine wires (or a balloon beater in a mixer) moved at high speed does the best job of introducing air into whites for even-size bubbles. Acid and sugar also affect bubble size and strength (see "What makes egg white foam stronger?" following). Whites foam best when whipped at a cool room temperature (high 60s to low 70s). Whites from the refrigerator warm quickly from incorporated air.

Why does the foam sometimes not achieve maximum volume?

Optimally, whites increase at least nine times in volume when whipped and hold short, distinct peaks. Underbeaten whites haven't firmed enough to hold bubbles. Overbeaten whites are stretched so much that they pop easily; you will see cottony bits of solidified (coagulated) white.

What makes egg white foam stronger?

Plain whipped whites make a fragile, short-lived foam; on standing, their own weight causes bubbles to burst, and the whites become liquid (and won't whip up again).

If cream of tartar (or similar acid) is added to whites as they are whipped, the egg white proteins become stronger: acid coagulates, or stiffens, them slightly. You can add cream of tartar to any recipe that uses plain whipped whites, such as a souffle, but it's still important to incorporate whites and cook the mixture right away. You need 1/8 teaspoon cream of tartar for each 2 tablespoons (1 large) egg white.

Sugar also strengthens egg white protein, keeps bubbles small, and keeps the foam pliable. In recipes that call for sweetened whipped egg whites, it's still a good idea to add cream of tartar as well, for increased stability.

How much sugar you add and how you add it affect the texture and behavior of the foam dramatically. Once a foam is established (no liquid white remains in bowl), sugar added at a steady rate (about 1 tablespoon every 30 to 45 seconds) dissolves uniformly and forces whites to make small bubbles by slowly increasing osmotic pressure. When whites are stiff enough to retain soft or rigid peaks, they're still pliable enough to mix with other ingredients.

If sugar is added before a foam is established, the whites become so plastic or stretchy that they can't incorporate enough air to make a stiff foam. If sugar is added too rapidly, the beating action won't dissolve it, and bubbles will be uneven.

Why do whites sometimes never get foamy, or collapse?

Fat keeps whites from foaming; it lowers the surface tension of the whites, and bubbles can't form. The culprit is usually a bit of egg yolk or a greasy bowl.

Foam will collapse if the bowl is so small that foam covers the top of a mixer beater--air gets beaten out instead of in. Expect 1 large egg white (2 tablespoons) to take up 1 cup of space.

What does a copper bowl do for egg whites?

A bowl made of copper has two advantages. One is its fine heat conductivity; the second is its metal ions.

As whites are beaten, the friction of the beaters quickly warms whites above the optimum temperature and bubbles get bigger. A copper bowl transfers heat rapidly from the whites, keeping them cooler than they would be in a bowl of glass or another metal. Copper ions, which are released during beating, fortify whites much as cream of tartar does and give the foam a creamy color.

More questions?

If you encounter other cooking mysteries and would like to know why they happen, send your questions to Why?, Sunset Magazine, 80 Willow Rd., Menlo Park, Calif. 94025. With the help of Dr. George K. York, extension food technologist at UC Davis, Sunset food editors will find the solutions.
COPYRIGHT 1993 Sunset Publishing Corp.
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Copyright 1993 Gale, Cengage Learning. All rights reserved.

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Author:Anusasananan, Linda Lau
Article Type:Column
Date:Jul 1, 1993
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