Why is there foam in my egg mixtures?

Why is there foam in my egg mixtures?
Air bubbles trapped in a mixture.
A foam is created by incorporating air, usually by beating, and capturing the air in tiny bubbles. Eggs are excellent at foam formation. You can beat egg whites, egg yolks or whole eggs into a foam.
When you beat egg white, it becomes foamy, increases 6 to 8 times in volume and stands in peaks. When you heat the foam, the tiny air cells expand and the egg protein coagulates around them, giving permanence to the foam. Egg-white foam is responsible for the structure of angel food cake, meringues, puffy omelets and soufflés.
For egg whites that reach their greatest volume, allow the whites to stand at room temperature for about 30 minutes before beating.
Fat inhibits the foaming of egg whites, so be sure beaters and bowls are clean and that there’s no trace of yolk in the whites. Use only metal or glass bowls because plastic bowls tend to absorb fat.
Adding an acid ingredient helps to stabilize egg-white foam. The most commonly used acid ingredient is cream of tartar (1/8 teaspoon for each 1 to 2 whites) although some recipes call for lemon juice or vinegar.
Opinion among food scientists is divided on salt. Since salt may decrease foam stability, it’s best to add it to other recipe ingredients.
If you underbeat egg whites, the volume of the finished product will be less than desired. Overbeaten whites form clumps which are difficult to blend with other ingredients. Because overbeaten egg whites also lack elasticity, they can’t expand properly when heated. The finished product may be dry or have poor volume, or may even collapse.
Combine an egg-white foam with other ingredients immediately after beating, before the foam has time to drain or shrink.
An egg-yolk foam may double or triple in volume but doesn’t reach nearly the volume of egg-white foam. Beaten yolk foam is an important part of the leavening for puffy omelets and sponge cakes and is sometimes also used for soufflés.
Whole egg will also form a foam, but the volume is much less than the foam of beaten white and the foam is less thick than the foam of beaten yolk.


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