September 1, 2014
Egg whites are the common name for the protein-rich albumen found within an egg’s hard shell.
Like egg yolks, they serve a very specific purpose outside of breakfast. By themselves and a healthy amount of whipping, egg whites are used for creating foams. (Similarly combined with the appropriate ingredients, help egg whites stabilize mousses, meringues, and ganaches.) The mechanical stresses of a whisk, egg beater or mixer physically change the shape of the egg white proteins unwinding them and allowing sulfur-sulfur bonds between amino acids on the long chains. These disulphide bounds occur at any point where a methionine or cysteine sits along these nutritive and functional strings.
The end result is a stable network of unfolded proteins that maintains its shape under the right conditions. Hydrophobic amino acids line up against the air bubbles that get incorporated into the whipped egg whites effectively holding them in place, but any fats present are happy to occupy this space; egg yolks and oils prevent stable foams from taking shape.
Similarly, overbeaten egg whites also hold their structure poorly.
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