How Egg Whites Expand

The white portion of the egg is referred to scientifically as albumen. The protein found in the egg white, or albumen, is albumin. Egg whites have excellent foaming ability. When egg yolks, which contain a fatty substance that destroys the albumen’s ability to foam, are removed, egg whites alone can increase in volume by up to 8 times. This is possible through close teamwork by the two proteins albumin and ovalbumin. When the egg whites are beaten, the albumin protein forms a stable mass of tiny air bubbles, while some of the protein molecules bond and form a fragile network that holds the moisture in place (an egg white contains about 85 percent water). This alone would suffice if the beaten egg whites were not to be cooked, but because air expands when it is heated, the network of denatured proteins on the surface would be destroyed and immediately collapse if it were not for the ovalbumin protein. While the ovalbumin does not play an important role when the egg whites are simply beaten, it coagulates when heated, forming its own network in the meringue and making it resistant to collapse as the water evaporates. In other words, the ovalbumin protein makes it possible to change a liquid foam into a solid dry mass with heat.