Egg proteins change when you heat them, beat them, or mix them with other ingredients. Understanding these changes can help you grasp the many roles that eggs can play in the cooking process. Proteins are made of long chains of amino acids; in an egg white these are globular proteins which means that the long protein molecule is twisted, folded and curled up into a spherical shape. To keep the protein in that shape there is a variety of weak chemical bonds which keep the protein curled up tight as it drifts placidly in the water that surrounds it.

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The most well known use of egg whites is the meringue or a souffle. The proteins in egg whites are the building blocks of a meringue and to utilise these proteins they must first be partially broken down through a process called denaturation: this is done by beating raw egg whites to make a soufflé or a meringue, this action incorporates air bubbles into the water-protein solution. Adding air bubbles to egg whites unfolds those egg proteins, similar to the action of heating them.

To understand why introducing air bubbles makes egg proteins uncurl, you need to know a basic facts about the amino acids that make up proteins. Some amino acids are attracted to water; they’re hydrophilic, or water-loving. Other amino acids are repelled by water; they’re hydrophobic, or water-fearing.

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Egg-white proteins contain both hydrophilic and hydrophobic amino acids. Since the egg white protein is curled up into a spherical shape surrounded by water, the hydrophobic amino acids are in the centre of the sphere and the hydrophilic amino acids are outside of the sphere closer to the water.

When an egg protein is exposed to an air bubble, the protein is still exposed to the water. This causes the protein to uncurl so that the water-loving parts are immersed in the water—and the water-fearing parts can stick into the air. Once the proteins uncurl, they bond with each other, creating a network that can hold the air bubbles in place, when this network happens it is called binding or coagulation and the result is a foam. Whipping or beating the egg whites break the chemical bonds that hold the chains in its original ball form, allowing them to uncoil into their original long strands. When you heat these captured air bubbles, they expand as the gas inside them also is heated. Treated properly, the network surrounding bubbles solidifies in the heat, and the structure doesn’t collapse after the bubbles burst.

It is important to not to overbeat the egg whites because if the protein molecules are over stretched, they will eventually become weak and unstable. If this happens, the mixture may collapse in the bowl or later in the oven. Just as it is important to not over beat the egg whites, it is as important to have the ideal ingredients – it is advisable to use fresh eggs, because the fresher the eggs the better the result. Fresher eggs are more acidic and acid slows down the  coagulation process which will mean air can be incorporated during the beating process. You may find that many recipes often mention vinegar, lemon juice, or cream of tartar in the ingredients – this helps by increasing the ability of the mixture to incorporate air. Unlike regular baking, you should not add salt as this will have a counter effect and not facilitate foaming at all. Some people like to refrigerate their eggs, as this helps them to last longer – however for this process it is important to have the egg whites at room temperature. Cold eggs have stronger bonds between the protein molecules – just like beating helps to partially denature the proteins, so does heat via thermolysis (thermo = heat, lysis = pull apart) which is an endothermic reaction which means energy is absorbed by the egg whites. It is also best to use extra fine caster sugar as having smaller particles means it will dissolve better (regular sugar granules are too large and won’t work).

During the beating process, the sugar/egg white mixture will start to foam as the sugar granules dissolve in the water present in the egg white protein which in turn increases the strength and elasticity of the entire emulsion. The more you beat it, the more air is incorporated and the more bubbles will form – making the foam swell.

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Occasionally, you may see a professional cook using a copper bowl to beat the mixture, the chemical reason behind this is that the copper molecules will bind with the con albumin in the egg white. This will add support and prevent the collapse of the mixture as this bind delays coagulation by increasing the temperature so that again, the mixture can incorporate a bit more air. These factors all add to the ability to create the perfect foam. The baking process works by removing moisture and drying the mixture so that the proteins will coagulate evenly – it is recommended that the oven is set at 165° Celsius, any hotter and it will burn the meringue.

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So the next time you’re about to make a meringue, a Pavlova or even a souffle – we hope that some of these facts we have given you about egg whites and the chemistry part they play will help you to make the perfect dessert.