The Miraculous Egg
The chicken egg is an amazing invention of nature. It has an appealing ovoid shape and comes in all sorts of colors depending on the breed.
And aside from its original purpose as a self-contained chamber for the development and nourishment of an embryo, its place in cooking and baking is astonishing.
But before I get to that, take a good look at an egg. Crack it open onto a plate. Admire its white and yolk. Here’s a view looking down on the egg.
If the egg is fresh, came from a hen raised on organic feed that was allowed to hunt and peck for additional grubs, it’ll look proud. The white will stand high and the yolk will be a bright golden orange.
Made up mostly of fats and proteins, yolks embody richness and smoothness. The whites–fat-free, gloppy, and viscous–hold the promise of cloud-like meringues and airy cakes. Here’s a side view showing the height of the yolk and thickness of the white.
Whole eggs are a great team player in baking. They get mixed into batters for all sorts of custards, cakes and quick breads. When you separate the whites from the yolks, more worlds of possibilities open up for you. The whites make great foundations for a meringue dessert, a crisp cookie, divinity candy, angel food cake, a tender yet crunchy overnight meringue torte, or ethereal floating islands.
The yolks alone beaten into cake batters contribute extra moistness and tenderness. When added to ice cream bases they add a special unctuousness, and when heated carefully on top of the stove with sugar and milk, they become transformed into sweet sauces for ice creams, cakes, fresh fruit, puddings, pies, and tortes.
So, how do the parts of an egg work baking magic?
Let’s start with egg whites, and see what happens when we beat them into a foam to make a meringue or angel food cake. But before even that, we must make sure that the bowl the whites are beaten in is free of grease, because fat can ruin a foam just as surely as a nail deflates a tire.
Egg whites are essentially proteins dissolved in water. In an unbeaten white the proteins are folded up and separated from one another within the watery matrix. Beating causes air bubbles to become incorporated in the whites as the proteins unfold and connect with each other, entrapping the air within their framework.
These unfolded proteins are said to be denatured—they’re no longer coiled up—and it is in this denatured state that they gradually form a delicate lattice network keeping the bubbles of air separate from the water around them.
Acid, usually in the form of the white powder “cream of tartar,” is added to an egg-white foam at this stage of beating to “stabilize” it, meaning that it strengthens the protein around the air bubbles. What’s interesting is that only a small amount of this solid salt of tartaric acid is needed to do the job, around 1/16 teaspoon per white.
Salt, on the other hand, extends beating time and makes for a less stable foam. But, when added to the flour (for flavor) and folded in at the end of beating, it has no negative effect on the foam.
As you continue beating, more and more proteins are denatured, the lattice network increase, and less light can pass through the whites. The whites lose their transparency and turn white because they reflect the light reaching them.
Without getting too technical, uncooked foams, like those in mousses and chiffon pies, owe their lightness only to certain kinds of egg white proteins that are denatured and stable without heat. In baking, though, another egg white protein, ovalbumin, which accounts for more than half of all albumen proteins, has the job of maintaining the air bubbles in the heat of the oven, whether in a meringue, soufflé, or angel cake.
The oven heat causes the air bubbles in a foam to expand. If it weren’t for the ovalbumen, the bubbles would eventually pop and the cake or meringue or soufflé would collapse. What makes ovalbumen special is that it coagulates readily when heated, resists collapse, and creates a solid foam from a liquid one. Pretty neat I’d say.
Sugar is a mixed bag in its effect on egg whites. If added too early during beating, it delays foaming and will reduce lightness and volume. This is why recipes say to beat the whites until they hold a soft peak before adding sugar. Sugar is beaten in gradually after this point to allow it sufficient time to dissolve in the foam. It adds sweetness, makes the egg foam stable in the oven’s heat, and encourages browning.
Let me know if you’ve got any egg questions.
You’ll see how this all plays out in my next post when you make Chocolate and Pecan Meringue Smooches. And don’t be surprised if you get some real ones afterward!