The Kitchn's Baking School Day 1: Learn all about eggs.
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Welcome to Baking School! In day-to-day cooking, eggs can be scrambled, poached, or boiled to create easy, straightforward dishes all on their own. But when it comes to baking and pastry, the importance of their role changes from breakfast food to a vital ingredient for giving structure, texture, and flavor. The function and behavior of eggs can really vary depending on how we treat them in these recipes, and just knowing more about the different parts of an egg — the whites and the yolks — can help make even the trickiest pastries feel a little more approachable.
So before we dive head-first into all things pastry, let's take a closer look at the mighty egg!
A Few Basic Things You Should Know About Eggs
At the grocery store there are dozens of different types of eggs — brown ones, whites ones, sometimes even green ones; eggs that are medium, large, and extra large. You might even see eggs from chickens, quails, or ducks!
So what should you buy for baking and pastry? Stick with large chicken eggs, unless otherwise specified in your recipe; most U.S. baking and pastry recipes are designed to be made with large-sized chicken eggs.
What's In an Egg?
Crack an egg open and you'll see the large, transparent egg white with the round, yellow yolk in the middle. The white is made almost entirely of proteins and water; the yolk, on the other hand, is packed full of nutrients, vitamins, and fats.
Look closely and you'll also see a thin white strand floating somewhere in the mix. This is called the chalazae and it anchors the yolk to the white and to the inside of the shell, keeping the yolk suspended.
A large egg (still in its shell) weighs about 2 ounces total; that's about 1 ounce for the white, 2/3 ounce for the yolk, and a fraction of an ounce for the shell itself. Inside the shell, a large egg has about 3 1/4 tablespoons of total egg matter — 2 parts white to 1 part yolk.
Not all eggs are created equal, though, and there can still be some small variance between eggs even within the same size category. On average, though, the large eggs will all be roughly the same.
Some recipes may specify eggs by weight instead of volume, calling for something like 4 ounces egg whites instead of 2 egg whites. In these cases, it's a good indication that precise measurements are important for this recipe, and so it's best to weigh the eggs using a kitchen scale. In a pinch, however, you can use the general weights for whites and yolks given above.
What Eggs Do in Baking Recipes
Eggs play an important role in everything from cakes and cookies to meringues and pastry cream — they create structure and stability within a batter, they help thicken and emulsify sauces and custards, they add moisture to cakes and other baked goods, and can even act as glue or glaze.
Between the yolks, the white, and the whole egg, the functions of an egg can overlap and vary widely from recipe to recipe. Let's take a look at each of these and see how they affect a recipe.
The Role of Egg Yolks: Fat
Recipes that use just the yolk of an egg typically do so for the yolk's fat content and emulsifying abilities. The fat gives baked goods extra-rich flavor and a velvety texture. The yolk also has the unique ability to bind liquids and fats together, creating an emulsion that prevents them from separating. This emulsion process helps create a more homogenous mix of ingredients — aiding in an even distribution of liquid and fats throughout a recipe for smooth batters, satiny custards, and creamy curds.
When yolks are heated, the proteins they contain unfold and gel together. This is a delicate situation; t0o much heat and the proteins will gel too much and turn curdled and grainy, but when warmed gently over low heat, egg yolks have a great ability to thicken products like sauces and custards. Again, their emulsifying properties enhance and thicken cream when they are cooked together.
The Role of Egg Whites: Foam!
When egg whites are used alone, they perform an entirely different role from the yolks, especially when whipped. Whipping and using egg whites in a recipe does not have to be as intimidating as you may think, and we'll be talking much more about this in a few days. For now, just know that whipping egg whites means incorporating millions of little air bubbles within the white. This creates a fairly stable foam that we can use to make everything from a soufflé to meringue. To help stabilize egg whites even further, we can add acidic elements, like cream of tartar and lemon juice.
One of the best ways to use whipped egg whites is as a natural leavening agent in something like a delicate cake or a soufflé. In the heat of the oven, the air trapped in the foam starts to expand, causing the recipe rise without the need for things like yeast or baking soda. In fact, whipped egg whites are how many classic baked goods, like sponge cakes, got their lift in the days before baking soda and baking powder!
Egg whites can also be whipped with sugar to make meringue, which can then be baked into crunchy meringue kisses, made into billowy pavlovas, or dolloped on top of desserts like baked Alaska. Sugar makes whipped egg whites incredibly stable — you can even pipe it using a piping bag into stars, kisses, and toadstools.
While the idea of "light" and "airy" whipped egg whites might make you think that more is better, it is possible to overdo it. Over-whipped whites will become clumpy, grainy, and difficult to fold into your batter. Also, using too many whites in a batter can wind up making the final product dry.
The Role of Whole Eggs: Fat and Foam
When you use whole eggs in a recipe, you get some of the best properties of both the yolk and the white. While whole eggs aren't quite as good as straight yolks at creating an emulsion, they are still excellent binding agents, especially in cakes, cookies, and other baked goods. Eggs also firm up and solidify when heated, giving crucial structural support to delicate desserts and pastries. At the same time, eggs make baked goods more tender, creating light textures, soft breads, and delicate crumbs.
When mixed with sugar (like in a cake or cookie batter), eggs help trap and hold air — not quite as well as whipped egg whites, but enough to give the finished product some lightness and lift. The combination of eggs and sugar also adds a great deal of moisture and flavor to a recipe.
Yolks and whites can also be used separately in the same recipe. This truly is the best of both worlds, with the yolks providing richness to a base or batter while the whipped whites do their job of lightening and leavening. Chiffon cakes and soufflés are good examples of this kind of recipe.
Master the Basics of Egg Science & Safety
Now that you have a basic understand of what eggs do in a recipe, make sure you know the basics of how and why they cook, and when they're safe to eat.
What Is Egg Coagulation?
Coagulation is what happens when you cook eggs. When raw eggs are exposed to heat and then gel into a solid very quickly, we call this coagulation. Eggs begin to coagulate at 140°F and will set more firmly as the temperature rises. Over-coagulation, or "curdling," may occur when the eggs are cooked at too high a temperature, or if they're cooked for too long. If you have ever experienced a grainy custard or a rubbery cake, this may be the culprit.
What's Important to Know About Egg Temperature?
Depending on the recipe, eggs may need to be room temperature when they get mixed with the other ingredients. Recipes for cakes and other baked goods often call for room-temperature eggs because they bind and emulsify better than cold ones. Additionally, room-temperature egg whites whip up better than their colder counterparts. If a recipe doesn't specify the egg temperature, it's usually safe to assume that the temperature isn't crucial to the recipe and the eggs can be added either straight from the fridge or at room temperature.
By the way, if you need to separate your eggs, do it while they are cold; the yolks are less likely to break and it's easier separate the yolk from the white. Also, to quickly warm up refrigerated eggs, just cover cold eggs in a bowl with warm tap water for a few minutes while you gather your remaining ingredients.
Trace amounts of salmonella — the bacteria responsible for many incidents of food poisoning — can sometimes be found in raw eggs. Although it's rare for someone to actually get sick from consuming raw or undercooked eggs, it's best to be careful, especially when serving egg dishes and desserts to people with compromised immune systems, the elderly, the young, and pregnant women. In these cases, be extra sure to cook eggs and egg dishes thoroughly (to 160°F), or use pasteurized eggs. Also, be mindful of cross-contamination between raw eggs and other ingredients.
How to Crack an Egg Like a Pro
Now that you've learned quite a bit about eggs — ready to crack a few? The baking pros always crack their eggs by rapping them on a flat surface or the inside wall of a mixing bowl. This avoids small bits of jagged shell getting forced inside the egg, which can puncture the yolk and leave tiny, annoying bits of shell to fish from the bowl. If you do get a bit of shell in your bowl, use a larger piece of the shell left in your hand to scoop it out; the sharp edge of the egg shell will break the surface tension and make it easier to scoop out the stray shell.
It's also best to crack eggs into a smaller bowl, separate from your actual mixing bowl. This makes it easier to scoop out the stray bits of shell, and also helps prevent having to start completely over if you accidentally break a yolk that you needed left whole — throwing away one broken egg (or saving it for dinner!) is better than tossing a whole mixing bowl of ingredients.
Every Baking School lesson has three homework options. Maybe you’ve already got one down, or you just have time for a quick study session. So pick one, and show us by tagging it with #kitchnbakingschool on Instagram or Twitter.
Attempt to crack an egg using only one hand. Watch this video for guidance.
Practice whipping an egg white until it becomes grainy (so you never do it again!). Or slowly cook an egg yolk until it coagulates. Observe the different ways eggs can change as you do one of these homework assignments.