The Excellent Egg

“A box without hinges, key, or lid,
yet golden treasure inside is hid.”

– One of Bilbo Baggins’ riddles for Gollum, The Hobbit.

What can thicken a sauce, emulsify a custard, or leaven a cake? What can give a shiny glaze to a new loaf of bread, be whipped into sugary clouds of confection, or keep that mohawk sharp, beautiful, and pointing skyward? (Sorry, ’80s flashback there.) I am talking, of course, about the most excellent egg. Understanding the properties of the different parts of an egg, i.e. the whites and the yolks, can help make baking, especially pastry-making, a little less daunting.

Leavening

Eggs help with leavening when they’re aerated. Egg whites are especially good for leavening, but there are some sponge cakes and soufflés, and sauces such as sabayon, where beaten yolk foam is important.

Whipping Eggs

Whole eggs, just the whites, or just the yolks can all be whipped to create volume. Egg whites can expand greatly, up to 6 to 8 times in volume, while beaten yolks may only double or triple. Whole eggs will form a foam but it’s much less volume than beaten whites and not as thick as beaten yolks. Also unlike the whites, yolks or whole eggs usually need an assist from sugar but the foams they create are more stable than those from egg whites only.

Egg Whites

Egg-white foam is behind the structure of meringues, soufflés, and angel food cake.

Tips

• Let whites sit at room temperature for 30 minutes before beating to get greatest volume.
• Use glass or metal bowls and avoid plastic. And keep them clean! Any fat – a trace of egg yolk, butter on your spatula, oil in the bowl – will diminish the foaming ability of the whites.
• Add a little acid to help stabilize the foam, e.g. cream of tartar (1/8 tsp for every 1-2 egg whites) or lemon juice or vinegar.
• Use immediately after beating to avoid shrinkage. (I cannot write that word and not think of a certain Seinfeld episode.)
• Underbeating leads to lack of volume and overbeating leads to clumps which don’t blend with other ingredients and don’t expand well when heated.

Emulsifying

Desserts such as custards and crème brûlée benefit from the egg’s ability to emulsify. You can thank the lecithin in the yolk for that, as it is both emulsifier and gelling agent. (And the only naturally occurring emulsifier available in a food. I told you eggs were awesome.) The custard-egg combos that can cause problems, however, are those like pastry cream because they’re thickened with starch. Eggs contain amylase which will consume the starch and eventually make your custard runny. That’s why you want to be sure that starch-thickened custards come to a boil, albeit a brief one, because amylase is only deactivated at boiling temperature.

Custard Tips

• For baked custards, use a bain-marie, or water bath. Line a roasting pan with a kitchen towel and place ramekins on top, then pour your custard mixture into the ramekins. Pour boiling water into the pan until it’s halfway up the sides of the ramekins. (Easiest to do this with the roasting pan already in the oven.) Bake until the custards are just set. The water bath provides a barrier from the direct heat so the custard cooks gently.
• The trick for cooking stirred custard, such as the crème pâtissière used in a French fruit tart, is to cook it low and slow in a large saucepan over low heat, stirring constantly with a wooden spoon. It’s really easy to overheat so keep a close eye. You could also cook it in a double boiler, as you would do when melting chocolate.
• Take it out of the oven/off the heat as soon as it’s done.
• Strain custard mixture through a fine sieve before baking (baked custards), or after cooking on the stove (stirred custards).