Why Do Some Recipes Call for Eggs to Be 'Room Temperature?'
For seasoned home cooks, recipes often feel more like inspiration than prescribed paths that need to be followed to a T. But one recipe instruction that often feels superfluous, and isn’t, is the directive to use room temperature eggs in baking. The biggest incentive to skip this step is usually time. If the only thing standing between you and some impromptu cheesecake is waiting while your refrigerated eggs warm on the counter, who among us wouldn’t want to skip this and be 30 minutes closer to eating cheesecake?
Unfortunately, baked goods are always better when you do adhere to this step. The reason comes down to protein coagulation. Eggs, like all living matter, are made up of a diversity of proteins whose structures change when the temperature changes. The most visually obvious example of this is the change in the texture you’ll notice between a raw egg you’ve just cracked and the same egg after you’ve fried it—that’s because heat has changed the proteins’ structure from a thick liquid to a solid. The same principle is true of a refrigerated egg, which is usually around 40 degrees Fahrenheit, and a room temperature egg, which is, well, the ambient temperature in your home. While the protein structure change is less obvious to the naked eye than the difference between a raw egg and a cooked egg, the temperature upgrade is still minutely changing the proteins inside both the egg yolk and white. This has several benefits in baking, depending on the recipe at hand.
For any batter that needs to be well-mixed (which is pretty much all of them), room temperature egg yolks break down and combine with egg whites much more easily than cold egg yolks. Working with room temperature eggs ensures a smooth, evenly-mixed batter with no stray yolk speckles. In this way, an egg is no different than another baking ingredient commonly asked for “at room temperature”: butter. We instinctively know that combining butter with other ingredients is more difficult when the butter is cold than if it’s softened; the same is true for eggs. One way that you can proceed forward with cold eggs here, if you didn’t have time to bring them up to room temperature, is simply to whisk them until the yolk and white are totally combined and no visible streaks remain, before adding to the remaining ingredients. But if you add cold eggs whole, directly to batter, they will have a hard time smoothly mixing with other ingredients.
For baked goods that rely on eggs for volume, a room temperature egg is also preferable. The height you need to achieve in something like a souffle or a mousse comes from introducing air into eggs, which is done more easily, to both yolks and whites, at room temperature.
Lastly, in recipes with a high fat content, such as cheesecake, working with cold eggs can negatively impact the mixture by bringing the overall temperature down. This can sometimes curdle dairy products, and no one wants to eat curdled cheesecake.
If you’re in the U.S. where eggs need to be refrigerated for health reasons, take care not to leave your eggs on the counter for more than about 30 minutes. If you didn’t have time to plan ahead for this and need to quickly bring up the temperature of eggs, you can also submerge them in tepid water for 10 to 15 minutes (too hot, though, and you will just end up with boiled eggs).
In the end, the most important contexts in which to use room temperature eggs are in high-fat recipes or recipes that require big volume from eggs. The context where using cold eggs instead of room temperature eggs would be least noticeable is probably for thorough mixing.