from Fine Cooking # 101, pp. 26-27
Occasionally, I am impatient. I like to skip steps whenever I can, especially if those steps seem nonsensical. If it’s time to make a cake, and the recipe says to let the ingredients come to room temperature before combining them, I used to think, “Come on. Surely there’s no real reason I can’t use the butter if it’s a little firm?” Same with the eggs. Is moving them from the fridge to the countertop really going to make a difference?
When it comes to the science of baking, the answer is a resounding yes. Bake a cake with frigid butter and eggs and you’ll end up with something resembling a pancake. That’s why some recipes call for “room temperature” ingredients, a frustratingly general concept, especially from a scientific point of view. Think about it: The temperature of a room varies wildly based on location, season, and availability of a heating or cooling system. There must be a smarter way to gauge the temperature, right?
Better lift with butter
Let’s start by looking at what we want the butter and eggs to do. First at bat, butter. One of the things that distinguishes it from liquid fats like oil is that butter has the ability to hold air. Many cake and cookie recipes tell you to beat sugar into butter “until light and fluffy,” which creates air bubbles. (This is called the creaming method.) The more bubbles you have, the higher the confection will rise. If your butter is too cold, though, the fat and sugar won’t mix, resulting in few bubbles. (Butter that’s too warm isn’t good either—it will melt, so the bubbles won’t have any support and will disappear.)
Research shows that it’s best to bake with butter that’s about 65°F, which is actually cooler than room temperature in most homes. So how do you tell if your butter is the right temp? Short of using an instantread thermometer in a stick of butter, I like to use the thumb method. I learned this from master baker Carole Walter, author of the cookbooks Great Cakes and Great Cookies. She suggests holding a wrapped stick of butter in your hand and pressing firmly with your thumb. There should be a slight indentation. She refers to this butter as “slightly firm,” a more descriptive (and practical) phrase than “room temperature.”
(A pie aside: If you’re making a piecrust, your butter needs are completely different. You want the butter very cold so that it remains in small solid pieces while being worked into the flour. These small pieces ensure a flaky crust, because they melt in the oven and leave steam pockets.)
|To chill or not to chill
Talk of leaving eggs or butter out at room temperature tends to raise red flags in the food safety department. Here’s the straight story.
Butter can be left out on the counter (for easier spreading) without fear of food poisoning. However, most butter makers recommend refrigerating to maintain the best flavor. (It’s pretty easy to spot rancid butter: It turns a deeper color and becomes less opaque.)
Eggs can carry salmonella, so the risks of not refrigerating are a bit higher. Markets in other countries regularly store eggs at room temperature, but the USDA recommends refrigerating them, because a colder temperature will inhibit the growth of bacteria. Since it’s a simple matter of a quick soak in warm tap water to bring eggs in the shell up to temperature for baking (see Quick rescue), it’s best to keep them chilled.
Eggs are also crucial in giving loft to baked goods. The white of the egg is 90 percent water and 10 percent protein; when you beat an egg, it’s the protein that traps the air bubbles, and when incorporated into baked goods, these bubbles expand in the heat of the oven. Egg whites can be whipped up to eight times their volume, but this maximum air-trapping happens only when the eggs are warm; in warm eggs, the whites and yolks are looser, so it’s easier to incorporate air into them (which is the whole point).
Warmer eggs are also better when you’re mixing batter for cakes and cookies, because if you introduce cold eggs to a warmer butter-sugar mixture, the fat in the butter could harden. That would impede integration of the butter and eggs, which is why you’re creaming them to begin with.
But you do want your eggs to be cold if you need to separate the whites and yolks. Cold eggs are easier to separate, so if your recipe calls for the yolks and whites to be separated, do it before warming the eggs.
The good news is, if your eggs and butter are cold, it doesn’t take long to bring them to a respectable baking temperature.
Knowing the science behind ingredient temperatures makes me no less impatient when it comes time to mix up a cake. But knowing that cold eggs and butter will result in a dense, less tender cake tempers my haste—especially when the wait is shorter than an episode of Firefly.