Courtesy of Joanne Chang
To try Joanne's recipe for maple-buttermilk cake with caramelized apples, click here.
My husband, Christopher, loves to tease me that I grew up in a bubble. It seems the only temperature at which I'm perfectly comfortable is a temperate 70 degrees Fahrenheit. I'm still uncomfortable riding around in a car with the windows down in the summer (you have AC, why not use it?), and for most of the harsh Boston winter I live in layers from hat to triple layers of socks, huddled by the nearest heater.
Go right ahead and call me fussy; I prefer to think I am simply not accustomed to either cold or heat. Likewise, when people say that baking is tricky, they may not realize that in so many different ways, temperature plays a huge role in success or failure. It helps to understand when and why something needs to be ice-cold, chilled, room temperature, hot, or caramelized. Seeing things from the ingredients' point of view takes the mystery out of baking—so you can march confidently into the kitchen and make something sweet.
If it is at room temperature, sugar can work its magic and aerate the butter.
Let's start at the cold end of the spectrum. The most common example of the importance of chilling ingredients is making flaky pie dough. Most recipes instruct you to start with butter that is straight from the refrigerator. Be honest now: Do you do that? You will once you understand why. To make pie dough, you mix butter into flour and then add liquid. If the butter is from-the-fridge-cold, it won't completely mix into the flour and some will remain in pieces, ideally the size of grapes. As you roll out your dough, these grape-sized pieces of butter get elongated by the rolling pin and you end up with long flat sheets of butter within your dough.
Most butter contains about 15 to 17 percent water. When the pie dough goes into the oven, the water turns to steam, which is what helps create layers in your dough. In other words, it is the sheets of butter that make your pie dough flaky. If your butter is somewhat warm, then you end up with something that is more like cookie dough than flaky pie dough. Not the end of the world by any means—and a tender, crumbly pie dough is still a good dough—but for a pie crust that flakes and shatters and impresses with its many layers, keep your butter cold, cold, cold.
When do you want your ingredients to be at room temperature? There are two good examples of this. The first is when you are combining sugar and butter for a cake or cookie. If you look at sugar under a microscope you see why they are called sugar crystals. They have jagged edges, and when you mix sugar into room temperature butter, these edges act as an army of little workers with shovels carving out miniscule air pockets within the butter. If your butter is too cold, the sugar—try as it might—can't dig its way through the hard chilled butter; if the butter is too warm, the sugar merely sloshes around, not really being effective at all.
If it is at room temperature, however, that sugar can work its magic and aerate the butter. The act of combining butter and sugar together in this way is actually called "creaming" because when done properly the butter turns light and white like cream. Once you've created a multitude of air pockets, the baking powder or soda you add to the cake/cookie later on expands these air pockets and you end up with a light, tender, fluffy pastry. And all because you started with room temperature butter!
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A second example of when ingredients should be at room temp is when you add a liquid such as milk or buttermilk or eggs into a cookie or cake batter. Imagine the butter and sugar you've just creamed together: an aerated fluffy room-temperature glorious mass. The next step in the recipe calls for adding eggs or other liquid to the butter-sugar. If your eggs/liquid are cold and not at the same temperature as what you are about to mix them into, the butter will immediately harden into little cold pellets. And when you bake your cake/cookie you'll end up with lots of little holey pockets from the butter bits. Not good! To keep your crumb even and soft, make sure your ingredients are at the same temperature when combining them, ensuring seamless emulsification.