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.
Moving on to warmer temperatures, there's a valuable baking technique called tempering that will prevent you from making scrambled eggs when you are trying to make a pastry cream or ice cream base. First you start with something like milk or cream that you heat up in a saucepan until it just about comes to a boil. In a separate bowl you mix eggs and sugar. Now you want to combine the hot liquid with the egg-sugar mixture. Do you just mix the two together? Noooooooooo. That's like jumping into the pool, cannonball style. In pastry you want to dip your toe in, one toe at a time, and slowly ease your way in.
Thus we have tempering. Take a little bit of the hot mixture and whisk it slowly into the cold mixture. Keep adding a bit of hot to the cold until the cold is no longer cold. Once about half of the hot mixture is combined with the cold you can easily combine the rest of the ingredients together without fear of making sweetened scrambled eggs.
Pastry is logical and consistent and wonderfully fun.
Oven temperature is just as crucial as ingredient temperature. What happens if your oven is too hot (i.e. it reads 350 degrees but in actuality it is at 450 degrees)? Your carefully made cake or cookie crusts over and the inside never has a chance to bake properly, remaining gummy and gloppy while the outside is hard and overbaked. Wah! On the flip side, if you don't wait for your oven to heat up to the correct temperature and you put something in the oven, your cake/cookie batter or tart dough will slowly start to melt and you'll end up with something more like a hockey puck than a fluffy cake or a tender cookie. So don't take the instruction, "Preheat oven to x degrees" lightly.
Finally if you are making something with cooked sugar syrup (buttercreams, candies, caramels, fudge) the temperature of the syrup will determine the final consistency of the sweet. Sugar combined with water makes something so simple that it's called (no joke) simple syrup. It's great for sweetening tea. Cook the syrup to what is called soft ball stage (when you take a bit of it and drop it into a cup of ice water you can form a soft ball) and you have the beginnings of a buttercream. Keep going to hard ball stage (you get a hard ball when you drop a bit into ice water) and you can start to make fudges. There's hard crack stage for hard candies like lollipops, and finally caramelization stage when the sugar syrup turns caramel color. Invest in a candy thermometer for best results, and open up another world in pastry.
You may read this and think: High maintenance! Picky! Temperamental! But I hope you'll view it like this: Pastry is logical and consistent and wonderfully fun, and once you understand the importance of various temperatures you're on the road to becoming a great baker.