Today is Pi Day, the best day of the year for mathematicians and bakers—and especially mathematicians who bake.
In honor of Pi Day—3/14—and word play, many celebrate by making pie. Though pie is a venerated American tradition, the idea of making pie crust from scratch can be terrifying. Besides, why would you make your own pie crust when you can buy a perfectly fine premade one from the store?
Well, because you can easily make a better pie crust on your own, with a little help from science. And the mystery of pie crusts becoming far less daunting when you understand the chemistry (which is all baking is, really).
The balance of key ingredients
First, you need to know that, despite all the fancy permutations you might find in cookbooks and online, there are really just three things that make up pie crust: flour, water, and a fat of some kind (we’ll get to that). Some people include a fourth ingredient: sugar or salt.
At a very basic level, the flour combines with the water to activate the gluten. The gluten gives the dough it’s stretch and strength. Too much gluten and your pie crust will be tough and leathery. Too little and you’ll have weak dough that tears and loses its shape when baked. Balance is key here. (If you want to make a pretty pie, with a lattice or some other decoration, you’ll need a stronger, more glutinous crust.)
The fat is where the beautiful flakiness of pies comes from. The flour coats the fat pockets and then, during the baking process, the fat pockets create the space between the flour layers, leaving flaky, airy perfection.
Temperature is arguably the most important factor for making good pie crust. Warm pie dough is the enemy. Pie recipes always require multiple chilling periods—don’t skip them! (This matters especially when you’re using butter as your chosen fat.) In his book, Cooking for Geeks, Jeff Potter explains:
Chilling the ingredients prevents the butter from melting, which would allow the water in the butter to interact with the gluten in the flour, resulting in a less-flaky, more bread-like dough.
The ideal temperature is usually “room temperature”—generally considered to be 68-72°F. Before you roll out the dough, you want the dough disc to feel like a cold stick of butter.
If you’d prefer to be more specific, Serious Eats’ J. Kenji Lopez-Alt recommends keeping the dough and all the other ingredients between 65° and 70°F. On a hot day or if you’ve been pre-heating the oven and it’s starting to get toasty inside, the temperature in your kitchen could easily reach 80°F—so the temperature of the flour stored in your cabinet or measuring cup could be well above room temperature. You also don’t want the butter to be too cold because it won’t mix into the flour properly.
It’s not unreasonable to refrigerate the bowl, the dry ingredients, the measuring cup, and the rolling pin. If your kitchen feels hot to you, then it’s definitely too hot for the dough.
Which fat should I use: butter, shortening, or lard?
Each has pros and cons.
Because butter melts at a lower temperature than shortening or lard (see the temperature section), it can be the most difficult to work with. But many bakers will argue it’s worth it because butter just tastes better, giving you the most flavorful crust possible. And butter allows the crust to brown better than other fats.
Lard, rendered pig fat, used to be popular, but these days it makes a lot of people squeamish—and it definitely doesn’t work for people who don’t eat pork. Also, it can be difficult to find good lard that doesn’t taste a little piggy, and most people don’t want piggy pie crust. But if you can get good lard, it can enhance the flakiness of a bread or crust. Also, since lard melts at a higher temperature than butter, it keeps its structure better than butter does at room temperature.
Shortening experienced its heyday in the last century. The fat solid doesn’t lose its texture at room temperature so it’s easy to mix in without melting (and overdoing it on the gluten). It can also create a stronger crust with a mealier texture, which can be better for some types of filling like custard or meringue, or for pies with decorative crusts that require more structure. But the downside to shortening—besides the fact that most people don’t have it in their kitchen—is that it has no taste, and adds nothing to the flavor.
Some recipes call for a combination of the fats, usually butter with a bit of shortening, to capitalize on the pros of each—taste from butter and texture from shortening.
How should I mix my pie dough: pastry cutter, food processor, or by hand?
A lot of big-name chefs are really into food processors right now. Lopez-Alt has even created a pie dough recipe that can only be made with a food processor. The reasons why are clear: food processors are fast, easy, and have relatively good temperature control. When you use your hands, it’s easy to overheat the dough, causing the butter to melt, and we all know how that ends.
However, there are some well-known food bloggers fully in the pastry-cutter camp. Smitten Kitchen’s Deb Perlman says pastry cutters always give her a flakier crust, and food processors just don’t give you enough control over the texture of the dough. “In the end,” she says, “it is so much harder to overwork your dough and over-mix your butter by hand than it is when you use the food processor.”
Serious Eats’ Stella Park advocates hand mixing because handling dough is a “joy”—her old-fashioned recipe requires no fancy tools and is all butter. Erin McDowell, from Food52, also encourages hand mixing for increased control (unless you have hot hands, in which case she suggests a food processor).
How do you pre-bake, or “blind bake,” a crust?
Pre-baking, also called blind baking, is when you half-bake the crust before adding the filling. It’s necessary for custards, meringues, and other fillings that aren’t normally in the oven long enough for the crust to fully bake. Lopez-Alt recommends using an aluminum or glass pie pan for pre-baking, as opposed to a ceramic pan because ceramic insulates too well.
The most important part of pre-baking is weighing down the crust so it holds its structure. Without filling to keep it in place, crust will fall apart. You can use pie beads to weigh the crust down, or a number of cheaper options you probably already have in your house. Any sort of dry bean or rice will work, as will granulated sugar. To keep the weights from sticking, place a layer of aluminum foil between the dough and whatever you use as a weight.
In any case, before you pre-bake, be sure to chill the dough for at least 15 minutes.
What is the best way to roll out my dough?
Most recipes recommend using flour to keep the dough from sticking to the countertop or other surfaces. Perlman rolls her dough out on plastic sheets to avoid adding extra flour that could increase the gluten and make the dough tougher. You can also use silicon mats to roll out the dough without adding flour.
Most bakers have a preference of rolling pins: French (tapered) or American (handled). And it’s just that, a preference. Feel free to use whichever you feel most comfortable with. If you don’t own a rolling pin, a wine bottle will do the trick.
Why do some recipes have extra ingredients, like apple cider vinegar or vodka, in them?
Apple cider vinegar and vodka are meant to help address common problems that arise when making pie crust.
Apple cider vinegar is added to help tenderize the crust. The theory is that gluten is inhibited in acidic environments and will make for a more tender crust. It’s a contested proposition, but the owners of the famous NYC pie shop Four and Twenty Blackbirds use apple cider in their basic butter pie crust (and I’ve made it, it’s good).
The vodka crust method was developed by Lopez-Alt when he was a recipe tester for Cook’s Illustrated. The Kitchn writes that vodka keeps the dough moist while you’re working with it, and then the alcohol cooks off during baking, leaving a flaky crust. However, the dough can be sticky and not everyone likes it.
In the end, none of the pie crusts are definitively better than any of the rest, but they do have different results. Ultimately, your pie crust is up to you and what you want to eat—but knowing the chemistry behind the kitchen work will help you make it exactly how you want.