The Whys of Pies

Whenever I serve a homemade pie, it seems to have a curious effect on people. First, delight. But then, despair, as my guests detail their pie woes, from custard pies that crack as they cool to crusts that are tough or too crumbly.

When a pie lets you down, it’s very disappointing, especially at Thanksgiving. To spare you that grief, I’d like to explain how to avoid five common problems. Once you know your way around them, you’ll be well on your way to pie success.

Read Your Thanksgiving Pie Questions Answered for more pie tips & tricks and visit The Guide to Thanksgiving Dinner for hundreds of recipes, menu planning tools, and how-to videos.

Challenge: A tough crust

This ubiquitous problem results from two common mistakes: adding too much liquid and overworking the dough. The moment liquid—in this case, water—meets flour, a strong, elastic protein known as gluten begins to form. And as you mix and knead the dough, you make the protein stronger and your crust tougher.

Piecrust recipes are designed to keep gluten at bay; they use very little liquid and call for minimal mixing. Unfortunately, recipes can’t tell you exactly how much water to add or exactly how long to work the dough—you need to get a feel for these things. But as a general rule, less is best. Mix in liquid very sparingly, using just enough for the dough to hold together when you squeeze it, and handle the dough as little as possible.

Challenge: A crust that shrinks in the oven

If this happens, chances are your dough hasn’t had enough rest. Blame gluten, that stretchy protein that forms when wheat flour meets water. Even though pie dough contains very little water, some gluten does develop when you mix the dough, and this elastic protein makes the dough rebound when you roll and shape it. But if you let the dough rest in the fridge for several hours after you’ve mixed it, you’ll give the gluten strands time to relax and adjust to their new shape, so the dough won’t resist when you try to roll it out. Then, more important, the dough needs to rest again after you’ve rolled it out and shaped it into a piecrust. With all this rest, the dough will shrink less when you bake it.

Challenge: Pumpkin pie that cracks as it cools

Pumpkin pie filling is a type of egg custard. Custards thicken during baking as the egg proteins coagulate, tightening and shrinking. In the process, the liquid custard mixture transforms into a thick, moist, silken solid (or so we hope). Cracks form in a custard when the egg proteins overcoagulate—i.e., overcook. The trouble is, a pumpkin pie or other custard might not look overcooked when you pull it from the oven, but then as it cools, it cracks. What’s going on? Residual heat continues to cook the filling even after you’ve set your pie on the cooling rack, so the proteins continue to shorten, tearing open cracks in your perfect custard. To minimize cracking, it’s a good idea to remove pumpkin pie from the oven as soon as the custard filling sets but before it’s firm; the filling should jiggle a bit in the center when the pan is nudged.

Challenge: A crust that isn't flaky

After deliciousness, flakiness is probably the quality most admired in a piecrust. So how do you get all those crisp, flaky layers?

First, start with very cold fat and let it remain in fairly large pieces—pea-size to 1/2-inch bits—as you blend it into the flour. If the fat starts to feel soft, stop what you're doing and freeze the ingredients for about five minutes to let the fat solidify again. You don't want it to start melting or mixing with the flour too much, or your pastry will turn out crumbly rather than flaky.

To create flakiness, the fat needs to remain solid so that when you roll out the dough, the fat can flatten into thin, firm sheets sandwiched between layers of dough. Then, when the pie goes into the hot oven, the sheets of cold solid fat will hold their shape long enough for the dough layers on either side of the fat to set, creating thin layers of crust. As the fat melts, steam will puff the dough layers apart, creating the crust's flaky texture.

Challenge: A too-crumbly crust

There’s certainly a place in the world for tender pastry that crumbles like a shortbread cookie—just not in a pie dish. If your crust is so crumbly that it falls apart, the fat was probably too soft and too thoroughly blended into the flour. When flour and fat are blended, the fat essentially forms a waterproof barrier around the flour particles; thus, gluten can’t form when you add liquid and mix the dough.

Though it’s good to minimize gluten to prevent toughness, you don’t want to eliminate it altogether, because without those strong structure-building proteins, a crust has trouble holding its shape. So, how do you get a crust that’s tender but not too crumbly? A little compromise is all it takes. It’s OK to work a little of the cold fat into the flour for tenderness, but you also need to make sure that plenty of the fat remains in large, firm pieces.