Fat chunks

Building flakiness

Color chemistry

Steam vents

Thickening molecules

Serving temperature

Crust composition

Apple slice structure

Pie geometry

Fine-tune crust texture by paying attention to the size of butter pieces as you combine them with flour. When you add water to the flour-butter mixture, the butter impedes the water from interacting with flour to form gluten. Too much gluten formation leads to a tough crust. So if your butter chunks are too big, less fat comes in contact with the flour, leaving more of the flour vulnerable to water, which is bad for your crust. Aim for pieces of different sizes: almond-size chunks, to make bigger air pockets, and smaller, pea-size ones, to ensure fat is evenly distributed throughout the dough.

Apples are a major source of steam during baking: they lose up to a third of their weight, most of it water that is converted to steam. If all that steam were trapped inside your pie, it would swell significantly. You can easily release the steam by cutting vents into the crust.

When flour meets water, a gluten protein network forms, which gives your dough structure. But you don’t want gluten to form so extensively that it toughens the crust. Replacing a portion of water with alcohol or vinegar can help impede gluten formation. Rum and vodka were among the students’ favorites; beer and carbonated water also make an airy crust, but the effect is less potent. If you replace all the water with alcohol, you’ll be able to taste it (in the case of a rum-infused crust, not such a bad thing).

Temperature is critical for texture when serving pie. The filling of a pie straight from the oven will be more runny (molecules flow more quickly past each other at higher temperatures), so let it cool well before you eat it. That also allows the pectin in the fruit filling to solidify. The resulting slice will better keep its form when it is cut and served on a plate.

Butter, which consists of tiny water droplets dispersed in a matrix of fat, is a crucial source of flakiness. The water droplets turn to steam during baking and become trapped in the crust, resulting in air pockets. People usually equate high-fat content butter with higher quality, but butter with slightly higher water content, and less fat, may be good when it comes to pie. American butters typically have higher moisture contents and yield a flakier, more porous crust compared with European butters.

Not all the liquid from the apples converts to steam; some of it seeps into the filling, which can make it runny and lead to a soggy crust. A bit of flour or cornstarch helps because their molecules, which are larger than water molecules, take longer to move past each other. The filling will ooze, rather than pour, onto the plate. Chia seeds have a similar effect, though they can get stuck in your teeth.

The famous Maillard reaction (the chemical reaction that occurs between amino acids, which comprise proteins, and sugar molecules like lactose) that is essential for color and flavor happens faster at a higher temperature. For a browner, more flavorful crust, set your oven to at least 375 degrees, and before baking, brush the pie with egg wash (protein) with heavy cream mixed in (more protein, and lactose).

As a pie bakes, water from the apples converts from liquid to gas, and air pockets expand. Simultaneously, the apples shrink in volume and soften, so they fall into crevices more readily. This can result in a sizable space between crust and filling. For a truly fruit-packed pie, slice apples flat instead of cutting them into wedges, and pat them down in the crust to make sure they lie flat, which minimizes collapse later.