This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Pie makes everything better; it even makes understanding science easier--just ask Amy Rowat. Rowat is an assistant professor of integrative biology and physiology at UCLA who just so happens to be quite a pie aficionado. She combines these traits to teach various aspects of science.
“Pie is a great medium to learn about science. To understand the science of pie demands a knowledge of concepts from phase transitions to Maillard reactions that stem from multiple fields including physics, chemistry, and engineering,” Rowat tells me. She adds, “Pie also provides a powerful medium to practice the scientific method - it is easy to ask an interesting scientific question about the how and why of a pie; a hypothesis can easily be tested by experimentation; the ingredients are reasonably inexpensive and readily available; and the results of baking experiments are almost always delicious.”
As part of her class, Rowat’s students partake in an independent pie project. Unsurprisingly, these edible experiments are popular amongst her students. They use it as an opportunity to develop and test a hypothesis. The scientific focus can vary--sometimes it may focus on a classic, like dissecting their grandmother’s banana cream pie. Other times, they may have a more modern edge, like experimenting with alcohol in the pie’s crust. This isn’t to intoxicate the pie or those consuming it; it’s believed alcohol may inhibit gluten formation, resulting in a crust that is flakier than one made just with water.
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In honor of Pi(e) Day, Rowat shared a few different scientific aspects of pie:
Crust texture and color. To promote a flaky and tender crust, vinegar can help to reduce the formation of protein networks that are known as gluten, which makes bread chewy and traps gas bubbles. However, vinegar also lowers the pH, which slows the Maillard reactions; these result in browning and generation of flavor compounds. Adding alcohol, like vodka or bourbon, instead of vinegar will give you a more tender crust than water alone, and makes for a lovely golden brown and tasty crust.
Temperature. It is critical when dealing with dough. Start by cooling your fat (butter or lard) in the freezer (~10-15 minutes for ~2 x 2 cm cubes); this ensures that even after the dough has been worked by your fingers, you will still have some sizable fat chunks that are ~mm to cm in diameter - these chunks of fat translate into a flaky crust as they create air pockets after the fat melts and water evaporates during baking. After rolling out, the dough warms up again; place the entire pie in the freezer for about 10 minutes before baking so the crust maintains its shape while it bakes.
Taste. Salt is essential for a flavor-balanced pie. Recipes that call for a 'pinch of salt' could learn something from science about the value of being quantitative and reproducibility! A 'pinch' is all too often underestimated. For a pie crust for a sweet pie, ~1.6 g salt per 125 g flour.
Filling texture. Tune the texture of your filling using thickening molecules. Ingredients such as cornstarch or flour help to increase the viscosity of a fruit pie filling when they mingle with each other in hot fruit juice and make it less runny; during baking, fruits release water that could otherwise make your filling too liquidy.
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Image by author.
Ready to experiment with the science of pie? Here’s one recipe to get started:
Cherry Pie
(via Epicurious)
Makes 1 (9-inch) pie
INGREDIENTS
(For Pastry)
2 1/2 cups all-purpose flour
1 1/2 sticks cold unsalted butter, cut into 1/2-inch cubes
1/4 cup cold vegetable shortening (preferably trans-fat-free)
1/2 teaspoon salt
5 to 7 tablespoons ice water
1 tablespoon sugar
(For Filling)
3 tablespoons quick-cooking tapioca
1 vanilla bean or 1 1/2 teaspoons pure vanilla extract
2 tablespoons cornstarch
1/2 teaspoon cinnamon
1/4 teaspoon salt
1 1/4 cups sugar
6 cups fresh or frozen (not thawed) pitted sour cherries (2 pound)
Whole milk for brushing
Special equipment: an electric coffee/spice grinder; a pastry or bench scraper
PREPARATION
Make dough:
1. Blend together flour, butter, shortening, and salt in a bowl with your fingertips or a pastry blender (or pulse in a food processor) just until mixture resembles coarse meal with some roughly pea-size butter lumps. Drizzle 5 tablespoons ice water evenly over mixture and gently stir with a fork (or pulse) until incorporated.
2. Squeeze a small handful of dough: If it doesn't hold together, add more ice water, 1 tablespoon at a time, stirring (or pulsing) until incorporated. Do not overwork, or pastry will be tough.
3. Turn dough out onto a work surface and divide into 8 portions. With heel of your hand, smear each portion once or twice in a forward motion to help distribute fat. Gather all dough together with pastry scraper. Divide dough with one half slightly larger, then form each piece into a ball and flatten each into a disk. Wrap each disk in plastic wrap and chill until firm, at least 1 hour and up to 2 days.
Make filling and bake pie:
1. Preheat oven to 425°F with rack in middle and put a large baking sheet on rack.
2. Finely grind tapioca in grinder.
3. Split vanilla bean lengthwise and scrape seeds into a large bowl with a small knife. (If using extract, add with fruit.) Whisk in ground tapioca, cornstarch, cinnamon, salt, and sugar, then add cherries and toss well. Let stand 30 minutes. 4. Roll out larger piece of dough (keep remaining piece chilled) on a lightly floured surface with a lightly floured rolling pin into a 14-inch round. Fit into a 9-inch pie plate. Trim any excess dough to leave a 1/2-inch overhang. Chill shell while rolling out top crust.
5. Roll out remaining dough on a lightly floured surface with a lightly floured rolling pin into a 12-inch round.
6. Toss cherries well again, then add to shell and cover with top crust. Press edges of crust together, then trim, leaving a 1/2-inch overhang. Fold overhang underneath, then crimp decoratively and brush top crust with milk. Cut out 5 (1- by 1/2-inch) teardrop-shaped steam vents 1 inch from center and sprinkle with sugar (1 tablespoon).
7. Bake pie on preheated baking sheet 30 minutes, then cover edge with a pie shield or foil and reduce oven temperature to 375°F. Continue to bake until crust is deep golden and filling is bubbling in center, 50 minutes to 1 hour more. Transfer pie to a rack to cool completely, 3 to 4 hours.