Pi Day is celebrated on March 14th (3/14) around the world. Pi (Greek letter “π”) is the symbol used in mathematics to represent the ratio of the circumference of a circle to its diameter — which is approximately 3.14159.
As mathematician Manil Suri explains in the New York Times:
“Pi is irrational, meaning it cannot be expressed as the ratio of two whole numbers. There is no way to write it down exactly: Its decimals continue endlessly without ever settling into a repeating pattern. No less an authority than Pythagoras repudiated the existence of such numbers, declaring them incompatible with an intelligently designed universe.
And yet pi, being the ratio of a circle’s circumference to its diameter, is manifested all around us.”
How did Pi turn into a yearly holiday celebrated by eating pie?
The March 14 celebration of Pi Day – the annual celebration of a never-ending number, began at the San Francisco Exploratorium.
The San Francisco Exploratorium, as their website notes, is not just a museum: “it’s an ongoing exploration of science, art and human perception—a vast collection of online experiences that feed your curiosity.”
But perhaps more importantly, the website explains that in 1988, three years after the death of Exploratorium Founder Frank Oppenheimer (brother of J. Robert Oppenheimer), the staff gathered to soul search and brainstorm. Former staff physicist Larry Shaw made the link between March 14 (3.14) with the digits of pi (3.14159…), and saw it as a great opportunity to promote the Exploratorium. Pi Day was born.
Pi Day became an annual Exploratorium tradition for staff and the public, and the idea snowballed into something much bigger. Now it’s celebrated by math lovers and educators worldwide. In March 2009, Pi Day became an official U.S. national holiday.
Mathematician Evelyn Lamb observed wryly in the Chicago Tribune:
“ . . . classrooms and libraries around the country have nerd-friendly gatherings where students eat pie and maybe have a little fun with math. I scoff at the goofy marketing gimmicks, but I have to respect the fact that Shaw started a math holiday recognized by people all over the world that has been so successful that it now has scoff-at-able marketing gimmicks.”
A math holiday: what a great idea indeed! So what kind of pie should one have to celebrate?
In almost any survey one can locate on the web, apple comes out on top as the most popular pie. But here’s a surprise: a 2017 Harris poll on Pi Day indeed found apple pie got the highest percentage of votes, but coming in second was pizza pie! No problem: have pizza first, then apple pie for dessert. Here is a recipe for one of my favorite apple pies:
This particular recipe from the Chicago Tribune includes two ingredients to the usual list (cheddar cheese and alcohol) that add a great twist to a great pie:
Cowgirl Apple Pie
Prep: 1 hour, plus 1 hour to chill
Bake: 40 minutes
Makes: One 9-inch pie
1 disk cheddar pastry, see recipe
3 pounds (about 7) apples (a mix of tart, such as Granny Smith, and crisp, such as Gala)
6 tablespoons unsalted butter
¾ cup sugar
¼ cup whiskey or brandy (or sub 1 tablespoon cider vinegar)
1 tablespoon fresh lemon juice
½ teaspoon ground cinnamon
¼ teaspoon fine salt
1. Slice: Peel, core and slice apples 1/4-inch thick.
2. Soften: Heat butter in a wide skillet over medium-high heat. Slide in apples; cook until softened, about 5minutes.
3. Thicken: Add sugar, whiskey, lemon juice, cinnamon and salt. Cook, stirring, until syrup clings to apples, about 5 minutes.
4. Cover: Scrape cooked apples into a buttered 9-inch cast-iron pan (or a buttered 9-inch pie plate).
5. Roll: Roll out pastry; trim to a 12-inch circle. Fit pastry over apples, tucking in edges. Snip a vent into the center.
6. Bake: Set pan on a rimmed baking sheet. Slide into a 375-degree oven and bake until pastry turns golden brown, 35-40 minutes. Cool and enjoy.
Cheddar pastry: In a food processor, pulse until mixed: 1 cup flour, 2 teaspoons sugar, 1/4 teaspoon fine salt. Drop in 5tablespoons cold unsalted butter, 2tablespoons cold shortening and 3/4 cup shredded sharp cheddar. Pulse until mixture looks crumbly. Turn out into a large bowl. Drizzle in about 3 tablespoons cold water, mixing gently with a soft spatula until pastry comes together. Pat into a disk. Wrap and chill 1 hour.
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