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Rhubarb Π

March 14, 2011

I decided – kind of at the last minute – to make a pie this weekend. It may have been to avoid packing; it may have been because I was craving rhubarb.

It may have been because, even though pie is one of the great loves of my life, I always seem to forget about Pi Day until after the fact.

I wasn’t going to let it pass me by this year, and I remembered a story about a rhubarb pie my grandmother used to love. The only problem was that I had never actually tasted that pie or seen the recipe. My family likes to talk about food almost as much as we like to eat it, so there are dozens of dishes I only know through family legend.

Luckily, I have an obliging mother who went through a pile of decades-old food magazines and recipe clippings to scan this 1965 classic for me. Thinking about the years my grandmother spent amassing recipes – clipping them out of magazines, copying them in shorthand – makes me really grateful for Google.

True to its old-school source, this pie filling only has 5 ingredients: rhubarb, sugar, salt, butter and cornstarch. (Well, tapioca actually, but cornstarch is what I had.)

I was confused: where was the innovative twist? The secret ingredient? I guess the lesson hidden in this family legend is that it’s ok for rhubarb to taste like rhubarb, without a lot of distractions. I was skeptical about the huge amount of sugar, but I stuck to the recipe and it was a perfect balance of tangy and sweet that let the rhubarb do the talking.

When I first spread out the rhubarb, it seemed a little sparse. I had a feeling why, so I did a little math:

The recipe calls for a 9-inch pie plate, but I only have a 10-inch pie plate. If I had wanted my filling to be the same height (h) as the recipe intends, how much more filling (volume, or V) do I need? (Let’s assume all the pie plates involved have straight sides.)

Formula for the volume of a cylinder: V = Πhr²

For a 9-inch-diameter pie plate:       V = Πh4.5²          or           V = Π*h*20.25

For my 10-inch diameter pie plate:  V = Πh5²             or           V = Π*h*25

25Πh / 20.25Πh = 1.2195

Divide 25 by 20.25 (=1.2345) and we know that my pie dish’s volume is about 23% larger than that of a 9-inch pie plate. In other words, I can multiply each amount in the recipe by 1.2345 in order to adapt it to a 10-inch pie plate.

Or I can skip all that and just have a thinner layer of pie filling – it bakes faster.

This crust was not very co-operative. It was probably the temperature or humidity, but sometimes it seems like pie crust has a mind of its own. It knows when you are under pressure, when Pi Day is coming and you are about to leave the country. It knows when you want a really pretty picture to put on the Internet, and it is determined to get in your way.

Delicious with strawberry cheesecake ice cream.

Happy Pi Day!

Rhubarb Π

from Good Housekeeping’s 1965 Pie Manual

Double-crust for a 9-inch pie (recipe below)
1 1/2 cups granulated sugar
1/4 teaspoon salt
1/4 cornstarch (or quick-cooking tapioca)
1 egg-white, lightly beaten
4 cups rhubarb (about 1.5 lbs), chopped into 1-inch pieces
2 Tablespoons unsalted butter

1. Preheat oven to 425°F.
2. In a small bowl, combine sugar, salt and cornstarch.
3. Place bottom-half of pie crust in a 9-inch pie dish, brush lightly with egg white.
4. Spread out half of the rhubarb in the pie dish. Top with half of the sugar mixture. Repeat with the remaining rhubarb and sugar.
5. Dot with butter.
6. Cover with the rest of the pie crust. If using a circle, cut vents in the top for steam to escape. Alternatively, create a lattice crust.
7. Brush the top with egg white. Bake until the top is lightly browned, 20-25 minutes, then cover the top with aluminum foil. Return to the oven and bake until filling is cooked-through, 10-20 more minutes.
8. Let finished pie cool for a few hours before serving, in order for the filling to set. Serve with ice cream or sweet custard.

Like a lot of fruit pies, this is even better the next day after the juices are soaked into the crust.

Basic Pie Crust

Makes 2 crusts for a 9-inch pie plate

2 1/2 cups all-purpose flour
1 teaspoon salt
3/4 cup butter or vegetable shortening (I usually use 6 Tblsp of each)
~5 Tablespoons ice water

1. In a medium bowl, mix together flour and salt.
2. Cut butter and/or shortening into the flour with your fingertips until lumps are the size of small peas.
3. Add water a little at a time until the dough holds together in a ball. Divide dough in half to create two crusts.
4. If you are using butter, chill the dough for an hour before rolling it out. (Butter is a bit more temperature-sensitive than shortening, in my experience.)

One Comment leave one →
  1. Aunt Chrissy permalink
    March 14, 2011 3:10 pm

    Loved, loved, loooooooooooved this in every way there is to LOVE it…(sentimentally…aww, my baby sister, my mother, my grandmother, my great-grandmother…pi…your crazily impressive mathematic equations…the photography, oooh, and I want to EAT THAT PIE RIGHT NOW!…and, yes….Hanah and Scott are coming home!!! ) Love you, darling, and can’t wait to see the next recipes from the good ol’ USA.

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