Ancient Cooking: Pi(e) Day and the Science of Baking

Who doesn't love pie on Pi Day?

Watch the video, or read the transcript below!

 

Science All Around


At WOW STEM we've talked about things like discovering fundamental laws of motion, novel types of viruses, and how plants respond to light. But science isn't just these big discoveries made in labs or universities. If you stop to think about it, you'll see tons of science and math in normal, everyday activities like buying groceries, knitting a sweater, or baking a pie.


For lots of the historic women we've talked about at WOW STEM, the reason that they were able to make their incredible discoveries was because they came from rich families and were lucky enough to have financial support for their work and education. So many women throughout history, and even today, don't have that privilege. But that doesn't mean that they weren't participating in science! Lots of important inventions and discoveries were made by people doing what was traditionally considered "women's work"- things like cleaning, sewing, and cooking. Although we will never know the names of many of these women, they still deserve to be celebrated. Let’s talk about baking!


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I don’t know about you, but I’ve had plenty of baking mishaps when I’ve forgotten an ingredient or made an incorrect measurement. Creating a recipe from nothing is a lot of work. It requires careful, scientific experimentation and plenty of failures. At some point someone had to develop the recipes for foods we eat every day. And chances are high that that person was a woman who spent years of her life experimenting in her kitchen and perfecting her recipes. So in celebration of March 14th (3/14), also known as Pi Day, we’re baking a pie and learning about the science that goes into it!


For more about the irrational beauty of the number π, check out our other celebratory post: Ancient Mathematics: Baking a Pi.

 

Crust


We’ll start by making the crust. The main ingredients for the crust are flour, fat, and water. The fat will make our crust very crispy and flaky because oil and water are what’s called immiscible, meaning they do not mix. Our flour will absorb the water molecules, and then when we add butter, the water in the dough will refuse to mix with the oily fat molecules. This creates distinct layers in the crust and creates the flaky texture we love in a pie crust!

A bowl of butter cut into slices.

In the flour is a protein called gluten. Gluten is very stretchy when it’s hydrated, or in contact with water. You can make gluten even stretchier by kneading the dough because this gives the gluten proteins a chance to stick to each other and form long chains!

Dry flour in a canister.

Some peoples’ bodies can’t process gluten very well, so gluten-free flours use other types of proteins to replace gluten’s stretchiness. No other proteins are quite as stretchy and strong as gluten, but over many years food scientists have done a great job at making gluten-free foods very tasty and enjoyable!

 

Filling


Now that our crust is done, we’ll move on to the filling. Today my filling is going to be strawberries, blackberries, and blueberries. These berries are made of plant cells, which are pretty different from the cells in our own bodies.

A bowl of blackberries, strawberries, and blueberries. Madelyn is holding a blackberry toward the camera.

One of the main things that makes plant cells different is that they have a rigid cell wall that is made of cellulose, which is a kind of fiber. Fibers and starches are made up of long strands of individual sugar molecules, linked together very strongly!

Cartoon of a plant cell with its rigid cell wall and its organelles.
Plant cells are pretty different than animal cells. One huge difference is that plant cells have a rigid cell wall made of cellulose.

Diagram of a cellulose molecule
Cellulose is a chain of individual sugar molecules which are linked strongly to each other. The strong cellulose molecule makes up the stiff wall of a plant cell.


But this strong linking means that our body cannot break down most of the fibers and starches from plants. This is why we cook a lot of our food– the heat from cooking breaks down the starches and fibers into shorter chains of sugars. Then our body can process those nutrients more easily.


Cooking also changes the taste of a lot of foods, because of microscopic chemical changes that happen during the process. This berry might be a little tart when it’s fresh, before it’s added to the pie. But cooking will break down some of its starch and fiber into individual sugar molecules, which our taste buds will identify as “sweet”. And it certainly doesn’t hurt that this recipe calls for additional sugar!


The recipe also calls for some corn starch. Because cooking breaks down the cellulose in the plant cells, that means that the water stored inside will begin to leak out! Adding more starch back into the mixture will thicken it and prevent the filling from getting too watery. The starch will stick to the water molecules which have escaped from the berries. Because the water molecules are stuck to the starch, they will not flow very easily, and the filling won’t be too runny.


 

Topping


Alright while my pie is baking, I’m going to make some fresh whipped cream to go with it. Heavy cream is what’s called a colloidal suspension. This means that it’s made up of large particles that are floating around inside a fluid. In cream, the large particles are globs of fat that are floating in water. The reason that the fat forms globs is because fats and water do NOT like to mix, so the fat molecules stick together in an attempt to avoid as much water as they can. This leads to them forming globs instead of spreading evenly throughout the water.

Milk under a microscope. Colloidal suspension of fat globs in water.

But when I start whisking the cream, two things start to happen. First, the whisk is breaking up those fat globs. Second, air is being forced into the cream. The fat molecules hate water a lot, but they don’t mind the air that much. So as the whisk breaks apart the fat globs and adds air, the individual fat molecules will link up in long chains and trap the air in the gaps! The fat molecules would much rather stick together in globs, but if that isn’t an option, they’re content to spread into chains and hang out with air instead– really anything to stay away from water.

Madelyn holds a whisk with whipped cream sticking up off the end.
Breaking up the fat globs and forcing air into the cream results in a stiff mixture that is light and fluffy!

 

Time to Eat!


I can tell that my pie is done when the crust is a nice golden brown! That's when I can tell it has that sweet, nutty, toasted flavor. While it was baking the heat kickstarted a reaction between the proteins and sugars in the crust. The proteins and sugars went through a series of complicated chemical changes called the Maillard reaction. The result is that indescribable flavor that makes browned vegetables, meat, and bread so delicious.

Madelyn taking the pie out of the oven and showing that it has finished baking.

I didn’t write this recipe myself, but it blows my mind that at some point someone figured out the best way to make a pie crust, and someone else discovered that whisking cream makes it fluffy and delightful, and waaaay before that humans discovered that cooking plants made them sweeter and easier to digest. Today I made a pie using a recipe I found on the internet, but thousands of years and thousands of women’s culinary discoveries and kitchen experiments from around the globe made this recipe possible. What a great way to celebrate Pi Day. Happy baking!

A slice of pie on a plate with a dollop of whipped cream on top. To the right of the plate is a mug with the symbols square root of negative one, 2 cubed, capital sigma, and pi. Beneath these symbols it says "...and it was delicious!"

Credits:

Written by Madelyn Leembruggen

Edited by Caroline Martin

Cartoons by Sachi Weerasooriya


Primary sources and additional readings:

Mixed Berry Pie recipe by Sabrina Snyder

What is Gluten? The Science Behind Great Dough from Serious Eats

Carbohydrates from Khan Academy

Cream Science: On Whipping, Butter, and Beyond from Serious Eats

 

Keep celebrating Pi Day with these activities!


Expand (10 minutes): Learn about the irrational beauty of the number π, and try estimating its value using every day objects, by checking out our other celebratory post: Ancient Mathematics: Baking a Pi!


Play (10-15 minutes): Since the decimals of π go on forever, you can find almost any string of numbers inside it. You can use this website to search for particular digits in the number, like your birthday or your lucky number.


Experiment (45-60 minutes): We learned that gluten is a protein in flour that makes dough strong and stretchy. How do different amounts of gluten affect a dough? With a grown up's help create some Great Balls of Gluten! to find an answer...


Investigate (20-30 minutes): One crazy cool way to calculate the value of π is with probability! If you randomly drop a bunch of toothpicks on a sheet with long, straight parallel lines, the toothpick will land on one of those lines with a probability that depends on π. You can learn about this phenomenon, "Buffon's Needle", in a real life experiment or with a computer simulation. How many toothpicks do you need to get close to the real value of π?


Deepen (15-30 minutes): To learn more about the basics of calculating the area and circumference of circles, and how that relates to π, check out Khan Academy's great introduction.


Experiment (30-45 minutes): The Maillard reaction is a series of complicated chemical reactions that are kickstarted by the heat of cooking. It's what is responsible for the golden brown color and sweet, nutty flavor of a pie crust. You and your grown up can Smell the Maillard Reaction in your own kitchen!