The Chemistry Of The Perfect Cookie

ROXANNE KHAMSI: Here’s a quick challenge for you. With some serious food holidays approaching, check your cookie chemistry. Because sometimes your cookies, while tasty, just aren’t crispy enough for your discerning cousin, or aren’t chewy enough for your favorite aunt. So how do you engineer the perfect cookie?

Jennifer Powers is a science educator at the Oregon Museum of Science and Industry, OMSI, in Portland, Oregon. And she wrote an education resource for us on this topic.

Hi, Jennifer.

JENNIFER POWERS: Hi. Thanks for having me.

ROXANNE KHAMSI: If you look at a cookie as a science experiment, there are a ton of variables in there. But we’re going to talk about just one: sugar. What’s the importance there, besides sweetness?

JENNIFER POWERS: Yeah, there’s actually a lot of science that goes into the different types of sugars. And the type of sugar that you choose to put in your cookie dough, it’s significantly going to change how that cookie turns out. So maybe you want a crispy cookie, or maybe you want a chewy cookie, and the type of sugar that you choose is going to determine the crispiness or the chewiness, or at least partially determine the crispiness or the chewiness of your resulting cookie.

ROXANNE KHAMSI: And one can’t really engineer a half chewy, half crispy cookie. You kind of have to go all in, right?

JENNIFER POWERS: Yeah. You can always do a balance, right? And that’s the fun of this activity, is it’s really about digging in and finding the cookie that works for you, and trying things out until you get there. And who doesn’t love making a ton of batches of cookies in order to find the best cookie for you, right?

ROXANNE KHAMSI: You have to find the crowd-pleaser.

JENNIFER POWERS: Exactly.

ROXANNE KHAMSI: So if you play with the type of sugar in the mix, what effect does that have on the final cookie? What’s the magic in the sugar?

JENNIFER POWERS: So the key to sugar actually has a lot to do with the moisture in your cookie dough. So if you’re going with all-white sugar, white sugar is almost 100% sucrose. But if you go with a mixture of white and brown sugar, brown sugar contains more fructose and glucose. And the size of the molecules there are going to hold on to different amounts of moisture in your cookie dough.

Sucrose is a bigger molecule, and it’s just not able to hold on to as much moisture. So if you’re looking for a crispy cookie, using more white sugar is going to dry out your dough a little bit more, and you’re going to get crispier cookies. But if you add in some brown sugar, or completely go all in, do all brown sugar, you’re going to have more fructose and glucose molecules, they’re smaller, they’re going to hold on to more moisture, and you’re actually going to end up with a chewier and more moist cookie.

ROXANNE KHAMSI: So you’re describing a really cool tweak that we can make with the sugar we use in order to change the chewiness and crispiness of the cookie. Is that effect different from the one we would get just by baking the cookies a little less?

JENNIFER POWERS: That’s the fun about experimenting with the chemistry of cookies, right? Because we’re talking about moisture levels here, not really about sugar. Sugar is a way to change the moisture level in your cookie. And you’re right, if you leave the chewiest, most brown sugar-concentrated cookie dough in the oven for too long, you’re still going to end up with a crispy cookie. So it’s a balance. It’s a balance of finding the right temperature to bake your cookie at, the right amount of time, and the right sugar and other ingredients, in order to come out with just the perfect cookie for you.

ROXANNE KHAMSI: So here’s our challenge. Try this at home. Engineer the perfect cookie.

Jennifer Powers is a science educator at the Oregon Museum of Science and Industry, in Portland, Oregon.

If you want to dive deeper into kitchen chemistry, you can find her resource on our website, at sciencefriday.com/holidayscience.

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