How do you engineer the perfect cookie? Let these food scientists show you

Lesa Tran Lu has a Ph.D. in chemistry, but she's perhaps best known as the scientist who can teach you to engineer the perfect cookie. "Perfect," however, is a subjective matter, she said. 

The daughter of fortune cookie makers, Tran learned to bake at a young age. She also taught an immensely popular entry-level chemistry of cooking class at Rice University.

"I can teach you the science of making the perfect cookie for you, but by no means do I claim to have the perfect recipe," she said. 

A basic understanding of baking chemistry can help you tailor your baking to your preferences. 

"Baking is science," she said. "You make predictions, make observations, analyze it and refine your model and repeat it all over again. That's exactly what the scientific method is." 

Katie Button is the chef and owner of Curate in Asheville and holds degrees in chemical and biomolecular engineering. She said it's important to be clinical about your tweaks. In baking, small changes can yield big results.

"Start with a recipe you like and change one thing, and keep the rest the same," she said. "Learning about baking and the chemistry behind baking, it makes you wonder how we ever landed on the perfect cookie."

Here's how to get started finding yours.

What do baking soda and powder do?

Baking powder and baking soda are both chemical leaveners, meaning they create gas bubbles in baked goods, helping them rise.

"So you get this nice crumb, not something that's dense and compact and hard," Button said. 

Yeast is too slow-acting for cookies. Baking powder and soda are best for cakes, cookies and quick breads.

But both baking powder and soda need acid to activate. In the case of soda, the baker adds the acid. In biscuits, that could be buttermilk. In cookies, brown sugar will do the trick.

Baking soda acts fast, and the chemical reaction occurs as soon as it comes into contact with acid. 

Baking powder is essentially baking soda with a powdered acid that's activated by water. It's often labeled as double acting, which means it contains a selection of acids that dissolve at different points during baking. It creates thicker yet lighter cookies.

"Baking soda alone does not give as much rise," Tran said.

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What else does sugar do?

Sugar makes things sweet, but it's also key to texture.

Brown sugar contains molasses, which is acidic. As such, it reacts with chemical leaveners to lend more lift. 

"The molasses that helps (brown sugar) have its color is also very oozy, which means it has more moisture retention, meaning it's not going to contribute to a crisp cookie," Tran said. 

A higher white sugar ratio will yield a cookie that's more crisp than chewy. Like a soft cookie but with crisp edges? Roll your dough in granulated sugar, Button advised.

"And then when the cookies are cooling, the sugar, which melts when it's cooking, recrystallizes afterward and adds a nice crunch and crisp," she said.

What is gluten, really?

Gluten is a protein found in flour that gives structure to baked goods. Those proteins are activated by water and developed through mixing. Once moisture and movement come together, gluten proteins form bonds with each other.

"That creates a complex structure you can move and bend and roll and knead," Button explained.

The more the gluten gets worked, the more bonds get formed between the proteins, which creates a "pull" or chew, she said. While it's essential to work gluten for bread, that's not so much the case with cookies. 

"The important thing is not to develop the gluten too much," she said. "You want a more tender texture, which is why you take certain precautions with cookies." In other words, don't beat or blend your batter too much. Stir everything together quickly, and then hands off. 

What else do I need to know?

• Your dough's temperature before it goes into the oven impacts texture. Cooling it in the fridge or freezer will help cookies stay thicker.

  "Room temperature dough heats faster and has a wider spread on the cookie sheet, while cooling it keeps it thicker because the melting rate is slower," Tran said. Further, dough that's been rested has time to develop more complex flavors and textures because the dough molecules are allowed to "open up," she said. 

• The protein in eggs adds structure to cookies. Eggs also add fat and water, so the best egg replacements have similar fat and water content. For that reason, a flax egg, a mix of flax meal and water, makes a good substitute.

• Fat is flavor, sure. But it's also texture. Incorporating air into your fat by creaming it adds lift to your baked goods. Use melted butter if you want a cookie that's dense, not cakey.

Mackensy Lunsford is the food and culture storyteller for USA TODAY Network's South region and the editor of Southern Kitchen.

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Reach me: mlunsford@southernkitchen.com