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Since I was little, my mom and I have used a couple of secret moves to make the flavors in our cookies sparkle. Slipping espresso powder into our chocolate chip cookie dough gives the cocoa flavor an extra kick. Tossing a slice of bread into a cookie container, like magic, would make treats stay softer for a few extra days. We didn’t know why these tricks worked — only that the cookies tasted great.
Ahead of the holidays, I spoke to scientists and baking experts to find out the chemistry and physics behind these and other baking techniques that can take your treats to the next level. By playing with the basic elements in your cookies — sugar, protein, aromatics and moisture — you can unlock entirely new flavors without changing the texture of your favorite family recipe.
Here are four basic tricks to start.
Too often, making homemade caramel corn and caramel apples ends with pans crusted over with crystallized sugars. Luckily for your cookies, scientists and chefs have discovered a simple way to infuse desserts with a caramel flavor without the burned, melted mess.
When heated, sugar doesn’t exactly “melt.” Instead, it decomposes and liquifies into a completely new substance: caramel.
In 2008, scientists at the University of Illinois at Urbana-Champaign were searching for the precise melting temperature of sugar when they made a sweet discovery about how it decomposes.
Trapped within pockets of sugar crystals is a supersaturated sugar water called mother liquor. By heating white granulated sugar at a low temperature over time, the researchers could caramelize the mother liquor without affecting the physical structure of the surrounding sugar.
Toasting your sugar gives it a caramel flavor and a beige color. Image by Jamie Leventhal
Scientists previously thought that caramelization happens around 320 degrees Fahrenheit, but the Illinois team found that mother liquor is more heat-sensitive, caramelizing even before the surrounding sugar — called sucrose — can liquify. Bakers used this science to develop new techniques for lacing their baked goods with caramel.
One pastry chef, Stella Parks, created a low-and-slow recipe for toasting large batches of sugar at a low temperature, over a long period of time, before baking. Her method darkens and caramelizes the sugar while keeping its crystalline structure intact, which helps retain the original texture of the cookies.
Parks stumbled onto the technique before hearing about the University of Illinois study, when she accidentally left a pan of sugar in an oven for a few hours. After the study was published, she finally understood the chemical mechanism behind what was happening.
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“There’s no flavor to sugar, it just tastes sweet,” said Parks, a James Beard award-winning author. “By toasting it, the sucrose undergoes thermal decomposition, and that’s where it starts developing these caramel compounds.”
Parks said that the toasted sugar adds a little hint of bitterness and a toffee, nutty flavor. (In my kitchen, toasting the sugar filled the air with a euphoric dream of caramel cotton candy and sticky-sweet scented positivity.)
Unlike brown sugar or molasses, which can alter a cookie’s texture, you can substitute toasted sugar for white granulated sugar without risk of altering the structure. Toasted sugar fits best in recipes with strong vanilla or nutty flavors — like sugar cookies — or for recipes that often come out too sweet — like meringues.
Caramelizing the sugar beforehand brings bright notes to your cookies, but you can further expand your dessert’s flavor profile by playing with proteins.
The Maillard reaction, which we explored in “How to cook the perfect Thanksgiving turkey, according to science,” happens when the amino acids in proteins and sugars react with heat and time to break down and recombine into thousands of new flavor compounds. It’s what makes the crust of a steak brown and exploding with flavors.
Chocolate chip cookies brown in the oven because of the Maillard reaction. Image by Jamie Leventhal
Parks recommends throwing a little malted milk powder into your cookie batter to capitalize on the Maillard reaction. Malted milk powder adds a butterscotchy note, and its milk solids fuel the reaction to make cookies browner and more flavorful than before.
For more advanced bakers, you can also brown the butter, depending on the recipe.
Brown butter and malted milk powder work well in recipes that could use a boost of flavor, like a shortbread, but can go unnoticed in especially fragrant cookies like gingerbread.
If your favorite cookie has a chocolate element — say, the classic chocolate chip — then you can fine-tune those deeper flavors by lifting their aromas.
I detest coffee-flavored desserts, but my mom’s deft pinch of espresso powder in our chocolate chip cookies amplifies the deeper chocolatey undertones of the cookie — without adding any coffee taste. But how?
The answer lies in substances called volatile organic compounds. These chemical aromas evaporate into surrounding air, which is what causes baked goods to smell so irresistible. Both chocolate and coffee contain a compound called pyrazine, the thing responsible for that dark and slightly bitter taste.
You can enhance the chocolatey aromas of your cookies with espresso powder. Image by Jamie Leventhal
Kent Kirshenbaum, a biochemist at New York University, explained that flavor perception is determined by both odors and tastes, so adding more aromatics to the cookie could let us detect the understated flavors we didn’t notice before.
“A lot of times, we’ll use a milk chocolate that has a really nice melting profile, but doesn’t always have the strong chocolate flavors,” Kirshenbaum said. “Adding some espresso grounds to your cookie dough helps to amp that back up because we’re providing those pyrazine molecules.”
But why do we taste chocolate and not coffee? Because our perceptions of flavor are guided by our expectations, Kirshenbaum said. In other words, though chocolate and coffee both contain pyrazines, we’re more likely to experience chocolate because that’s what our brains expect in the cookie.
Shelly Schmidt, the food chemist whose lab at the University of Illinois at Urbana-Champaign made that all-important caramelization discovery, explained that cookies become stale because of a difference in water activity between the sweet treat and the room. This contrast causes water molecules in the cookies to evaporate into the drier air in an equalizing process. Out in the open, water molecules leave the wetter cookie to create a balance in humidity with the larger, less humid room.
Schmidt said that the low humidity in a kitchen would pull moisture from a fresh cookie sitting out on the counter. If you want to preserve the texture of your cookies, simply throw in a piece of sliced bread to the storage container. But be warned — every time you open the lid to grab a treat, you’re exposing the cookies to dry ambient air. To keep moisture in for longer, simply replace stale bread with a fresh piece every few days.
“The bread has a very high water activity, like 96 percent, so it’s going to give back water and help the cookie from drying out,” Schmidt said.
Whether you’re a seasoned baker or a nervous novice, it’s easy to go wrong with a new recipe for holiday snacks.
When I baked cookies for this story, I accidentally liquified the sugar, dropped half an eggshell into the stand mixer (which I was able to fish out, for the record) and forgot to remove three trays of cookies from the oven during a phone interview, burning the bottoms.
In the end, the new and scientifically improved cookies were a scrumptious success; our staff gobbled down more than 100 in a single day on two separate occasions. Because sometimes, when it comes to cookies, as food author Jeff Potter succinctly put it, “The one right in front of me is always the best one.”
2 ½ cups (14 ounces) roughly chopped mixed dark, milk and/or white chocolate (not chips)
2 ¾ cups (12.5 ounces) all-purpose flour, such as Gold Medal
2 sticks (8 ounces) unsalted butter, soft but cool — about 65 degrees Fahrenheit
1 packed cup (8 ounces) light brown sugar
1 cup (7.25 ounces) white sugar*
2 teaspoons Diamond Crystal kosher salt (half as much if iodized), plus more for sprinkling
1 teaspoon baking soda
½ teaspoon baking powder
1 tablespoon vanilla extract
⅛ teaspoon grated nutmeg
1 large egg, straight from the fridge
Our science modifications
*1 cup of toasted sugar instead of white sugar
2 tablespoons of malted milk powder
1 tablespoon of espresso powder
Recipe from BraveTart: Iconic American Desserts by Stella Parks. Copyright © 2017 by Stella Parks. Reprinted with permission of W.W. Norton & Company, Inc. All rights reserved.
Jamie Leventhal is an Associate Producer of Digital Video for the PBS NewsHour. She started at NewsHour as a Science & Social Media News Assistant, and covers topics on science, global health and tech. She earned a journalism degree from Northwestern University, and has previously worked at Popular Science and Quartz.
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