Picture your perfect cookie. Is it chewy or crunchy? Gooey or crisp? Fluffy or dense?
Either way, you owe your favorite cookie attributes to chemistry. By manipulating chemical reactions it is possible to produce the perfect cookie, whatever that may be.
A primary attribute of the perfect cookie is desired thickness. What exactly makes a cookie spread in the oven? The chemistry of egg proteins limit exactly how much a cookie can spread horizontally. Proteins inside an egg are very sensitive to temperature. As the temperature rises, they become more intertwined to form a solid structure. They create a sort of shell, or skeleton for the cookie, providing structure and strength that prevent the cookie from collapsing in the oven.
One way to manipulate the cookie’s size is to regulate butter temperature. Starting with melted butter means the dough is wetter, and will spread out faster. For a plumper, thicker cookie, try cold butter. Butter temperature also affects texture. It changes size and shape of the air pockets that remain after the water in the butter is converted into gas. Melted butter means more small holes, creating an overall chewier cookie. Cold butter creates larger air pockets for a fluffier cookie.
What makes a cookie rise? Around 212 degrees Fahrenheit, the water trapped in the dough becomes steam and pushes through the dough, causing it to rise. The baking soda or powder will break down into carbon dioxide gas which, as it escapes, will cause the cookie to rise even further. These escaping gases puncture the dough, creating an additionally light and flaky structure.
Substituting baking soda for baking powder will create a fluffier, lighter cookie. Powder contains more leavening elements because it produces carbon dioxide gas as it's mixed into the dough as well as during the cooking process.
Now, for flavor. As the cookie is about to finish baking, some real chemical magic begins to happen. As sugars in the dough begin to break down, the previously colorless, odorless sugar crystals undergo a process called caramelization. Here’s where things get pretty atomic. As the process of caramelization occurs, volatile chemicals are produced that create the characteristic caramel flavor. As the temperature rises, the sucrose decomposes to form glucose and fructose. Then, the individual sugars condense and lose water to react with each other. The result is a liquid that abounds with complex aromas and tastes.
Though a cornerstone of cooking and baking, caramelization is still a little understood process comprised of many complex reactions. If anyone out there is studying this, I volunteer to help with research!
Adding a mixture of darker sugars will super-charge the flavor through a process called the Maillard reaction. Plain ol’ white sugar doesn’t work well because it contains predominantly sucrose. Darker sugars, molasses, honey and brown sugar for instance, are packed with glucose and fructose, which when combined with heat produce rich and complex flavors through the Maillard reaction.
Nothing spreads holiday cheer quite like a meticulously engineered sugary treat. Through chemistry and a little kitchen magic, you can have the perfect cookie!