You like thin and crispy cookies, but your parents like soft and chewy and your friends like chewy AND crunchy. How do you satisfy them all? Let's take a look at each of the ingredients in a cookie and see how they affect the final product, so that you'll be able to make your perfect cookie! Here, I'll focus on the spread and texture, as well as the taste and sweetness to craft your cookies.
Background
Chocolate chip cookies are a classic dessert that have been around for decades after they were accidentally invented in the 1930s. Although they may look simple (just cookies and chocolate, what more could there be?), the chemistry behind how they are made is actually quite complex. The biggest variation between two different cookies is usually in their texture, whether it's a thick, soft cookie from a local bakery or a thin, crunchy one from a prepackaged box in the snack aisle of a grocery store. But what causes such a stark contrast in the mouthfeel of the cookie?
Chocolate chip cookies are one of my favorite desserts, but I am a bit particular about their taste and texture. I have tried many different recipes from cook books and internet articles, but the results are often not what I want. Some cookies were too crunchy, similar to eating a bag of tortilla chips, while others were far too underbaked and soft. I wanted to achieve my ideal cookie, one that is crunchy on the edges but chewy in the interior. In terms of taste, store-bought cookies are generally too sweet and can sometimes just taste like a mouthful of sugar. Thus, I wanted to create a batch of cookies that would be mildly sweet with stronger flavors of the chocolate chips, vanilla, and brown sugars coming into play.
How could I create such a cookie though? I decided the best way would be to learn how each ingredient (variable) influenced the cookie and to experiment with various controls (keeping certain ingredients constant while changing others) to determine my final recipe. There are several ingredients in a cookie, and it would take forever to try experimenting with all of them, so learning the chemistry of the baking process could make choosing my variables a lot easier!
Procedure
Making cookies is relatively simple compared to other desserts that require more technical precision. A little extra flour or a little less sugar won't make too much of a difference. However, for scientific purposes, it's best to measure everything in grams for more precision and try to stick to the exact proportions. For my specific recipe with servings and measurements click here.
I started by preheating my oven so that it would be at the exact temperature I needed when the cookies were ready to be baked. As shown on the image to the left, oven thermometers can be helpful in determining what the exact temperature of your oven is, because it's often different from the number you set the dial to! Next, I began with measuring out the dry ingredients - flour, baking soda, baking powder, and salt - on an electronic balance, making sure not to add too much or too little of any ingredient before mixing them all together.
In another bowl, I creamed together my butter and sugars until they were light and fluffy - making sure not to overmix or undermix!
I then added my egg and vanilla extract. The final step before baking was to mix the wet and dry ingredients. I added half the flour mix into the wet ingredients first, before incorporating the other half to ensure there weren't any left over flour clumps (as depicted in the image to the right). I gently folded in the chocolate chips.
Finally, I used a tablespoon to scoop uniform amounts of dough and rolled them into balls. I baked the cookies in the preheated oven for approximately 12 minutes to make sure they weren't overbaked, as that would ruin the chewy interiors! I took the cookies out of the oven when they are slightly brown on the edges.
As I tasted my freshly baked cookies, they were warm with an initial crunch that gave underway to a chewier inside. The gooey chocolate chips melted in my mouth and the flavors of butterscotch and vanilla were a lot more complex without plain sugar overpowering them. My cookies had a great spread for those crunchy edges, but my baking time and temperature made sure they didn't lose their softer centers or burn. They were a success! If you want to know how I finally created this perfect recipe for my heavenly cookies, let's get into the nitty gritty science.
Science!
Let's first break cookies down into their separate ingredients and dive into how these ingredients interact with each other to form such mouthwatering treats!
Flour: The main differences in different kinds of flour are due to their protein content. When flour is mixed with water from the wet ingredients, it develops gluten, a network of interconnected proteins found in bread.
Cake flour has a relatively low amount of protein, leading to less gluten formation. Thus, cookies made with only cake flour will be very soft, almost like a cake. Bread flour cookies, on the other hand are very chewy, as they have high protein content.
The amount of flour also affects the texture of the cookie, as it holds up the structure. A small amount of flour compared to butter will create spread-out cookies like a wafer. Extra flour compared to butter will give a dense cookie that barely spreads with doughy centers.
Overall, bread flour = chewy cookies, cake flour = soft cookies, all-purpose flour = in the middle (just right for me!).
Butter: Gluten from flour and water can't form in fat, so butter will prevent it from forming. The more butter you use, the less structured your cookie will be without those gluten networks, and the more your cookie will spread.
Additionally, butter is made mostly of water and fat. When the cookie dough reaches 92 degrees, the butter starts to melt and all the water initially inside the butter turns into steam. Since the butter is melting, the cookie dough turns more liquid as well and gradually spreads out from a round ball to a flatter circle. As the cookies spread, the edges thin out and begin to set earlier on.
Overall, more butter = more spread.
How we use the butter in the recipe also affects the final cookie. When we cream the butter with the sugars, air is incorporated as the mixture becomes fluffy and some of the sugar dissolves. This air later helps the cookies rise as they bake. That's why we use softened butter rather than melted butter, as liquid butter will create air bubbles that will later collapse, leading to denser and chewier cookies. On the other hand, butter straight out of the fridge that is too cold and won't expand easily, so it also won't capture much air. Finally, it's important not to over-cream or under-cream the butter. Under-creamed butter causes a wet and gritty mess, while over-creamed butter causes the butter to separate and become soupy.
Overall, perfectly creamed, cool butter = lighter cookies.
Eggs: Eggs prevent cookie dough from spreading completely flat because they are full of protein. When individual proteins are exposed to high heat (around 144 degrees), they bind together to create strong bonds that hold the cookie together. This determines the final shape and structure of the cookie.
To break down eggs even further: egg whites provide a good amount of water and protein. Egg proteins trap air bubbles and water vapor. Additionally, they are the main source of water in a cookie dough recipe, leading to the cookie rising when baking. Egg yolks also provide some moisture and protein, but they provide a well-emulsified source of fat. When cooked, egg yolk proteins coagulate which keeps the cookies fudge-like.
Overall, more egg white = more rising, more egg yolks = more fudgey texture.
Sugars: The type of sugar and how you use the sugar can affect the cookies. The edges and and bottoms of cookies are the hottest, which is where sugar granules melt together and caramelize, producing rich, sweet flavors.
White sugar is crystallized sucrose, a disaccharide made of a fructose molecule and a glucose molecule linked together. It is mildly hygroscopic (meaning it likes to retain moisture) and has a neutral pH (close to water). Brown sugar is mostly crystallized sucrose, but also has glucose, fructose, and trace minerals that give it richer flavor and a slightly acidic pH (<7). Brown sugar also caramelizes more readily, leading to more intense butterscotch and caramel flavor. It is important to not that glucose and fructose are much more hygroscopic than sucrose.
When slightly acidic brown sugar reacts with basic baking soda, this causes the cookies to rise more when baking, limiting their spread and creating a thicker cookie. White sugar is not acidic, so it doesn't react with baking soda to cause the cookie to rise and the cookie spreads instead. As white sugar is less hygroscopic and retains less moisture, these cookies will also end up more crisp.
Overall, white sugar = thin and crisp, brown sugar = thick and moist + richer flavor.
Baking Soda and Baking Powder: Baking soda is pure sodium bicarbonate, a basic powder (pH > 7). When it's dissolved and water and mixed with an acid, a reaction occurs that releases water and carbon dioxide. Baking powder is baking soda mixed with powdered acids, but the acids and base don't react when dry. However, when a liquid is added, the acids and base dissolve and react with each other, creating the carbon dioxide bubbles without needing a separate acid. Most baking powders have 2 acids, one that reacts immediately when mixed with water, and another that reacts later during the baking phase after it's heated.
Thus, using more baking soda or baking powder creates a cakier cookie, as they both react to release carbon dioxide bubbles which cause the cookies to rise. To tie it all together, as the butter melts and the cookie spreads, this frees up water, which in turn dissolves baking soda. This baking soda is then able to react with the acidic components of brown sugar, creating gases that cause the cookies to rise up and have more air pockets.
More baking soda/powder = thicker, cakier cookie.
Temperature: Temperature isn't a physical ingredient, but it definitely affects all the components of baking a cookie! First, the starting temperature of the dough affects the texture. Freezing the dough before baking causes the dough to solidify so it spreads less while baking.
When baked at a lower temperature, cookie dough has more of a chance to spread out, leading to flatter, wider cookies with uniform texture. On the other hand, cookies baked at higher temperatures spread less. It's a good idea to bake higher than 356 degrees so that caramelization of the sugars occurs, which will give cookies browned tops and rich, caramel flavors.
The most important science behind a chocolate chip cookie happens at 310 degrees: the Maillard Reaction. This reaction gives cookies their brown color and caramel taste (and also gives bread or meat a brown crust). The Maillard Reaction takes place when sugar combines with amino acids from protein. Proteins in the flour and the eggs brown along with the sugar, producing nutty flavors. This is actually not a single reaction but a complex series of reactions that depends on factors such as pH, temperature, and available moisture. The reactions occur under alkaline conditions, so baking soda is perfect for extra browning!
Conclusion
Phew, that was a lot of information! All of these reactions only take about 10 minutes to occur. All in all, my perfect cookie tried to have more spread for those crispy edges, but just enough leavening to keep the center chewy. This meant using all-purpose flour, more butter which I creamed when barely softened, equal amounts of egg yolks and whites (1 egg), and a combination of baking soda and baking powder. I controlled the temperature and used more brown sugar than white for richer toffee/caramel flavors. Each ingredient interacts with the others to lift or spread or give flavor to the cookie, and it's amazing how they all combine! Now that you know how each different factor can affect cookies, I hope you can design your own perfect cookie recipe!
Link to my chocolate chip cookie recipe (chewy AND crispy cookie).
Link to my post on the history & culture of cookies in general and chocolate chip cookies.
Want to Learn More? (always cite your sources, kids)
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