The Science Behind Chocolate Chip Cookies

This recipe does not call for very many ingredients, but each one serves an important purpose beyond just adding flavor to the cookies.  Changing anything about this recipe, including the ingredients, the amount of an ingredient used, the order in which they are combined, or the baking temperature could result in a different or inferior final product.  

In almost all chocolate chip cookie recipes, including this one, the first ingredients the recipe calls for are softened butter,  granulated sugar, and brown sugar.  Often recipes will suggest softening butter before creaming it with both of the sugars until the mixture is light and fluffy.  This step is crucial, hence why it is included in almost every recipe.  Creaming the butter and sugar together serves two purposes.  The first is to incorporate air (The Science of Good Cooking).  This is done through the physical process of creaming the softened butter.  Melted butter would not whip the same way that softened butter does, and would therefore not incorporate enough air into the cookies.  

The second purpose of this step is to dissolve the sugar (The Food Lab).  Butter is an emulsion of fat and water.  Sugar is a hydrophilic molecule, meaning that it is attracted to water (The Science of Good Cooking).  When softened butter is creamed together with the sugar, the sugar molecules dissolve in the water, allowing the cookies to have a sugary taste while still being moist.  About half of the granulated sugar in this recipe will dissolve during the creaming process and more will dissolve while the cookies are baking (Joachim).  Brown sugar makes the cookies softer and chewier and also contributes to the flavor of the cookies, giving them a slightly butterscotch taste due to the molasses (Miller).  

The next step in this chocolate chip cookie recipe is to add the eggs and the vanilla extract into the creamed mixture and mix until combined.  The vanilla extract adds a little bit of moisture into the cookies, but overall, the main purpose of the vanilla extract is flavor.  There is, however, a lot of chemistry behind the inclusion of eggs in this recipe.  There are two parts of the egg that are made up of different components.  The yolk is mostly protein and water, whereas the yolk contains protein and a lot of fat.  The water of the yolks bonds with the flour and provides some structure and moisture, while the yolks make the cookies chewy (Joachim).  

Next, the recipe instructs you to mix all of the dry ingredients together and incorporate them into egg-butter-sugar mixture.  These dry ingredients include flour, baking soda, baking powder, and salt.  Flour serves as the “base” for the cookies and is probably the main ingredient that provides structure to the cookies (Land O’Lakes).  The amount of flour used in a recipe determines if the cookies are tender, crispy, chewy, or tender (Joachim).  The flour combines with the WATER to create web-like structures (The Food Lab).  There is gluten in flour, but fat coats some of the gluten and prevents some of it from forming, so the butter and the egg yolks help keep the cookies tender and prevent them from becoming tough due to the gluten.  When it comes to making cookies, it is safer to stick with all-purpose flour, as opposed to bread flour.  Bread flour has a higher gluten content which means that it creates a tougher final product (Land O’Lakes).  

Baking soda and baking powder are both leavening agents which help to add air into the cookies.  Baking soda is simply NaHCO3 and requires an acidic ingredient to start the chemical reaction and release CO2.  Baking powder, however, has an acidic component already included in it, so all that it needs is water to release CO2 (The Science of Good Cooking).  Eggs are slightly acidic, so they help baking soda release some CO2 in this recipe, but this recipe also calls for some baking powder to help the process of releasing CO2.  

The salt in this recipe is mainly there for taste.  Salt is often used to cut some of the sweetness of a recipe so that it is not too overpowering.  It can also help the flour form some gluten too (Land O’Lakes).  This recipe calls for sea salt which is coarser and therefore doesn’t incorporate into the batter as well, causing an occasional salty bite.  Now it’s time for the fun part, the chocolate chips! The purpose of the chocolate chips is to add flavor to the cookies.  

The recipe that I used for this project, suggests baking the cookies at 375 degrees F.  This is probably a good temperature if you like cookies that are chewy and gooey in the middle. Baking the cookies at 375 allows the outside to set and leaves the inside slightly undercooked (Gore, 2019).  The caramelization of the granulated sugar occurs at 356 degrees F which will give the cookies a darker color and a slightly caramel flavor (Miller and Joachim).  If you want a chewier cookie, bake them at 325 degrees F for a longer period of time (Gore, 2019).  

The adaptation that is the most interesting to me is that of butter.  Butter is an interesting ingredient in chocolate chip cookies because it serves multiple purposes.  The biggest one is the flavor.  Butter can be replaced with other fats such as shortening or vegetable oil, but cookies made with substitutions will lack the buttery flavor that normal chocolate chip cookies have (Gore, 2019).  As mentioned above, fats also help to prevent too much gluten from forming and keep the cookies soft and tender (The Food Lab).  Part of the reason why butter is the favored fat in many cookie recipes is because it is an emulsion of water and fat.  The water in butter helps to dissolve the sugar and give it a sweet taste.  The water also prevents the cookies from getting too dry.  Shortening and vegetable oil are both straight fat, so they don’t have the benefit of extra water.  

Some people substitute the suggested softened butter for melted butter, thinking that it does not make a difference, but it does.  Using softened butter requires creaming the butter and sugar together in order to fully combine them.  In order to combine melted butter and sugar, all you have to do is stir a little bit.  By not creaming them together, you miss out on the extra air that is incorporated through the process of creaming (The Science of Good Cooking).  This causes fewer air bubbles and more spreading when the cookies go into the oven.  Not creaming also causes less sugar to be dissolved in the water, creating a final product that isn’t as sweet (Joachim).

As you can see, there is a lot of science involved in making chocolate chip cookies. Every decision made in the kitchen can lead to a different finished product.  Substitutions can be made, but it’s important to think about all of the purposes that the ingredient serves and to verify that the substitute ingredient can serve those purposes as well. 

Pictures taken by me.