THE CHEMISTRY OF BAKING (BROWNIES EDITION)

By Shahd Nimir 

Some have compared the art of baking to magic. Ingredients mix to form delicious pastries and treats in less than a few hours. This “magic” is all thanks to the science of chemistry. Chemistry is the study of the structure, properties, and composition of substances as well as the transformations that they undergo and the energy released or absorbed during this. The way that different quantities of ingredients create several varieties of batters and doughs is caused by their properties. Chemistry is mainly applied in the actual baking part. To get more in-depth with this, we will further dive into the chemistry behind baking a household favorite: brownies. 

The Mixing Bowl

Every brownie recipe begins with two key ingredients: Sugar and fat. Although vegetable oils and margarine are sometimes used for the fat, butter is the more popular option, and for good reason. The water content in butter is more than that in oil but less than that of margarine, which is important to the texture of the brownies. Additionally, butter is more favored due to its flavor profile. The butter can either be creamed with the sugar or melted and combined with it. The key difference is in the result. When the butter is creamed, it produces a more cake-like texture compared to melted butter which results in more fudgy brownies. This is because when butter is creamed with sugar, air particles get trapped in between the butter and sugar crystals and as the brownie bakes, the air tries to escape, giving the brownie a more fluffy and cakey texture. Although the water in the butter dissolves some of the sugar, the larger fat content doesn’t allow for most of it to dissolve since the sugar is a polar substance and the fat is nonpolar and “like dissolves like”. Chocolate of some form is then added to this mixture. Melted chocolate chips or a chocolate bar contains more oil content compared to cocoa powder which has a richer profile. All these ingredients combined, result in a grainy textured batter.

Next eggs and flour are incorporated into this mixture. When the eggs are added to the grainy sugar and butter mixture, they act as a binder that gives the batter a more cohesive structure. This is due to the lecithin found in egg whites. It acts as an emulsifier that allows immiscible solvents to create a more homogeneous mixture. As the eggs are beaten, they add air into the batter. When the flour is added to this mixture, the starch granules act as sponges that absorb the water in the mixture and expand, creating a thicker consistency. Additionally, proteins known as glutenin and gliadin absorb water to form gluten. Gluten is responsible for the consistency of the batter and the final structure of the final product. With the addition of salt and vanilla extract, this batter is ready for the oven. 

Into the Oven: 

Only when heat is introduced does the real magic begin to happen. A series of reactions take place in the oven as the batter turns into the final product. One of the main players here is rather unexpected: water. Although water is not directly an ingredient in this brownie recipe, it is present in large amounts in both the eggs and butter. Before any of the reactions occur the water entrapped in the battle begins to vaporize and release itself. As it does so, It pushes through the batter, forcing it to rise. As mentioned before, when the eggs are beaten into the batter, they incorporate air which causes it to act as a leavening agent. As this gas is released, it causes the brownies to expand. All of this is allowed by the elasticity that the protein chains gluten gives the batter. After it has completely baked, the gluten allows it to keep its final structure. 

Another key ingredient in the baking process is sugar. As the temperature reaches close to 300°F we experience our first series of reactions: the Maillard reactions. When the amino acids and proteins react with the reducing sugars, the proteins, and sugars form ring-like compounds that are responsible for the browning of the crust and the release of the aroma of the brownies. The next chemical reaction that occurs is caramelization. It is the pyrolysis of sugar. Essentially, the sugar is heated to the point where it loses its water molecules and rearranges into a new structure. Caramelization is responsible for both the color and structure of the final product. Caramelization generally occurs at higher temperatures than the Maillard reactions but after the system reaches a certain temperature, the two can occur simultaneously. 

After the brownies are done baking, they begin the cooling process. When brownies first come out of the oven, it is difficult to cut them without them crumbling. This is because the high temperature does not allow a network of proteins and starches to set. As it cools down, it begins to solidify, allowing it to better hold its shape. Finally, the treat is ready to be enjoyed. 

Fudgy brownies 

Ingredients: 

½ cup butter 

1 cup sugar 

½ cup of unsweetened cocoa powder

¼ tsp salt

1 tsp vanilla extract

2 large eggs

3 tbsp espresso (Optional) 

½ cup flour

¼ cup chocolate chips (Optional)

Steps: 

1. Melt half a cup of butter (1 stick) and wait for it to cool down before combining it with the sugar and cocoa powder.
2. Add salt and vanilla extract to the mixture along with 2 beaten eggs. 
3. Add the espresso and make sure to fully mix the wet ingredients before the flour.
4. Pour the batter into a pan and add chocolate chips at the top. 
5. Bake the brownies for 20-35 minutes at 350°F
6. Wait at least 10-15 minutes for brownies to cool down  before cutting and enjoy!

Works Cited 

Ang, Jill. “The Chemistry of the Perfect Brownie.” WiTech, WiTech, 13 Feb. 2023, wi-tech.org/2023/02/13/the-chemistry-of-the-perfect-brownie/#:~:text=Eggs%20and%20yeast%2C%20which%20are,%2C%20breads%2C%20and%20even%20brownies. 

Beal, Janet. “The Chemistry of Baking Brownies.” LEAFtv, 13 Dec. 2021, http://www.leaf.tv/articles/the-chemistry-of-baking-brownies/. 

Claire, Jillian, “The Chemistry of Baking” (2014). Senior Theses. 23. https://scholarcommons.sc.edu/senior_theses/23

Gray, Eileen. “Science of Flour in Baking.” Baking Sense®, 27 Mar. 2023, http://www.baking-sense.com/2017/03/29/baking-ingredients-flour/#:~:text=Wheat%20flour%20is%20composed%20of,flour%20is%20about%2070%25%20starch. 

Lawandi, Janice. “The Complete Guide to Leavening Agents in Baking.” The Bake School, 30 Sept. 2022, bakeschool.com/leavening-agents-in-baking/. 

Science, Chef. “The Science of Caramelization – Food Chemistry Basics.” FoodCrumbles, 4 Apr. 2022, foodcrumbles.com/caramelization-honeycomb-making/. 

Usselman, Melvyn C. and Rocke, Alan J.. “chemistry”. Encyclopedia Britannica, 2 Jul. 2023, https://www.britannica.com/science/chemistry. Accessed 5 September 2023.