Molecular Gastronomy

The chemistry behind baking

How to Bake a Cookie – In Terms of Chemistry

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Baking a cookie is pretty simple. You can either buy pre-made cookie dough and just place little balls of the dough in the oven, or you can make cookie dough from scratch then bake it. However, did you ever look at baking a cookie through a chemistry aspect? Believe it or not, a series of chemical reactions takes place while baking a cookie!

Here is a recipe for chocolate chip cookies, in terms of both “English” and chemistry.


  • 3/4 cup sugar – sucrose
  • 3/4 cup packed brown sugar – sucrose and flavoring
  • 1 cup butter – fat
  • 1 large egg – emulsifier, albumin, fat, protein
  • 2 1/4 cups-all purpose flour – gluten
  • 1 teaspoon baking soda – sodium bicarbonate (NaHCO3), serves as a base
  • 1/2 teaspoon salt – NaCl
  • 2 cups semi-sweet chocolate chips – flavoring


1. Preheat oven to 375 degrees.  Mix sugar, brown sugar, butter, vanilla and eggs in a large bowl.

  • There is no chemical reaction that occurs while mixing these ingredients. There are only physical changes, no chemical changes.

Stir in flour, baking soda, and salt.

  • As stated in the previous post, flour forms gluten. Gluten makes the mixture more elastic, so the flour is added later in the process to keep these gluten complexes small. This is why the dough is able to break apart. If it were to be elastic, then it would just end in a messy, goo-ey mess, and it would harder to form smaller pieces from the dough. The baking soda serves as a leavening agent to soften the mixture.

3. Stir in chocolate chips.

  • The chocolate chips do not have a significance in terms of a chemical reaction; they simply serve as an ingredient to add flavor to the cookie.

4. Drop dough by rounded tablespoonfuls 2 inches apart onto ungreased cookie sheet.

  • The size of the dough is not just important in terms of preference. The size of the dough determines the results of the cookie. Carbon dioxide (CO2) bubbles form throughout the entire cookie, but only the outer edge of the cookies caramelize.

5. Bake 8 to 10 minutes or until the cookies become light brown.

  • While baking, the heat allows for the sucrose (sugar) to break down into glucose and fructose. This causes a polymer chain which allows for the cookie to have a light brown, shiny crust. When the sodium bicarbonate (baking soda) absorbs heat, a chemical reaction occurs – 2NaHCO3 –> Na2CO3 + H2O + CO2. The carbon dioxide from the reaction can be seen from the bubbles in the cookies. The NaCl (salt) slows down the production of the carbon dioxide and prevents these bubbles from becoming big. The fat (butter) controls the formation of gluten from the flour, which contributes to its lighter texture. It also serves a role in the taste of the cookie. The emulsifier, or fat and protein from the egg yolk hold the dough together (the main purpose of an emulsifier), while the albumin from the egg whites support the bubbles. 

6. The centers will be soft.  Let cool completely then remove from cookie sheet.

7. Remove from cookie sheet and place on wire rack or on a table to finish cooling.

  • The cooling allows for the completion of the caramelization process (this gives it the brown-ish color), and it also allows for the structure developed by both the gluten and the egg to set.

Notice how some of the reactions relate back to our previous posts? All these reactions seem to be common in baking! Check back later to see any additional chemistry that is involved in baking or any other reactions that occur in baking! (:

Author: Erica Rowane Bautista


* This recipe was reworded and taken from this website. Information was also taken from our previous posts.


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