Cookie Science

3 minute read

Updated:

Over the last few years, I’ve been reading Serious Eats and trying to comprehend the roles of ingredients when baking cookies.

I’m going to try to summarize them here, so they can serve as a concise tldr if you want to understand how a modification might affect the outcome.

Let’s form the common groundwork for how a cookie transform, physically and chemically, over time:

  1. Dough spreads. As the butter warms, the dough will become more like a batter and spread out.
  2. Edges set. The outer edges are thinner than the center and cook faster. The edge is also spreading to “new” parts of the pan, which are hotter than center.
  3. Cookie rises. The butter melts and the dough slackens, allowing moisture to move more freely. The butter releases its own water as well. Moisture will steam and try to escape, lifting dough. This high water activity allows baking soda to dissolve and activate, causing further rise.
  4. Proteins and starches set. Proteins, gluten and egg, and starches harden once a high enough temperature is reached.
  5. Sugar caramelizes. Sugar melts into liquid. On other surface (pan), where the temperature is high enough, caramelization takes place.
  6. Maillard reaction occurs. At higher temperatures, the rate of Maillard reaction quickly increases.
  7. Cookie cools. Once taken out of the oven, the caramelized, liquid sugar cools back to a solid. The air inside pockets cools, causing slight collapse. More if the cookie structure is lacking.

Creaming

Creaming butter and sugar will lighten the cookie with aeration. This will result in:

  • Less spreading. The lighter dough has better insulation properties, preventing butter from warming too quickly and spreading.
  • Leavening, for cakier cookie. Creaming, by itself, is not sufficient to make a cakey cookie but it’s a key technique to enable it.
  • Tender cookie. The aeration allows for steam to escape, which reduces gluten formation. You want the opposite if you’re going for a chewy cookie.

Sugars

Sugar assists in leavening during the creaming process. It also caramelizes, adding flavour as well as giving the cookie-bottom crisp.

These notes are summarized from Stella Parks’ article on Serious Eats.

Brown Sugar

Brown sugar is white sugar with molasses added back. The presence of molasses changes the properties of the cookie dough.

Molasses is acidic and this will lower the pH of the dough:

  • Inhibits browning
  • Encourages gluten formation
  • Speeds up egg coagulation, setting the dough sooner

Molasses increase the hygroscopic nature of sugar. The increased moisture results in:

  • More moisture in end product
  • Harder to cream, not as effective mechanical leavening

With these properties, brown sugar is a good candidate to make chewy and thick cookies.

Fats

Fats inhibit gluten formation, resulting in tender cookies.

Fats melt when baking, increasing the spread rate and resulting in thinner cookies.

Eggs

Whites

Egg whites provide protein and moisture. As the cookie bakes, this is good to trap the steam produced, which gives more rise. The moisture increases gluten formation, which give structure and allow for a taller cookie.

Egg whites and butter tend to be the primary source of water in a cookie dough.

Yolks

Yolks provide fat, which contributes to tenderness and preventing gluten formation. They also provide a lot of flavour, whether that’s desired or not.

Flour

Bread flour has higher gluten content and will make for a chewy cookie. Cake flour will be more tender and… make a cakey cookie.

Using more or less flour is more like consequences of the other ingredients. More flour in the dough is like less sugar and fat, which makes a chewy and thick cookie. It does not spread as much (less fat) and not crisp as much (sugar). The extra gluten will allow for more structure, so can have tall cookies.

Less flour is like more sugar and fat. You can get a crisp cookie that spreads thin and caramelizes a lot.

A cold dough will spread less, as the center takes longer to warm up and let butter melt.

A hotter oven will set the cookie quicker, by caramelizing the bottoms. This will result in less spread and perhaps taller cookie.