choc chip lead photo

Have you ever wondered about the science part of what you are baking? What does the egg yolk do? Why add baking soda? Why bake at a certain temperature? What does butter actually do? In this article, the scientific aspect of what is going on to make your chocolate chip cookie turn out perfectly wonderful has been thoroughly investigated by Food Lab scientist, Kenji Lopez-Alt.

For the past few months, I’ve had chocolate chip cookies on the brain. I wake up in the middle of the night with a fresh idea, a new test to run, only to discover that my 10 pound flour bin has been emptied for the third time. Did I really use it all up that fast? I’d put on my coat and walk out in the cold New York winter night, my sandals leaving tracks in the snow as I wander the neighborhood, an addict searching for a convenience store that will sell me flour at 3 in the morning.

I’m talking chocolate cookies that are barely crisp around the edges with a buttery, toffee-like crunch

You see, I’ve never been able to get a chocolate chip cookie exactly the way I like. I’m talking chocolate cookies that are barely crisp around the edges with a buttery, toffee-like crunch that transitions into a chewy, moist center that bends like caramel, rich with butter and big pockets of melted chocolate. Cookies with crackly, craggy tops and the complex aroma of butterscotch. And of course, that elusive perfect balance between sweet and salty.

Some have come close, but none have quite hit the mark. And the bigger problem? I was never sure what to change in order to get what I want. Cookies are fickle and the advice out there is conflicting. Does more sugar make for crisper cookies? What about brown versus white? Does it matter how I incorporate the chocolate chips or whether the flour is blended in or folded? How about the butter: cold, warm, or melted?

So many questions to ask and answers to explore! I made it my goal to test each and every element from ingredients to cooking process, leaving no chocolate chip unturned in my quest for the best. 32 pounds of flour, over 100 individual tests, and 1,536 cookies later, I had my answers.

How Cookies Crumble

Most traditional chocolate chip cookie recipes start with the same basic ingredients and technique: butter and sugar (a mix of white and brown) are creamed together with a touch of vanilla until fluffy, eggs are beaten in one at a time, followed by flour, salt, and some sort of chemical leavening (baking soda, baking powder, or a bit of both). The mixture is combined just until it comes together, then spooned onto a baking sheet and baked.

When you bake a cookie, here’s what’s going on, step-by-step.

  • The dough spreads:. As the butter warms, it slackens. The cookie dough begins to turn more liquid and gradually spreads out.
  • The edges set: As the cookie spreads, the edges thin out. This, coupled with the fact that they are fully exposed to the heat of the oven and are constantly reaching hotter areas of the baking pan, causes them to begin to set long before the center of the cookie does.
  • The cookie rises: As the butter melts and the cookie’s structure loosens, 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 develop a more open interior structure.
  • Egg proteins and starches set: Once they get hot enough, egg proteins and hydrated starches will begin to set in structure, finalizing the shape and size of the finished cookie.
  • Sugar caramelizes: At its hottest areas—the edges and the underbelly in direct contact with the baking dish—sugar granules melt together, turning liquidy before starting to caramelize and brown, producing rich, sweet flavors.
  • The Maillard reaction occurs: Proteins in the flour and the eggs brown along with the sugar in a process called the Maillard reaction—the same reaction responsible for giving your hamburger or bread a brown crust. It produces nutty, savory, toasted flavors.
  • The cookie cools. Once it comes out of the oven, the process isn’t over yet. Remember that liquefied sugar? Well as the cookie cools, that liquid sugar hardens up, which can give the cookie an extra-crisp, toffee-like texture around the edges. Meanwhile, the air inside cools, which causes the cookie to deflate slightly, though when fully baked, the structure lent by eggs and flour will help it retain some of its rise.

It’s a simple technique that hides more complicated processes underneath. So how do you decipher what’s going on? My first course of action was to test out these basic ingredients one at a time in order to determine how they affect the final outcome.



Butter is where most recipes begin, and it provides several things to the mix.

It keeps cookies tender. When flour is mixed with water (such as the water found in eggs), it develops gluten, a tough, stretchy network of interconnected proteins that set up as they bake. Gluten can’t form in fat, thus butter will inhibit its overall formation, leading to more tender results. The higher the proportion of butter to other ingredients, the more tender your cookie will be (and consequently, the more it will spread as it bakes). I found that a ratio of 1 part butter to 1 part sugar to .8 part flour was about right for a cookie that spreads moderately but doesn’t end up cakey.


Cookie Fact #1: More butter = wider spread and more tenderness


Butter is essential for flavor. Substituting butter with a less flavorful fat like shortening, lard, or margarine yielded sub-par cookies. Butter is about 80 to 83% butterfat, 15% water, and 3 to 5% milk protein. These proteins brown as the cookie bakes, adding nuttiness and butterscotch notes to the final flavor of cookies.


Cookie Fact #2: Butter Gives The Most Flavor


Because of shortening’s different melting qualities (and the fact that it has no water content), shortening-based cookies come out softer but more dense than those made with butter.


How butter is incorporated can also affect texture. In the early creaming stages of making a cookie, cool butter is beaten until it’s light and fluffy. During the process, some air is incorporated and some of the sugar dissolves in the butter’s water phase. This air in turn helps leaven the cookies as they bake, giving them some lift. Melting butter before combining it with sugar and eggs leads to squatter, denser cookies.


Cookie Fact #3: Melted Butter = Denser Cookies, Creamed butter = cakier


I asked myself: if browning milk proteins provide extra flavor to cookies, how could I boost that flavor even more?

My friend Charles Kelsey, the man behind the fantastic Brookline, MA sandwich shop Cutty’s, developed a simple chocolate chip cookie recipe for Cook’s Illustrated magazine back in 2009. In his recipe, he made the ingenious discovery that browning the butter before adding it to the mixture would give the cookies a much more pronounced nuttiness.

But this created some other problems. Since the butter can’t get hot enough to brown milk proteins until all of its water content has evaporated, brown butter adds no moisture to dough. This produces a couple of interesting results. Without water, sugar that is mixed into browned butter cannot dissolve (sugar molecules are highly hydrophillic and will dissolve readily in water, but not in fat), which makes it subsequently more difficult for them to melt into each other as the cookie bakes. The cookies ended up missing out on some of that caramelized toffee flavor I was after.


Cookie Fact #4: Less Dissolved Sugar = Less Caramel Flavor


With less water, you also end up with less gluten development, thus a cookie made with browned butter is softer and more tender than one made with creamed or plain melted butter. Soft and chewy is good, but I wanted a slightly better balance.


Cookie Fact #5: Creamed Butter = Lighter and firmer, Melted Butter = Denser and chewier


So how do I get the flavor benefits of browned butter while still allowing for sugar to dissolve and caramelize properly? The answer turned out to be in the eggs.



Before we jump to the solution, let’s take a quick look at what eggs have to offer in a cookie.

Egg whites provide a good amount of water, as well as protein. Egg proteins are particularly good at trapping and retaining bubbles of air or water vapor. The higher the proportion of egg white in a cookie, the more it rises during baking. Because of the extra water, you also get more gluten formation, which again leads to a taller cookie (provided you use enough flour to absorb that extra water). Other than the small amount in the butter, eggs are the main source of water in a cookie dough recipe.

Egg yolks also provide some moisture and protein, but more importantly they provide a well-emulsified source of fat. When cooked, egg yolk forms a tender protein coagulum that can keep cookies tender and fudge-like. A high proportion of egg yolk leads to a more brownie-like texture in a finished cookie.


By keeping the total mass of egg added to a dough the same but altering the proportion of white to yolk, you can achieve a variety of textures. Two whites and a yolk, for instance, produces the more open structure of the top cookie in the photo above, while three yolks and no whites produces the denser, fudgier texture of the cookie on the bottom.


Cookie Fact #6: Extra Egg Whites = Taller Cookies. Extra Egg Yolks = Fudgier cookies


Turns out that the combination I like best is actually a 1 to 1 ratio of egg whites to egg yolks, which conveniently is exactly how eggs naturally come. Ain’t that something?

Going back to my initial problem of wanting the flavor of browned butter but disliking the way it prevented sugar from properly dissolving, I asked myself, what if I were to flip the script for these cookies: instead of creaming sugar and butter and adding eggs, why not beat together the eggs and sugar then add the butter?

I tried it, beating brown sugar, white sugar, and vanilla with whole eggs in a stand mixer until the mixture became pale, aerated, and ribbony, with a nearly completely smooth texture.* To this, I added my browned butter, which instantly cooked the eggs and curdled them, turning the mixture into an oddly sweet and vanilla-y scrambled egg custard. Lesson learned: let that browned butter cool before adding it.

*A sugar and water solution becomes fully saturated at room temperatures at a ratio of about 2 parts sugar by mass to 1 part water (that is, you can’t dissolve any extra sugar because it will stay granular). My working recipe contained about 4 ounces of egg and 10 ounces of sugar, so perfect smoothness was an impossible goal.

My next attempt with cooled brown butter fared better, but the finished cookies ended up with an oddly uniform texture and a relatively smooth top rather than the cragginess I’d been getting earlier.


Turns out that you actually want a balance between dissolved sugar and undissolved sugar to keep things texturally interesting.


There are 21 scientific facts included in this article. We have provided you with 6 of them. For the rest of this fascinating and well written piece, click here for the original:–p8CA.twitter


By: J. Kenji López-Alt

And courtesy of