Science of the Chocolate Chip Cookie

There are some that believe that baking is an art not a science.  I disagree.  The fact is there is a lot of science in art.   To ignore the science behind the ingredients, combinations and reactions to create the finished product and only pay attention to that final product is a myopic view of baking.  Those who ignore the science will find it difficult to stray from the recipe.

I consider the creation of a good recipe an art.  There is a creative aspect of feeling out ingredients and exploring how the flavors and textures interact to create an appealing finished product.  But to truly make a recipe great you have to take into account the science and effect of the ingredients ratios.

Whenever I think of these variables I come back to the example of the Chocolate Chip Cookie - a simple cookie recipe created by Ruth Graves Wakefield and traded to Andrew Nestle for a lifetime supply of chocolate - is probably the most well known American recipe.

The recipe consists of 9 common ingredients (flour, baking soda, salt, butter, granulated sugar, brown sugar, vanilla extract, egg and chocolate chips).  Just about every chocolate chip cookie recipe out there contains variations in quantity and type of these same ingredients.  It is the variations that make the cookie. 

Here are the proportion of ingredients for Nestle Toll House Chocolate Chip Cookies, which typically are a thinner, soft to almost crisp cookie:

• 2 1/4 cups all-purpose flour
• 1 teaspoon baking soda
• 1 teaspoon salt
• 1 cup butter, softened
• 3/4 cup granulated sugar
• 3/4 cup packed brown sugar
• 1 teaspoon vanilla extract
• 2 large egg
• 12 oz Semi-Sweet Chocolate Chips

The key variables to consider when making cookies are the flour, leavening, fat, sugar and egg.  Each will have an individual effect on the finished product.  Here are the effects:

Flour:  All-purpose flour serves as a middle ground.  Flour soaks up varying amounts of sugar based on the gluten content.  If you want a puffy, soft cookie use a low gluten cake flour.  It soaks up less moisture leaving that moisture to create steam puffing the resulting cookies.  If you want chewy go in the other direction and use a high gluten bread flour.  The high gluten content allows the flour to soak up much more moisture leaving the resulting cookie crumb soft and chewy.

Leavening: The acidity of the batter determines how quickly the batter sets.  Baking Soda lowers acidity and therefore raises the set temperature which will allow the batter to flatten out more before it sets resulting in a flat cookie.  Swapping out Baking Soda for Baking Powder, an acid, increases the acidity lowering the set temperature creating a taller thicker cookie.

Fat:  Most recipes call for unsalted butter.  While butter is a fine ingredients and works well in most cases, a substitution of shortening will allow the cookie to spread less because it has a higher melting point.  The higher melting points gives the batter more time to rise and set before the cookie starts to spread. The temperature of the fat also effects the finished product.  Melted butter will result in a more chewy cookie than softened butter.

Sugar: Most recipes call for a combination of granulated (white) sugar and brown sugar.  While many recipes do not specify light versus dark brown sugar, you should be aware of the ratio you choose to use.  The level of molasses (stuff that makes the sugar brown) will effect your cookie.  Molasses sucks up moisture and retains moisture making for a more chewy cookie. If you want a really chewy cookie you could use only dark brown sugar.

Egg: Eggs puff, milk spreads.  If you want a flatter cookie substitute one of the eggs with 2 ounces of milk.  You can also reduce the puffing from the egg by removing the whites of one of the eggs.

Of course you could spend time and many batches of cookies trying to make the perfect cookie to your liking or you could just try these:

Perfect Chocolate Chip Cookies
Slightly adapted from original Recipe found on Cooks Illustrated
Printable view

In order to make sure the sugar dissolves as much as possible, be sure to whisk the mixture during its rest, as instructed in step 3.  Also, avoid using a non-stick skillet to brown the butter.  The dark color of the non-stick coating makes it difficult to gauge when the butter is sufficiently browned.  Use fresh brown sugar, as older (read: harder and drier) brown sugar will make the cookies too dry.  This recipes will work with light brown sugar, but the resulting cookies will not be as nutty and full-flavored.  If you're sensitive to salt, reduce the salt amount to 3/4 teaspoon.

1 3/4 cups (8.75 ounces) all-purpose flour
1/2 teaspoon baking soda
14 Tablespoons unsalted butter
1/2 cup (3.5 ounces) granulated sugar
3/4 cup (5.25 ounces) packed dark brown sugar
1 teaspoon salt
2 teaspoons vanilla
1 large egg
1 large egg yolk
1 1/4 cups semisweet chocolate chips or chunks
3/4 cup toasted, chopped pecans or walnuts (optional)

Preheat oven to 375 degrees.  Line 2 large baking sheets with parchment paper (or use a Silpat).  Whisk flour and baking soda together in a medium bowl and set aside.

Heat 10 Tablespoons butter in a 10-inch skillet over medium-high heat until melted, about 2 minutes.  Continue to cook, swirling pan constantly until butter is dark golden brown and has a nutty aroma, 1 to 3 minutes (if you have browned butter before you can also rely on smell).  Remove skillet from heat transfer browned butter to large heat proof bowl.  Stir remaining 4 Tablespoons butter into hot butter until completed melted.

Add both sugars, salt, and vanilla to bowl with butter; whisk until fully incorporated and then stir in egg and yolk.  Whisk mixture until no sugar lumps remain, about 30 seconds.  Let mixture sit for about 3 minutes, then whisk it for 30 seconds; repeat this process two more times.  After about 10 minutes, mixture should be thick, smooth, and shiny.  Stir in flour/baking soda mixture until just combined, about 1 minute.  Stir in chocolate chips and nuts (if using), giving the dough a final stir to ensure that no flour pockets remain.

Chill in the refrigerator for at least 30 minutes. This is my added step.  I find that a short refrigeration helps re-solidify (is that a word?) the butter and results in cookies that are plump and chewy.  If you like your cookies flat and crispy, do not refrigerate.

Now it is time to scoop.  Personally, I think cookie size it up to you.  I used a small cookie scoop, about 2 Tablespoons of dough per cookie.  Just remember to keep the dough evenly spaced (about 2 inches apart) and bigger cookies will take a little longer to bake.

Bake cookies one tray at a time until cookies are golden brown, still puffy, and edges have begun to set but centers are still soft, 10 to 12 minutes, rotating baking sheet halfway through baking.  Transfer baking sheet to a wire rack and cool.