The
Science of the Chocolate Chip Cookie
By FBWorld Team
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
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 cookies
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.
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: http://sweets.seriouseats.com/2013/12/the-food-lab-the-best-chocolate-chip-cookies.html?ref=pop_serious_eats#.UspW6-p8CA.twitter
By: J.
Kenji López-Alt
And courtesy of www.seriouseats.com
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