MICHAEL BRENNER: This week, we're
going to study the physics of baking.
Baking has arisen already on
several occasions in this course.
But so far, we haven't
been able to actually go
into the physics of baking, that
is, how do recipes for baked goods
work and produce the delicious
outcomes that we all so much enjoy?
And the reason for that, the reason that
we haven't discussed baking as of yet
is that, as you will see this
week, the physics of baking
involves many, in fact,
if not most of the ideas
that we've discussed
up until this point.
Baking involves elasticity, viscosity,
emotions, heat transfer, solubility,
many concepts like that.
And this week, we're
going to go through what
is going to be, on one hand, a
bit of a review of the concepts
that we've discussed
up until this point.
And on the other hand,
we're going to show you
how these ideas apply to baking.
So before we begin, I just
want to give one caveat.
We are not professional bakers.
We are scientists.
And our intent in this
week's baking discussion
is not to basically go through every
method and every technique that
is required to basically
make a baked good delicious.
What we're going to do is to expose
the basic scientific issues that
underlie baking.
And by putting them
together in your own mind,
they will hopefully help
you make sense of recipes.
And to help us with this,
we're very fortunate to be
able to visit the kitchen of
Joanne Chang of Flour Bakery.
JOANNE CHANG: Hi, I'm Joanne
Chang of Flour Bakery.
I'm going to be showing you today
how to make yellow birthday cake
and talking to you about all of the
science behind making birthday cake.
So first, let me show
you all the ingredients
we have for yellow birthday cake.
We have unsalted butter, granulated
sugar, we have eggs, and egg yolks,
and there's a little bit
of an element here as well.
We also have some buttermilk,
and then our dry ingredients,
which are flour, and then in this
container, our combined baking soda,
baking powder, and kosher salt.
OK, the first thing I do is I'm
going to put the butter into a mixer.
You could do this by hand, but I promise
you after about 10 minutes your arms
will be really tired.
So if you can, do it in a mixer.
Now, one of the things that's
important about the butter
is that we want it to
be at room temperature.
Now, why is it important that the
butter is at room temperature?
Because what we're going
to be doing is we're
going to be adding millions and millions
of minuscule microscopic air pockets
into the butter, and we're
going to do that with our sugar.
If you imagine sugar, it's
an actual crystal, right?
Sugar is a crystal.
And the crystalline structure
of the sugar, what it does
is it acts as tiny little
shovels into the butter,
and it digs all of these
little holes, and makes
a little minuscule pockets of air.
If the butter's too cold, then
the sugar can't do its work.
The shovels just are strong enough.
So you want to make sure you start
off with room temperature butter.
I'm going to slowly
start adding the sugar.
And as I'm doing this,
the butter is slowly
starting to get more and more worked up.
And I'm going to show this to you
once all of the butter gets put in.
Now, why is it so important that
I have all of these air pockets?
So if you imagine what you want
for the ideal birthday cake,
you want something that's nice
and light, and fluffy, and tender,
and velvety.
And the last thing in the world you want
is a really tough, hard-to-eat, chewy
cake.
So what we try to do in
the making of the cake
is create as many opportunities as
possible for science to do its magic,
and take all of these ingredients,
and turn them into something
light, and fluffy, and delicious.
So when I talk about this sugar
creating air pockets into the butter,
later on when I actually added all of
these ingredients to the cake batter,
and I put that batter into the
oven, all of those pockets of air
will expand in the oven once they
get into the heat of the oven.
And that is what is going to help
cause some of the rise of the cake.
And the rise of the cake is what's
going to make the cake really light
and fluffy instead of heavy and dense.
