So if we want to think scientifically about cooking,
we have to start by thinking a little bit about what food is made out
of because, after all, it is the constituents of food which
will be the major player in this adventure
that we're about to launch ourselves on.
Let's just start with the very basic fact, which is that all of us,
and all of our food, is made of molecules.
Now, there are simple molecules.
There's the molecules that's in the air around us.
There is, for example, carbon dioxide.
There's oxygen. There's water.
These are simple molecules.
They, of course, themselves are composed of atoms.
So carbon dioxide is composed of carbon and oxygen. Water
is composed of hydrogen and oxygen, and so on.
Food molecules are more complex than atoms.
And they're also more complex than simple molecules.
The molecules of cooking, namely fats, proteins, and carbohydrates,
tend to be much larger molecules, which themselves also
contain atoms such as carbon, nitrogen, oxygen, and so on.
And one of the unusual things about cooking
is that the basic molecules of food, the basic fats, the basic sugars,
that we will talk about tend to form very large networks or sort
of agglomerated structures which are what make up the structure of food
and also, actually for that matter, of us.
So let's just start with fats.
So fats are very common.
Examples of common fats that you might eat with
include olive oil, coconut oil, cocoa butter, shortening.
And fat has sort of two features that I would like to highlight right now.
So the first is that fats can either be in liquid or in solid form
at room temperature.
And, indeed, there are fats that are liquids.
There are fats that are solids at room temperature.
So the second feature of fats is that fats don't dissolve in water.
That's why when you try to make salad dressing and you mix oil and water,
for example olive oil and water, you will notice that the olive oil does not
actually mix itself in the water.
And even if you take your bottle of olive oil and water
and shake it up rapidly, they will, if you
let it sit for a while on the counter-top,
separate into the oil being on top and the water being beneath it.
And that is because oil and water don't mix with each other.
Or said differently, oil doesn't dissolve in water.
Now, this is sort of one of the defining features of oil.
And it is very different than the two other major components of food.
So now let's talk a little bit about carbohydrates.
So carbohydrates consist basically of sugars,
you know, sucrose, the sweet taste that you
tend to eat if you're trying to eat something sweet,
and also chains of sugars, which are starches,
are sort of longer chain sugars.
These are the sort of two main types of carbohydrates that exist in your food.
So either sugars or sugar chains.
Now, sugars actually have their own interesting properties.
So one property of sugar which at least I find interesting
is that sugar is really a very hard substance.
That is, if you try to crush it, a solid piece of sugar,
it's very difficult to do.
So for example, imagine taking rock candy.
Rock candy is really a solid.
It doesn't squish at all.
Compare that to either your skin or to Jell-o or to something
like that which tends to be squishy.
Sugar is very hard.
And this hardness, as we will discover in this class,
is a property of the molecules that make it up.
So the other thing which is interesting about sugar
is that sugar dissolves very well in water.
The solubility limit of sugar is two pounds per pound.
And that's really a sort of remarkable property of sugars.
So as I said, actually, the other main type of carbohydrate are starches.
And starches are what we call polymers, that is chains of sugar molecules.
So what you do is you take simple sugar molecules, like glucose or sucrose,
and you put them together in long chains.
And those chains are what makes up starches.
So examples include, for example, amylose,
which is a polymer of glucose monomers.
So you take a bunch of glucose monomers and stick them together
end by end to make a long chain.
And that makes up amylose.
Or there is what people call amylopectin,
which is the same thing, except instead of being a linear chain-like polymer,
it's actually branched.
So there are branches of polymer that are coming off of it in different ways.
In this course, many of our chefs will introduce you to new molecules,
like, for example, agar.
Ferran Adria is a great fan of agar-- agar, agar.
There's pectin.
There's guar gum.
There's methylcellulose.
There's gellan.
There's xantham gum.
There's a huge host of molecules which all are actually carbohydrates.
So whereas flour is made from wheat by milling and grinding wheat,
guar gum actually comes from plants.
Agar comes from seaweeds.
Gellan and xantham gum come from microbes.
And there's a whole host of different molecules
that are made by organisms on our planet that we can use,
and we do use, as part of our foods.
And we will see in the course of this class
that remarkable things can be made when you enlarge the set of molecules
that's at your disposal.
So now I want to turn to the third major component of food, which is proteins.
So proteins, of course, occur in many of the things that you eat.
So for example, if you look at a piece of steak, the red color in steak
comes from hemoglobin, at least in part, which
is a protein constituent of blood.
So milk actually has a protein in it that is called casein.
Albumin is a protein component of eggs, which
is the thing that is responsible really for the remarkable properties of eggs
when you heat and you cook them.
This is something that we will talk about extensively in this class.
And proteins, when considered as a molecule,
have their own interesting property which
is distinct from that of either fats or carbohydrates.
And that is the following.
So proteins dissolve in water.
That's the same as carbohydrates.
But what proteins do that is different is that when you heat up water
or you heat up the protein by a relatively small amount,
say 50 degrees Celsius even is often enough,
you can get the protein to change conformation.
The protein is an active molecule.
It doesn't keep the same shape as you cook it.
And, indeed, it is the changes in shape and configuration of proteins
that arguably are really at the heart of most of cooking
when you apply heat or other means, as we will again
see throughout this class.
So what is a protein?
So a protein is also a polymer.
It's a polymer in the same way that the starch molecules
that I described before are polymers.
Except in this case, instead of the monomers all being identical,
for example being a glucose or a simple sugar molecule,
proteins are polymers of amino acids.
And it turns out that there are 20 different types of amino acids
that compose the proteins that are part of life as we know it.
And these 20 amino acids, these 20 monomers,
themselves have different physical properties.
Some of them dissolve in water.
Some of them don't dissolve in water.
Some of them have electric charge.
Some of them don't have electric charge.
And as we go through this class, we will start
to see how the different components of proteins
give rise to the transformations that occur when we cook them.
What happens when you cook a protein, when you heat a protein,
is that the long strand tends to unfold into a long, extensible polymer.
So one can unfold-- and much of cooking, it turns out,
is related to the transformation in which a protein in a given food
is actually extended into a long polymer.
And when it does that, then it turns out that the polymers,
that is the different proteins that are in the food,
tend to stick to each other.
And they sort of coagulate, and you form a gelatinous mass.
And that process, the changing of a protein
from a compact shape to a big, gelatinous mass
of many proteins interacting, is at the heart of cooking an egg.
It's at the heart of making Jell-o.
It's at the heart of many of the food transformations
that we will see in this class.
And these can occur, as we will see, both by applying heat
or by applying changes in pH, by actually using
acid, it might be lemon juice or vinegar,
or by changing the salt concentration.
And so these are the various knobs that are
at play with proteins when you cook.
