Let me say from the beginning, I love to cook.  I’ve been cooking since I was a
small child (with my mother’s help during the early years of course), and have
always found the transformation of inedible (and sometimes unappetizing)
raw ingredients into fine cuisine particularly fascinating. While cooking is
often considered an art, it is also very much a science, and often it is the
first real exposure to science we have as children.  Needless to say, learning
some cooking skills early in life is very important—it is both a necessary life
skill, and a valuable science lesson! 

While we prepare and consume cooked food every day, seldom do we hear much about what is really going on when food is cooked.  What is really happening?  That is, what is really the difference between cooked food and raw food?  Usually, this can be boiled down (no pun intended) to just one word: heating.  
When we heat our food, several things take place:

1.    Proteins denature; that is, the shape of the proteins change, as the weak bonds and interactions within
their structures break and they unravel.  This is what causes the whites of an egg to go from clear to white as they cook.

2.    Changes in water content; in many types of food and cooking, such as roasting fresh vegetables,
heat causes some of the water to evaporate which changes the flavor and texture of food.  In other types of food, such as beans or dried pasta, the food absorbs water which makes it softer and more palatable.

3.    Cells walls are weakened or broken; vegetables (carrots, broccoli, etc.) have tough cell walls
made up of cellulose.  When they are heated the cellulose weakens and often the cells burst, resulting in a softer texture.

These are common effects for most cooking, and yet foods prepared in different ways look and taste very different.  This is because the method we use to cook our food can result in some different reactions, depending on the amount of heat used.  As an example, let’s look at potatoes.  
 
If we boil potatoes, they become soft and tender, but they remain pale in color and their flavor is rather bland—perfect for mashing with butter and milk.  However, if we fry our potatoes they turn a golden brown color and take on a pleasant flavor, which is good to enjoy without additional ingredients. These are the same potatoes, and yet the flavor and appearance is so different.  This is because when we fry potatoes (or roast them at a high enough temperature), two things happen to create this appearance and flavor: caramelization, and the Maillard reaction.  

Caramelization occurs when the sugars in the potatoes decompose (break apart) into volatile compounds (compounds that evaporate) and residual organic material.  The process is very complex, and involves many reactions, but the result is brown color and complex flavor.  Caramelization requires temperatures above 230°F (110°C), the exact temperature depending on what type of sugars the food contains.

The Maillard (pronounced May-ard) reaction happens when sugars react with amino acids (the building blocks of proteins) above 300°F (148°C), creating brown color and a complex variety of new flavor compounds.  This is another reason our potatoes turn golden brown when we fry them.  The Maillard reaction is also responsible for the aroma of roasted coffee, and gives baked breads and pretzels their brown crust.  The Maillard reaction and caramelization may make food look (and taste) similar, but the Maillard reaction involves sugars reacting with amino acids, while caramelization only involves sugar.  

TRY IT!


REMEMBER, THIS INVOLVES HIGH HEAT SO BE SURE TO HAVE A PARENT HELP YOU!!


Here’s what you’ll need:

1.    Potatoes, as many as you’d like, chopped into one-inch chunks

2.    A large enough pot to hold your potatoes and enough water to cover them

3.    A frying pan large enough to hold all your potatoes

4.    Two tablespoons of vegetable oil

5.    A spatula

6.    A spoon

7.    A stove 
 

Here’s what to do:

1.    Bring your pot of water to a boil over high heat.


2.    When the water starts to boil, begin heating your vegetable oil in your frying pan over medium-high
heat.

3.    When the oil in the frying pan is hot, and the water is boiling, add half of your potato chunks to
the boiling water, and half to the hot oil.  Be sure the potatoes in the oil are spread out.

4.    Carefully watch the potatoes in the oil, turning them every 3-5 minutes to make sure they don’t
burn.  Stir the potatoes in the boiling water every 5 minutes as well.

5.    After about 20 minutes, turn off the stove and remove your potatoes from the boiling water and the
oil.

6.    Allow them to cool for about 5 minutes before touching them.
  

Look at the potatoes.  What do the ones from the boiling water look like?  What about the ones from the oil?  How are they different?  Why do you think this is?  

 
Taste one of the potatoes from the boiling water. Describe the flavor and the texture. Now taste one of
the potatoes from the oil.  How are the flavor and texture different?  Why do you think that is?  Be sure to write down all your observations.

 
Make up a new experiment! 
What other foods could you try this with?  What other cooking techniques could you try (Hint: try the microwave!  Based on what you see, how do you think the microwave cooks food?)  Always be sure to have a parent or teacher help you and write down all your observations!

When I was only 5 years old, I remember watching a cooking show on television.  The chef was
making this delicious looking cream sauce, and at the end he added several pats of butter.  “Butter makes
everything better,” he said, as his concoction blended together perfectly.  Sometime later I sat down at the table with my mom, and a cup of hot apple cider...and I remembered the chef’s assertion about butter.  I can’t quite remember the face my mother made as I attempted to stir butter into my hot cider, but I do remember the result—greasy, yellow orbs floating menacingly in the pale brown liquid.  Apparently, butter doesn’t make EVERYTHING better!

So why could the chef make a perfect sauce with butter, while my apple cider wound up a disaster? 
The difference is caused by solubility.

Solubility is the ability of one material to become fully dissolved in another, usually liquid, material.  When one material is soluble in another, the two materials will blend together such that their individual molecules (their smallest building blocks) will be evenly blended together.  If one material is not soluble in another, this material will remain in globs, and never blend evenly within the other material.  For an example, let’s look at the butter again.  When the chef made his cream sauce, he put the butter into a mixture of heavy cream and other fats, in which the butter is soluble.  This is why the butter melted perfectly into the sauce.  I had put the butter into apple cider, a drink made mostly of water, in which butter is not soluble, causing globs of
butter to simply float around in the cider without dissolving.

So why should butter be soluble in fatty heavy cream, but not in watery apple cider?  The simplest explanation for this is that like tends to dissolve like—that is, fats will dissolve in other fats, but not in water.  Because of this, the fats in butter will blend well with vegetable oil, which is also a fat, but not in water.  Likewise, things that will dissolve in water—such as juice or coffee, which are made mostly of water—will not blend well with fats like butter or oil.  

There is also a more complex explanation for this, which is polarity versus non-polarity.  To understand what makes a molecule polar or non-polar, we have to look at what happens when the atoms (the most basic building blocks) that make this molecule bond with each other.  

When two or more atoms come together to make a molecule, like hydrogen and oxygen bonding to form water, they share their electrons—the extremely small negatively charged particles that make up the outer cloud of the atom.  These atoms may share their electrons equally, but sometimes one atom winds up pulling the electrons closer than the other.  This unequal sharing is what happens with water:  the oxygen molecule is more attractive to the electrons, and therefore the electrons want to be closer to the oxygen when it bonds with hydrogen.  Because the electrons are closer to the oxygen, it has a slight negative charge, while the hydrogen has a slight positive charge.  This slight negative charge to one end of the molecule, and slight positive charge to the other end is called polarity.  Because of this polarity, the water molecule is very good at dissolving other molecules that are polar or carry an electric charge, like sugars or salts.

On the other hand we have non-polarity.  This is what happens when the atoms of a bond share electrons equally, so no one atom holds the electrons closer than any other atom. As an example, let’s look at oil. Oil is made up of fats, or fatty acids, which are long chains of carbon and hydrogen atoms bonded to each
other.  All the carbon atoms in this chain have the same attraction for the electrons, and so all share them equally.  As a result, no one atom has extra charge, and the molecule is non-polar.  Because of this non-polarity, these molecules will dissolve other non-polar molecules, like the ones found in butter.  On the other hand, these molecules will not blend with polar molecules like water.

TRY IT!!


 Here’s what you’ll need:

 1.   Four clear drinking glasses

 2.   Two ¼ cups of vegetable oil

 3.   Two ¼ cups of water (tap water is fine)

 4.   Two teaspoons of sugar

 5.   Two teaspoons of lard or coconut oil

 6.   Four small spoons for mixing

  
Here’s what to do:


 1.   Line up all four of your glasses

 2.   Pour one quarter cup of water into one of the glasses and one quarter cup of oil into another glass.

 3.   Add one teaspoon sugar to the glass with the water, and another teaspoon of sugar into the glass with the oil.

 4.   Mix them both well with two of your spoons, one for each glass, for at least two to five minutes.


What happened to the sugar in the water?  Can you see any grains of sugar now?  Write down what you saw happen.

What happened to the sugar in the oil?  Did it dissolve?  Write down what you saw.

Based on these observations, is sugar polar or non-polar?  (Remember, polar things dissolve in water, while non-polar things dissolve in oil.)


Now for our next experiment:

 1.   Using your other two spoons, smear one teaspoon of lard or coconut oil onto the inside bottom and sides of each of the remaining two drinking glasses.

 2.   Add one quarter cup of oil to one of the glasses, and one quarter cup of water to the other glass.  
 
 3.   Stir both glasses well for at least five minutes.  Sometimes the lard or coconut oil is hard to dissolve, so be sure to mix for enough time!

 
What happened to the lard in the water?  Did it dissolve?  Is any still clinging to the bottom of the glass? Write down what you saw happen.
 
What happened to the lard in the oil?  Is there any still clinging to the glass?  Write down what you saw.
 
Based on these observations, is lard polar or non-polar?  (Remember, polar things dissolve in water, while non-polar things dissolve in oil.)

 
 
MAKE UP YOUR OWN EXPERIMENT!


What else can you test in oil and water?  Try other things you find in your kitchen, like salt, milk, juice, or baking soda.  Write down everything you test, and what you observe!

REMEMBER: Some things you might test are complex mixtures of things that are polar AND things that are non-polar, so they not completely dissolve in either water or oil.