Pots, Pans, and Potatoes: Why Methods of Cooking Determine Foods’ Color and Flavor

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! 

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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!