Every family has their own favorite desserts. Some families enjoy the creamy coldness of ice cream, some are happy with a fresh bowl of fruit like strawberries, and other families come from a deep tradition of baking. This week, we pay homage to all those families who pull out their mixing bowls and crank up the oven to make the ever popular…
COOKIE
As you know, cookies come in a variety of shapes, styles, and flavors. However, most cookies share the same common ingredients:
Flour Sugar Fat Eggs and Leavening agentsI could spend weeks explaining how the four basic concepts of science can be found within these basic ingredients. However, I was always taught that “Less is More” so let’s look at how these four concepts are found in the BAKING of our cookies:
For the record, I’m going to be discussing the baking of drop cookies (like chocolate chip or oatmeal cookies.) It’s not that I have a personal favorite (oatmeal cookies) and it is not my wish to offend any bar- or cut-out cookie fans, it’s just a random decision (yeah right) I have made for this post (because oatmeal cookies are the best.)
THE INGREDIENTS ARE ONLY THE FIRST STEP
The proportion of ingredients helps to create the crumbly, crisp, or chewy texture of a cookie. For example, shortbread cookies are made up of much more flour than water which helps to provide a crumbly texture. However, if your ingredients consist of more water than flour, you can end up with a crispier cookie, like a wafer. Drop cookies are somewhere in the middle. They have about half as much water in them as flour.
Where does the water come from?
Well, I’ve never seen a recipe for oatmeal cookies that require water as an ingredient. However, there is plenty of water within the eggs and fat (butter) of most drop cookies.
HERE COMES THE SCIENCE STUFF…
Flour and water help create the variety of cookies we know and love, but it is SUGAR that gives a cookie most of its structure and texture. Drop cookies tend to contain equal amount of flour AND sugar.
The high DENSITY of sugar molecules within the soft cookie dough of drop cookies goes through several changes as you heat them up in the oven and cool them off on the counter.
Remember – A molecule is a group of ATOMS which are bonded together. In the case of sugar, you are looking at a large number of Carbon, Hydrogen, and Oxygen ATOMS.
Sugar molecules tend to stick together very well. Thousands (if not millions) of sugar molecules are bound together in every single visible grain of sugar! When heat energy is added to this collection of molecules, they tend to shake or vibrate away from each other. You have seen this happen when ice melts… The molecules of water absorb heat from the environment and moves away from each other to form liquid water. Well…
SUGAR DOES THE SAME THING!
THE SECRET INGREDIENT IS DIFFUSION
As the solid sugar molecules break apart (DISSOLVE) in the presence of heat, the molecules tend to move away from each other by the process of DIFFUSION. And the cool thing is that you can witness this diffusion every time you bake drop cookies. Your little ball of soft dough spreads out all over the cookie sheet.
How does this happen?
The liquefied sugar, combined with the water in the eggs and butter, cause the soft dough to spread out onto your cookie pan during baking. That’s right! The dough DIFFUSES throughout the cookie sheet.
What happens after you turn off the heat?
This is an easy one to answer. Let’s return to our story about water… What happens to liquid water when you take away all of its heat energy (think of a glass of water inside a freezer.) You guessed it! The liquid water will freeze into a solid.
This is what happens to liquefied sugar as well! The sugar molecules change back from a liquid into a solid and give your drop cookie a firmer, cake-like texture.
A SERIES OF UNFORTUNATE EVENTS…
Unfortunately, the average life of a homemade cookie is very short. Even if you store them in an airtight container, they will eventually show their age. This follows the LAW OF CONSERVATION which states that ATOMS cannot be created or destroyed, only rearranged.
During the demise of your oatmeal cookies, no ATOMS are altered in any way. It is the process of DIFFUSION that is responsible for their untimely “death.” Let me explain:
It is true that the texture of drop cookies changes rapidly over the course of a few days. These soft and chewy cookies tend to DIFFUSE their water into the environment rather easily. Without this water, your cake-like oatmeal cookies tends to resemble a hockey puck. Yuck…
So if you have learned anything from all of this it should be…. EAT THOSE COOKIES AS FAST AS YOU CAN!
Learn more about chemistry concepts (and many more) in the Classic Science: Series for the Family and be certain to come back every Thursday or subscribe to The Blog of Mr.Q to learn more about how to teach science during breakfast, lunch, and dinner!
