Written by: on December 2, 2016 @ 10:42 am

Cookies – it’s as easy as throwing some ingredients in the bowl and popping them in the oven right?  Sure mixing up cookies is pretty easy but the real work begins once you close the oven door. There are actually several fun chemical reactions that happen once your cookies are baking in the hot oven.  Most basic cookie recipes call for flour, butter, eggs, salt, baking soda, and white and brown sugars.  From there creativity abounds as you add flavors and mix-ins.  Each ingredient plays an important role in creating your favorite ooey gooey cookie.

Mix it up:

As you mix your cookies, flour is the most important ingredient of all because of gluten.  Gluten is a sticky, stretchy, strong protein found in wheat.  It is necessary to create structure in breads and baked goods, but it actually doesn’t exist until you start baking!

When flour becomes wet, the gluten inside of it activates via the combination of two proteins (glutenin and gliadin) and your dough becomes sticky and has more structure.  You develop the gluten by kneading your dough, which stretches the gluten and encourages it to form a network.  Bread involves a lot of kneading but cookies and other baked goods require a light hand.  You can overmix your dough and create a tough cookie!

So mix it up and pop your cookies in the oven and get ready to watch all the different reactions that happen to turn your dough in to a delicious cookie.

Heat it up:

As the dough heats up in your 375 degree oven, butter begins to melt around 92 degrees.  Butter is an emulsion, which is a mixture of two things that don’t want to stay together.  In the case of butter, those two things are fat and water.  As the butter melts, the dough ball spreads and loses its structure.  If you chill your cookies prior to baking you’ll actually have less spread.  This is ideal for holiday cut-out cookies, because the cookie bakes and forms a solid structure faster than the butter melts to a liquid.  Chilled cut-outs keep their shape whereas warmer dough yields weird amoebic shapes.

As the water pulls away from the butter emulsion it bubbles and is released from the cookie as steam.  The fat in the butter actually coats the gluten and “shortens” it by preventing it from forming longer strands.  This is simply why you don’t have super puffy, twice-their-volume cookies.

At 144 degrees the protein molecules from your egg begin to uncoil and connect to form a solid structure.  Then at 212 degrees water completely boils off and the cookie dries out leaving wonderful airy pockets.  How did those pockets get there?

Give it a Rise:

There are two ways to give your baked goods a rise:  yeast or sodium bicarbonate.  Yeast is actually a living creature that activates when combined with warm water, starch, and sugar.  As it consumes starch, its “food”, it releases carbon dioxide, giving life to bread and many other baked goods.

Cookies on the other hand utilize sodium bicarbonate, usually baking soda, which creates carbon dioxide when it heats up.  If you’ve ever done a volcano experiment with vinegar and baking soda it’s a similar reaction except the baking soda is reacting to heat rather than an acid! Water vapor escaping from the dough in combination with the carbon dioxide released by our baking soda is ultimately what makes our cookies light and airy.

Why not baking powder?  The main difference between baking powder and baking soda is that baking powder carries an acid with it, which means that it reacts both when it’s mixed in the dough and also later when it’s heated.  Baking powder creates extra leavening and a fluffier cookie.  Many recipes call for either one or a combination of both.

Golden Brown:

The most exciting part about baking is the wonderful golden brown color and delicious flavor created in the process.  Both of these elements happen thanks to the Maillard reaction and carmelization.

The Maillard reaction occurs around 310 degrees when proteins and sugars break down and realign into rings.  The rings reflect light and create that wonderful golden brown color.  White granulated sugar is mostly sucrose so doesn’t participate as well in the Maillard reaction, which is why a lot of cookie recipes call for both white and brown sugar.  Brown sugar has both glucose and fructose, which happily create rich, complex flavors via the Maillard reaction.

At 356 degrees the magic really happens when carmelization kicks in.  Carmelization is when sugars break down with high heat to create a wonderfully rich, nutty flavor.  Carmelization doesn’t occur at lower temperatures so cookies baked at 350 or lower have a more mild flavor and color.  Playing with the temperature can totally change the flavor of your cookie!

So mix up some cookies and observe some chemical reactions first hand.  Best part is you get to eat the results of your labor!  The following basic recipe can be customized with different flavors and toppings.

Basic Sugar Cookie Recipe:

  • 3 c. all-purpose flour
  • 1tsp baking powder
  • 1/4tsp baking soda
  • 3/4tsp salt
  • 1 c. (2 sticks) butter
  • 1 1/4 c. sugar
  • 1 tsp vanilla extract
  • 1/4tsp almond extract
  • 1 egg

Optional topping:  regular, or colored decorating sugar to sprinkle on top prior to baking

  • Preheat oven to 375 degrees.  Line pans with parchment paper.
  • Mix all dry ingredients except sugar in a bowl
  • In a separate mixing bowl cream the butter and sugar together until smooth and fluffy
  • Beat in the egg and vanilla and almond extracts
  • Add the flour mixture gradually mixing after each addition
  • Spoon tbsp portions of dough on to your pans.  Flatten each ball with a glass to about a ¼ inch thickness
  • Optional:  Sprinkle the tops with sugar!
  • Bake at 375 for 10-12 minutes.  10 minutes for a softer cookie; 12 minutes for a crunchier, more golden cookie.  Remove from oven and transfer to a wire rack to cool

Tip:  For roll out cookies you can cut into festive shapes, add an additional ½ cup of flour to the recipe.

Catogories: Experiments: Science Made Fun, Fun Fact Friday, Hear It From A Scientist, Uncategorized

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