Who doesn’t enjoy a warm cookie fresh out of the oven this time of year — or any time of year? What is it about the combination of flour, butter, sugar and eggs that makes such a delicious desert? This article is going to make your enjoyment of the fresh cookie even greater by combining it with another favorite — science!
Baking cookies involves a complex series of chemical changes — and a couple of physical changes, too. These changes turn your ball of dough into the delicious cookie that you love. The first physical reaction occurs at 92 degrees Fahrenheit. That is the temperature at which the butter starts to melt. The melted butter spreads the cookie out into its flatter shape. At this point, all the ingredients are still the same and there is no change in taste.
As the butter melts, water is released. The water begins to turn to steam, which takes up more space than liquid water. This causes the cookie to begin expanding and become puffy. If you quit cooking the cookie now, it will still taste like your raw dough as all the changes so far have been physical changes to the appearance of the cookie.
At 144 degrees, the first chemical reaction begins as the proteins from the eggs you added begin to rapidly expand and change structure. As the proteins expand, they act like long fibers that hold the cookie together. You already knew that the proteins in eggs can hold things together when heated — the same thing happens every time you cook an egg.
At about the same time the proteins are changing, another chemical reaction is taking place. Have you ever mixed baking soda with an acid (like vinegar)? Sure you have! Well, the same thing is happening in your cookie. The baking soda that you put into the cookie is now reacting to some of the natural acids in the cookie dough to produce bubbles of carbon dioxide. As the cookie continues to cook, the carbon dioxide bubbles escape and leave air pockets in the cookie. The air pockets from the escaped gas give the cookie the light and airy feel.
As the cookie continues to warm, some of the remaining water evaporates, which starts to dry out the cookie. And now it’s time for one of the most important reactions — the maillard reaction.
The maillard reaction begins at 310 degrees, when the proteins and sugars break down and rearrange into a molecule shaped like rings. These ring-shaped molecules reflect light in a way that gives a brown color. This reaction also produces aromas and new flavors as new molecules are made. The aromas from this reaction are what you smell as the cookie is just about done.
If the cookie heats up to 356 degrees, another reaction, called caramelization, occurs. This chemical reaction breaks down the remaining sugars in the cookie and turns them into a hardened caramel. This process produces additional brown color and additional flavorings.
At this point, your cookie is ready for the best part — eating! You can sit back and enjoy the chemical and physical reactions you produced. Some people like to cheat and eat the cookie dough before it is cooked. Not to take the fun out of it, but that is not a great idea. The eggs you put into the dough might contain a type of bacteria called salmonella. Salmonella makes almost 150,000 people sick every year. It can live for weeks on surfaces and can even live after being frozen. Only when salmonella reaches a temperature of 136 degrees does it die. That one quick bite of uncooked cookie dough could come back to get you with a couple of days of very bad stomach pains, so cook that dough first!
So there it is. Next time you enjoy a fresh cookie right out of the oven, you now know that it is so great because of science. Science is pretty sweet, isn’t it?
