In a video animation through Ted-Ed, Stephanie Warren explained the basic chemical reactions that take place when baking cookies.
“Don’t let that apron deceive you. Bakers are mad scientists. When you put the raw cookie dough into the oven, you’re setting off a series of chemical reactions.”
When the dough is placed in to the oven and reaches 92 degF, the butter begins to melt, causing the dough to start spreading out. Butter is an emulsion, which is a mixture of two substances that do not want to stay together. In butter’s instance, those two substances are water and fat. As the butter melts, water is released and expands into the cookie, pushing against the dough from the inside as it gets hotter.
The narrator then explains that the eggs used in the dough may have contained salmonella bacteria before cooking, which causes over 142,000 cases in the U.S. each year. The salmonella bacteria can live for weeks outside the body, until temperatures reaching 136 degF. When the dough reaches that temperature, the bacteria will die.
The next change begins with the proteins in the dough mostly provided by the eggs at 144 degF. When the protein is exposed to heat, then transform from string-like bunches into long strings that get tangled up, which is observed through a more solid yolk in the egg and more substance to the dough.
Water boils away at 212 degF, causing the cookie to dry out, stiffen, and crack. The backing soda reacts with acids in the dough to expand and create air pockets.
Want to learn more? More Cookie Chemistry can been seen in this video. Enjoy!