Cocoa powder and cookies
Cocoa powder holds a special place in my heart as the ingredient that got me into food science. During my senior year of college, I wanted to pursue research in food science but my school didn’t have any faculty in that area. Amazingly, one of the chemistry professors had a connection to a local chocolate factory, agreed to advise me on an out-of-the-ordinary project, and secured seven different types of cocoa powder for me to
play with test. You know, scientifically.
But enough nostalgia: mostly I love cocoa powder for the chocolate power it wields. While solid chocolate contains cocoa butter and sugar and sometimes milk and other things to make it delicious on its own, cocoa powder is the real deal, straight up chocolate flavor for baked goods. Using cocoa powder lets us adjust the sugar and fat content and all the rest independently, which makes cocoa powder a powerful tool for chocolate desserts.
In the case of the cookies I made earlier this week, cocoa powder brings not only great taste but also structure. Made from pressed cacao beans, cocoa powder is high in vegetable starches. When they encounter water and heat, the starches swell up and release some of their long, chain-like molecules into the liquid around them, forming a sort of mesh that traps everything in its place and helps turn cookie dough into solid cookies. This process, called gelation, also gets credit for thickening any fruit pies that contain cornstarch and preventing soupy gravy.
Flour usually provides most of the starch in cookies, but in my chocolate cookies it shares the limelight with cocoa powder. With both of these powdery ingredients providing liquid-guzzling starch, too much of either can lead to an unappealing dry texture. For super-chocolatey cookies that stay rich and tender, we drop the amount of flour to let cocoa powder play a starring role in structure as well as flavor.