The chemistry of cookies - Stephanie Warren

Smelling nutty, toasty aromas is a reliable doneness cue because Maillard reactions and caramelization produce volatile aromatic compounds that diffuse into the air once browning has progressed enough.

Caramelization requires higher heat (starting around 356°F) because sugar molecules need that thermal energy to decompose and rearrange into the compounds that give caramel its sweet, nutty and slightly bitter flavors, so a 350°F oven won’t drive those pathways appreciably.

Initial Maillard products are chemically reactive and undergo secondary reactions with each other and other food components, causing a cascade that produces a much wider range of flavor and aroma compounds.

Around 310°F, amino acids and reducing sugars undergo Maillard reactions that form heterocyclic (ring-like) compounds, which change surface color and produce volatile molecules responsible for browned, savory flavors.

Baking soda reacts with acidic ingredients to release carbon dioxide gas, and the expanding CO2 inflates the dough matrix to create airy pockets and a lighter texture.

When the water in a cookie reaches boiling it evaporates, removing moisture and reducing plasticity so the dough contracts, stiffens and develops surface cracks while leaving behind voids.

Around 144°F egg proteins unfold and form new bonds with neighboring chains, coagulating into a linked network that firms up runny ingredients and gives body to the dough.

Salmonella cells are killed once dough reaches roughly 136°F because heat denatures essential bacterial proteins and disrupts cellular structures, rendering the bacteria nonviable.