Ever wonder what creates the deep, nutty, toasty, savory wonderfulness on seared meat, coffee beans, bread crusts, or dark beer? The popular answer is caramelization, but no- caramelization involves decomposition of sugar molecules in things like cooked fruits and, well, sugar.
The next answer that may come to mind is protein denaturation. Also wrong– protein denaturation, responsible for meat and egg changing color as it cooks as well as many other culinary applications, does occur in a sense… but not really. Another answer a chemistry geek may come up with is enzymatic browning (think of what happens when an apple or avocado turns brown), but that change, as the name reveals, involves little functional proteins called enzymes to convert one substance(s) into others. No, no, no– the answer is much more complex. So complex that science has yet to fully explain it!
The reactions that give way to these much-sought-after flavors are the Maillard Reactions (pronounced my-YAR [French], not MAY-lard as so many people say… it’s a pet peeve of mine, granted not one that I have to put up with in many circumstances). These reactions are so ill-defined that they don’t have individual names.
In general, foods that are not mostly sugar (i.e. the foods listed above) with high amounts of protein undergo these reactions around 310 F (foods cooked lower than this temp, like roasts, don’t have as much reaction occur). Basically what happens is that a reducing sugar (that means nothing unless you’ve taken biochem [while awake]) and an amino acid, both either bound or free, react, form an unstable intermediate, and then decompose again into “hundreds of different by-products”. The flavors and aromas are more complex (and better, in my mind) than simple caramelization because of the presence of nitrogen and sulfur in the proteins, which allow for a bigger variety of compounds. Remember the browned cheese of this meal? Also thanks to Maillard.