The Maillard reaction (pronounced "my-yard") is a culinary phenomenon that occurs when proteins in meat are heated to temperatures of 310 F or higher, causing them to turn brown.
Named for the French chemist Louis-Camille Maillard who discovered the process at the start of the 20th century, the Maillard reaction is similar to the process of caramelization, where carbohydrates like sugar turn brown when heated.
While caramelization is not the identical chemical process as the Maillard reaction, the effects are visually very similar.
What the Maillard Reaction Does to Food
The Maillard reaction is what produces the thick, dark-brown crust on the surface of meat when it's cooked using high-temperature, dry-heat cooking techniques. The meat must be dry before putting it in the pan. Excess moisture will interfere with the browning process and tends to produce a gray exterior rather than brown. You'll want to make sure that you get your pan very hot before adding the meat. A cast-iron skillet (like this one) is excellent for browning meat because it gets very hot and maintains its temperature very well.