The Maillard reaction (pronounced "my-yard") is a culinary phenomenon that occurs when amino acids and reducing sugars combine causing them to turn brown and yield a distinctive flavor. It can occur in meats and proteins, along with other foods, including pan-fried dumplings, cookies, bread, toasted marshmallows, and more.
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. The difference lies in the chemical reactions that are taking place in the food.
A Chemical Process
More than just cooking, the Maillard reaction creates the brown coloring in cooked meat and other foods in a quite specific way. The amino acids and simple sugars in the protein are rearranged when heat is applied. They arrange themselves into rings. The rings form collections of rings and reflect light in a certain way that gives the food its brown color. This change in molecules is also responsible for flavors and aromas, two key elements of cooking (and eating). The Maillard reaction will present itself differently in different food. It all depends on the type of food and the ingredients you are cooking with. For example, both steak and cookies will undergo the Maillard reaction, but it will look, smell, and taste quite different and distinct from each other. The Maillard reaction is food specific.
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 is excellent for browning meat because it gets very hot and maintains its temperature very well. The high temperature of the cooking is key to the Maillard reaction. The high heat will increase the rate at which the chemical reaction takes place and will also accelerate the speed of water evaporation.
Even if the temperature is very high, if the food is wet, the Maillard reaction will not take place. The moisture in the food will prevent the temperature from rising above the boiling point of water. The temperature won't be raised sufficiently and the reaction cannot occur.
Challenges to the Maillard Reaction
Many chefs are challenged to create the conditions to make the Maillard reaction occur. The cooking surface must be hot and dry, but the challenge is to cook in the inside of the food without burning or charring the outside. Removing excess water from the food by blotting or even drying at low temperatures is effective. So is fast heating, like a deep fryer, super hot griddles, or even a blow torch.