What Happens During the Maillard Reaction
When food is heated to high temperatures, amino acids (building blocks of proteins) and reducing sugars start to break down and combine with each other. These broken pieces recombine into hundreds of new compounds that were not present in the raw food. This creates entirely new flavors, smells, and brown colors that did not exist before cooking.
Why It Matters in Cooking
The Maillard reaction is responsible for most of the appealing flavors and aromas in cooked food. Without this reaction, many foods would taste bland and unappetizing. Cooks use this reaction intentionally by searing meat at high heat, toasting bread, roasting vegetables, and grilling foods to create these desirable flavors and textures.
Conditions Needed
The Maillard reaction requires three main things: proteins, sugars, and heat. The food must be heated to at least 300°F (150°C) for the reaction to start. The reaction happens faster at higher temperatures and is stronger in foods with more protein and sugar content. This is why browning meat at high heat creates better flavor than cooking it slowly at low temperatures.
Common Examples
You experience the Maillard reaction every time you eat browned foods. A seared steak gets its brown crust and rich flavor from this reaction. Toast gets its brown color and nutty taste from the Maillard reaction. Roasted coffee beans, caramelized onions, and crispy french fries all owe their delicious flavors to this chemical process.
Difference from Caramelization
Many people confuse the Maillard reaction with caramelization, but they are different processes. Caramelization is when only sugar is heated until it browns, while the Maillard reaction requires both proteins and sugars to brown together. The Maillard reaction creates many different flavor compounds, while caramelization creates mainly sweet, bitter flavors. 
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