More and more coffee shops are choosing to place roasters at their storefronts to roast beans themselves, which allows them to control costs while also maintaining quality. Walking down the street, you can often smell the blended aromas released by roasting coffee beans—the blue-green scorched smokiness of burning plant fibers, the creamy pale-yellow sweetness, the brown toast-like bread aroma, all interwoven together. These rich smells largely owe their existence to the Maillard reaction during roasting. The Maillard reaction is a series of reactions that occur when amino acids and reducing sugars in food are heated, and it can be broadly divided into three stages: early, middle, and late. During the process, various aromatic compounds and pigments are produced, playing a key role in the layering and variation of coffee's final flavor. This article will outline the stage divisions of the Maillard reaction, its chemical pathways, and its significance for coffee flavor.
The Maillard Reaction
In recent years, many coffee shops have set up roasters at their storefronts to roast beans on site, which both reduces costs and allows them to control quality independently. As a result, the unique aroma of roasting coffee beans often drifts through the streets, mingled with the blue-green scorched smokiness of burning plant fibers, a creamy pale-yellow sweetness, and the brown bread-like aroma of toast—multiple scents blending together. These richly layered flavors mostly originate from the Maillard reaction that occurs during roasting.
The Maillard reaction can be divided into three stages. First, the early stage:
Carbonyl-amine condensation and Amadori rearrangement.
Second, the middle stage:
The Amadori rearrangement product, fructosamine, dehydrates to form HMF (hydroxymethylfurfural);
Fructosamine loses its amino group and converts into reductones;
Amino acids react with dicarbonyl compounds.
Third, the late stage:
Aldol condensation;
And polymerization reactions that produce melanoidins.
In addition to carbohydrates, proteins make up about 11% of the weight of green beans, and the amino acids contained in these proteins are exactly the raw materials needed for the Maillard reaction. The so-called Maillard reaction refers to a series of reactions that occur when amino acids and reducing sugars (such as glucose, fructose, lactose, etc.) in food are heated. This reaction produces quite a variety of aromatic compounds and pigments, such as Pyridines, Pyrazines, Oxazoles, Thiazoles, and Pyrroles. The Maillard reaction plays an important role in the flavor of cooked food. Whether it's the darkened, aromatic surface of grilled sausages, crispy-outside-tender-inside roast chicken, or fragrant toasted bread, the unsung hero behind the color, aroma, and taste of these grilled foods is the Maillard reaction.
Coffee itself contains a vast and complex array of chemical substances. In addition to the compounds mentioned above, it also includes other organic acids, inorganic acids, plant alkaloids, and other components. It's not only the sweet and pleasant parts—slightly bitter compounds also give coffee flavor a broader range of layers and variations, together creating coffee's uniquely rich taste.
The above content is compiled by CoffeeHunters, a coffee news website.
