What are the "Maillard Reaction" and "Caramelization" in the Coffee Roasting Process?

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A Brief Explanation of Reactions During the Coffee Roasting Process by FrontStreet Coffee

The roasting process is generally divided into three stages, where the first two stages can sometimes be combined. The first stage is loading beans into the roaster, during which moisture migrates from the interior to the surface of the beans, and the coffee beans are dried. This stage may not show much visual effect, but the steam expelled from the roaster carries the aroma of fresh grass and warm hay. This is immediately followed by the second stage of moderate roasting, where complex caramelization and Maillard reactions bring us the familiar coffee aroma. The density of coffee beans during roasting decreases, becoming drier and more brittle. The combination of various factors improves their permeability and makes their components more soluble. When roasting is complete, the beans are discharged from the roaster, entering the third stage of cooling and degassing.

The Maillard Reaction

The Maillard reaction, proposed by French chemist L.C. Maillard, is a non-enzymatic browning reaction widely found in the food industry. The Maillard reaction is a series of reactions between reducing sugars and proteins or amino acids, catalyzed by heat. After reaching a certain temperature, the Maillard reaction occurs. Through complex reaction processes, brown or even dark brown large molecular substances called melanoidins are produced, along with other substances.

The Maillard reaction brings flavor, mouthfeel, color, and complexity to coffee.

The Caramelization Reaction

Raw coffee beans contain a certain amount of sucrose, which is also the main source of coffee sweetness. During the first crack period, the caramelization reaction occurs. In the caramelization process, sugars in coffee beans undergo dehydration under heat, producing two types of substances: first, sugar dehydration polymers, commonly known as caramel or sauce color; second, degradation products, mainly some volatile aldehydes and ketones, which can continue to condense and polymerize to form dark-colored substances.

The caramelization reaction deepens the color of coffee beans and creates aromas of fruit, caramel, roasted nuts, and more.

Applications in Food Roasting

Both of these reactions commonly occur during food roasting processes. When baking bread, they give the bread a golden color and emit a rich aroma, while when roasting coffee beans, they make the coffee beans darker while releasing more complex flavors.

The Importance of Roasting Time

Understanding the reactions that occur during coffee bean roasting makes it even more important to recognize that the roasting process is crucial. If it's even a second too short, insufficient caramelization will result in monotonous and dull aromas, lacking layered flavors, which adversely affects the quality.

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