What happens to coffee beans during roasting?

Roasting is fundamentally a controlled thermal degradation of the green coffee bean’s cellular structure. While often simplified as 'drying' and 'browning,' the process is a high-stakes management of chemical kinetics. It begins with the endothermic drying phase, where the bean sheds its initial moisture. As internal temperatures climb toward 150°C (302°F), the Maillard reaction initiates—a non-enzymatic browning process between amino acids and reducing sugars. This is the engine of flavor, producing pyrazines (nutty/earthy notes) and furans (caramel/sweet notes). Simultaneously, Strecker degradation occurs, further refining the aromatic profile. A common misconception is that roasting 'adds' flavor; in reality, the roaster is merely unlocking the potential established by the producer. If a farmer has meticulously managed fermentation to preserve high sugar content, the roaster must navigate the roast curve carefully to avoid degrading those sugars into acrid, carbonized compounds. The physical structure also changes: the bean becomes porous as CO2 builds up, creating the cellular matrix necessary for extraction. The roaster’s primary tool, the Rate of Rise (RoR), is not just a graph line but a measure of how effectively they are navigating the delicate balance between developing sweetness and avoiding 'baking'—a state where the bean loses its structural integrity and flavor complexity, resulting in a flat, hollow cup. Ultimately, the roaster is a steward of the producer's work, tasked with preserving the terroir through precise thermal management.