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Why can overroasting coffee beans reduce their flavor and aroma?

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Paper bags filled with roasted coffee beans, ground coffee, and instant coffee granules arranged closely together. — coffee Roasted coffee beans, ground coffee, and instant coffee in paper bags.

The characteristic aroma and flavor of coffee are developed through complex chemical transformations that occur when beans are heated to temperatures between 180 and 250 °C (356 to 482 °F).12

While these high temperatures are necessary to develop the bean's qualities, roasting for too long can destroy the volatile compounds responsible for those desirable flavor and aroma profiles. Essentially, excessive heat exposure causes these delicate compounds to break down or dissipate, leading to a reduction in the quality of the final beverage.12

In some cases, such as with certain dark roasts, beans may be intentionally overroasted to mask natural harshness, though this process inherently sacrifices the nuanced flavors and aromas that might otherwise be present.1