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Why are coffee beans roasted before brewing?
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Roasted coffee beans, ground coffee, and instant coffee in paper bags.
Coffee beans are roasted to develop their essential aromatic and gustatory qualities, which are not present in their raw, green state. By subjecting the beans to high temperatures ranging from 180 to 250 °C (356 to 482 °F), complex chemical transformations occur within the bean, producing the characteristic aroma of coffee.12
Beyond flavor development, the roasting process serves several functional purposes:
- Physical Transformation: The heat causes the beans to expand by 30–100 percent and changes their texture to a porous, crumbly state, making them easier to grind.2
- Gas Release: Roasting releases steam, carbon dioxide, and carbon monoxide from the beans.2
- Quality Control: In cases where beans have been decaffeinated, roasting helps remove trace solvent residues. Additionally, deliberate over-roasting can be used to eliminate the natural harshness found in certain varieties, such as Robusta.21
Care must be taken during this process, as roasting for too long can destroy the volatile compounds responsible for the coffee's flavor and aroma. For more details on the process, see coffee roasting.12