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What changes happen to coffee beans during roasting?
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coffee
Roasted coffee beans, ground coffee, and instant coffee in paper bags.
During the coffee roasting process, green coffee beans undergo significant physical and chemical transformations when heated to temperatures between 180 and 250 °C (356 to 482 °F).12
Key changes include:
- Chemical Transformations: Complex reactions develop the bean's characteristic aroma and gustatory qualities.12
- Gas and Volatile Release: The process releases steam, carbon dioxide, carbon monoxide, and other volatiles.2
- Physical Expansion: Internal gas pressure causes the beans to expand by 30–100 percent.2
- Weight and Texture: Beans lose 14 to 23 percent of their weight, turn a deep brown color, and develop a porous, crumbly texture.2
- Residue Removal: For beans that have been decaffeinated, roasting removes remaining solvent residues.2
Care must be taken, as roasting for too long can destroy essential flavor and aroma compounds.12