Coffee roasting is far more than a heat process – it’s a complex chemical symphony involving hundreds of reactions that develop the coffee’s signature aroma and flavor.
🌡️ From green to golden – The physical phase
Green coffee beans start as hard, odorless seeds. As the temperature rises (above 150°C), moisture evaporates, beans expand, and color changes begin – setting the stage for chemical transformations.
🔬 The Maillard reaction – Flavor foundation
Between 150°C and 200°C, the Maillard reaction takes place. It’s a reaction between amino acids and sugars that produces deep, roasted notes like caramel, nuts, and chocolate.
🍬 Caramelization of sugars
As heat increases, sugars inside the beans caramelize, creating sweet, rich, and sometimes slightly bitter flavors, depending on roast level and duration.
💨 CO₂ Degassing and aromatic balance
During roasting, beans release carbon dioxide (CO₂), which continues to escape for days after roasting. This degassing stage is crucial for the freshness and aroma profile of the final brew.
🌈 Roast level and flavor impact
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Light roast: floral, citrusy, bright acidity
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Medium roast: balanced sweetness, acidity, and bitterness
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Dark roast: full body, chocolatey notes, low acidity
📚 Conclusion
Roasting is both science and art – and understanding its chemistry helps us better appreciate every sip of a well-crafted coffee.