What is degassing in roasted coffee?

During roasting, the Maillard reaction and caramelisation produce significant volumes of carbon dioxide that become trapped inside the bean's cellular structure. Degassing is the process of that CO₂ slowly escaping after roasting - it starts immediately and continues for days to weeks depending on roast level, grind state, and storage conditions.

It matters in two practical ways. For packaging: freshly roasted coffee needs time to degas before it's sealed airtight, otherwise CO₂ builds up inside and can rupture the bag. Most specialty roasters use one-way valve bags that let CO₂ escape without letting oxygen in, allowing earlier packaging without the risk. For brewing: coffee that hasn't degassed sufficiently - particularly for espresso - can produce uneven extractions and a harsh, carbonic edge. Most roasters recommend resting espresso for at least five to ten days after roasting before use.

Lighter roasts degas more slowly than darker ones. Ground coffee degasses dramatically faster than whole beans, losing freshness much more quickly in the process - another reason to grind as close to brewing as you can.