What is first crack?
First crack marks a key turning point in roasting, when beans shift from absorbing heat (endothermic) to releasing it (exothermic). Built-up steam and gases like carbon dioxide escape with an audible cracking sound, similar to popcorn popping. The beans expand, release chaff, and start to produce smoke.
At this stage, surface temperature drops briefly in what’s known as an endothermic flash – caused by rapid water release. Roasters often reduce heat at this point to control development more precisely.
When does first crack happen?
It usually begins around 193°C, though this can vary slightly depending on origin, moisture, and roast set-up. Roasters tend to reduce the heat of their roast once first crack happens.