Roasting
Exothermic Phase
The stage of roasting where chemical reactions within the bean begin releasing energy as heat, starting at first crack. The exothermic phase requires roasters to reduce applied heat to prevent a runaway temperature rise.
Vertieft
Once first crack begins, the pyrolysis and caramelization reactions generate their own heat, and the bean temperature can accelerate rapidly if burner power is not reduced. This energy release is what creates the audible crack as gas pressure exceeds the structural strength of the bean. Roasters often cut gas by 20-50% approaching first crack to maintain a gently declining rate of rise through the development phase. Failure to manage the exothermic phase leads to scorching, tipping, or a roast that crashes too quickly.