What is first crack in coffee roasting?

First crack is the moment you've been listening for. As the roast progresses, steam and gases build up inside the bean until internal pressure fractures the structure - producing an audible crack, similar to popcorn. That sound signals a fundamental shift: the beans move from absorbing heat (endothermic) to releasing it (exothermic).

Physically, the beans expand noticeably, shed chaff, and begin to develop the colour and character associated with roasted coffee. Most of the development reactions that define a coffee's final flavour happen from first crack onwards, which is why it marks the start of the development phase and why roasters pay close attention to when it arrives.

For specialty roasters, the timing and pace of first crack provides real-time feedback on how the roast is tracking. If it comes earlier than expected, the roast is running hot; later than expected, and you may need to add heat to maintain momentum. Experienced roasters can hear a lot about a profile just from the sound and pace of first crack alone.