What is second crack?
Second crack is the stage in roasting when beans give off a sharper, quicker cracking sound – caused by the build-up of gas pressure inside a now more brittle bean structure. Unlike first crack, which is driven by water vapour escaping, second crack is driven by gases like CO₂ breaking through the cellulose matrix of the bean.
It usually begins around 224°C. By this point, the coffee is visibly darker, oils start rising to the surface, and smoke becomes thicker and more pungent. This stage is typical of dark roast profiles.
Second crack moves fast, and if not carefully controlled, can quickly lead to overdevelopment. Roasting too far into this phase can produce smoky, bitter, or even burnt flavours, with acidity and origin characteristics becoming muted or lost.