Second Crack

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title: "Second Crack" tags: [coffee/roasting] status: Draft aliases: [] related: []

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Second crack is a later stage in coffee roasting where the beans produce quieter, sharper cracking sounds as the bean structure breaks down further and oils begin to migrate to the surface.

What causes it
At higher temperatures, the cellulose structure of the coffee bean fractures. Unlike first crack, which is driven largely by steam pressure, second crack is caused by the thermal breakdown of the bean’s cell walls and the release of gases.

When it occurs

• Typically around 220–230 °C (428–446 °F) bean temperature

• Occurs after significant development beyond first crack

Why it matters
Second crack marks the transition into very dark roasting. Flavours shift toward smoky, bitter, and carbonised notes, while acidity and origin character diminish. Oils often become visible on the bean surface.

For home roasters, reaching second crack requires close attention, as the margin between a dark roast and burnt coffee becomes very small.