A second audible cracking event during roasting, around 224–230 °C bean temperature, when the bean's cellulose structure breaks down further and oils start to migrate to the surface. The sound is quieter than first crack but faster and denser — a fine, continuous crackle rather than a series of distinct pops, closer to cereal in milk.
Second crack defines the territory where coffee starts to taste primarily of roast rather than of bean. Beyond it, origin character — fruit, florals, terroir — gets quickly muted by carbonized notes: cocoa, cedar, eventually tar.
What changes physically
After second crack, beans appear oily on the surface. The Maillard reaction has run its course and pyrolysis has taken over — the bean is essentially carbonizing. Sugars caramelize, then burn. CO₂ generation increases dramatically, which is why dark roasts degas faster and stale faster than light roasts.
When you want it
- French roast and Italian roast are pulled deep into second crack. Expect bittersweet, smoky, low-acidity cups. Terroir mostly disappears.
- Vienna roast sits at the edge of second crack — heavier body and chocolate notes, but origin still partially audible.
- Specialty filter roasting stops before second crack on principle: there's no point developing the bean past the point where its origin character disappears.
If you're brewing pour-over from a bag that's clearly oily and shiny, you have a dark roast. Coarser grind, lower temperature (88–92 °C), shorter contact time. Recipe geometry that works for a Nordic roast will over-extract a French.
