What Happens During First Crack

TL;DR: First crack happens around 196°C (385°F) when steam pressure fractures the bean. By then, Maillard reaction has created hundreds of flavor compounds.

The Buildup

Green beans are ~10–12% water. As heat rises, Maillard kicks in at 140–165°C (nutty, caramel aromas). Caramelization starts above 170°C as sucrose decomposes.

The Crack

At ~196°C, internal pressure fractures cell walls — audibly. Beans expand 50–100%, become porous, and shift from endothermic to exothermic.

CO₂

First crack = serious CO₂ production. This is what you see during bloom when brewing.

The Decision Point

Stop after first crack = light roast. Push further = medium. Continue to second crack (~224°C) = dark.

Try This

With a home roaster, pull beans at first crack, 1 min after, and 2 min after. Brew all three. Taste the transition.