What is the first crack in roasting?

First crack ('1C') is the audible popping that occurs around 196-205 °C bean temperature. It is caused by the bean's cellular structure rupturing under the combined pressure of residual steam and CO2 built up by Maillard reactions. It marks the start of the development phase, signals that the bean has shed its grassy mass, and opens the aromatic territory that is readable in the cup.

First crack triggers when internal cell pressure exceeds the mechanical strength of the cell wall. At this point moisture has dropped below 2 %, the bean has expanded by 40 to 60 % compared with its green size, and melanoidins from the Maillard reaction are accumulating. The sound, similar to popcorn but drier and less intense, typically lasts 60 to 120 seconds on a 5-10 kg batch. It rarely starts with all beans at once: you first hear isolated pops (first-first crack), then a steady rhythm (rolling crack), then a slowdown (tailing off).

In modern profiling, first crack is the reference anchor. Roasters log the 'time to first crack' (TFC, typically 7 to 9 minutes on a specialty batch), the exact trigger temperature (196-205 °C, varying with bean density, altitude and green moisture), and the length of the rolling phase. They then measure the Development Time Ratio (DTR): time past first crack divided by total time. A 20 % DTR with 1C at 8'30 gives a roast of about 10'38. Too early a 1C (TFC < 7 min) usually signals an aggressive heat application that has baked the bean; too late a 1C (TFC > 10 min) risks baking through extended low-drive roasting.

First crack also separates two chemical regimes. Before: endothermic (the bean absorbs energy to dehydrate and drive Maillard). After: exothermic (pyrolysis releases heat, which can run the curve away if the burner is not cut in time — the classic beginner mistake). Lesser-known fact: convection roasters (such as Loring) handle this transition more smoothly than traditional drum roasters, thanks to their modulable hot-air recirculation — one of the technical selling points of Loring, Giesen or Probat Probatone versus pure drums. A Brussels or Ghent crew switching from a drum to a Loring usually has to relearn 1C piloting for several weeks.

Benchmarks around first crack