Understanding First Crack and Development Time

What is happening at first crack

As the bean heats, moisture inside turns to steam and pressure builds against the cell walls. Around 196 to 205 degrees Celsius the structure gives way and the bean audibly fractures, expanding in volume by roughly half. That sound is first crack.

Chemically, a great deal of what we recognise as roast flavour is being formed in the minutes around and after first crack. Sugars are caramelising, amino acids and sugars are reacting in Maillard browning, and acids are degrading. This is not a moment to walk away from.

Development time and DTR

Development time is everything from the start of first crack to the moment you drop the batch. Development time ratio, or DTR, expresses that as a percentage of total roast time. A twelve-minute roast with a two-and-a-half minute development phase has a DTR just above twenty percent.

Conventional targets sit between eighteen and twenty-five percent for most profiles. Too low and the cup tastes grassy, bready or sour. Very high, and you flatten the acidity and lose the origin character you paid for.

Treat DTR as a diagnostic, not a target. It is one of the clearest signals that something changed, but it does not by itself tell you whether a roast tastes good.

Judging crack reliably

First crack is not a single instant. It starts with a few isolated pops, builds into a rolling phase, and tapers off. Dropping during the first pops is a different roast from dropping after the rolling phase ends.

Relying on sound alone is fragile - roaster noise, extraction fans and background noise all interfere. Confirm with the tryer. Pull a sample, look at the surface, smell the escaping gases, and taste a bean once it is cool enough.

Log the moment you judge crack to have started, and stay consistent about which part of the crack you call the start. Consistency matters far more than precision here.

And second crack

Second crack is a quieter, more crackling sound that begins in the region of 220 to 230 degrees Celsius as cell walls fracture further and oils migrate to the surface. It marks the transition to dark roasting and rapidly destroys origin character.

For most origins, second crack is a boundary you approach deliberately rather than cross by accident. If you hear it and did not intend to be there, your heat was too high late in the roast.