Roasting coffee produces two distinct audible cracking sounds, and roasters use them as landmarks.
First crack
Around 196 °C. Water inside the bean turns to steam, pressure builds, and the bean’s structure gives way with a sound like popcorn.
The bean expands substantially and loses most of its remaining moisture. Everything before first crack is drying and browning; roasting proper starts here.
A light roast is dropped shortly after first crack ends.
Development time
The stretch between the end of first crack and the drop. This is where sweetness develops and where sourness turns into acidity.
Roasters talk about development time ratio — the proportion of the total roast spent after first crack, usually 15 to 25%.
Under-developed coffee tastes sour, grassy and thin no matter how you brew it.
Second crack
Around 224 °C. A sharper, quieter, more brittle sound, as the cell structure fractures further and oils migrate to the surface.
Medium-dark is at the start of second crack. Dark is through it. Beyond, the coffee tastes of roast and little else.
Why oily beans are dark
Oil on the surface means second crack. It also means the bean stales faster, since the lipids are exposed to air.
What it means for buying
If a bag’s beans are shiny with oil, expect roast flavour rather than origin flavour, and expect it to go stale sooner.
Last reviewed 8 August 2026