Roasting, green to black

Roasting turns a hard, grassy seed into something brittle and aromatic in about ten to fifteen minutes. Move the scrubber to watch one bean darken, and see where each roast level sits on the curve.

Before second crack

Full City

Weight lost
14–16%typical
First crack
about 196°C typical
Second crack
about 224°C typical

Balanced sweetness and body; caramel and chocolate begin.

Drying Browning Development 196° 224° °C First crack Second crack
Schematic bean-temperature curve: the shape, not a recipe. The crack temperatures are typical readings; real values depend on the beans, the roaster and where the probe sits. Weight lost is typical for each level.

What happens in the drum

Drying

The beans arrive holding around a tenth of their weight as water. The first stretch of the roast drives it off; the beans turn from green to yellow and smell of hay and bread.

Browning

Sugars and amino acids react and caramelise, building colour and most of coffee's aroma. Pressure from steam and gas inside the bean ends in the audible pops of first crack.

Development

After first crack the roaster decides how far to go. Stop soon after and origin character and acidity lead; carry on into second crack and roast flavours, oils and bitterness take over.

Roast names are trade conventions, not a standard: one roaster's City is another's Full City. Colour meters give a number, but scales differ between instruments, so this page does not quote them.

Roasting machines in the atlas

148 machines

Home air roasters 2

Home drum roasters 6

Sample roasters 15

Shop drum roasters 63

Shop fluid-bed roasters 3

Industrial roasters 59

Before the roaster

What reaches the roaster was shaped long before: by the variety, the processing method that dried it, and the grade it was sold under. The figures above are typical values, given as such; they are general roasting knowledge rather than measurements by this atlas.