Foundational
Roasting basics: from green bean to roasted coffee
What actually happens to a coffee bean during roasting, from drying through first and second crack.
Drying and browning
Green coffee beans start with significant moisture content. Early in roasting, heat drives off this moisture (the drying phase) before the bean's temperature can rise enough for browning reactions, including Maillard reactions between sugars and amino acids, to begin developing colour and flavour.
First crack
As internal pressure builds from steam and carbon dioxide, beans undergo an audible 'first crack' — a physical fracturing of the bean structure. This point is a common reference marker: many light roasts are stopped shortly after first crack.
Second crack and further development
Continuing to roast past first crack leads eventually to a second, generally quieter crack associated with darker roast levels, where roast-derived flavours increasingly dominate over origin character and oils can migrate to the bean's surface.
Cooling and resting
Beans must be cooled quickly after reaching target roast level to stop the roasting process precisely; freshly roasted beans are then typically rested for a period (commonly a few days to two weeks) to let excess CO2 degas before brewing.
Purpose-oriented roast styles: espresso, filter and omni
Light, medium and dark describe roast colour and degree of development. Espresso roast, filter roast and omni-roast are a different, overlapping category: they describe the brewing method a roaster had in mind, not a fixed colour. An espresso roast is typically medium to medium-dark, developed for body and balance under the pressure and short contact time of espresso. A filter roast is typically lighter, aimed at preserving acidity and origin character for the longer, lower-pressure contact time of filter and pour-over brewing. An omni-roast sits in between as a deliberate compromise, giving one product reasonable (rather than optimal) results across both. None of these three are standardised colours — roasters vary in what they label each one, so the name is a signal of brewing intent more than a precise, comparable specification.