All coffee guides · Roasting
Home roasting can teach you how heat changes coffee, but it involves hot surfaces, smoke, chaff and fire risk. Start with a purpose-built coffee roaster and read its complete operating and emergency instructions before your first batch.
Green coffee beans are dense, grassy-smelling and pale green or blue-green in colour. Roasting drives out moisture, triggers the Maillard reaction (browning and flavour development), caramelises sugars, and builds up CO2 pressure inside the bean that eventually causes the cell walls to crack — a sound called first crack. Continued roasting causes further cell expansion, more sugar caramelisation and, eventually, second crack where the structure begins to break down. Light roasts are stopped shortly after first crack; medium roasts develop through the first crack resting phase; dark roasts approach or pass second crack.
Use a purpose-built home coffee roaster within its stated batch limits. Follow its location, ventilation, clearance and electrical requirements. Stay with it throughout roasting and cooling, and keep its chaff collector clean. Do not repurpose an ordinary popcorn popper or assume a domestic pan is a safe substitute.
Buy green coffee intended for roasting from a specialist supplier. Look for lot, harvest, origin and processing information, and try a small quantity first. Compare current delivered prices and account for roasting weight loss; savings are not guaranteed.
Green beans turn yellow and smell grassy around 140-160°C — this is the drying phase. Around 170-180°C, the Maillard reaction begins and the beans turn tan, smelling of bread or hay. At around 196-205°C, first crack begins: a sharp popping sound, one crack at a time, like popcorn. Beans expand significantly. Stopping here produces a light roast. As the cracks slow and stop, you are in the development phase — the "rest" between first and second crack. Medium roasts are stopped here. Second crack begins around 225-230°C: a faster, quieter cracking sound. Beyond second crack lies dark roast territory, and at the extreme end, the beans begin to burn.
Use the roaster’s prescribed cooling cycle and safe handling procedure. Do not bypass cooling or handle hot beans and parts. Once cool, store the coffee in suitable packaging. Resting time varies with roast and brewing method; follow the supplier’s starting advice and compare flavour over several days.
Consider equipment cost, ventilation, batch size, cleaning and the time needed to learn. Never leave a roast unattended. Follow the manufacturer’s emergency instructions if a roast behaves abnormally. Choose home roasting for the process and control it offers; a fixed payback period cannot be promised.
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