Roasting coffee at home: from green bean to a fragrant cup

Why roast coffee at home?

Roasting turns a green bean — hard, almost odourless — into the fragrant, brittle bean you grind. Most of the flavour in your cup is decided here: too light and the coffee is sharply sour, too far and it is bitter with no fruit left. A home roast does not need expensive equipment, but it does need patience and a notebook.

At the Cà Phê Phố roastery we roast three mornings a week, never more than 5 kg at a time. Everything learned from more than two thousand batches fits into a few rules — enough to get your first batch right without setting the kitchen on fire.

Green beans: what to buy first

Green coffee is unroasted, still hard, and smells like dry grass. You can buy it from roasters or agricultural suppliers. Three things to check:

• Even size: beans of the same size finish at the same moment. Mixed sizes scorch in places and stay raw in others.
• Moisture: beans that are too dry roast fast and lose flavour; beans that are too damp go mouldy in storage. Buy two to three months' worth at a time.
• Harvest date: green beans still breathe. The most recent crop usually tastes cleaner than older stock.

Arabica or Robusta?

Arabica is aromatic, bright and low in caffeine; Robusta is heavier, bitter and stronger. Beginners should start with Arabica: it is easier to drink and makes roast mistakes obvious. If you love the traditional phin profile, try a medium-roast Robusta — or read Arabica and Robusta: two beans, two characters before buying.

Three basic roast levels

Level	End temperature	Bean colour	Flavour	Best for
Light	196–205°C	Yellow-brown	Bright acidity, flowers, fruit	Pour-over, high-quality Arabica
Medium	210–220°C	Chestnut brown	Balanced, sweet, toasted	Phin, espresso, every day
Dark	230–240°C	Dark brown, glossy	Bitter, smoky, chocolate	Iced coffee with milk

One warning: "dark" does not mean "roast it longer to be safe". Above 240°C most aromatic compounds are destroyed and the cup is only bitter and burnt.

Gear you actually need

You do not need a professional roaster. The minimum:

1. A heavy cast-iron pan or a small drum roaster — a thin pan scorches unevenly.
2. An infrared thermometer — so you know the pan temperature instead of guessing.
3. A sieve or a small fan — to cool the beans and blow away chaff.
4. A metal tray — spread the beans to cool fast; never leave them in the pot.
5. A notebook — time, temperature, cracks and what you smelled.

The 12-minute process

1. Preheat the pan over medium heat for three minutes, to about 180°C.
2. Add 200 g of green beans and stir constantly for the first 30 seconds so the faces do not scorch.
3. Hold the temperature around 200–215°C. The beans move from green to yellow to brown.
4. Listen for first crack around minute seven to nine. That is the sugar in the bean starting to caramelise.
5. Choose your stop. For a medium roast, stop 30–60 seconds after first crack. For dark, wait another one or two minutes, but do not reach second crack.
6. Cool immediately on the metal tray, stirring for three or four minutes until the beans are only slightly warm.

What should the first batch look like?

Roast 100–150 g, no more. Small batches are easier to control and you will not mind losing one. Write everything down: temperature, crack times, colour and smell. The second batch will differ from the first, and that is normal.

Resting and storage

Freshly roasted coffee releases CO₂ — degassing. Rest light roasts three to five days, medium roasts five to seven, dark roasts two to three. Store in an airtight one-way valve container, away from light and heat. Do not refrigerate: moisture makes beans fade faster.

Grind only what you are about to brew. The more even the grind, the cleaner the cup.

To finish

A home roast will not make you an expert in one batch. But it teaches quickly that flavour is not magic: it is temperature, time and attention. If you want to go further, Vietnamese phin shows how to brew the beans you just roasted. And if you would rather start with roasted coffee, the Autumn collection is open for pre-order.