We roast it ourselves: inside the roastery

We roast our own coffee in Lisbon, every week. It would be cheaper not to. Buying finished coffee from a good roaster is a perfectly respectable way to run six cafés, and for a while it was how we ran them. What we wanted was the ability to change one variable and taste the result four days later on our own bars, instead of writing an email and waiting for the next batch. A roast is a heat transfer problem with a deadline. Green coffee is dense, uneven and around ten per cent water. Over roughly ten to twelve minutes we have to dry it, cook it and stop it at the exact point where sugars have developed but not burned. Here is the sequence, in the order the drum gives it to us.

Green to yellow

The beans go in at charge temperature and immediately pull heat out of the drum. For the first few minutes almost nothing aromatic happens: we are boiling water out of the seed. It smells of hay, bread dough, sometimes of grass. Get this phase wrong and nothing later can rescue it — too fast and the outside dries ahead of the core, leaving a bean that will taste both roasted and raw; too slow and the coffee flattens into cardboard before it has had a chance to be sweet. Somewhere around the four to five minute mark the colour turns from sage to pale yellow and the smell shifts to toasted cereal. That is yellowing, and it is our first checkpoint.

Maillard and first crack

With the free water gone, the interesting chemistry starts. Amino acids and reducing sugars react — the Maillard reaction — and build the aromatic backbone of the coffee, along with the melanoidins that will later give it colour and body. Sucrose begins to caramelise. The beans go from yellow to tan to cinnamon, the chaff loosens, and the room starts to smell like something you would want to drink. Then first crack: pressure inside each bean, mostly steam and carbon dioxide, breaks the cell structure with an audible pop. It sounds like distant popcorn. What we listen for is not the first pop but the shape of the sound — whether it arrives as a tight cluster of cracks over twenty seconds or straggles over a minute. A tight crack means an even roast. A straggling one usually means uneven moisture or uneven bean size, and it tells us to expect a wider, less focused cup.

Development and drop

Everything after first crack is development, and it is where a coffee is either finished or ruined. The reactions are now exothermic: the beans generate their own heat, so we cut energy and manage the coast to the drop. Too short and there is trapped sharpness and a raw, grassy edge under the fruit. Too long and the origin quietly disappears into generic roast — sweeter for a moment, then flat, then ashy. For our filter roasts development is a smaller share of the total time than for espresso, where a little more gives us the sweetness and solubility a 30 g shot needs. We drop on a combination of three things: bean temperature, elapsed time and colour on a hand tray held next to the previous batch. Then we cool fast. A slow cool is a roast that keeps going after you thought you had stopped it.

Locked, not clever

Once a profile tastes right we write it down and stop improvising. It is recalibrated monthly against a reference roast, because green coffee changes as it ages, and because a drum behaves differently in February and in August. Everything we roast leaves within days, our own cafés get it on a weekly cycle and wholesale partners receive fresh stock every week on the same schedule.

A clever roast wins a tasting once. A locked roast is the reason the coffee you liked in March is still the coffee you buy in July.