Saturday, six in the morning, at the Marché de l'Abattoir, by the exit of the Manufakture car park, in Anderlecht. The air hung heavy, like a wet blanket. Air humidity for coffee roasting read 85%. The beans pulled from the sack were cold, damp to the touch, slow. Golden started gently. The metal didn't sing straight away — it grumbled.
Seven hours later: same sky, same market, same beans, same sack. Humidity: 23%. Dry, cutting air, almost electric. The same beans cracked earlier, drier, more nervous. We adjusted, pulled the heat back, let the air do what it knows.
Two batches. The same day. Two coffees that don't resemble each other.
What nobody tells you about air humidity and coffee roasting
Open any roastery blog and you'll read the same thing: humidity is the enemy of consistency. Industrial roasters adjust gas, airflow and charge temperature to cancel out seasonal variation. Their goal is for January's batch to be identical to August's. Noble. And the exact opposite of us.
In a climate-controlled workshop the air is a constant. You never hit 85% in the morning and 23% in the afternoon — the walls protect you. We have no walls. We have the sky, which this Saturday dropped the humidity from a wet blanket to a dry blade in a matter of hours.
The moisture in the bean and the moisture in the air are not the same thing, but they dance together. Heavy air means slower heat transfer, a longer first phase, a core that cooks differently. Dry air speeds everything up: development arrives fast, the aromatics sharpen, the margin for error thins out. This isn't theory. It's what we felt today, by hand, between flame and wind.
What air humidity in roasting does to your cup
The morning batch came out round, deep, with a sweetness that lingers. That's the coffee for Monday's espresso, when you want weight.
The afternoon batch came out brighter, more nervous, with an acidity that lifts its head. That's the coffee for Sunday's filter, long, when you have time to listen to it.
Same origin. Same Saturday. Humidity signed the difference. The sky wrote two recipes in a single day; we only held the pen.
Air humidity and coffee roasting never repeat
That's what industry can't sell: singularity. On Sunday the humidity will climb again overnight and fall differently, with the northeasterly wind stiffening. Tomorrow's batch won't be today's. Not because we changed anything, but because the air changed.
If you want coffee that's always identical, there are excellent roasteries for that. If you want the coffee of one particular morning, with its irreplaceable humidity caught inside the bean — that's here, only at the weekend, only while the batch lasts.
Come on Saturday or Sunday to the Marché de l'Abattoir, by the exit of the Manufakture car park, in Anderlecht. Take the bag in your hand. Ask what time it was roasted. Morning or afternoon — it's not the same thing, and that's all that matters.
See which batches are still available and reserve ahead.
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