At 8am on Saturday, the forecast for Anderlecht shows 15°C (59°F), 88% humidity and a north wind. We take all three as they come, with no roof and no wall. Weather and outdoor coffee roasting comes down to exactly that: three variables we cannot stop, and one man, Laurent, who reads them and sets the fire and the timing on Golden so each batch reaches its flavour target.
Each of the three hits a different moment of the roast and calls for a different move from Laurent.
Weather and outdoor coffee roasting: three moments
Ambient temperature and coffee roasting: before the first batch
A cold morning shows up in the metal first. At 14°C (57°F), the drum and the air pulled in by the burner start lower than at 20°C (68°F), and Golden needs longer to reach charge temperature. Laurent lets it heat up for longer before the first green bean goes in, so the first batch starts like the ones after it.
Humidity and coffee roasting: the first minutes
Green coffee enters the drum holding 8 to 12% water. The first minutes of the roast are the drying phase, when that water leaves. When the surrounding air is heavy, drying takes longer at the same flame. Laurent gives more fire at the charge, accepts a slightly longer drying phase and watches two signs: the bean turns from green to yellow, and the smell of grass turns into a smell of bread.
Wind and roasting coffee on gas: the whole time
Wind works from the first minute to the last, because it pulls at the flame under the drum. A gust flattens the flame and carries the hot gases off before they have handed their heat to the metal. Laurent watches the flame more than the clock, sets the windbreak on the windward side and corrects the gas when he sees the fire spread.
Weather and outdoor coffee roasting this weekend on Golden
Today's forecast, Friday 25 September (Open-Meteo, Anderlecht), shows two dry days that still differ.
Saturday opens with all three on the same side: 15°C at 8am, 88% humidity and a north wind rising to gusts of 28 km/h (17 mph) around 10am. The first batch will need a long warm-up, more fire at the charge and the windbreak in place from the start. By 4pm, at 20°C and 61% humidity, the work should settle down.
Sunday morning reads the same on the thermometer (15°C, 80%), but the wind barely moves, under 7 km/h (4 mph). The afternoon climbs to 24 to 25°C (75 to 77°F) and humidity drops to 43%. Then Laurent will start with a lower fire at the charge, since the warm, dry air helps the drying.
A full day between those two ends is in the morning batch and the afternoon batch, and a humid weekend, with its numbers, in what we changed on Golden in humid weather.
Weather and outdoor coffee roasting: the same flavour target
The target stays the same on both days. A filter batch comes out as a filter batch, an espresso batch as an espresso batch. What changes is the route there: an extra minute of warm-up, the gas valve a notch higher or lower, the windbreak moved to the other side.
Closed roasteries feel the seasons too: a Perfect Daily Grind guide from March 2026 cites a coffee that needs 9 minutes of roasting in summer and 9 minutes 30 seconds in winter to meet the same standard. For us, the outside air counts from one batch to the next. That is the idea behind Weatherroir: same origin, same roaster, same flavour target, different conditions every time.
From weather and outdoor coffee roasting to the bag at home
Pascal Mormal, a meteorologist at the Royal Meteorological Institute, is forecasting (DH, 24 September) a heat peak on Tuesday: 27°C (81°F), maybe even 30°C (86°F), about 12 degrees above the seasonal norm. The bag you pick up this weekend will go through it. Two moves cover it:
- Heat: keep the bag in a cupboard, away from a sunny window, the oven and the hob. Heat speeds up staling, so storing coffee in hot weather starts with where you put it.
- Humidity: close the zip after every dose and keep the bag away from the steam of the kettle and the dishwasher.
Pour over coffee over ice, for Tuesday
- 20 g coffee, ground one step finer than your usual filter
- 120 g ice in the carafe under the dripper
- 180 g water at 93°C (199°F): 40 g for the bloom, 30 to 40 seconds, then the rest in two pours
- everything through in 2:30 to 3:00; with the melted ice, the final ratio is 1:15
If it tastes watery, grind one step finer or go up to 22 g. If it tastes harsh and bitter, one step coarser. One change per day.
If you come by the coffee roaster at Marché de l'Abattoir on Saturday around 9am, look at where the windbreak stands and ask Laurent how long he let Golden warm up before the first batch. He will answer in minutes.
You will find us on Saturday and Sunday at Marché de l'Abattoir, by the Manufakture car park exit, Anderlecht. For coffee roasted outdoors in Anderlecht without the trip, the weekend batches are also in the online shop.
Brut. Sauvage. Imprévisible.
