Saturday morning at the stand, one request comes up more than any other: "give me the darkest one, I need it strong." Dark roasted coffee looks powerful in the bag and leaves a bitter streak on your tongue. The colour of the bean tells you one thing only: how far Laurent took the fire on Golden. Strength in the cup is set somewhere else, and caffeine follows its own track.
Dark roasted coffee: three different things we call strong
Concentration
How much dissolved coffee sits in the water. The ratio decides it. 15 g of coffee in 250 ml of water gives a denser drink than 12 g in the same water, whatever the roast colour.
Roast degree
How far the fire went. Inside the drum the bean loses water and mass: around 12 % for a light roast, up to 20-25 % for a very dark one. Sugars caramelise, then start to burn. Bitterness and the smoky note come from there, and we read them as power.
Caffeine
The molecule that keeps you awake. It handles drum temperatures well (beans usually drop between 200 and 215°C), so per gram of coffee it stays close to the same at any colour.
Why dark roasted coffee tastes stronger
With every extra degree the roasting reactions run further and part of the sugars turn into bitter compounds. Your tongue translates bitter into strong. Add a heavier body and the oil that surfaces on the bean after second crack. A few degrees lower, the same reactions give you the chocolate note in outdoor roasted coffee.
What the research says about caffeine in dark roasted coffee
A 2024 study in Scientific Reports, led by Zachary Lindsey at Berry College, took Ethiopian coffee, roasted it to five degrees and brewed it in an AeroPress at a 1:15 ratio with 1, 2 and 10 minute extractions: 30 combinations, measured by HPLC.
Under identical brewing conditions, the light and medium batches delivered more caffeine in the cup than the dark ones. Roasts pushed far showed lower extraction yields, and at equal extraction yield the picture flips, with dark coffee coming out higher on caffeine. The highest caffeine values showed up in batches that had lost around 14 to 16 % of their mass, so light to medium roasts, and the authors write that extraction yield weighs more than roast degree on its own.
The test at home: dark roasted coffee next to a light roast
Take two coffees from the same roastery, one light and one dark. Weigh 15 g of each, grind at the same setting, pour 250 ml of water at 93°C, same method, same time. Drink them one after the other.
Concentration is identical in both cups. The dark one will read fuller and more bitter, so you moved the flavour while the amount of coffee in the cup stayed put.
One detail ruins the test: a scoop of dark roasted coffee weighs less than the same scoop of light roast, because the bean expanded and lost mass. The scale stays the only reliable reference, as we showed when we measured how many grams a spoon of freshly roasted coffee holds.
Making dark roasted coffee stronger: work the ratio
Move from 1:16 (15 g in 240 ml) to 1:14 (17 g in 240 ml). Same coffee and same roast colour, and the cup comes out clearly denser.
Quick troubleshooting:
- bitter and drying on the tongue (common on a dark roast, where the porous bean gives up faster): drop the water to 90°C and grind one step coarser;
- watery and sour (more common on a light roast): grind one step finer and take the water to 94°C;
- less caffeine at the same strength: keep the ratio and shorten the contact time.
How dark roasted coffee comes out at Golden, Saturday and Sunday
Laurent reads the morning air, the temperature, the humidity and the wind, then adjusts the fire and the time on Golden. For filter batches he cuts the fire shortly after first crack, exactly at the point we described here. For espresso he takes the batch one step further. The colour in the tray is the result of that decision, made outdoors at Marché de l'Abattoir, by the exit of the Manufakture car park in Anderlecht. We roast and sell on Saturday and Sunday, and the batches sit in the coffee catalogue.
On Sunday 20 September, from 9:30 to 19:00, car traffic will be stopped across the whole Brussels Region, and the trams and buses keep running. Walk or take the tram, and ask Laurent where he cut the fire on the batch in the tray. Then try the 1:14 ratio at home and tell me whether the strength you were after came from the colour or from the scale.
Brut. Sauvage. Imprévisible.
---
