On Sunday 1 November at 9 am, the roasting bulletin showed 6 degrees at the Marché de l'Abattoir, Anderlecht. That morning Laurent roasted an Ethiopia medium-light and a Brazil medium on Golden, two bags meant for different cups. If your coffee comes out bitter or sour at home, the cause is almost always in the brewing and only sometimes in the bag. This guide separates the two, symptom by symptom, with a ten-minute test at the end.
Taste first: sour, acidic or bitter?
Many wrong adjustments start with the wrong word. Before you touch the grinder, name what you taste.
Acidic means your mouth waters, like after a bite of apple. The feeling fades fast and leaves something sweet behind. You can name a fruit: lemon, orange, blackcurrant, green apple. Acidity is a quality, especially in filter coffee.
Sour means your mouth tightens and the taste lingers. The cup feels thin, like coloured water, with a hint of vinegar or unripe fruit. The water pulled too little out of the coffee.
Bitter means a dry tongue and a taste that settles at the back of your mouth. The last sips are the harshest. The water pulled too much, or pulled the wrong things.
Sour and bitter in the same sip? The water ran through unevenly: part of the coffee was washed too much, part too little. The usual cause is a blade grinder, which leaves big chunks mixed with a lot of dust.
The recipe you start from
An adjustment only makes sense against a fixed recipe. Weigh once, write the numbers on the bag and change one thing per morning.
- Filter (V60 or machine): 15 g coffee to 250 g water at 93°C. All the water is through in about 3 minutes.
- Espresso: 18 g ground coffee, 36 g in the cup, 25 to 30 seconds from pump start.
- French press: 30 g coffee to 450 g water, ground coarse like breadcrumbs, 4 minutes.
- Moka pot: basket filled level, without pressing, hot water from the kettle up to just below the valve, medium heat.
A kitchen scale and a timer are all you need for the rest of this guide.
Bitter or sour coffee: the fix for each symptom
Find your symptom and apply only the fix below it. One grinder step per morning, then taste again.
Sour and thin, runs fast
The grind is too coarse for your method. Go one step finer and keep the dose. With espresso the sign is clear: an 18 g shot that runs in under 20 seconds tastes sour. One step finer, and stop at 36 g in the cup.
If the filter cup stays sour after that step, check the water. Brew two cups: the first with water poured as soon as the kettle clicks off, the second after one minute with the lid open. If the second is thinner and more sour, your bag wants water straight off the boil.
Strong and sour at once
You used too much coffee for your water. It sounds odd, but a big dose with the same water gives an intense, sour cup. For filter, going beyond 17 g per 250 ml rarely gains you anything in taste. For espresso, do the coin test: place a small coin on the tamped coffee, lock in the portafilter and take it out straight away, without running the pump. A light mark on the coin means there is enough headroom. If the coin has sunk into the coffee, lower the dose by 0.5 to 1 g.
Bitter and dry, runs slow
The grind is too fine. With espresso the shot passes 35 seconds and drips. With filter, water still sits on top after 4 minutes. One step coarser, and repeat.
French press: only the last sips are bitter
You pushed the plunger hard all the way down and poured to the last drop. The fines resting on the bottom rise up and keep extracting in the cup. Lower the plunger only until it touches the coffee and leave 1 to 2 cm in the jug. If the second cup is bitter after 15 minutes, the coffee sat on the grounds too long: move it to a thermos.
If the plunger is hard to push and thick sludge stays in the cup, the grind is too fine. One step coarser.
Moka pot: bitter with a burnt taste
You left the pot on the heat until it started to hiss. In that phase, steam and very hot water push through the grounds. Watch the stream with the lid open: it first runs dark, like honey, then turns blond with big bubbles. At the first change in colour, take the pot off the heat and cool the base for a few seconds under cold water. On a gas hob, keep the flame under the base so it does not climb the sides. Wash the funnel and filter plate after every use, old grounds give a burnt taste too.
First cup good, second cup bitter
Your dose changes from day to day. Weigh every dose. With a blade grinder, grind in 3-second bursts and shake between them. Bitterness will still come back in some cups, because blades make a lot of dust. A burr grinder fixes the problem at the root.
Flat, dull, limescale in the kettle
Brussels tap water is hard. Try the same recipe with water from a filter jug or a soft bottled water with low dry residue. If the cup gets rounder, you have found the cause. You notice the difference fastest with a moka pot.
When it comes from the bag, and how to tell
Sometimes the sourness comes from the roast. The bean left the drum before its sugars developed enough. The sign is in your nose, before any water: the dry ground coffee smells of grass, hay or raw cereal. In the cup, the sourness arrives with those same notes, and a finer grind will not fix it, because the bean lacks the sweetness that would balance it.
Laurent drops filter batches a little earlier than espresso batches, to keep the fruit, with a margin of a few seconds. When the weather shifts from one Saturday to the next, Laurent adjusts the fire and the time on Golden so the bean reaches the same point. On a morning like 1 November, with 6 degrees at 9 am and 10 degrees at 1 pm, Laurent corrects in small steps through the day. How Laurent reads the air before each batch is covered in detail in the guide to weather, fire and batch.
Two situations look like a roast defect but have another cause:
- The bag is too fresh for espresso. A bag from the stall, opened two or three days after roasting, gives a slow shot, very thick crema and a sour taste, because of the gas still trapped in the beans. Wait 2 to 3 days, then go back to your recipe. For filter and french press, the same bag already works.
- The acidity belongs to the origin. The Ethiopia from 1 November is washed, roasted medium-light, with white flowers, citrus and honey on the label. It is made for V60, filter and Chemex, and its acidity is intended. If you want a cup without bright acidity, take the Brazil Cerrado from the same day: natural, medium, chocolate and nuts, acidity rated 2 out of 5.
The ten-minute test: two cups
This test tells you whether the sourness comes from you or from the bag. You need one bag, a scale and a grinder with steps.
- Grind 30 g and split it into two equal doses: cup A at your usual setting, cup B one step finer.
- Before adding water, smell the dry grounds. Note whether they lean toward grass or hay.
- Brew both with 15 g to 250 g water at 93°C, identical in every other way.
- Let them sit 5 minutes so they reach the same temperature, then taste one after the other.
There are three readings:
- B is sweeter and the sourness is gone: the sourness came from brewing. Keep the finer setting.
- B is more bitter, the sourness stays, and the dry grounds smelled of grass or hay: the sourness comes from the roast. Keep the bag and bring it to the stall.
- Both are lively, taste of fruit and finish sweet: that is acidity. If you do not like it, choose an espresso batch or an origin like Brazil.
For bitterness, run the same test the other way: B one step coarser. If B comes out sweeter and cleaner, stay there. If B is still bitter, check the french press plunger or the end of the moka brew, above.
Repeat the test once with every new bag. Ten minutes tell you whether the old setting still holds.
What to tell Laurent at the stall
A precise remark helps Laurent more than a score. "Sour, grassy, even with the finer grind" shows Laurent exactly where to look. "Wasn't great" leaves Laurent guessing. Bring three things written on the bag: the roast date, your recipe (grams, water, time) and what happened with cup B.
Laurent puts your remark next to the day of the batch. Every roasting day has its bulletin, with hourly temperature, humidity and wind: the roasting bulletin for 1 November. To understand why an Ethiopia and a Brazil behave so differently in the same cup, the blending guide puts them side by side.
If you would rather stop chasing the bag, the Meteo Koffie Club brings you coffee roasted by Laurent every month, with the date and weather of the batch on the bag, so you know from day one when to run the test again. The stall, the hours and the ritual around Golden are in the guide to the open-air roastery.
Saturday and Sunday, Marché de l'Abattoir, Anderlecht. Bring the bag and cup B.
Brut. Sauvage. Imprévisible.
