If your Chemex coffee is sour, change these in order: grind one step finer, then raise the water to 94 to 96 °C (201 to 205 °F), then slow the pour so the brew takes about four minutes, and only then add coffee. Sour means the water pulled out the sharp part of the coffee and stopped before the sweet part. Everything below makes the water do more work.
Why does a Chemex cup taste sour?
A sour cup is under-extracted. The acids dissolve first, the sugars come later, and a cup that runs out of time or heat stops while it is still sharp. In a Chemex that usually means the grind is too coarse, the water is too cool, or the pour is too fast. It is not usually a sign of bad beans.
If the cup is thin and watery rather than sharp, you want a different page: Chemex coffee too weak. If it is harsh and dry at the back, that is the opposite problem, covered in Chemex coffee too bitter. For the generic brewer-agnostic version of this fix, see pour-over coffee too sour. This page only covers what is different in a Chemex.
What do you change first, second and third?
| Order | Change | How much | What you should notice |
|---|---|---|---|
| 1 | Grind finer | One step on your grinder | The brew slows and the sharpness softens |
| 2 | Hotter water | 94 to 96 °C (201 to 205 °F), rinse the filter with hot water first | Less sharp, more sweet |
| 3 | Slower pour | Small circles, total time about 4 minutes | Rounder body |
| 4 | Longer bloom | Water at twice the weight of the coffee, 30 to 45 seconds | Even extraction from the start |
| 5 | More coffee | Move from 1:16 to 1:15 | Last resort, since it adds strength more than sweetness |
Change one thing per brew and taste before you change the next. If you change three at once you will not know which one worked.
Why does the Chemex filter matter for sourness?
The Chemex paper is thick, and it slows the water down when the grind is fine. That is why step 1 is only one step. Go too far and a sour cup becomes a bitter one, because the water now has all the time in the world. A good check is the clock: if the water is gone in under three minutes, you have room to grind finer. If it takes more than five, you have gone too far and should come back one step.
Because the brewer is large, it also loses heat fast. Pre-wet the filter with hot water and pour the rinse out. A cold brewer takes heat out of the water, and that alone can push a decent cup toward sour.
How much coffee should you use before you touch the ratio?
Our default is 1:16. For most Chemex brews that is the right number, and the table below shows where it lands so you can check you are not simply under-dosing.
| Water | Coffee at 1:16 | Level tablespoons (5 g each) |
|---|---|---|
| 300 g (10 oz) | 19 g | About 4 |
| 500 g (17 oz) | 31 g | About 6 |
| 700 g (24 oz) | 44 g | About 9 |
For exact numbers per pot size, see how much coffee for a 6 cup Chemex, how much coffee for a 3 cup Chemex and the how much coffee per cup page. If your dose is already near these numbers, leave it alone and fix the grind and the water first.
Does the coffee you use matter?
Yes, and this is our judgment rather than a label fact. Some coffees are bright on purpose. The roaster says of No. 4 Conjuncture that Kenya is acidic on purpose, and that if it tastes sour rather than bright, you should grind finer. So a sharp cup from a Kenya is not always a mistake, but the same fix applies.
If you want a coffee that is hard to push into sourness while you dial in, the roaster says No. 6 Hegemony has low acidity and heavy body, which makes it very hard to ruin. No. 10 Folklore is described as mild and round, the kind of cup that does not fight back. We would start with Folklore in a Chemex, then move to something brighter once your cups are even.
Our pick
No. 10 Folklore
Piura and Amazonas, Peru · 1,100 to 1,700 m · Fully washed, sun dried · Caturra, Bourbon, Catuai, Pache, Catimor · Medium
Salted caramel, citrus and silky on the label, mild and round, a cup that is easy to read while you adjust the grind.
Browse all ten coffees if you want to compare, or read the No. 10 Folklore brewing guide for the roaster-based recipe.
Questions people ask
Why is my Chemex coffee sour?
It is under-extracted. The grind is probably too coarse, the water too cool, or the pour too fast. Grind one step finer first.
What temperature should Chemex water be?
Use water at 94 to 96 °C (201 to 205 °F) and rinse the filter with hot water first so the brewer does not pull the temperature down.
How long should a Chemex brew take?
About four minutes in total. If the water is gone in under three, grind finer. If it takes more than five, come back one step.
Free printable
Keep the ratio chart on your fridge
One page with grams, level tablespoons and scoops for every cup size and for coffee makers from 2 to 14 cups. Leave your email and the download link appears right here.