Sour coffee almost always means underextraction: the water ran through the grounds too fast, was too cool, or the grind was too coarse, so less flavor made it into the cup than should have. Grind a notch finer, make sure your water is just off the boil, and let the brew run ten to fifteen seconds longer. Try one change at a time and the sourness should drop on the next cup.
The four usual causes
| Cause | What it looks like | Fix |
|---|---|---|
| Grind too coarse | Water runs through fast, cup tastes thin and sharp | Grind one notch finer |
| Water too cool | Cup tastes flat and sour at the same time | Brew with water just off the boil, not lukewarm |
| Brew time too short | Cup tastes watery up front, sour on the finish | Slow your pour, or grind finer to slow the flow |
| Not enough coffee | Weak and sour together | Use a full 60 g of coffee per liter of water |
Why grind size matters more than anything else
Grind size controls how much surface area the water has to work with and how fast it passes through. A coarser grind gives water less time and less surface, so it extracts less of the coffee's sugars and pulls out mostly the sharp, acidic compounds first. That is the sour taste. Move the grind a small step finer, one setting at a time, and taste again before changing anything else.
Does the ratio matter as much as the grind
Yes. A weak brew, meaning too little coffee for the amount of water, tastes sour and thin even at the right grind and temperature. We brew Common Sense and Good Sense at 60 grams of coffee per liter of water. If you are eyeballing scoops instead of weighing, that is the most common place people fall short.
Does roast level make a coffee more or less forgiving
Lighter roasts tend to hold onto more of the raw bean's natural acidity, so mistakes in grind or brew time show up as sourness sooner. None of our ten coffees are roasted especially light. No. 1 Common Sense is a medium roast with cocoa, red apple and brown sugar notes, and it is one of the more forgiving cups we sell if your technique is still inconsistent.
Our pick
No. 1 Common Sense
Huila and Medellin-Antioquia, Colombia · 1,300 to 1,500 m · Fully washed, solar dried · Castillo, Caturra, Colombia, Typica · Medium roast
A balanced medium roast that stays drinkable even when your grind or timing is slightly off, which makes it a good coffee to practice technique on.
A quick way to test which cause it is
- Weigh your coffee and water. If you were guessing, that is likely your answer.
- Check your water is hot enough, just off a full boil.
- Grind one step finer than usual and brew the same recipe again.
- If it is still sour, slow your pour by ten to fifteen seconds.
Change one variable at a time so you know what actually fixed it. Our pour-over guide for Colombian coffee and drip coffee maker pick both use the 60 g per liter ratio referenced above, so they are a good place to check your numbers against.
Could the coffee itself be the problem, not your brewing
It is possible but less common than the four causes above. Stale coffee tends to taste flat and dull rather than sharply sour, so flatness is a better sign of age than sourness is. We do not print a roast date on the bag; instead we roast to order. Our FAQ explains how that works and how to store beans once they arrive.
What if you already checked everything above
If you have weighed your dose, used hot water, and adjusted your grind and still get a sour cup, try one more variable: your kettle. A kettle that reads hot but has actually cooled while you weighed and ground your coffee is a common, easy to miss cause. Reboil, then pour immediately. If the problem persists across two different coffees and two different brew methods, the water itself, not the coffee or the method, is the most likely remaining culprit.
You can also browse all ten coffees to see which roast and process might suit your taste.
Fix the grind first. Most sour cups start there.
Questions people ask
Is sour coffee the same as bad coffee?
Not necessarily. Sourness on its own usually means the brew pulled less flavor out of the grounds than it should have, not that the coffee itself is bad. The same beans brewed correctly can taste completely different.
Does coffee get more sour as it cools?
It can taste different, not more sour from underextraction. As coffee cools, some flavors fade and acidity can stand out more by comparison. If a cup tastes fine hot and sour once it drops in temperature, that is a separate effect from the grind and brew time issues covered here.
Can bottled or filtered water fix sour coffee?
Only if your tap water has an unusual mineral or chlorine taste that is adding to the problem. Water rarely causes sourness by itself. Start with grind, temperature and brew time before you change your water.
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.