How do I fix sour coffee?

Why coffee tastes sour or sharp, and the four changes that fix it — the opposite adjustments to bitter coffee.

Difficulty: beginner
Time: 10 min
Read: 2 min

Short answer

Sourness is under-extraction: you have not pulled enough out of the grounds. Grind finer, use hotter water, extend the brew time, or increase the dose. Change one variable at a time, or you will not know which fixed it.

Sour and bitter are the two ends of the same scale. Bitter means you have gone too far; sour means you have not gone far enough. Recognising which you have is the whole diagnosis, and the fixes are exact opposites.

What you'll need

Your usual brewing equipment
Burr grinder (optional)
Thermometer or variable-temperature kettle (optional)

Step by step

Confirm it is sourness rather than acidity.Sour is sharp and puckering at the sides of the tongue, and often thin. Pleasant acidity in a light roast is bright and fruity — that is a feature, not a fault.
Grind one step finer.Finer grounds have more surface area, so more is extracted in the same time. This is the most effective single change.
Use hotter water — closer to 94–96°C.If you have been letting the kettle stand a long time, use it sooner. Cool water under-extracts.
Extend the brew time.Cafetière from 4 to 5 minutes; pour-over slower; espresso a longer shot.
Check your dose is not too high for the water.Too much coffee for the water leaves each ground under-extracted. Around 60g per litre is the standard.
Preheat the brewer and the cup.Cold equipment drops the water temperature several degrees, which is enough to cause sourness.
Change only one variable at a time and taste between.Change three and you have learned nothing even if the result improves.
If nothing helps, check how fresh the beans are and how light the roast is.Very light roasts are harder to extract fully and need finer grinding and hotter water than medium ones.

Tips

A blade grinder produces both dust and boulders. The boulders under-extract and taste sour no matter what else you do — a burr grinder is the fix.
Uneven extraction in a pour-over shows as sourness. Pouring evenly and keeping the bed flat matters more than most people expect.
Sour and bitter together usually means uneven extraction — some grounds over-extracted, some under. That is nearly always a grind consistency problem.

Common mistakes

Treating sourness like bitterness — The fixes are opposite. Coarsening the grind for sour coffee makes it worse.
Letting the kettle cool too long — Water much below 90°C under-extracts, particularly with a lighter roast.
Brewing in a cold cafetière or dripper — It drops the brew temperature by several degrees, which is enough to cause sourness.

Questions people ask

Is sour coffee under-extracted or over-extracted?

Under-extracted. Bitter is over-extracted. If you are unsure, note where you taste it — sour is sharp at the sides of the tongue, bitter lingers at the back and dries the mouth.

Why is my light roast always sour?

Light roasts are denser and harder to extract, so they need a finer grind and hotter water than a medium roast at the same brew time.