Why does my coffee taste sour?

Quick answer: Sour coffee is almost always under-extracted: the water didn’t pull enough out of the grounds. Grind finer first. If that doesn’t fix it, make sure the machine is fully heated, use a little more coffee, and let the shot run longer.

Sharp, thin or lemony coffee has a short list of causes. Here they are in the order to try them.

Last updated: September 2026

Sour vs bitter

Sour usually means under-extracted: sharp, thin, salty or lemony, often with a fast, pale shot. Bitter usually means over-extracted: harsh, dry and lingering. They need opposite fixes, so it’s worth being sure which you have. If yours is harsh rather than sharp, see why coffee tastes bitter.

The causes, in the order to check them

Grind too coarse. Water rushes through without extracting enough. Go a step or two finer and try again. This fixes most sour espresso.
Shot too fast. A double espresso typically takes about 25–30 seconds. If yours pours in 15, grind finer or dose more.
Too little coffee. An under-filled basket lets water channel through. Use a scale to dose consistently.
Machine not fully heated. Cool water under-extracts. Let the machine warm up fully, run a blank shot to heat the portafilter, and pre-warm your cup.
Uneven tamping or channelling. Water finds the easy path and misses most of the coffee. Level the grounds and tamp evenly.
Very light roast. Light roasts are brighter and harder to extract. Grind finer, or try a medium roast from our beans guide.
Very fresh beans. Beans used within a few days of roasting can give sour, gassy shots. Let them rest for a week.

Bean-to-cup machines

You can’t control the shot as closely, but the same logic applies: set the grinder a step finer, increase the coffee strength setting, and raise the temperature setting if there is one. Change the grind setting only while the grinder is running, and give it two or three cups to settle.

If sourness appeared suddenly on a machine that used to taste fine, check it needs descaling: scale can stop the water getting hot enough.

Frequently asked questions

Why is my espresso sour and watery?

It’s under-extracted, usually because the grind is too coarse or there’s too little coffee in the basket. Grind finer and dose a little more.

Should I grind finer or coarser if coffee is sour?

Finer. A finer grind slows the water and extracts more. Go coarser if the coffee is bitter.

Can old beans make coffee sour?

Stale beans tend to taste flat rather than sour. Very fresh beans, used within a few days of roasting, are more likely to taste sour.

Why did my bean-to-cup start making sour coffee?

Check the grind and strength settings, then check whether it needs descaling. Scale can stop the machine reaching full temperature.