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Why does my coffee taste sour or bitter?

How to tell sour from bitter from dry, and what to change for each in pour-over and espresso, based on tasting studies and blind tests.

Sour and bitter are the two most common complaints about a home brew, and they usually call for opposite fixes. So the first job is working out which one you've got.

Telling them apart

  • Sour hits right away. It's sharp, a little like lemon, and it fades quickly.
  • Bitter builds more slowly and lingers after you swallow.
  • Dry isn't a taste at all. That rough, drying feeling on your tongue and gums, like over-steeped black tea, is astringency. People often call it bitter.

The timing cue comes from Lance Hedrick, and it's the most useful one there is. Some acidity is also meant to be there: a bright, citrusy coffee isn't a fault. Sour is a problem when it's sharp and thin, with nothing sweet behind it.

If it's sour

Sourness follows strength. In tasting studies at UC Davis, how sour a drip coffee tasted tracked the amount of acid in the cup, and that rose with strength, not with extraction. The sourest cups were strong and under-extracted. The least sour were weaker and well extracted.

That gives you two fixes, and most advice only mentions the first:

  1. Grind finer. This raises extraction, the classic fix for an under-extracted cup.
  2. Use more water. A longer ratio, say 1:15 to 1:16.5, lowers strength and sourness with it, and extracts a little more on the way. The pour-over ratio guide has the numbers.

For espresso, pull a longer shot. Hedrick's rule of thumb is about 5 g more in the cup from the same dose, and more than that if your shots are already long.

If it's bitter

Bitter and roasty flavours peak in cups that are both strong and highly extracted. Roughly in the order to try:

  1. Grind coarser. In Hedrick's blind grind test on a V60, the two finest brews were harshly bitter and the coarsest was his favourite.
  2. Use cooler water. In his temperature test, the 96 °C brew turned roasty and bitter while 90 and 93 °C tasted best, on a light roast. He finds hot water adds bitterness faster than a finer grind does. Dark roasts are usually brewed cooler still, around 85 to 90 °C.
  3. Check your water. In a 2026 study, water high in bicarbonate made coffee less fruity and more roasted and bitter, while calcium and magnesium on their own changed little. Hard tap water is often high in bicarbonate, so a brew with filtered or low-mineral bottled water is an easy test.

For espresso: about 5 g less in the cup, or a slightly bigger dose.

If it's dry and rough

That's astringency, and it has its own causes. In Hedrick's pour-count test, brews made with four or five pours turned astringent, and stayed that way even when he re-ground them to match the strength and extraction of a one-pour brew. Very light roasts get there sooner.

Try fewer pours, gentler pouring, or extracting a little less overall. Scott Rao traces most astringency to channeling: water finding a fast path through part of the bed and over-extracting it.

If it's sour and bitter at once

That usually means uneven extraction: some of the coffee gave up too little, some too much. Researchers modelling espresso reasoned that uneven flow through the puck should taste under- and over-extracted at the same time.

The grind setting usually isn't the fix. In espresso, look at puck preparation: clumps in the grounds, or a shot that spurts from one spot. In pour-over, look at how you pour. James Hoffmann found that pouring into the centre dug a crater in the bed, while steady pours in circles stirred it most evenly.

Change one thing at a time

Every one of these moves more than one thing. Grind finer and drop the temperature in the same brew, and you won't know which one helped. Change one setting, brew, taste, write it down.

Perco saves the grind, ratio, temperature and your tasting notes with each brew, so the last change and how it tasted sit side by side.

Sources