Sour or bitter: which way to go
Coffee's compounds dissolve at different speeds, so the taste changes as more of the coffee is extracted. Under-extracted cups tend to taste sour and thin, and over-extracted ones bitter and drying. A sour cup usually stopped too early (under-extracted): grind finer or use hotter water. A bitter cup usually went too far (over-extracted): grind coarser or use cooler water. Change one thing at a time, and change it a little.
You'll often read that acids dissolve first, then sugars, then bitter compounds. That tidy order is a simplification: the bitter, slow end is better supported than the sour, fast one, and UC Davis researchers propose that coffee's sweet impression comes mostly from aroma and low bitterness, not dissolved sugar. Our note on the extraction sequence sets out what has been measured.
The brew time is a useful clue. If a V60 finishes in two minutes instead of three to four, the grind is likely too coarse. For a conventional shot, an espresso that runs in fifteen seconds instead of twenty-five to thirty is likely ground too coarse; turbo shots run that fast on purpose.
Weak is a different problem
Strength is how much coffee is dissolved in the cup; extraction is how much was pulled out of the grounds. A cup can be well extracted and still weak, because there simply wasn't enough coffee for the water. Weak means use more coffee for the same water, not a finer grind. The Brew Guide gives you the grams for your cup.
When it tastes sour and bitter at once
That usually means uneven extraction: some grounds over-extracted while others were bypassed. Blade grinders cause it by making dust and boulders together, and so does water channeling through a pour-over bed or an espresso puck. Even out the grind and the bed before chasing the dial.
What it asks about
- Sour: sharp, tangy, thin, like under-ripe fruit.
- Bitter: harsh, ashy, drying finish.
- Weak: watery, thin, not enough coffee.
- Too strong: heavy and intense, more than you want.
- Sour and bitter: both at once, hollow in the middle.
- Bright, is that right?: lively, fruity acidity you are not sure about.
- Flat: dull, papery, no aroma.
- Tastes off: stale oil, metallic, chlorine or musty notes.
- Muddy: silty, gritty, heavy sludge.
- Runs too fast: shot pours in under 25 seconds.
- Barely drips: shot drips slowly or not at all.
- Drips too fast: a phin that empties in about a minute.
- Stalls: a phin that hasn't dripped for more than 5 minutes.
Want to see where your cup sits between sour and bitter, weak and strong? Try the Extraction Map.
Related guides
- Extraction yield explained
- Why coffee tastes bitter
- How to dial in espresso
- Fixing channeling and uneven extraction
- Grind Guide
Sources
- Jonathan Gagné, The Physics of Filter Coffee (2021): V60 method; extraction and strength.
- Scott Rao, The Professional Barista's Handbook; Espresso Extraction: espresso dose, ratio, time and temperature; batch brewing.
- Specialty Coffee Association, Coffee Brewing Control Chart, revised March 2019 (Version 3) (2019): reference region: extraction 18–22%, strength 1.15–1.45% TDS.
- Nguyen Coffee Supply, How to Use & Clean a Vietnamese Phin Filter (2020); phin filter FAQ (2020): drip troubleshooting: too fine, a wet filter or trapped gas (lift the press about 2 seconds); less than 2 tablespoons in a 4 oz phin may drip fast; add hot water if it is too strong.
- JayArr Coffee, Coffee Knowledge Synthesis (seventeen sources): §6 recipes, §17 method comparisons, §19 key numbers, §23 brewer base parameters.