Bitter or Sour Coffee? How to Fix It With Grind Size
If your coffee tastes sour, sharp, bitter or harsh, the beans are rarely the problem. Most of the time, it's the grind. The good news is that grind size is also the easiest thing to fix — usually within a brew or two.
This guide explains what's going on in the cup, how to tell sour from bitter, and exactly which way to adjust.
The Short Answer
- Sour coffee = under-extracted. Grind finer.
- Bitter coffee = over-extracted. Grind coarser.
That's it. The rest of this guide explains why, and what to do if changing the grind isn't enough.
What Is Extraction?
When hot water meets ground coffee, it dissolves flavours out of the grounds. They don't all come out at the same speed:
- First: bright acids and fruity flavours.
- Next: sweetness, caramel and body.
- Last: heavier, bitter and drying compounds.
A good cup stops in the sweet spot — enough time to bring out the sweetness, but not so long that the bitterness takes over. Grind size controls how fast you get there. Finer grounds extract faster; coarser grounds extract slower.
Sour or Bitter? How to Tell
People often mix the two up. Here's a quick way to tell them apart:
| Under-extracted (sour) | Over-extracted (bitter) | |
|---|---|---|
| Taste | Sharp, tangy, lemony, salty | Harsh, burnt, ashy, like over-stewed tea |
| Where you feel it | Sides of the tongue | Back of the tongue and throat |
| Texture | Thin and watery | Dry, leaves your mouth feeling furry |
| Finish | Short — the flavour disappears quickly | Lingering and unpleasant |
| Fix | Grind finer | Grind coarser |
Acidity Isn't the Same as Sour
A light roast like our House Roast is meant to taste bright — think cherry and a lively, juicy finish. That's pleasant acidity, and it's balanced by sweetness. Sourness is sharp and unbalanced, with no sweetness behind it. If the cup tastes juicy and sweet, it's working. If it makes you wince, it's under-extracted.
Roast Flavour Isn't the Same as Bitter
Dark roasts like our Honduran naturally have deeper, chocolatey, roasty notes. That's not a fault. Over-extraction is when the cup turns harsh and drying on top of those flavours.
How to Fix It, Step by Step
- Keep everything else the same. Use the same amount of coffee, the same amount of water and the same water temperature. Change only the grind.
- Make a small adjustment. One or two clicks on a hand grinder, or one step on an electric one. Big jumps make it hard to find the sweet spot.
- Brew and taste. Is it better, worse, or has it flipped from sour to bitter? If it flipped, you've gone past the sweet spot — go halfway back.
- Write it down. Once you've found a setting you love, note it for that coffee.
Quick Fixes by Brew Method
V60 and Pour-Over
- Sour and drains in under 2:30? Grind finer.
- Bitter and takes over 3:30? Grind coarser.
Full recipe in our V60 guide.
French Press / Cafetière
- Sour or weak? Steep 30–60 seconds longer, or grind a little finer.
- Bitter or silty? Grind coarser, and pour the coffee out as soon as you've pressed — leaving it on the grounds keeps it extracting.
Espresso
- Sour and runs fast (under 20 seconds)? Grind finer.
- Bitter and runs slow (over 35 seconds)? Grind coarser.
Cold Brew
- Weak or thin? Steep longer or use more coffee.
- Bitter or muddy? Grind coarser or steep for less time.
Using Pre-Ground Coffee?
If you buy ground coffee, you can't change the grind — but you can still steer the taste. Our French Press/Cafetière and Cold Brew grinds are set for those methods, so use the other dials instead:
- Too sour or weak: steep a little longer, or use a bit more coffee.
- Too bitter: steep a little less, or use slightly cooler water (around 92°C).
If you're using a ground coffee in a brewer it wasn't made for — say, cafetière grind in a V60 — you'll struggle to get it right. That's the point to switch to whole beans and a grinder.
If the Grind Isn't the Problem
If you've adjusted the grind and something's still off, check these:
- Your grinder. Blade grinders produce a mix of dust and chunks, so you get bitter and sour in the same cup. A burr grinder like the Hario Mini Mill PLUS fixes this.
- Your ratio. Too little coffee for the water gives a thin, sour or hollow cup. Start at around 1g of coffee to 15–17ml of water.
- Water temperature. Boiling water can push bitterness; lukewarm water under-extracts. Aim for 92–96°C — roughly 30 seconds off the boil.
- Freshness. Stale coffee tastes flat and papery whatever you do. Check the roast date and see our guide to storing coffee.
- Dirty kit. Old coffee oils in a cafetière mesh or grinder turn rancid and add bitterness. Clean them regularly.
Frequently Asked Questions
Why does my coffee taste sour?
Usually because it's under-extracted — the water hasn't had enough time or contact to pull out the sweetness. Grind finer, brew a little longer, or use slightly hotter water.
Why does my coffee taste bitter?
Usually because it's over-extracted. Grind coarser, shorten the brew, or use water that's slightly off the boil. Leaving coffee sitting on its grounds after brewing also makes it bitter.
Can coffee be both sour and bitter?
Yes — that's the classic sign of an uneven grind, usually from a blade grinder. The fine dust over-extracts while the big pieces under-extract. A burr grinder is the fix.
Does dark roast coffee taste more bitter?
Dark roasts have deeper, roastier flavours by nature, and they extract more easily, so they can turn bitter faster. Try a slightly coarser grind or cooler water with dark roasts.
Find Your Next Coffee
Every George's Coffee bag is hand roasted to order in Yorkshire, with the roast date on every bag — so freshness is never the problem. Browse the full range, or start with our grind size chart.
Happy brewing!