Coffee Grind Size Explained: Why Your Coffee Tastes Sour or Bitter
If your coffee often comes out too sour, too bitter, or strangely weak, the root cause is usually your coffee grind size. Most people blame their beans or their coffee maker, but grind size controls how fast water extracts flavour, and when it’s wrong, the coffee will always taste off.
In this beginner-friendly guide, you’ll learn what grind size actually means, how it affects flavour, and how to choose the right grind for any brewing method. Once you understand this, sour or bitter coffee becomes very easy to fix.
For a complete, detailed version with charts and a FREE downloadable brewing blueprint, you can read my full guide here:
👉 https://yummcoffee.com/blog/coffee-grind-size/?utm_source=tumblr.com&utm_medium=backlinks&utm_campaign=dm2-a3-tyt
What Coffee Grind Size Really Means
Coffee grind size simply describes how large or small the coffee particles are after grinding.
Coarse grinds are big pieces (like sea salt).
Medium grinds resemble sand.
Fine grinds are as soft and powdery as flour.
This difference matters because it directly affects how quickly water pulls flavour out of the coffee. Large particles allow water to pass quickly, leading to less extraction. Small particles slow water down, creating more extraction.
If the grind is too coarse, coffee brews too fast and ends up sour or weak. If the grind is too fine, water flows too slowly and extracts too much, creating bitterness.
Why Sour Coffee Happens
Sour coffee is almost always a sign of under-extraction. This means water didn’t pull enough flavour from the coffee grounds. Common causes:
Your grind size is too coarse
The water passed through too quickly
Brew time was too short
Sour coffee often tastes sharp, lemony, acidic, or hollow — like biting an underripe fruit.
How to fix sour coffee:
Adjust the grind finer
Extend the brew time slightly
Ensure the water is hot enough (92–96°C)
Most sour brews improve instantly with a finer grind.
Why Bitter Coffee Happens
Bitter coffee is caused by over-extraction, where water spent too much time in contact with the grounds and dissolved too many compounds.
This usually happens because:
The grind is too fine
The brew time is too long
The filter or basket restricts flow
Over-extracted coffee tastes harsh, smoky, or overly intense, similar to steeping black tea for too long.
How to fix bitter coffee:
Adjust the grind coarser
Shorten the brew time
Check for clogged filters or baskets
Small adjustments can dramatically reduce bitterness.
The Right Grind Size for Each Brewing Method
Here are simple, beginner-friendly starting points:
Espresso → Fine grind (like table salt)
Moka Pot → Medium-fine grind
AeroPress → Fine for 1-minute brews; medium-fine for 2–3 minutes
Pour-over (V60/Kalita) → Medium-fine grind
Chemex → Medium-coarse grind
Drip Coffee Machine → Medium grind
French Press → Coarse grind
Cold Brew → Extra coarse grind
These are starting points only. You will need to adjust slightly depending on the beans, the grinder, and your taste preferences.
How to Fix Bad Coffee Using Grind Size
If a cup tastes wrong, grind size is the fastest way to correct it.
Sour → grind finer
Bitter → grind coarser
Weak → grind finer
Sludgy or muddy → grind coarser
This simple rule works for every brewing method.
👉 Read the full detailed guide (with charts + troubleshooting + FREE Brewing Blueprint):
https://yummcoffee.com/blog/coffee-grind-size/?utm_source=tumblr.com&utm_medium=backlinks&utm_campaign=dm2-a3-tyt
Final Thoughts
Coffee grind size affects every part of extraction and flavour. Once you understand how to adjust it, you can confidently fix sour, bitter, or weak coffee without changing anything else in your recipe. Grind size is the most powerful tool you have for brewing better coffee at home.