Two Different Problems
"Weak coffee" can mean two completely different things. The fix depends on which problem you actually have.
Critical Distinction
Low strength = not enough coffee dissolved (fix with ratio).
Low extraction = not enough material extracted from the grounds (fix with grind, temperature, time).
These are independent variables. You can have strong coffee with low extraction (concentrated but sour). You can have weak coffee with high extraction (watery but balanced). Or you can have both problems at once.
Quick diagnostic test:
Weak but balanced
Coffee tastes diluted, light-bodied, not very intense. But it is not sour or unpleasant.
→ Strength problem (ratio)
Weak and sour/sharp
Coffee tastes watery AND has sharp, acidic, or grassy flavors. Thin body with unpleasant finish.
→ Extraction problem (grind/temp/time)
Fixing Low Strength (Ratio Problem)
If your coffee tastes balanced but just not strong enough, you need more concentration. This is a simple ratio fix.
Solutions (pick one):
- 1.Use less water: Keep coffee dose the same, reduce water. Example: 20g coffee with 280g water instead of 300g (1:14 instead of 1:15).
- 2.Use more coffee: Keep water the same, increase coffee dose. Example: 22g coffee with 300g water instead of 20g (1:13.6 instead of 1:15).
Both approaches work. Most people find it easier to adjust water amount because it does not require changing grinder settings or bloom ratios.
Common Mistake
Do not grind finer to fix weak coffee unless it also tastes sour or unbalanced. Grinding finer increases extraction, not strength.
Fixing Low Extraction (Weak AND Sour)
If coffee tastes watery AND sour or sharp, you have under-extraction. Not enough material has dissolved from the grounds, so what little you extracted is unbalanced.
Step 1: Grind Finer
This increases surface area and allows more material to dissolve. Go 2-3 clicks finer on your grinder.
Step 2: Raise Temperature
Hotter water dissolves more material. If brewing at 90°C, try 93-95°C. For very light roasts, use boiling water (100°C).
Step 3: Extend Contact Time
Pour more slowly to increase total brew time. Or if using immersion (Clever, AeroPress), steep longer before drawing down.
Step 4: Improve Agitation
Stir or swirl your bloom vigorously. This ensures all grounds contact water evenly and prevents dry pockets or channeling.
Make one adjustment at a time. If coffee becomes balanced (not sour) but still feels weak, then adjust ratio for more strength.
When You Have Both Problems
Coffee that is weak, watery, AND sour has both low strength and low extraction. Fix extraction first, then adjust ratio.
Correct order of operations:
Fix extraction
Grind finer, raise temperature, extend time. Keep ratio constant. Taste until coffee is balanced (not sour).
Adjust strength
If coffee now tastes balanced but still too light, reduce water to increase concentration (e.g., 1:15 → 1:14).
Warning
If you add more coffee (stronger ratio) without fixing extraction, you will have strong AND sour coffee. You need to solve extraction first.