# Why Does Your Coffee Taste Bad? The Extraction Diagnostics Guide
The difference between exceptional espresso and a cup that tastes like burnt paper comes down to a single concept: coffee extraction. Extraction is the process by which water dissolves soluble compounds from ground coffee. Get it right, and you unlock complexity, sweetness, and clarity. Get it wrong, and you get sourness, bitterness, or weakness.What you will learn from the Brew Fixer
How to diagnose extraction defects: Identify whether your coffee is under-extracted, over-extracted, weak, or has mineral/water quality issues.
The three levers that control extraction: Grind size, water temperature, and contact time. Which one should you adjust first? The Brew Fixer tells you.
Method-specific recommendations: The ideal grind for a V60 is completely different from the ideal grind for a French press. Get personalized advice for your brewer.
Texture references and feedback loops: Know exactly what grind size to target by comparing with familiar materials (fine powder, sea salt, sand).
# The Three Dimensions of Coffee Extraction
Extraction percentage is the mass of dissolved solids divided by the mass of the original dry coffee. Specialty coffee aims for 18-20% extraction across all methods. Anything lower tastes sour; anything higher tastes bitter.- Grind size controls surface area. Finer grinds extract faster because water has more surface to dissolve compounds from. Coarser grinds extract slower.
- Water temperature controls dissolution rate. Hot water (94-96°C) extracts faster; cool water (85-90°C) extracts slower. Temperature also affects which compounds dissolve first.
- Contact time is how long water stays in contact with coffee. Pour-overs (2:30-3:30 min), Aeropress (1:30-2:00 min), French press (4:00-5:00 min).
# How to Diagnose Sour Coffee (Under-Extraction)
Sour coffee tastes like lemon, lime, or apple—acidic and sharp. It means water did not spend enough time extracting solids from the coffee. The simplest fix is almost always grind finer to increase surface area and slow down the water.- Grind the coffee finer (reduce grind size by 5-10 µm)
- Or extend brew time slightly (add 15-30 seconds)
- Or increase water temperature to 95-96°C
# How to Diagnose Bitter Coffee (Over-Extraction)
Bitter coffee tastes burnt, ashy, or woody. It means water spent too long extracting solids—past the point of desirable compounds and into undesirable ones. The fix is almost always grind coarser to increase water flow and reduce contact time.- Grind the coffee coarser (increase grind size by 5-10 µm)
- Or reduce brew time (subtract 15-30 seconds)
- Or reduce water temperature to 92-93°C
# How to Diagnose Watery Coffee (Weak, Thin)
Weak coffee lacks flavor and body. It usually means either your grind is too coarse, your brew ratio is too high (more water than coffee), or your coffee is stale. Dialing in the grinder is the fastest solution.- Use a finer grind so water has more surface to extract from
- Use more coffee (increase brew ratio)
- Brew slightly longer or at higher temperature
# How to Diagnose Astringent Coffee (Drying, Mineral Taste)
Astringency feels drying in your mouth—like you have sucked on a grape skin. It is usually caused by hard water (high mineral content) combined with over-extraction. This one is trickier because it requires both grind adjustment and water quality improvement.- Use filtered water to reduce minerals (target TDS 60-150 ppm)
- Grind coarser to reduce over-extraction
- Try slightly cooler water (90-92°C)
# Grind Size Chart: What Does Each Grind Look and Feel Like?
| Grind Name | Particle Size | Texture Reference | Best Methods |
|---|---|---|---|
| Extra Fine | 5-15 µm | Fine powder, cocoa | Espresso, Turkish |
| Fine | 15-30 µm | Powdered sugar | Moka pot, Aeropress |
| Medium-Fine | 30-50 µm | Sand, sea salt | V60, Chemex, Pour-over |
| Medium | 50-70 µm | Beach sand | Drip machine, Flat-bottom filters |
| Coarse | 70-90 µm | Coarse sand, rock salt | French press, Cupping |
| Extra Coarse | 90+ µm | Peppercorns, breadcrumbs | Cold brew, Percolator |
# Water Quality: TDS and Its Effect on Extraction
Total Dissolved Solids (TDS) is the measure of mineral content in water. Tap water varies widely by region: some cities have 50 ppm (soft water), others 300+ ppm (hard water). Coffee extraction is sensitive to water quality.- Too soft (0-50 ppm): Water over-extracts, coffee tastes salty and thin.
- Ideal (60-150 ppm): Sweet, balanced extraction with full body.
- Too hard (200+ ppm): Minerals bind to coffee compounds, creating astringency and drying mouthfeel.
Quick Water Quality Fix
If you suspect hard water, try brewing with filtered water or bottled water for comparison. If the coffee immediately tastes better, you have found your culprit. Invest in a simple water filter pitcher (Brita, PUR) or a whole-house filter.