Two Dimensions
The most common confusion in coffee brewing is conflating strength with extraction. These are two separate, independent variables:
- •Extraction (Yield): How much of the coffee was dissolved (percentage of coffee mass extracted)
- •Strength (TDS): How concentrated the final beverage is (percentage of dissolved solids in water)
You can have a weak cup with high extraction, or a strong cup with low extraction. These dimensions move independently.
Common Mistake
"This coffee tastes weak" could mean underextracted, under-concentrated, or both. Diagnosing which dimension is off is essential to fixing the problem.
Strength (TDS)
Strength is measured as Total Dissolved Solids (TDS), expressed as a percentage of the liquid's mass. It tells you how concentrated your coffee is.
Typical TDS Ranges:
- •Filter coffee: 1.15% - 1.55% TDS
- •Espresso: 8% - 12% TDS
- •Cold brew: 1.5% - 2.5% TDS
Strength is controlled by brew ratio. More water = lower strength. Less water = higher strength. This is true regardless of extraction.
Yield (Extraction %)
Extraction percentage tells you what portion of the coffee bean made it into your cup. It's about efficiency and flavor balance, not concentration.
Typical Extraction Ranges:
- •Underextracted: <18% (sour, thin, lacking sweetness)
- •Target range: 18-22% (balanced, sweet, complex)
- •Overextracted: >22% (bitter, dry, astringent)
Extraction is controlled by grind size, temperature, time, and agitation. It measures how thoroughly you dissolved the coffee, not how strong it tastes.
The Coffee Compass
Because strength and extraction are independent, you can map coffee quality on two axes:
Weak + Underextracted
Sour, watery, unpleasant
→ Grind finer + add less water
Strong + Underextracted
Sour, intense, unbalanced
→ Grind finer
Weak + Overextracted
Bitter, thin, hollow
→ Grind coarser + add less water
Strong + Overextracted
Bitter, heavy, astringent
→ Grind coarser
The center of this compass—balanced strength and optimal extraction—is the target zone where sweetness, clarity, and complexity emerge.
Why They're Independent
Consider two examples:
Example 1: High extraction, low strength
20g coffee, 400g water (1:20 ratio), finely ground, long contact time
Result: 21% extraction (well-extracted), 1.05% TDS (weak). Tastes balanced but diluted. Solution: use less water (1:15 ratio) to increase strength without changing extraction.
Example 2: Low extraction, high strength
20g coffee, 250g water (1:12.5 ratio), coarsely ground, short contact time
Result: 16% extraction (underextracted), 1.55% TDS (strong). Tastes intense but sour. Solution: grind finer to increase extraction without diluting strength.
Mastering coffee brewing means learning to adjust these dimensions separately. Brew ratio changes strength. Grind, temperature, and time change extraction.