Extraction Principles

Coffee extraction is a physical-chemical process where water acts as a solvent for soluble compounds in ground coffee.

Control Variables

  • Particle size (milling)
  • Coffee/water ratio
  • Water temperature (92-96ºC)
  • Water quality (75-150 ppm TDS)
  • Contact time

Technical Ranges

  • Optimal extraction: 18-22%
  • TDS espresso: 8-12%
  • TDS filter: 1.15 - 1.45%
  • Espresso ratio: 1:2
  • V60 ratio: 1:15 - 1:17
  • French press ratio: 1:15

Sensory Interpretation

Under-extraction (<18%)

  • Light organic acids predominate
  • Salty sensation
  • Low body
  • Short ending.


Usual cause:
• Grinding too coarse
• Insufficient time
• High ratio (too much water)

—

Optimal Zone (18–22%)
• Integrated sweetness
• Bright but controlled acidity
• Midbody
• Aromatic persistence

Here, a balance is achieved between:
Acids → Sugars → Bitter Compounds

—

Over-extraction (>22%)
• Dominant bitterness
• Astringency
• Dry feeling
• Loss of aromatic clarity

Usual cause:
• Excessive fine grinding
• Prolonged time
• Low ratio

TDS Measurement and Extraction Performance

The refractometer allows you to measure the TDS (Total Dissolved Solids), that is, the percentage of soluble solids present in the final beverage.

TDS indicates the concentration of coffee in the cup, but not the total extraction yield.
To know the actual extraction percentage, it is necessary to relate the TDS to the coffee/water ratio used.

Indicative ranges:
• Espresso: 8–12% TDS
• Filter (V60, Chemex): 1.15–1.45% TDS
• Optimal extraction yield: 18–22%

Instrumental measurement allows us to objectify what we sensorially perceive as under-extraction, balance, or over-extraction.