TDS (total dissolved solids)

The percentage of the brewed liquid that is dissolved coffee, by mass, vs water. Espresso TDS sits around 8–12%; filter coffee around 1.2–1.5%. Measured with a refractometer.

Why it matters — TDS tells you the strength (concentration) of the brew. Combined with brew weight and dose, it gives you extraction yield — the most precise dialling-in tool available.

Good to know

• Always measure TDS at room temperature — hot coffee gives slightly different readings.
• TDS doesn't tell you flavour quality; it tells you concentration. A 12% TDS espresso can taste great or terrible depending on what's been extracted.

Related: Refractometers