Refractometer

A handheld optical device that measures the refractive index of brewed coffee, converting that reading into TDS (total dissolved solids). Common brands include VST and DiFluid.

Why it matters — A refractometer turns dialling-in from taste alone into a measurable process. Combined with brew weight and dose, you get extraction yield — the most rigorous way to know if you're under- or over-extracting.

Good to know

• Always cool the sample to room temperature before measuring — hot coffee gives different readings.
• Calibrate the device with the included reference fluid every few months. A miscalibrated refractometer is worse than no refractometer.

Related: Refractometers