Total Dissolved Solids (TDS)

TDS is the percentage by mass of dissolved coffee compounds in the finished beverage, measured with a handheld refractometer. For drip and pour-over, the SCA "ideal" range is roughly 1.15% to 1.45% TDS at an 18% to 22% extraction yield. For espresso, TDS is much higher, typically 8% to 12%. The measurement turns subjective brew tweaks into data: useful for dialling in batch brew, less commonly used at home.