Total Dissolved Solids (TDS) measures brew strength, while Extraction Yield measures efficiency.
Differentiating TDS from Extraction Yield
TDS (Total Dissolved Solids) measures how concentrated your coffee is (usually 1.2% to 1.5% for filter coffee, and 7% to 12% for espresso). Extraction Yield (EY%) calculates what percentage of the solid coffee bean was actually dissolved into the cup.
Brew beans contain about 30% soluble material. The best-tasting compounds (enzymatic sugars, malic acid, aromatic oils) dissolve first (18% to 22% EY). Beyond 22%, heavy bitter tannins and astringent plant fibers dissolve, ruining the cup.