The L-(+)-tartaric acid isomer of tartaric acid is industrially produced in the largest amounts. It is obtained from lees, a solid byproduct of fermentations. The former byproducts mostly consist of potassium bitartrate (KHC4H4O6). This potassium salt is converted to calcium tartrate (CaC4H4O6) upon treatment with milk of lime (Ca(OH)2):[19]

KO2CCH(OH)CH(OH)CO2H + Ca(OH)2  Ca(O2CCH(OH)CH(OH)CO2) + KOH + H2O

In practice, higher yields of calcium tartrate are obtained with the addition of calcium chloride. Calcium tartrate is then converted to tartaric acid by treating the salt with aqueous sulfuric acid:

Ca(O2CCH(OH)CH(OH)CO2) + H2SO4  HO2CCH(OH)CH(OH)CO2H + CaSO4