An experimental study is presented concerning solubility and primary nucleation kinetics of monohydrate citric acid from pure and selectively impure (KH2PO4, MgSO4. 7H(2)O and FeSO4. 7H(2)O) aqueous solutions. The metastable range of pure solutions is wide, ranging from 6 to 14 degrees C, and the order of primary nucleation, equal to 2.51, is quite low. The addition of the tested impurities, which are usual fermentation aids, at concentrations lower than wt. 1%, produces negligible effects on the solubility and slightly enhances the primary nucleation rate. However, the presence of these compounds modifies the crystal habit at birth: in particular, the addition of MgSO4. 7H(2)O and FeSO4. 7H(2)O makes these crystals more elongated, but this effect diminishes as the crystals grow.