The electrodialytic separation of lactic acid from grass silage juice, which is a complex mixture, containing inorganic salts, sugars and amino acids in high concentrations, was investigated in detail. The separation was carried out in two steps. In the first step, lactate together with other charged compounds were separated from the neutral ones, such as sugars and non-ionic amino acids, at pH 6.7. In the second step, lactic acid was recovered from the inorganic salts at pH 2.0. Each step was divided into different phases (time periods). For each phase, the performance in electrodialytic separation of lactic acid was investigated and discussed. This performance is characterized in terms of mass transfers, current efficiencies, energy consumptions, and water transfers. The obtained data show that the first electrodialysis (ED) step at pH 6.7 is significantly less effective than the second ED step at pH 2.0. Higher energy consumption and lower current efficiency as well as longer operation time were observed during the first ED step. High concentration of uncharged compounds, such as sugars and non-ionic amino acids likely caused the negative effects during the separation of salts as well as lactate. (C) 2004 Elsevier B.V. All rights reserved.