The processing of acid whey, a by-product of cream cheese making, casein production and strained yogurt manufacture, has been a challenge in the dairy industry. The high lactic acid concentration causes operational problems in downstream spray drying operations due to increased powder stickiness. In this work, electrodialysis, a well proven demineralisation technology is used to remove the lactate ions from acid whey. If the ratio of lactic acid to lactose is to be reduced to the same level found in sweet whey, 80% of the lactate ions must be removed. For both laboratory prepared solutions and acid whey samples, the lactate ions were removed at a slower rate compared to other anions present in the system. Increasing the pH (from pH 4.6 to pH 6) of the feed solution led to a small enhancement in the rate of lactate ions removal at 5 degrees C. No impact was observed, however, at 30 and 45 degrees C where membrane resistance and solution viscosity is lower. To achieve the same level of lactate ion removal, the processing time in a batch process was three times shorter at 45 degrees C, compared to that at 5 degrees C. This means that significantly less membrane area is required in a continuous industrial electrodialysis operation. The energy consumption (similar to 0.014 kW h/kg whey processed) for achieving 90% demineralization of the acid whey was comparable to the energy requirement reported for sweet whey demineralization in a typical commercial electrodialysis unit, illustrating the feasibility of this approach. (C) 2015 Elsevier B.V. All rights reserved.