A process for preparing lactic acid and/or a lactate salt via the fermentation of carbohydrates obtained from lignocellulosic material. In particular the process includes: a) treating a lignocellulosic material with an alkaline agent including a caustic magnesium salt in the presence of water to provide a treated aqueous lignocellulosic material; b) saccharifying the treated aqueous lignocellulosic material in the presence of a hydrolytic enzyme to provide a saccharified aqueous lignocellulosic material including fermentable carbohydrates and a solid lignocellulosic fraction; c) fermenting the fermentable carbohydrates in the saccharified aqueous lignocellulosic material by way of lactic acid producing microorganism in the presence of an alkaline agent including a caustic magnesium salt to provide an aqueous fermentation broth including a magnesium lactate; and d) isolating lactic acid and/or lactate salt from the fermentation broth; wherein the saccharification step b) and the fermentation step c) are performed as two separate steps.