Use of flocculating agents for separating the solid residue in hydrolysed fermentation substrates

A process of producing fermentation product comprising the steps of,

• (i) hydrolysing a particulate polysaccharide based plant derived material in an acid medium using an acid having a pKa below 4 in a concentration of at least 10% by weight, and thereby forming an acidic aqueous mixture comprising dissolved sugar and solid matter,
• (ii) subjecting the acidic aqueous mixture to one or more separation stages in which solid matter are removed from the acidic aqueous mixture to obtain an aqueous phase,
• (iii) adjusting the pH of the obtained aqueous phase to a pH of at least 4,
• (iv) fermenting the dissolved sugars of the aqueous phase by a microorganism to produce a fermentation product,
• (v) isolating the fermentation product,
• characterised in that in at least one separation stage in step (ii) a flocculating agent is added to the acidic aqueous mixture in an effective amount to flocculate the solid matter and the flocculating agent is selected from the group consisting of water soluble polymers, water-swellable polymers, and charged microparticulate material and the separation stage includes mechanical means selected from the group consisting of a filter press, centrifuge, belt press, horizontal belt filter, and pressure filter, to separated the solid matter as cake solids.