Production of a fermentation product

A process of separating suspended solids from a fermentation liquor by subjecting the liquor to a solids-liquid separation stage,

• wherein the fermentation liquor is produced in a fermentation process for the production of a fermentation product,
• which fermentation liquor comprises lignin,
• wherein the solids-liquid separation stage comprises
• treating the fermentation liquor with an anionic polymer having an anionic content of at least 50% by weight and having an intrinsic viscosity of at least 4 dl/g (measured in 1 M NaCl at 25° C.) wherein the anionic polymer is formed from anionic monomers selected from the group consisting of (meth) acrylic acid (or salts), maleic acid (or salts), itaconic acid (or salts), fumaric acid (or salts), vinyl sulfonic acid (or salts), allyl sulfonic acid, and 2-acrylamido-2-methyl sulfonic acid (or salts), optionally in the presence of a water-soluble non-ionic acrylamide monomer,
• flocculating the suspended solids and lignin in the fermentation liquor
• and
• subjecting the fermentation liquor to a mechanical dewatering stage selected from at least one of, a centrifuge, a screw press, a filter press, a belt filter press, a horizontal belt filter or a pressure filter to separate the flocculated suspended solids and lignin as cake solids, wherein the cake solids contain mainly lignin,
• with the proviso that the solids-liquid separation stage does not include a cationic polymer having an intrinsic viscosity (IV) of at least 4 dl/g.