NOVELTY - Improving (M1) the efficiency of separation of solid biological matter from the aqueous liquid phase resulting from the acid hydrolysis of naturally occurring carbohydrate containing substrate comprising the addition of flocculating agent to the aqueous solids bearing mixture, is new.    USE - The method is used for improving the separation of solid biological matter (claimed), which are useful in a fermentation process to produce fermentation products, e.g. ethanol, glycerol, acetone, n-butanol, butanediol, isopropanol, butyric acid, methane, citric acid, fumaric acid, lactic acid, propionic acid, succinic acid, itaconic acid, acetic acid, acetaldehyde, 3-hydroxypropionic acid, glyconic acid, tartaric acid and amino acids (such as L-glutaric acid, L-lysine, L-aspartic acid, L-tryptophan, L-arylglycines or their salts).    ADVANTAGE - The production of fermentation products can be significantly improved by applying flocculating agents to the separation of the hydrolysate from the solid product. The solid product can be more efficiently dewatered by the process and that a higher cake solids can be achieved. Since the solid product can be more efficiently dewatered, there is a reduced requirement for separation equipment capacity, and equipment that is less capital intensive and less expensive to operate. The method provides higher cake solids, with less trapped residual aqueous liquor, i.e. a higher proportion of the sugar liquor is available for converting into fermentation product. The method requires less wash water, therefore, improves both the productivity and efficiency of the process. The method achieves fast and efficient separation of solids. The action of the flocculating agent greatly enhances the separation of the solids from the liquor when compared to separation using solely mechanical method. Therefore, the liquor contains much lower levels of extraneous suspended cellulosic solids. The method provides more lignin as solid mass compared to known processes, which can be burnt or used for the manufacture of chemicals.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for the production (P1) of fermentation product comprising:    (a) hydrolyzing a particulate polysaccharide based plant derived material in an acid medium to form an aqueous mixture comprising dissolved sugar and solid matter;    (b) subjecting the aqueous mixture to separation stages in which solid matter are removed from the aqueous phase;    (c) adjusting the pH of the obtained aqueous phase to a pH of at least 4;    (d) fermenting the dissolved sugars of the aqueous phase by a microorganism to produce a fermentation product; and    (e) isolating the fermentation product.    At least one separation stage in step (b) comprises addition of a flocculating agent to the aqueous mixture.