A process of producing fermentation product comprising the steps of, (i)
forming an acidified suspension of particulate plant derived material
comprising a first polysaccharide which is more readily hydrolysable and
a second polysaccharide which is more difficult to hydrolysable, (ii)
allowing the first polysaccharide to undergo hydrolysis by action of the
acid at a temperature of at least 50.degree. C. under conditions such
that the first polysaccharide is hydrolysed and thereby forming a mixture
of an aqueous liquor containing dissolved sugar and a solid residue
containing the second polysaccharide, (iii) subjecting the mixture to one
or more separation stages in which the solid residue and aqueous sugar
liquor are substantially separated from each other, (iv) optionally
washing the residue substantially free of acid and sugar, (v) adjusting
the pH of the aqueous liquor to at least 4, (vi) passing the aqueous
liquor from step (iv) into a fermentation stage where the dissolved
sugars arc acted upon by a microorganism in a fermentation broth to
produce a fermentation product, (vii) contacting the second
polysaccharide by an enzyme, said enzyme hydrolyses the second
polysaccharide to the component sugars, and allowing the component sugars
to be acted upon by a microorganism in the fermentation broth to produce
the fermentation product, (viii) separating the fermentation product from
the broth, characterised in that the separation stage(s) in step (iii)
is/are assisted by flocculation of the solid by-product, employing one or
more flocculating agent(s) selected from the group consisting of water
soluble polymers, water swellable polymers and charged microparticulate
material. Typically such fermentation products include for instance
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 salts of any of these acids.