may be any water soluble polymer that contains functional groups which ionize in water it may be cationic or anionic a group of preferred anionics is anionic polyacrylamide e g a copolymer of acrylamide and acrylate such as sodium acrylate some preferred cationic polymers are those contaning tertiary or quaternary amine groups an example is cationic starch having diethylamino ethyl groups or 2 hydroxy 2 trimethylamino methyl ethyl groups attached to the hydroxyl group in the 6 position of the repeating glucose unit of the starch molecule another example is cationic polyacrylamide e g a copolymer of acrylamide with n dimethyl amino methyl acrylamide dimethyl amino ethyl methacrylate or trimethyl amino ethyl methacrylate a further example is cationic polyamine such as quaternary polyamine and polyethyleneimine use of the above mentioned polyelectrolytes is particularly advantageous in papermaking where these polymers may simultaneously act flocculants or retention aids the amount of polyelectrolyte is preferably 2 1000 ppm preferably 10 200 ppm in the reaction mixture or 0 1 10 kg ton of dry matter particularly 0 3 3 kg t for reasons of economy microbial lipases are preferred examples of suitable enzymes are lipases derived from strains of pseudomonas especially ps cepacia ps fluorescens ps fragi and ps stutzeri candida especially c antarctica e g lipase a or b see wo 88 02775 and c cylindracea humicola especially h brevispora h lanuginosa h brevis var thermoidea and h insolens chromobacterium especially c viscosum and aspergillus especially a niger the amount of lipase will typically correspond to a lipase activity of 1 000 100 000 lu kg dry.