The reactions with beet pulp were carried out under the same conditions as the previous substrates (Figure ). Beet pulp shows an increase of the soluble fraction from 45 % without catalyst up to around 65 % which neither can be increased with a higher milling duration nor a higher acid content. The relatively high soluble fraction without acid can be explaind by the high contents of extractives in water which are of course also soluble after the mechanical treatment.