Abstract An in vitrodigestion procedure to obtain fibre rich substrates to determine the in vitro fermentability of differently processed pea and wheat products has been developed. Samples are incubated at 37 °C stepwise with human α-amylase, porcine pepsin and porcine pancreatin for 15, 30 and 90 min respectively to simulate the events taking place in the upper gastrointestinal tract. The digestion products are removed by dialysis and the retentates freeze-dried. Fermentation experiments with fresh human faecal material were carried out to check the influence of the digestion procedure on in vitrofermentation patterns. Depending on food product and processing conditions considerable differences in digestibility were found. Wheat flakes containing large amounts of ungelatinized starch turned out to be poorly digestible. The fermentation experiments showed that high amounts of starch mask the fermentation patterns of the fibre fraction. The results of digested samples varied more, even if only a small proportion of digestible nutrients had been removed. It can be concluded, that an in vitrodigestion is necessary prior to fermentation experiments. Possibilities for the improvement of the digestion procedure presented here, in order to more closely approach physiological conditions, are discussed.