Autohydrolysis-based pretreatments enable extraction of hemicellulose from wood tissue prior to the paper pulp cooking processes enabling their further use as platform chemicals and in material applications. In this study, hot water extraction of birch meal was conducted in a small flow-through system. The combination of high surface area of the milled material with increased driving force induced by constant flow of freshwater, together with fast evacuation of extract, enabled a detailed study of the dissolution process. Based on the findings, deeper insight into acidification and autohydrolysis progress was obtained.