The hydrolysis of rye straw and rye silage in liquid hot water (LHW) as a pretreatment process for the utilization of lignocellulosic material (LCM) was investigated. Two different types of reactors, a batch autoclave (BA) and a continuous-flow (CF) apparatus, were used in this work. For both setups a certain time was needed to heat the reactor up to the desired temperature. The temperature profiles for both reactors were calculated and accurately predicted in order to assure comparable and defined operating conditions. For this purpose, a modified severity factor was used that accounted for the different temperatures during the heat-up phase in the reactors. The experimental results show that high degrees of biomass solubilization are possible using LHW, however, the yield of undesired degradation products increases with treatment severity as well. The particle size of the biomass and the substrate concentration seem to have no influence on the solubilization. The solubilization of rye silage seems to be easier compared to rye straw as parts of the protecting hemicellulose-lignin matrix have already been degraded by lactobacilli. The glucose formation and decomposition from rye straw were investigated using a simplified model according to the pattern of a single consecutive reaction following first-order kinetics and the results were compared to literature data dealing with the LHW treatment of starch as well as pure cellulose. Taking into consideration the advantages and disadvantages of the reactor types used, an optimal reactor concept is proposed for future investigations. (c) 2008 Elsevier B.V. All rights reserved.