The objective of this work was to produce C-5 sugars from the hydrolysis of the spent grains of the brewery. The total sugar recovery and formation of by-products were evaluated as a function of the reaction temperature (140, 160, 180 and 210 degrees C), flow rate (10 and 20 mL min(-1)) and the solvent/feed ratio (S/F: 64, 80 and 112). The total carbohydrate yields were dependent on the hydrolysis temperature. Arabinose was the main product, followed by xylose and the arabinose yield increased with increasing the S/F ratio and the flow rate. Yields of furfural were sensitive to flow rate. The hemicellulose content of the residual solids was reduced by approximately 90% after hydrolysis, with the parallel formation of carbonyl and carbonized species. The effects of flow rate on the efficiency of converting hemicellulose into simple sugars were complex, suggesting roles for the formation of autocatalytic acids.