Biogas production is known to be the most sustainable bioenergy technology available owing to its utilization of waste biomass. Due to the widely ranging energy contents of major organic carbons and their diverse degradation pathways, as well as their highly varying hydrolysis capacities, predicting methane yield is not as simple as predicting the production of other biofuels. This study investigated the hydrolysis behaviour of organic compounds using the operational conditions of real-scale biogas plants (hydraulic retention time (HRT) of 15, 20, 30, and 45 days) and explored a new approach to determine the biochemical methane potential (BMP), which can be used to predict the methane yield of a wide range of agro-industrial wastes. The degradation of hemicelluloses and cellulose increased gradually, closely following first-order degradation kinetics, at longer retention times. In spite of their longer retention times, only 45% of hemicelluloses and 34% of cellulose decomposed. The newly proposed BMP model was validated using 65 internal and external datasets. The model error (RMSE P ) was in the range of 37.4–87.7 NL CH 4 kg VS −1 while the relative model error (rRMSE P ) was in the range of 12.1%–47.8%. The model fits best to gently lignified biomass, but the overestimated results obtained with woody biomass and winter harvested grass indicate that further investigation of the hydrolysis of well-lignified biomass is required to enhance the precision of the model.