Throwing longstanding habits over the pile may be necessary to improve biogas production, in particular when it comes to the process temperature. Its effect on biogas production was investigated with lab-scale reactors operated in fed-batch mode (cattle slurry and maize straw) at 10-55 degrees C over six months. Biochemical and microbial changes were comprehensively investigated. Production was highest and most efficient at 45 degrees C with an average methane yield of 166 NL kg(-1) VS, and thus 12.8% and 9.6% higher than at 37 and 55 degrees C. Temperature significantly affected the microbiota and higher temperature provoked a shift from Bacteroidetes/Proteobacteria to Firmicutes. A transition from hydrogenotrophic to acetoclastic methanogenesis was observed from 10 to 45 degrees C, while the trend was reversed at 55 degrees C. The results contest the textbook notion of preferred and most efficient temperatures for AD and suggest reconsideration of the temperature range around 45 degrees C for efficient manure-based co-fermentation.