This paper investigates if it is possible to produce inocula to counteract high acetic acid (CH 3 COO − ) concentrations during thermophilic anaerobic digestion. To this end, fermenter sludge was exposed for different durations to either gradually increasing CH 3 COO − concentrations or directly exposed to a high concentration (150mM). Altogether, these enrichments led to inocula with a distinct decrease of representatives of Methanobacteriales, while those of Methanoculleus spp. were hardly affected by any treatment. After the inoculation, good agreements of the abundance of Methanosarcinales and Methanoculleus spp. with total DNA content and methane production rate were apparent. In addition, a gradual adaptation of the inoculum for at least 4weeks led to a significant increase of Methanosarcina spp. during the subsequent fermentation. These results demonstrate the potential of bioaugmentation to relieve the start-up of an anaerobic digestion suffering from high CH 3 COO − loads, especially pointing to the robust acetoclastic genus Methanosarcina.