In biomethane potential (BMP) tests, different sources and origins of inocula might cause significant variations in the tests' results, preventing from acquiring a harmonised and standardised evaluation of the different substrates. In this study, a method to produce standardised and storable inocula was elaborated. For the development of the different investigation steps a control sludge originated from a wastewater treatment plant was utilised. Freeze-drying was applied in the framework of this study as a long-term conservation method for the anaerobic inocula. In order to ensure a closed system with anaerobic conditions at all times, a test system was developed to allow accurate and representative mass balance experiments. The test results demonstrated that inocula conservation and re-suspension in BMP tests is possible; the limit value of the expected methane yield of a positive and lyophilised reference control, was reached. However, a lag phase of 7-10 days was obtained, possibly due to the damage of microorganisms as a consequence of the conservation process. Further investigations need to be carried out to optimise the conservation process of the produced inocula or an initial preparation phase should be considered to reduce the lag phase. (C) 2019 Elsevier Ltd. All rights reserved.