In accordance with embodiments of the herein disclosed subject matter it is described a stirring device (200) for a biogas fermenter wherein the stirring device (200) is configured for stirring a fermentation material and comprises a shaft (102) rotatable about an axis of rotation and a mounting structure (106) attached to the shaft (102). The mounting structure (106) has a first connection surface (112) and the second connection surface (114) and a stirring element (116) is attached to the first connection surface (112) and the second connection surface (114). The first connection surface (112) and the second connection surface (112) are located at opposite sides of the shaft (102) with the shaft being located between the first connection surface (112) and the second connection surface (114). The stirring element (116) may be configured to be spaced from the shaft (102) when the stirring element (116) is attached to the first connection surface (112) and the second connection surface (114). According to an e
