TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: At least one part of the stirring unit is adjustable above the upper end of the fermenter wall. The rotational axis of the stirring device is adjustable beyond the upper end of the fermenter wall. The stirring unit is completely adjustable above the upper end of the fermenter wall. The support unit comprises at least one support rod, which is obliquely extending upwards from the fermenter wall. The adjusting device comprises at least one control unit, which is arranged outside the fermenter interior, and at least one adjusting unit arranged within the fermenter interior. The control unit and the adjusting unit are coupled with at least one gas-tight joint passage. The gas-tight joint passage is arranged below the fermenter roof, preferably in the fermenter wall. The control unit is arranged below the upper end of the guide unit, preferably below the upper end of the fermenter wall. The adjusting unit comprises at least one deflection device. The deflection device comprises at least one gimbal joint device, at least an angle drive device and/or at least one flexible shaft. The adjusting unit comprises a coupling unit inclined to horizontal. The deflection device is arranged between the coupling unit and the joint passage. The stirring unit is pivotally provided. The swivel angle is adjustable through an angle adjusting device. A distance of the guide unit is dimensioned from the inside of the fermenter wall such that the stirring unit is pivotable towards the fermenter wall. At least one platform is provided, preferably fixed on the fermenter wall and/or the support unit. A gas-tight closable service opening is provided in the fermenter roof. The service opening is provided above the guide unit. The service opening is provided in a service frame, and the gas-tight joint passage is provided at the service frame. The adjusting unit is connected with the control unit through at least one gas-tight joint passage. The adjusting unit is provided for adjusting the height of the stirring unit, and/or for adjusting an angle of the stirring device.