System for detecting at least one presence of foam (9 2 , 9 3 ) of a medium in a bioreactor plant , wherein the system comprises: - a bioreactor plant comprising at least one single-use container for receiving the medium that may comprise the foam (9 2 , 9 2 ), and an exhaust port ; - at least two capacitive sensor units (10 A , 10 B , 10 C ) which are attached at at least two different situating positions (A1-A3; B1-B6; C1, C2) of the bioreactor plant , wherein one sensor unit (10 A , 10 B , 10 C ) of the at least two capacitive sensor units (10 A , 10 B , 10 C ) is arranged: at a first situating position (B2) in the immediate vicinity of the exhaust port or at a second situating position (C1) on or in the spatial vicinity of an exhaust hose of the bioreactor plant , wherein the exhaust hose is fluidically connected to the exhaust port ; and - at least one monitoring unit comprising at least one open-loop and/or closed-loop control unit , wherein the monitoring unit is designed to trigger an action, such as switching off a stirrer and/or a sparging, when the sensor unit (10 A , 10 B , 10 C ) arranged at the first situating position (B2) or the second situating position (C1) is triggered, wherein the capacitive sensor units (10 A , 10 B , 10 C ) each comprise at least one electrode system for a capacitive measurement and can detect the presence of foam (9 2 , 9 3 ) at the at least two situating positions (A1-A3; B1-B6) on the basis of the capacitive measurement; and wherein the capacitive sensor units (10 A , 10 B , 10 C ) are designed to transmit recorded data concerning the presence of foam (9 2 , 9 3 ) to the at least one monitoring unit for monitoring, open-loop control and/or closed-loop control of foam formation in the bioreactor plant on the basis of said data. - a bioreactor plant comprising at least one single-use container for receiving the medium that may comprise the foam (9 2 , 9 2 ), and an exhaust port ; - at least two capacitive sensor units (10 A , 10 B , 10 C ) which are attached at at least two different situating positions (A1-A3; B1-B6; C1, C2) of the bioreactor plant , wherein one sensor unit (10 A , 10 B , 10 C ) of the at least two capacitive sensor units (10 A , 10 B , 10 C ) is arranged: at a first situating position (B2) in the immediate vicinity of the exhaust port or at a second situating position (C1) on or in the spatial vicinity of an exhaust hose of the bioreactor plant , wherein the exhaust hose is fluidically connected to the exhaust port ; and at a first situating position (B2) in the immediate vicinity of the exhaust port or at a second situating position (C1) on or in the spatial vicinity of an exhaust hose of the bioreactor plant , wherein the exhaust hose is fluidically connected to the exhaust port ; and - at least one monitoring unit comprising at least one open-loop and/or closed-loop control unit , wherein the monitoring unit is designed to trigger an action, such as switching off a stirrer and/or a sparging, when the sensor unit (10 A , 10 B , 10 C ) arranged at the first situating position (B2) or the second situating position (C1) is triggered, wherein the capacitive sensor units (10 A , 10 B , 10 C ) each comprise at least one electrode system for a capacitive measurement and can detect the presence of foam (9 2 , 9 3 ) at the at least two situating positions (A1-A3; B1-B6) on the basis of the capacitive measurement; and wherein the capacitive sensor units (10 A , 10 B , 10 C ) are designed to transmit recorded data concerning the presence of foam (9 2 , 9 3 ) to the at least one monitoring unit for monitoring, open-loop control and/or closed-loop control of foam formation in the bioreactor plant on the basis of said data. <EOS>