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 in the immediate vicinity of the exhaust port or at a second situating position 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 or the second situating position 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 in the immediate vicinity of the exhaust port or at a second situating position 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 in the immediate vicinity of the exhaust port or at a second situating position 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 or the second situating position 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.