Fermentation control is the coordinated adjustment of process inputs so that a biological culture follows a specified operating trajectory. A control loop combines a measured variable, a target or control law, and an actuator that changes the vessel environment. Typical manipulated inputs include agitation, gas flow, feed rate, temperature, pH-control reagent, pressure, and antifoam addition ^[1]. Feedback control responds to deviations in measured temperature, dissolved oxygen, pH, or residual substrate, whereas feedforward and model-based strategies use an expected process response to anticipate changes ^[2]. The selected control objective may be stable growth, oxygen-limited production, suppression of overflow metabolites, maintenance of a physiological state, or reproducible product quality ^[3]. Sensor delay, calibration drift, sampling frequency, mixing heterogeneity, and actuator limits can make the measured value differ from the condition experienced by cells. Effective control therefore links instrumentation with a process model and a biologically meaningful objective. Control performance is judged by trajectory stability and product reproducibility ^[1][2][4].