AbstractSelf‐Cycling Fermentations rely on the accurate control over reactor volume to achieve consistent results for many successive cycles. Previous methods using separate vessels for measuring both harvested broth and nutrient supplements have the disadvantage of causing cumulative volume error in the reactor. This work describes the performance of a new control system based on the continuous monitoring of the combined weight of reactor and contents. Results indicate that during the growth ofBacillus subtilisATCC 10774, cycle periods with an average variation of less than 7% can be achieved for at least 77 consecutive generations of cells. The success of the control system was further demonstrated by evidence for the partial synchrony of cell divisio