Proper tuning of dissolved oxygen (DO) controller proportional integral (PI) values is essential for optimal cell culture performance in a bioreactor. When DO-PI values are optimized, gas flows are smoothed, and foaming and cell stress are reduced. Traditionally, this tuning has been performed by using nitrogen gas to purge oxygen from a test solution, thus simulating oxygen demand. That method has several drawbacks, however. First, nitrogen gassing cannot simulate the high demands of high-density fermentation. Second, nitrogen competes with other…