The concentration of dissolved oxygen in the 2-l fermenter was controlled manually. The aeration rate was started at 0.5 vvm with air and was later increased manually to 0.7 vvm or even 1 vvm in fermentations without protein expression to meet the oxygen demand. The pO2 was adjusted to values between 10 and 25% oxygen saturation by an appropriate mixture of air and oxygen. In the fermentations without protein expression, the stirrer speed was increased manually stepwise from an initial 1500 rpm to a maximum of 3000 rpm, when already aerating with pure oxygen. After a cell density of 175 g l−1, the glucose input rate had to be limited to keep the pO2 5% oxygen saturation.