Mixing time in airlift reactors during citric acid fermentation

Citric acid fermentations using strain Aspergillus niger were carried out i n three airlift reactors of volumes of 10, 35 and 200 liters. Mixing times were measured at the beginning and the end of fermentation. It has been sho wn that the mixing time at the end of fermentation is approximately equal t o the duration of one circulation period. This was due to the flow regime t ransition caused by the change of rheological properties of the mould broth during fermentation.