Aqueous feeds of 413 and 495 g/L glucose were fermented to ethanol at 90-95% conversion in a continuous flow extractive fermentation system with cell recycle. Compared to the continuous conventional fermentation of a 195 g/L glucose medium, the volumetric productivity was more than doubled in extractive mode, with no deleterious effects on cell viability, specific glucose consumption rate or ethanol yield. The use of an effective, biocompatible and stable in situ extractant with flash vaporization can also produce a concentrated ethanol vapour stream, reducing distillation costs of the product.