We report an extremely biocompatible solvent for plant cell walls based on a polar liquid zwitterion that dissolves cellulose, the most recalcitrant component of the plant cell walls. The polar liquid zwitterion does not affect the viability and activity of Escherichia coli, even at high concentrations. We demonstrate conversion of cell walls to ethanol via a starch-like process, namely successive dissolution, hydrolysis and fermentation in the same reaction pot.