Fermentation processes for production of ethanol include supplying a thermophilic microorganism lacking lactate dehydrogenase activity with sugars under conditions in which they metabolise them predominantly by the pyruvate-formate lyase pathway. Importantly, the processes also include supplying sufficient glycerol to convert all of the sugars to ethanol. A further embodiment of the invention includes supplying additional glycerol sufficient to convert the exogenous acetate present in biomass hydrolysates into ethanol. Any type of fermentation system can be used for these processes, but a preferred embodiment includes continuous cultures at high temperatures in which ethanol is removed continuously by vacuum evaporation.