Process for the manufacture of butanol or acetone

A process for the manufacture of butanol and/or acetone, comprising at least the steps of:

• obtaining pot ale, the pot ale being a byproduct of spirit distillation for production of malt whiskey, wherein the pot ale is a distillation residue from a copper distillation vessel comprising a distillable wash from a yeast fermentation of grain comprising malted barley;
• treating a carbohydrate substrate comprising draff, with the pot ale, to provide a treated substrate, said draff comprising spent grain consisting essentially of malted barley;
• and
• fermenting the treated substrate in the presence of a culture of butanol- and/or acetone-forming micro-organisms at an initial pH in the range of 5.0 to 6.0 and at a concentration of free copper ions of less than 20 μM to provide a fermented product containing butanol and/or acetone.