The invention relates to a process for producing a fermentation product that comprises fermentation of a carbon source in a reactor with a cell, capable of converting sugar, glycerol and acetic acid, wherein the carbon source comprises sugar and acetic acid, comprising the following steps:



a) Inoculating a optionally diluted carbon source with the cell;
b) optionally fermenting the reactor in batch mode;
c) adding carbon source comprising glycerol and optionally sugar gradually to the reactor;
d) after sufficient fermentation time, isolation of fermentation product from the reactor,
e) optionally keeping the remaining fraction after isolation of step d) as spent broth; and
f) optionally using the spent broth in step a) to dilute the carbon source.