Abstract: 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.

Abstract: The invention relates to a process for the aerobic propagation of yeast wherein the yeast is grown in a reactor, comprising the following steps: a) filling the reactor with carbon source and an initial yeast population, b) optionally growing the initial yeast population in the reactor in batch mode, c) measuring the pH in the reactor, d) adding lignocellulosic hydrolysate to the reactor in fed batch mode at a rate to set the pH in the reactor at a predetermined value, and e) after sufficient propagation, isolation of yeast from the reactor. The invention further relates to yeast propagated according to that propagation process and to a process for the production of fermentation product wherein sugar comprising hexose and pentose is anaerobically fermented to fermentation product with the propagated yeast.