A process for the production of ethanol through molasses fermentation

PCT No. PCT/SE86/00498 Sec. 371 Date Jun. 20, 1988 Sec. 102(e) Date Jun. 20, 1988 PCT Filed Oct. 30, 1986 PCT Pub. No. WO87/04724 PCT Pub. Date Aug. 13, 1987.Ethanol is produced by fermentation of beet or cane sugar molasses in a fermentor. The ethanol formed in the fermentor is recovered by operating a primary distillation step (PD) in circulation circuit with the fermentor (FI). From the fermentor (FI) a mash stream (5) is continuously withdrawn, and after separation and recirculation of the yeast contained in the mash (5), the yeast-free mash is supplied to the primary distillation step (PD). A part (14) of the bottom stream (13) from the primary distillation step (PD) is recirculated to the fermentor. By controlling the water input to the process circuit so that the concentration of non-fermentable substance in the fermentor (FI) during a first period of time is increased from a start value in the range 5-15% by weight DS to a value in the range 20-30% by weight DS and maintaining the last high concentration during a second period of time so that the average content of non-fermentable substance in the fermentor during said two periods of time exceeds 20% by weight DS, a on average very concentrated stillage can continuously be discharged from the process.