Development of an integrated simultaneous process of saccharification, fermentation, and distillation at high temperatures using thermotolerant yeast

Industrial bioethanol production is a complex, costly, and multi-step process that requires long processing times. To address this, we developed a high-temperature simultaneous process of saccharification, fermentation, and distillation (HT-SSFD). This process was performed in a single tank connected with a reduced-pressure distillation (RPD) unit, using the thermotolerant yeast Kluyveromyces marxianus . Simultaneous distillation promotes fermentation by reducing ethanol inhibition and reducing the generation of toxic reactive oxygen species. This method allowed stable fermentation at temperatures approximately 5 °C higher with a 1.6-fold increase in ethanol recovery compared with that achieved without RPD, thereby maximizing the benefits of high-temperature fermentation. It also significantly increased ethanol productivity and shortened the overall process time to distilled ethanol recovery. Furthermore, high yeast viability was maintained even after HT-SSFD, and the procedure could be repeated using a portion of the preceding batch as a preculture. HT-SSFD was also demonstrated to be conducted with other thermotolerant yeasts, although ethanol production efficiency varied. Therefore, HT-SSFD is a compact, stable, and efficient fermentation process that shows strong potential as a basis for future industrial bioethanol production technology. • Development of a high-temperature simultaneous saccharification, fermentation, and distillation process (HT-SSFD). • Processing in a single tank with a reduced-pressure distillation unit achieves a compact and efficient fermentation process. • Simultaneous distillation reduces the harmful effects of ethanol and reactive oxygen species. • High ethanol productivity and reduced process time to distilled ethanol recovery. • High yeast viability enables continuous cycling of the HT-SSFD process.