Yeast selection for fuel ethanol production in Brazil

TLDR

Brazil is a leading global ethanol producer whose plants have become increasingly efficient, yet few studies have examined yeast performance in its industrial fermentation processes. This study reports a 12‑year yeast selection program aimed at identifying Saccharomyces cerevisiae strains suitable for sugar‑cane‑based fermentation with cell recycling in Brazilian bioethanol plants. By recycling yeast cells, the process imposes adaptive evolutionary pressure that selects for strains with greater tolerance to the harsh industrial fermentation conditions. The selected strains improved ethanol yield, lowered production costs, reduced glycerol and foam, preserved high viability during recycling, and demonstrated strong industrial implantation, while highlighting distillery biodiversity as a valuable strain source.

Abstract

Brazil is one of the largest ethanol biofuel producers and exporters in the world and its production has increased steadily during the last three decades. The increasing efficiency of Brazilian ethanol plants has been evident due to the many technological contributions. As far as yeast is concerned, few publications are available regarding the industrial fermentation processes in Brazil. The present paper reports on a yeast selection program performed during the last 12 years aimed at selecting Saccharomyces cerevisiae strains suitable for fermentation of sugar cane substrates (cane juice and molasses) with cell recycle, as it is conducted in Brazilian bioethanol plants. As a result, some evidence is presented showing the positive impact of selected yeast strains in increasing ethanol yield and reducing production costs, due to their higher fermentation performance (high ethanol yield, reduced glycerol and foam formation, maintenance of high viability during recycling and very high implantation capability into industrial fermenters). Results also suggest that the great yeast biodiversity found in distillery environments could be an important source of strains. This is because during yeast cell recycling, selective pressure (an adaptive evolution) is imposed on cells, leading to strains with higher tolerance to the stressful conditions of the industrial fermentation.