The Brazilian technology of fuel ethanol fermentation – yeast inhibition factors and new perspectives to improve the technology

Brazil is the second largest producer of ethanol in the world and the first in the technology of ethanol from sugar cane. The Brazilian bioprocess of ethanol production is based on molasses or cane juice substrate. Currently, a fed-batch or continuous or mixed process is operated with a stable cell recycle and high yeast concentration. The ethanol efficiency is controlled by several industrial parameters of fermentation and depending on balance of these parameters and some chemical and microbiological inhibitors. Sucrose and ethanol concentration, acid treatment of yeast cells, temperature and pH, yeast cells flocculation, and some chemical inhibitors like organic acids and sulfite, beyond bacterial infection may affect synergistically the viability of Saccharomyces cerevisiae and ethanol production. These parameters will be extensively discussed in this chapter with focus on correct operation of the process to maximum ethanol production. The inhibitory effects of these problems will be discussed in the metabolism of the yeast, making difficult the operational procedures increasing the cost of the process and decreasing the ethanol efficiency. Other important aspects are screening of yeast strains, type of bacterial and yeast contamination, antimicrobial compounds used to control microbial contamination. New studies are been showed to control the yeast flocculation and bacterial infection to improve the ethanol production.