The technology for fermentation of sucrose-based media, mostly sugarcane juice, cane molasses, or beet molasses, can be considered as a mature technology espe­cially if the process is accomplished in batch regime. However, many research efforts are being made worldwide to improve the efficiency of this process, par­ticularly to increase the conversion of these feedstocks into ethanol as well as to gauge its productivity. Ethanolic fermentation can be carried out by discon­tinuous, semicontinuous, and continuous processes. In general, temperature and medium pH are quite similar in the different types of ethanolic fermentation: about 30°C and pH in the range of 4.0 to 4.5. Nevertheless, each one of these cul­tivation regimes presents very different performance indicators, especially con­sidering the ethanol volumetric productivity in terms of g EtOH/(L x h). Another performance indicator is ethanol yield defined as the grams of ethanol produced from one gram of substrate consumed (usually the carbon source, i. e., the sugars). Finally, substrate conversion is defined as the ratio between the amount of sub­strate consumed and the initial amount of substrate either loaded at the start of
fermentation for batch regime or contained in the feed stream for continuous regime. This indicator can be expressed in percentage. It is worth emphasizing that substrate conversion implies that the microorganisms consume the substrate not only for ethanol biosynthesis, but also for formation of new cellular biomass and other substances generated as fermentation by-products. S. cerevisiae is the most employed microorganism for industrial ethanol production from sucrose — based media.