Ethanol clarification processes

A classic example of a clarification process used in Brazil is that of ethanol production by yeast Saccharomyces cerevisiae. The viability of ethanol production is based on the efficiency of the clarifying operation, which depends on the recycling of yeast to the fermentation reactor and, consequently, the maintenance of high cell concentrations in the culture medium. " Another relevant aspect for the appropriate process performance is the selectivity afforded by centrifugation, keeping bacteria in suspension while yeasts and other larger solids can sediment. The separation occurs due to the density difference between bacteria and yeast, the latter being removed from the supernatant due to their lower density. The partial removal of bacteria, the main contaminant, is a fundamental factor for an effective fermentation. ... 

The physical processes of racking and clarification (with bentonite) help remove the enzyme fraction associated with particulate materials (Gortegs and Geisenheim, 1986). In addition, the activity of tyrosinase decreases during yeast fermentation, largely because of the production of ethanol. Consequently, clarified protein-stable wines made from relatively sound berries are unlikely to contain significant quantities of either laccase or tyrosinase and, hence, should undergo little enzymatic oxidation (Simpson, 1980). 

Considered to be spoilage microorganisms in winemaking (Drysdale and Fleet, 1988 Du Toit and Pretorius, 2002), growth of acetic acid bacteria results in oxidation of ethanol to acetic acid (the process of ace-tification). In addition, other odor- and flavor-active metabolites as well as polysaccharides including dextrans and levans may he formed (Colvin et al., 1977 Tayama et al., 1986). The latter can create problems during post-fermentation clarification and stabihty. 

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