Alcoholic fermentation inhibitory compounds

Patynowski et al. (2002) showed that yeasts produce an unidentified inhibitory factor (maybe a toxic metabolite) that could be responsible for the inhibition of bacterial growth. These results could explain the antagonism between yeasts and malolactic bacteria, since yeasts are known to produce compounds during alcoholic fermentation such as ethanol, SO2, medium-chain fatty acids and antibacterial proteins/peptides (Weeks et al. 1969 De Oliva et al. 2004 Comitini et al. 2005 Osborne and Edwards 2007). The nature and quantity of peptides and other molecules released by yeasts are different depending on winemaking techniques and the yeast strain. 

Wine yeasts are known to produce compounds during alcoholic fermentation that are inhibitory to malolactic bacteria including ethanol (Costello etal., 1983 Davis etal., 1986a Britz and Tracey, 1990), SO2 (Eschenbruch, 1974 Dott et al., 1976 Eschenbruch and Bonish, 1976 Suzzi et al., 1985 Romano and Suzzi, 1993 Henick-Kling and Park, 1994 Larsen et al., 2003), medium-chain fatty acids (Edwards and Beelman, 1987 Lonvaud-Funel et al., 1988 Edwards et al., 1990 Capucho and San Ramao, 1994), and antibacterial proteins/peptides (Dick et al., 1992). Of these... 

Since fermentation takes place in a dilute aqueous solution, the reaction continues until the alcohol concentration approaches about 14%. At higher concentrations, the process becomes self-inhibitory. By-products from starch fermentation to ethanol can include higher-molecular-weight alcohols, glycerine, and ethers. Usually no more than 10% starch is converted to these compounds. Atmospheric distillation, vacuum distillation, and membrane separation techniques can be used to recover ethanol from the final fermented product. The distillate bottoms, called stillage, are recovered as a by-product for animal feed. A biomass fermentation flow diagram is provided in FIGURE 12-2. 

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