Zinc interactions with brewing yeast: impact on fermentation performance

The effect of zinc on brewing yeast cells was studied in relation to zinc uptake, fermentation performance and flavour congener formation. Experiments using malt wort with variable supplements of zinc salts were conducted in small scale conical vessels and in pilot plant fermentors to reproduce industrial lager beer fermentations. During small scale fermentations, zinc was taken up completely from wort by yeast within the first 48h and the first 96h when zinc concentrations in wort were, respectively, 1.0 ppm and 4.85 ppm. Zinc impacted on fermentation performance with wort zinc levels required for optimal fermentation ranging from 0.48 to 1.07 ppm. These initial zinc levels corresponded to final zinc yeast cell contents of 14 and 108 fg/cell, respectively. In pilot plant fermentors, “preconditioning” of yeast by enriching cells with zinc prior to fermentation was found to benefit fermentation progress when zinc-deficient wort was employed. Flavour congener profiles appeared to be affected only at high zinc levels of 10 ppm, with elevated concentrations of higher alcohols and some esters (ethyl caproate and isoamyl acetate) being observed. We conclude that control of zinc bioavailability, including Zn-supplementation strategies (to both wort and yeast), play important roles in dictating brewing yeast fermentation performance and product quality