Zinc Interactions with Brewing Yeast: Impact on Fermentation Performance

J. Am. Soc. Brew. Chem. 69(4):214-219, 2011 The effect of zinc on brewing yeast cells was studied in relation to zinc uptake, fermentation performance, and flavor 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 48 and 96 hr, when zinc concentrations in wort were 1.0 and 4.85 ppm, respectively. Zinc impacted 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 benefited fermentation progress when zinc-deficient wort was employed. Flavor 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) observed. We concluded that control of zinc bioavailability, including Zn-supplementation strategies (for both wort and yeast), plays an important role in dictating brewing yeast fermentation performance and product quality.