Sulfate Metabolism during Fermentation¹

1 Presented at the 41st Annual Meeting, Kiamesha Lake, N.Y., May 1975.

Abstract

Overall sulfur balance and sulfate metabolism during fermentation of brewery wort by ale and lager yeast have been studied by [³⁵S]sulfate labeling experiments. Ale yeast derived 40 and 27% of the total sulfur assimilated during stirred flask and unstirred column fermentations, respectively, from wort sulfate. The corresponding values for lager yeast were 41 and 21%. The contributions of sulfate to H₂S evolved in the fermentor gases, and to medium SO2 formed during fermentation, have been examined. Ale fermentations produced < μg S of fermentor gas H₂S/I. medium and <0.2 μg S of medium SO₂/I. medium. Stirred flask lager fermentations evolved an average of 62 μg H₂S/I. of medium, 72% of which was derived from sulfate. Sulfate-derived H₂S constituted 64% of the total H₂S evolved during unstirred column fermentations (130 μg H₂S/I. medium). The effects of individually added amino acids (L-methionine, L-threonine, and L-cysteine) and heavy metals (Fe, Cu, and Zn) have been studied and are discussed in terms of literature results and yeast sulfur metabolism. The total bound SO₂ levels averaged 0.17 μgS/g and 11 μgS/g in beer from stirred flask and unstirred column lager fermentations, respectively. Radiochemical tracer experiments showed that all of the SO₂ formed in the latter experiments was derived from wort sulfate.

• Fermentation
• Hydrogen sulfide
• ³⁵S-labeling
• Sulfate
• Sulfur dioxide