Malt and Hop as Sources of Thiol S-Conjugates: Thiol-Releasing Property of Lager Yeast during Fermentation

The contribution of polyfunctional thiols (PFTs) to the overall flavor of a lager beer has been well documented, but their origin remains unclear. In comparison with Saccharomyces cerevisiae strains previously investigated (same conditions: 7 days at 24 degrees C, 3 days at 4 degrees C), we examined how Saccharomyces pastorianus yeasts are able to produce these PFTs from cysteinylated (Cys-) and glutathionylated (G-) conjugates. Up to 0.35% release was observed from G-conjugates against less than 0.08% for all yeasts studied so far. Lowering the wort nitrogen level and the fermentation temperature (12 degrees C) strongly increased the release efficiency and the ester/alcohol ratio from Cys-conjugates. However, it did not improve the release from G-conjugates and even prevented the yeast from producing any acetate. Although poor in free PFTs and their Cys-precursors, both Saaz hop and pale malt (classical ingredients for premium lager beers) confirmed to be significant sources of G-conjugates (especially those of 3-sulfanylhexanol and 3-sulfanyl-4-methylpentanol).

Automated summary

The contribution of polyfunctional thiols (PFTs) to lager beer flavor is significant but their origin is still unclear. Saccharomyces pastorianus yeasts were found to produce PFTs from cysteinylated and glutathionylated conjugates. Lowering wort nitrogen level and fermentation temperature improved the release efficiency of PFTs from cysteinylated conjugates, but had no effect on glutathionylated conjugates. Saaz hop and pale malt were identified as significant sources of glutathionylated conjugates.