A time-course assessment of polyfunctional thiol release and yeast gene expression in dry-hopped beers

Polyfunctional thiols contribute tropical fruit aroma to beer, yet their low abundance and complex precursor chemistry challenge brewing optimization. This study investigated thiol release kinetics and genome-wide transcriptional changes in a commercial lager ( S. pastorianus ) and ale ( S. cerevisiae ) yeast during pilot-scale fermentations, with and without dry-hopping. In non–dry-hopped fermentations, thiol production peaked early (Days 1–3), coinciding with peak glycolysis and FAN depletion. The lager strain produced higher 3SH levels than the ale, suggesting enhanced precursor conversion, whereas strain had no significant effect on 3S4MP. Dry-hopping increased total thiol content, but 3SH formation did not scale proportionally with hop load. Unexpectedly, both thiols continued to increase during post-fermentation processing, suggesting that thiol formation is not restricted to active fermentation. Transcriptomic analyses identified distinct temporal expression patterns among candidate β-lyases, transporters, peptidases, and nitrogen-responsive genes; however, transcript abundance alone did not explain thiol production, dry-hopping responses, or strain-dependent differences. Overall, thiol production reflects interactions among metabolism, gene regulation, and precursor availability.