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.