Wort Nitrogen and Yeast Strain Drive Thiol Release, Flavor Expression, and Fermentation Performance in Beer

Polyfunctional thiols (PFTs) contribute potent tropical and fruity aromas to beer at ng/L levels, but their release from cysteinylated and glutathionylated precursors depends on yeast activity and fermentation conditions. This study examined the effects of yeast strain and wort free amino nitrogen (FAN) on thiol biotransformation, fermentation performance, and sensory expression using beers brewed at pilot scale with Cascade hops across three FAN levels (110, 240, 360 mg/L) and five yeast strains, including an IRC7-knockout strain. Low wort FAN significantly enhanced thiol release (up to 3× more 3SH and 4MSP), yet wort prepared with medium or high FAN resulted in greater tropical aroma intensity and was associated with elevated esters. Sensory profiles varied with FAN and yeast strain, revealing off-flavors (diacetyl & sulfur/egg) at FAN extremes. The IRC7-knockout strain surprisingly maintained thiol production similar to its parent, suggesting alternative enzymatic pathways for thiol release. These findings highlight FAN's role in modulating volatile profiles and fermentation kinetics, offering practical strategies to optimize hop aroma and flavor balance in beer.