Nitrogen Dynamics in Dry-hopped Fermentations: Impact on Yeast Metabolism and Beer Flavor

Modern hop-forward beer styles remain highly popular, yet the impact of dry-hopping on fermentation biochemistry and yeast-derived flavors remains poorly understood. This study investigated the kinetics of fermentative aroma compounds and the key nutrients driving their production, such as free amino nitrogen (FAN), by comparing dry-hopped and non-dry-hopped ale and lager fermentations at the pilot scale.

Wort produced from Pilsner malt was hopped with Cascade (kettle and whirlpool additions) and optionally dry-hopped at the end of day 2 of fermentation. Dry-hopped fermentations exhibited greater attenuation and an approximately 0.5% higher ABV than their non-dry-hopped counterparts. Dry-hopping significantly increased FAN levels, with both ale and lager fermentations plateauing at ~120 ppm. Analysis of 20 common wort free amino acids by UPLC-MS/MS revealed that dry-hopping primarily increased the concentrations of alanine and glycine (slower-absorbing), as well as arginine and glutamic acid (fast-absorbing), which remained in the final beers. SPME-GC-MS/MS analysis of esters and higher alcohols showed that dry-hopping reduced the concentrations of most esters—including isoamyl acetate, 2-phenylethyl ethanol, ethyl octanoate, and ethyl decanoate—except for ethyl acetate. Polyfunctional thiol analysis via HPLC-MS/MS revealed higher 3-sulfanylhexanol (3SH) levels in lager beers than in ales, with dry-hopping doubling thiol concentrations in both. While non-dry-hopped beers exhibited strong 3SH production during early fermentation, dry-hopped beers continued accumulating 3SH post-dry-hopping, peaking at ~30% higher concentrations before declining toward the end of fermentation/lagering. This suggests that 3SH from dry-hopping may be lost or degraded late in fermentation.


By profiling ale and lager fermentations and their response to dry-hopping, this study provides new insights into the role of nitrogen from malt and hops in modulating the timed release of key aroma compounds. These findings can help brewers optimize recipes and fermentation conditions to enhance flavor.