Fate of Hop and Fermentation Odorants in Commercial Belgian Dry-Hopped Beers over 2 Years of Bottle Storage: Key-Role of Oxidation and Hop Esterases

The aim of the present work was to compare levels of short chain fatty acids, esters, terpenoids and polyfunctional thiols in (mostly bottle-refermented) commercial Belgian dry-hopped beers before and after 2 years of storage at 20 degrees C (the usual best-before date in Belgium). Among the hop-derived volatiles, the terpenoids linalool and geraniol, the polyfunctional thiols 3SHol, 3SHA and 3S4MPol, and the esters ethyl isobutyrate, ethyl isovalerate and ethyl heptanoate (up to 499, 53, 0.2, 2, 3, 84, 63, and 19 mu g/L, respectively) were found above their sensory thresholds in most fresh dry-hopped beers. The fermentation-derived esters reached concentrations similar to those previously reported for non-dry-hopped beers, with ethyl hexanoate and isoamyl acetate (up to 0.4 and 3.9 mg/L, respectively) often above their sensory thresholds. Except ethyl isovalerate (more than 85% still present), most hop odorants and fermentation esters showed degradation over the 2-year storage period: only 45%-70% of linalool, geraniol, and ethyl hexanoate and even less than 40% for polyfunctional thiols, ethyl isobutyrate, and ethyl heptanoate initial concentrations were detected after storage. How the dry-hopping process affects this degradation was further investigated in model media. Fermentation esters proved to be more strongly impacted in dry-hopped than in non-dry-hopped beers because of hop esterase activity. In addition to being aware of the need to avoid hop esterases, craft brewers are here advised to use bottle refermentation for its ability to regenerate some flavors and consume packaged oxygen. No deleterious effect of yeast, such as short chain fatty acid excretion, was evidenced.