HOP ALLYLIC ALCOHOLS ARE PRECURSORS OF SULFUR-CONTAINING ODORANTS IN FRESH BEER

Hop is known to bring methanesulfenic acid to wort, the precursor of an onion-like odorant in beer: dimethyltrisulfide.
Recently, 2-mercapto-3-methylbutanol was also suspected to be responsible of some onion off-flavors in beer.
In model media, 2-mercapto-3-methylbutanol, 3-mercapto-3-methylbutanol and 3-methyl-2-butene-1-thiol were shown to be synthesized from 3-methyl-2-buten-1-ol and hydrogen sulfide (radical anti-Markovnikov addition, electrophilic Markovnikov addition and nucleophilic substitution, respectively). The present work shows that these mechanisms also occur in pilot-scale beer productions by the presence of hydrogen sulfide excreted by yeast. 1.8 μg/L of 2-mercapto-3-methylbutanol was detected after fermentation of a wort spiked with 10 mg/L of 3-methyl-2-buten-1-ol.
A strong onion-off-flavor was also detected in the fresh beer.
Sensorial analyses were performed on purified 2-mercapto-3-methylbutanol (radical addition favored by adding hydrogen peroxide and catalytic traces of FeS). Its typical freshly-cut onion flavor revealed very different from the “onion soup” descriptor currently used to describe dimethyltrisulfide.

II International Humulus Symposium

J. Gros, S. Nizet, S. Collin

onion, polyfunctional thiols, sulfur flavors, hop, allylic alcohols

https://doi.org/10.17660/ActaHortic.2009.848.29