Episode 181: Tracking Biotransformation of Sulfur Compounds in Beer

A growing demand in utilizing biotransformation, a general term for the conversion of compounds through biological pathways, to improve the organoleptic profile of beer has changed the way hop forward beer recipes are approached. While the analysis of terpene biotransformation has been well documented, there remains a gap in knowledge in sulfur compounds due to their extremely low concentrations (sometimes in concentrations of parts per trillion) and high volatility. Analysis of sulfur compounds requires precise and sensitive analytical methodology in order to detect them. While sulfur compounds have been successfully detected using gas-chromatography mass spectrometry (GC-MS) a pulsed flame photometric detector (PFPD), and a GC sulfur chemiluminescence detector (GC-SCD), the research presented here utilizes a GC-SCD via stir bar-sorptive extaction (SBSE) methodology previously used to track aroma intensities in optimizing harvest picking windows. This work shows an identification of various thiols and sulfur compounds found in both un-hopped and hopped wort (with Amarillo® (VGXP01), Cashmere, Idaho grown Saaz (Osvald-72 c.v.), and Czech Saaz) and tracks them through the fermentation process confirming the volatility of some thiols and most notably the presence of 4-methyl-4-mercaptopentan-2-one (4MMP) in the final beer at a retention time of 9.5 minutes, a compound that contributes a catty, black currant/Sauvignon Blanc aroma character. Differences in hop varieties were compared with an American ale yeast, and the effect of yeast strain as well as temperature on thiol production with VGXP01 was compared between an American ale, German lager, Belgian saison, and Brettanomyces bruxellensis strain.

Special Guest: Tim Wallen.