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​Tracking Biotransformation of Sulfur Compounds in Beer​

A growing demand for utilizing biotransformation 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 to detect them. While sulfur compounds have been successfully detected using gas chromatography mass spectrometry (GC-MS), a pulsed flame photometric detector, and a GC sulfur chemiluminescence detector (GC-SCD), the research presented here utilizes a GC-SCD via a stir bar sorptive extraction methodology previously used to track aroma intensities in optimizing harvest picking windows. This work shows an identification of 10 thiol and sulfur compounds found in both un-hopped and hopped wort (with Amarillo^®, Cashmere, Idaho-grown Saaz, 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 in the final beer at a retention time of 9.5 min, a compound that contributes a catty, blackcurrant/ 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..​