Beer Photooxidation Creates Two Compounds with Aromas Indistinguishable from 3-Methyl-2-butene-1-thiol

Beer photooxidation (lightstruck reaction) creates the well-known, intensely flavor-active compound 3-methyl-2-butene-1-thiol (MBT). The sensory threshold in beer for this malodorous compound is 2–7 ng/L. Using solid-phase microextraction and multidimensional GC-olfactometry, we discovered two previously unidentified compounds with aromas indistinguishable from the “skunky” or “foxy” aroma used to describe MBT. These additional skunky aroma compounds undoubtedly contribute to the overall lightstruck character in beer. Additionally, we discovered that MBT and one of the two other compounds slowly formed during beer thermal oxidation in the absence of light.