Radioisotope Investigation of the Effect of Sunlight on Beer

Abstract

THE formation of mercaptan on exposing beer to sunlight has been recognized for many years. It has also been shown that the mercaptan develops parallel with the occurrence of the sunlight flavour^1,2. In the early report from this laboratory, according to the results of various model experiments with humulone and lupulone analogues, it was suggested that the flavour substance is a kind of mercaptan, especially prenyl mercaptan (3-methyl-2-butene-1-thiol)^3,4. Kuroiwa et al.⁵ have detected 3-methyl 2-butenyl mercaptan in ‘sunstruck’ beer as its 2,4-dinitrophenyl derivative by a chromatostrip method, and proposed isohumulones as the sole precursor of this mercaptan because when isohumulones in the model solution were replaced by humulones, lupulones and other related compounds, no ‘sunlight’ flavour could be detected.