Sunstruck Flavor Formation in Beer. Shuso Sakuma, Yukiko Rikimaru, Keita Kobayashi, and Masahiro Kowaka, Technology Development Department, Beer Division, Kirin Brewery Co. Ltd., 17-1 Namamugi 1-chome, Tsurumiku, Yokohama-shi, 230 Japan. J. Am. Soc. Brew. Chem. 49:0162, 1991.

When green-bottled beer is stored in an open plastic crate, the formation of sunstruck flavor becomes a problem. The tendency to form sunstruck flavor differed greatly between beer brands. To better understand factors that influence the formation of sunstruck flavor, the reaction pathway was investigated. As an index of sunstruck flavor, 3-methyl-2-butene-1-thiol was determined by a purge-and-trap technique after exposure of a beer sample to sunlight. The formation of 3-methyl-2-butene-1-thiol was greatly influenced by the transmittance of light through the beer bottle; isohumulones and riboflavin markedly accelerated its formation, and beer color greatly suppressed its formation. The photochemical sensitization of riboflavins was indispensable for the formation of 3-methyl-2-butene-1-thiol from isohumulones and sulfur-containing amino acids and protein in beer.

Keywords: Sunstruck flavor, 3-Methyl-2-butene-1-thiol, Riboflavin, Photochemical sensitization, Isohumulones, Amino acids