Composition and Pathway of Formation of Stale Aldehydes in Bottled Beer. Naoki Hashimoto and Tadashi Eshima, Research Laboratories of Kirin Brewery Co. Ltd., Miyahara-Cho, Takasaki, Gumma Pref., 370-12, Japan. J. Am. Soc. Brew. Chem. 35:0145, 1977.

Volatile aldehydes formed during storage of bottled beer on the shelf are generally considered to cause a stale flavor in beer. Oxidation of higher alcohols by melanoidins, oxidative degradation of isohumulones, Strecker degradation of amino acids, and autoxidation of unsaturated fatty acids are all involved in the formation of many kinds of volatile aldehydes. Evidence was presented in a previous paper that the aldehydes formed by oxidation of higher alcohols plus isohumulones may be the "stale aldehydes" specifically responsible for the stale flavor. Volatile aldehydes of oxidized beer were isolated as their 2,4-dinitrophenylhydrazone derivatives, and subjected to chromatography on a magnesia-Celite 545 column and thin-layer chromatography (TLC) on PEG 6000-impregnated silica gel plates. They were identified by gas chromatography (GC) and mass spectrometry (MS). The concentrations of alkenals and alkadienals, with six to twelve carbon atoms, formed by oxidation of higher alcohols plus isohumulones, were higher in oxidized beer than in fresh beer or oxidized unhopped beer, and a few of these compounds were only detected in oxidized beer. The aldehydes derived from higher alcohols and isohumulones underwent aldol condensation to form these unsaturated aldehydes. When a mixture of these unsaturated aldehydes (Table II) was added to fresh beer, a taste panel reported that the beer had a typical stale aroma.

Keywords: Flavor stability, Higher alcohols, Isohumulones, Melanoidins, Stale aldehydes.