Proposed Pathways for the Formation of Volatile Aldehydes during Storage of Bottled Beer¹

1 Presented at the 41st Annual Meeting, Kiamesha Lake, N.Y., May 1975.

Abstract

Volatile aldehydes formed during shelf storage of bottled beer seem to be the main cause of the stale flavor in beer. However, the origin of these aldehydes in beer has been controversial. Evidence is presented in this paper that 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 these volatile aldehydes in bottled beer. Moreover, the saturated aldehydes resulting from these reactions subsequently undergo aldol condensation to give longer-chain unsaturated aldehydes in beer. Conversely, unsaturated aldehydes tend to be oxidized to shorter-chain saturated aldehydes. Melanoidins act as hydrogen acceptors in the oxidation of higher alcohols and also as antioxidants in the oxidation of isohumulones and unsaturated fatty acids. Isohumulones in beer undergo oxidative degradation to form volatile aldehydes and also inhibit the oxidation of higher alcohols, amino acids, and unsaturated fatty acids by acting as an electron donor in these oxidations. Thus, the reactions involved in formation of volatile aldehydes are interrelated through the electron-transfer system in beer. On the basis of these findings, a mechanism is proposed for the formation of volatile aldehydes in bottled beer.

• Flavor stability
• Stale flavor
• Oxidation
• Melanoidins
• Isohumulones.