Stale flavors in beer.
The development of stale flavours in beer is accompanied by the absorption of oxygen. Polyphenols are oxidized or polymerized to produce haze and the products so formed probably catalyse other reactions such as the autoxidation of long chain unsaturated fatty acids to carbonyl compounds such as trans 2 nonenal. Although melanoidins act as reducing agents in beer it has recently been shown that their oxidation products can catalyse the oxidation of higher alcohols to aldehydes which contribute to stale flavours as suggested by Hashimoto. The various staling reactions can be controlled by storing packaged beer at low temperatures, by the exclusion of air during storage and filling while the removal of polyphenols by AT treatment has certainly been effective. The addition of antioxidants has met with limited success, sulphur dioxide will usually delay the onset of stale flavour but ascorbic acid and phenolic antioxidants are not always effective.
Keywords: beer flavour oxidation polyphenol off flavour