VIEW ARTICLE DOI: 10.1094/ASBCJ-49-0140
The Role of Copper, Oxygen, and Polyphenols in Beer Flavor Instability. A. J. Irwin, and R. L. Barker, and P. Pipasts, Brewing Research Department, John Labatt Ltd., 150 Simcoe St., London, ON, Canada N6A 4M3. J. Am. Soc. Brew. Chem. 49:0140, 1991.
The rate of flavor staling in beer is significantly increased by traces of Cu(II), even at levels below 100 µg/L. The Cu(II) catalyzes oxidation reactions that require prooxidants such as cysteine and 1,2,3-trihydroxypolyphenols to recycle the copper through its reduced state. Primary alcohols can be coupled to the oxidation process to yield aldehydes among the products. However, 2-nonen-1-ol is present in beer at concentrations that are too low for it to be a significant precursor of trans-2-nonenal. Model studies suggest that either partially oxidized fatty acids or bisulfite complexes may serve as precursors of the stale-flavored, unsaturated aldehydes that are produced in beer as a result of oxidation processes during aging. The oxidation process in model reactions is inhibited by ethylenediaminetetraacetic acid disodium calcium salt (EDTA), lysine, metabisulfite and 1,2-dihydroxypolyphenol species. Lysine and EDTA also inhibit the formation of aldehydes during beer aging.
Keywords: Flavor stability, Copper, Iron, Polyphenol, Oxidation, Fatty acids, Bisulfite complex