Top of the Ferrous Wheel–The Influence of Iron Ions on Flavor Deterioration in Beer

Beer inherently contains a diverse combination of metal ions, a part of which is iron. Brewers strive to keep iron levels as low as possible in wort and beer due to its negative influence on beer stability. Iron occupies a prominent role within the Fenton reaction, where Fe(II) ions are oxidized to Fe(III) by hydrogen peroxide, forming a hydroxyl radical and a hydroxyl ion. The accumulation of reactive oxygen species in wort and beer is detrimental to its oxidative stability, as their presence will accelerate many of the oxidation reactions commonly associated with the onset of unwanted flavor, aroma, and appearance. Aside from iron’s adverse influence on oxidative stability, iron concentrations as low as 0.05 mg/L can also impart an unpleasant metallic off-flavor. This review discusses the points of entry for iron across the brewing process, the role of iron in the oxidative deterioration of beer, and how iron contributes to metallic off-flavors.