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In contrast to other fermented beverages, beer quality generally diminishes over time. This diminishing quality hinges heavily on the oxidative degradation of beer compounds by reactive oxygen species (ROS), whose formation is in part catalyzed by Fe(II) ions via the Fenton and Haber-Weiss reactions. Consequently, ROS accumulation throughout the brewing process results in oxidative instability and accelerates numerous beer staling reactions, like those frequently associated with the onset of unwanted flavors, aromas, and an unaesthetic appearance. However, despite its critical importance to beer stability, the oxidative state of iron in wort and finished beer continues to be poorly characterized. In this investigation, the influence of kilned specialty malt utilization on total free iron and iron ion speciation in wort was determined by EBC Method 9.13.1. Further, the reducing power of each wort was determined via 2,2-diphenyl-1-picrylhydrazyl (DPPH). Here, we demonstrate that kilned specialty malt utilization influences total iron concentration, the balance between Fe(II) and Fe(III) ion species, and the reducing power of wort. Furthermore, our results reveal a negative correlation between mash pH and total iron concentration in finished wort. These results indicate that beer's oxidative flavor stability may be improved by using lower kilned malts and adjusting mash pH. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]