Effects of Mash Chelator Addition on Transition Metal Content and Oxidative Stability of Brewer's Wort

Oxidative stability in brewing refers to the ability of wort and beer to resist degradation by free radicals and reactive oxygen species. It is a critical quality aspect in beer production, as it affects both the shelf life and overall excellence of the final product. The catalytic role of iron, copper and manganese in radical-associated staling is widely acknowledged. In this context, the present study investigates the effectiveness of polyphenolic chelators (tannic acid, pomegranate and green tea extract) in enhancing oxidative wort stability by sequestering transition metals during mashing. The results, obtained from 12 comparable brews from two distinct pilot breweries, show that incorporating either pomegranate extract or tannic acid during mashing effectively lowers the levels of transition metals, specifically iron, in the brewhouse. Early mash addition of pomegranate extract (90 % ellagic acid) demonstrates the highest efficacy, with an almost 90 % decrease in iron levels and a nearly 80 % reduction in radical concentration, as measured in the final wort by ICP-OES and ESR spectroscopy, respectively. While the investigated chelators do not facilitate the removal of copper or manganese, their levels naturally decline during the brewing process. Chelator addition yields an average reduction of 40 - 60 % in total post-boil aldehydes. Furthermore, strong correlations are identified between iron levels, polyphenols and wort aldehydes after boiling, whereas only weak to moderate correlations with copper and manganese. Aldehydes levels, however, are greatly influenced by thermal stress throughout the brewing process. The findings suggest that natural chelators have the potential to enhance beer flavour stability by diminishing radical formation during brewing and lowering the amount of transition metals and aldehydes in the final product. However, further research is needed to fully understand the implications of these findings on beer stability, given the intricacy of staling.