Strategies to Reduce the Iron Intake During the Brewing Process with respect to Flavour Stability

Flavour stability represents a key aspect of beer quality, but remains a major challenge for brewing science and the brewing industry. The gradual deterioration of the organoleptic qualities of beer during ageing significantly diminishes its value in several respects, including market appeal, palatability and overall drinkability. While beer is inherently unstable due to its complex composition, strategic measures can be implemented to enhance the initial freshness of the product and slow the rate of flavour deterioration. The main objective of this thesis was to address this issue by specifically targeting the detrimental effects of transition metals (iron, copper and manganese), which act as catalysts for the generation of damaging radicals through Fenton and Haber-Weiss reactions. By sequestering and subsequently removing these metal ions using chelating agents, their deleterious effects can be avoided from the mashing stage onwards. A total of nineteen chelating agents were investigated for their ability to form filterable complexes with transition metals in brewing relevant setups. These included EDTA, citric acid, tartaric acid, quercetin, chlorogenic acid, ferulic acid, gallic acid, phytic acid, tannic acid, as well as extracts derived from green tea, pomegranate, grapeseed, reishi, cinnamon, curcuma, milk thistle, ginkgo, grapefruit seed and raspberry. In the initial model study, it was revealed that a typical wort pH of 5.60 provided a more favourable environment for the removal of transition metals through complex formation than a beer pH of 4.30. Of the first nine chelators listed, tannic acid (a high molecular weight polyphenol) showed the greatest efficacy. At wort pH, it significantly removed iron and copper from solution after 0.2 µm microfiltration (-94.0 % Feᴵᴵ, -96.8 % Feᴵᴵᴵ, -98.3 % Cuᴵᴵ) compared to chelator-free controls. Other chelators also exhibited noticeable effects at pH 5.60, albeit to a lesser extent, namely quercetin (-34.6 % Feᴵᴵ, -96.2 % Feᴵᴵᴵ), gallic acid (-72.6 % Feᴵᴵᴵ, -39.9 % Cuᴵᴵ), chlorogenic acid (-90.2 % Feᴵᴵᴵ) and ferulic acid (-9.4 % Feᴵᴵ, -11.6 % Feᴵᴵᴵ). Phytic acid demonstrated an undesirable property in chelating zinc (- 70.3 % Znᴵᴵ). Despite forming complexes, EDTA, citric acid and tartaric acid did not lead to reductions in metal concentrations, as the chelates were able to pass through the microfilter. A subsequent study, evaluating the performance of all nineteen chelators in wort during laboratory-scale ma