Transition metals in brewing and their role in wort and beer oxidative stability: a review

Beer inevitably changes over time: the colour will darken, haze may form, and stale flavours develop, while others fade. The challenge of maintaining the fresh flavour quality of beer (over a typical 9-12 month storage period) is generally the determining factor of a beer's shelf-life for brewers, as opposed to colloidal or microbiological stability. Fortunately, as early as the brewhouse, oxidative degradation can - to a certain extent - be controlled, enabling the shelf-life to be increased. This review considers the general issues of oxidative stability, mechanisms of ageing, ways of quantifying staleness and staling potential, and current practical approaches to prevent oxidative beer ageing. Emphasis is placed on the catalytic role of iron, copper and manganese on oxidation during brewing and storage; and how the removal and/or inhibition of these prooxidative transition metal ions leads to prolonged beer (flavour) stability.