The worldwide brewing industry, which contributes more than $331 billion to the global gross domestic product, spends considerable time and effort optimizing and standardizing their product to meet the desired aroma and flavor profiles of their consumers. Beer, a product made from malted barley and/or non-barley cereal adjuncts, hops, water, and yeast, is a deceptively complex matrix and dynamic chemical system that is intrinsically unstable in its finished form. This chemical instability is largely due to deleterious oxidation reactions that are catalyzed by transition metals (e.g., Fe, Cu, Mn) in beer derived from brewing ingredients and metal-leaching from brewing equipment and packaging. Trace levels of Fe, Cu, and Mn (&gt;50 µg/L) have been shown to catalyze reactions in which reactive oxygen species (superoxide radical, singlet oxygen, hydrogen peroxide, and hydroxyl radical) are formed primarily via Fenton and the Haber-Weiss reactions. This project focuses on understanding how the environment of copper affects the chemical stability of finished beer. EPR spectroscopy was used to analyze a commercial pilsner fractionated into five molecular weight ranges with exogenous Cu<sup>2+</sup> added. Results suggest that Cu is bound to a component that weighs less than 500 Da. Experiments use a phosphate buffer model beer matrix to explore how copper binds to components such as amino acids, hop compounds, and organic acids, all of which are contained in the smallest fraction. We determined that copper complexes bind with acids in three different ways: 1) Cu-hyperfine structure indicative of a mono-nuclear complex, 2) large groupings of nuclei that show spin-spin interactions, 3) a mix of the mono-nuclear and multi-nuclear complexes. Addition of thiols (like those from hop cones) are currently being added to the matrix for analysis. In the end, we hope to be able to provide brewers with some tools to combat oxidative staling in their finished products.

Effect of copper complexation on the chemical stability of beer

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