Impacts of Copper, Iron, and Manganese Metal Ions on the EPR Assessment of Beer Oxidative Stability

David Jenkins,Sue James,Frida Dehrmann,Katherine Smart,David Cook

doi:10.1080/03610470.2017.1402585

David Jenkins, Sue James + Show 3 more

Open Access

https://doi.org/10.1080/03610470.2017.1402585

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Abstract

ABSTRACTBeer flavor stability is a key quality parameter as brewers seek to maintain the quality of their product throughout the supply chain. The electron paramagnetic resonance (EPR) oxidative stability assay is one method that brewers are utilizing to optimize their process with regard to flavor stability without the time requirements of stored aging and sensory testing of beer. There are still gaps in our knowledge relating to the EPR measurement and the factors within the assay that affect the measured results. This investigation aimed to understand the influence that transition metal ions have on the measurement in four different beers (three lagers and one stout). The detrimental impact of copper and iron on the lag time (an indication of when staling may begin) of trial beers is demonstrated, while the influence of manganese is shown to differ between beers. The T450 value (an indication of how much staling may occur in a particular beer) is shown to increase with iron and manganese addition in most beers. However, copper reduces the T450 or maximum spin adduct concentration achieved and the potential reasons for this are discussed. Crucially for brewers, it has been shown that as little as a 10 ppb transition metal ion addition can make a detectable difference to the measured oxidative stability.

Highlights

Brewers spend a significant amount of time and effort ensuring that their product meets the desired flavour profile
The oxidative stability of a beer, assessed using electron paramagnetic resonance (EPR), is a dynamic property altered by reactions in the beer which occur over time and are influenced by environment, temperature
Beers were assessed at the commencement of the trial with the knowledge that they would likely be in different states of oxidative stability and that this would provide variation within the experimental design

Summary

Introduction

Brewers spend a significant amount of time and effort ensuring that their product meets the desired flavour profile. Pohl [24] reviewed the determination of metals in beer, discussing studies which together had measured iron in the range of 15 – 1006 ppb, copper 8 – 800 ppb and manganese 31 In this study transition metal ions were added to beers immediately prior to assessment for oxidative stability using the EPR assay.

Results

Conclusion