Impact of colour adjustment on flavour stability of pale lager beers with a range of distinct colouring agents

Abstract

The impact of colour adjustment on the flavour stability of a portfolio of locallybrewed pale lager beers with a range of colouring agents such as specialty malts, roasted barley, colouring beer and artificial caramel colorant was investigated. All brewing control parameters and beer specifications were defined and monitored under a rigorous regime in order to avoid processing factors that might interfere with or modify the two parameters under investigation. The colour appearance parameters of the beer samples at distinct ages (fresh, forced aged and 12 month-aged) were psychophysically assessed by means of sensory viewing method (magnitude estimation) by an expert panel of the Colour Imaging Group at the Department of Colour Science, University of Leeds. Likewise, the aforementioned samples were physically measured by tele-spectroradiometry and digital imaging system at two different environments. Significant differences between the beer samples at sameand distinct ageing conditions were detected in terms of lightness, colourfulness, hue angle, opacity and clarity, although all of the samples were colour-adjusted to the same colour units according to conventional procedures (EBC colour units). In addition, good agreement between the sensory viewing (magnitude estimation) method and telespectroradiometry was observed. In contrast, some discrepancies between the aforementioned methodologies and the digital imaging technology were detected. Flavour stability was assessed by the detection and quantification of fifteen flavour-active beer ageing compounds (10 aldehydes and 5 non-aldehydes compounds) by GC-MS using headspace-solid phase microextraction (HS-SPME) with on-fibre PFBOA [O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine] derivatisation for aldehydes compounds and on-fibre DVB-CAR-PDMS [divinylbenzene-carboxenpolydimethylsiloxane 50/30_m] derivatisation for non-aldehyde compounds. The results were correlated with the determination of the endogenous anti-oxidative potential (EAP) of the beer samples by electron spin resonance (ESR) using N-tert-butyl-α-(4- pyridyl)nitrone N’-oxide (POBN) and the sensory assessments provided by the I.C.B.D. sensory panel. Additionally, the quantification of organic radicals of the specialty malts, the roasted barley (whole intact kernel and milling fraction measurement) and the artificial caramel colorant were conducted by ESR. Based on the results of this holistic approach, a colouring agent was selected for improving the flavour stability of pale lagers according to its physicochemical-, sensorial and psychophysical effects as colour appearance.