DISCRIMINATION BETWEEN BEERS WITH SMALL COLOUR DIFFERENCES USING THE CIELAB COLOUR SPACE

Abstract

Commercial beers which recorded the same colours by either the European Brewery Convention (EBC) Recommended Method or by visual comparison against standard colour discs in a Lovibond Comparator, exhibited qualitative differences in their visible spectra. These differences, in turn, translated into measurable differences in colour, expressed as ΔEa,b, when described by the CIELAB colour system. Visual difference tests revealed that, in some cases, beers with the same EBC colour could be discriminated by observers under ideal viewing conditions. A threshold value for ΔEa,b, (which varied with EBC colour), below which no significant difference in beer colour could be detected by visual comparison, was determined by consideration of the corresponding ΔEa,b, values for these beers. This threshold was used to assess the accuracy of a rapid method for colour analysis which uses transmittance values at five selected wavelengths. This new method was shown to give ΔEa,b values, with respect to a reference method, which were within the limit of visually detectable colour differences. This, therefore, provides a valuable yardstick for assessing the worth of new tristimulus‐based colour measurement techniques and instrumentation. 1995 The Institute of Brewing & Distilling