Novel methods for the determination of colour and translucency in selected alcoholic beverages

Abstract

At present, the various beverage industries have a significant challenge to effectively monitor the colour and translucency of their products, whether this is by visual assessments or by physical measurements. The visual assessment of translucent beverages is hampered in that the different industry sectors often have their own words/scales for translucency assessments, with specificity across a narrow range of products making them not easily transferred to other sectors of the beverage industry. Several industrial sensory evaluation methods were compared and correlated in this study. Similarly, there is a lack of accurate instrumental measurements either of the colour or the translucency of translucent beverage products in samples that are both coloured and translucent. A new multiple path-length cell together with a digital imaging system have been designed. The cell was built to deliver a specified analytical path length distribution, the overall light scattering performance of the liquid body would behave to the expected analytical path. This cell was applied at-line to determine the colour and translucency critical control points (CCPs) throughout beer production. In this study, descriptive language and psychophysical models to assess colour and translucency were investigated using twelve so-called pseudo-beers (solutions of colorants and scatterers), six commercial beers and fifteen red wine samples. The colour appearance attributes of these samples were assessed by trained experts, who scaled lightness and hue compositions with less variation than their scaling of colourfulness. From the observers‘ performance, it was indicated that beers presented in glasses of different volumes and geometries had different visual colour appearance and that the perceived colour appearance was affected by different levels of scatterers. For the investigation of translucency, observers demonstrated that they could correlate different words or methodologies used for translucency evaluations. But they performed more consistently on the term ―transparency‖, and thus, scaling ―transparency‖ can reasonably be used as a term by which the translucency of a iii beverage might be judged. The magnitudes of colour/translucency changes between any two of the adjacent samples taken during the production of pilot-brewed beer indicated critical control points (CCPs) on colour/translucency monitoring throughout the brewing process. Five CCPs were established. Here, the novel cell and the digital imaging system were set as a off-line monitoring instrument to make determinations at each of the CCPs. The findings clearly showed that the colour/translucency results of most samples followed similar trends. Commercial final products were also tested with the new system, and the results were consistent with conventional methodology results and human observations. In comparison with conventional instruments and methods used for beer colour/translucency analyses, this novel system was demonstrated to be more sensitive, allowing for the simultaneous monitoring of colour of both in-process streams and final products. Some more improvements of the new system are still needed on translucency correlating with conventional methods, e.g. with EBC turbidity.