Abstract 106
Visual versus instrumental perception of haze – A review
Tech. Q. Master Brew. Assoc. Am. 45 (2): 90-98, 2008
K.J. Siebert
Visual perceptions of turbidity are of interest to brewers in two main situations. For clear beers, the most interesting item is the threshold, or the least amount of turbidity that can be perceived with the unaided eye. For intentionally cloudy beers, both the degree of cloudiness and qualitative aspects of appearance are of interest. Hazes isolated from beers are largely water soluble, so diluting them to various extents produces artifacts. Synthetic polymer beads have known size, shape, density and surface chemistry and can be suspended at known concentrations. Polymer spheres with diameters between 0.15 and 10.3 µm were each suspended in different colored solutions. Thresholds were determined using the Ascending Method of Limits. When expressed as weight or number concentration the thresholds varied greatly, but when expressed as measured turbidity were quite similar, regardless of particle size or solution color. This result appears contrary to anecdotal accounts, but can be explained by the effect of instrument calibration. Surprisingly, reducing illumination intensity led to generally lower thresholds (greater sensitivity) up to a point, but further reductions produced higher thresholds. Using light-colored rather than black viewing backgrounds led to much higher thresholds. Suprathreshold particle suspensions were subjected to Magnitude Estimation (ME) and Sensory Descriptive Analysis. Equations predicting ME or instrumental turbidity as a function of sample characteristics were developed. Principal Components Analysis was applied to Descriptive Analysis results and indicated that panelists responded to only two fundamental properties (degree of cloudiness and homogeneity/non-homogeneity).
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