Is there a need to re-define the methods to evaluate wine color

Weincampus Neustadt, Dienstleistungszentrum ländlicher Raum Rheinpfalz, 67435Neustadt an der Weinstraße

Abstract

Both the Glories method and the CIE L*a*b*/L*C*h⁰ system are used in analytical protocols to expredd the chromatic characteristics of wine [1-4]. Both emthodes allow for the interpretation of color intensity, color hue, and other chromatic characteristics. They are utilized in scientific studies to compare experimental treatments and many innovations have been assessed on whether they could retain a higher color intensity or yield ore color brilliance. The validity of the two methods and the explanatory power of the respective color parameters were investigated by comparing the two methods with data from a sensory study. Data intervals from 0.5 to 5 nm and different scan speeds were tested as spectrophotometer settings. A trained panel evaluated 112 dark red, light red and white wines from different grape varieties, origins, and vintages. The correlation between Glories system and the CIE color space was found to be strong for dark red wines (r > -0.9). Lighter red wines and white wines (L* > 20) do not correlate with the same quality, except for the correlation between CI and L* (r > -0.9). In comparison with the human perception, the red and white wines could not be distinguished well with the Glories’ system. The CIE color space was found to be more suited to depict the perceived color for red and white wines. In recent years, the CIE re-defined the color distance calculation within the CIE L*a*b* color space due to non-uniformities. The CIEDE2000 color distance ΔE₀₀ was proposed [4–6] for a better approximation of the erceived color than the Euclidean color distance ΔE^*_ab. A just noticeable distance (JND) test was carried out using triangle testing for the wines segmented into three wine color area: dark red, light red, and light yellow. For dark red wines, the JND was ΔE₀₀ = 1.4 or ΔE^*_ab = 3.1, respectively. For light yellow wines, the JND was found to be much lower values at ΔE₀₀ = 0.64 and ΔE^*_ab = 0.60. And for light red wines, the JND was found to be very high at ΔE₀₀ = 3.4 or ΔE^*_ab = 8.1, respectively. The CIEDE2000 formula resulted in lower JND values than the Euclidean color distance. Although still not uniform for the huge diversity of wine colors, the ΔE₀₀ provides better comparability and is suggested for future studies.