1. ANALYSIS OF THE COLOUR PROFILE OF PORT WINES USING COLORIMETRIC AND VISUAL APPROACHES
Francisco A. G. Soares da Silva*(1), Francisco M. Campos(1), Manuel L. Ferreira(2), Natália Ribeiro (2), Bento Amaral(2), Tomás Simões(2), Cristina L. M. Silva(1)
(1)CBQF - Centro de Biotecnologia e Química Fina – Laboratório Associado, Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Arq. Lobão Vital, Porto, Portugal; (2) IVDP – Instituto dos Vinhos do Douro e Porto, Rua de Ferreira Borges 27, Porto, Portugal; *Corresponding author:
Results
Introduction
Correlation of sensorial results with colorimetric method (CR-400)
Ruby Port wines
During wine tasting, colour is normally assessed on the outer rim of the wine in a tilted glass, since most wines are too opaque to be analysed in the middle of the glass. Therefore, depending on the depth of observation considered, the perception of wine colour can be different [1-3]. The current official (OIV) method for measuring wine colour is based on UV/Vis spectrophotometric determination of the spectrum. However, wine colour can also be measured using a reflectance colorimeter, using a reflective background. This latter method allows for the determination of the CIELab colour parameters L*, a* and b* at different volumes/depths using a cylindrical container, allowing for the analysis of a “depth” colour profile of the wines.
Colorimetry is nowadays the most common instrumental technique used for measuring colour in foodstuff. Colorimetric determinations are normally based in the measurement of reflected light from a sample, under a standard illumination source, but can also be used in translucent samples.
In this work, the colour profile of Port wine samples were analysed using the colorimetric approach described above. An untrained panel (not trained) was asked to assess the colour hue of the wine samples in Petri dishes, using an unstructured line scale, with the goal of obtaining a correlation with the colorimetric readings at the same depths.
n =12
RSD < 34%
n =12
RSD < 59%
n =12
RSD < 81%
Methods
Samples
Representative Port wine samples (n=40) from different categories/styles were kindly supplied by IVDP. Samples were selected for their different ages and colour profiles.
n =10
RSD < 103%
n =10
RSD < 61%
Port wine samples
Aged in bottle (Ruby-style)
(n=20)
Vintage 2013 & 2014 n=5
Late bottled vintage n=5
Reserve Ruby n=5
Ruby n=5
Aged in wood cask (Tawny-style)
Tawny n=5
Reserve Tawny n=5
10 years n=5
20 years n=2
30 years n=2
40 years n=1
Fig.1: Plots of correlation between Hue angle (H*) and sensorial scores by the panelists for Ruby Port wines at different depth. Standard deviation of sensorial scores is presented in each sample, as the maximum value of RSD of each plot.
Colorimetric method:
Tawny Port wines
The colorimetric measurements were made with a Konica Minolta Chroma meter 400 (CR-400) which measured the reflected radiation and calculated the corresponding CIELab parameters. A prior calibration of the colorimeter was performed using the white calibration tile provided with the equipment, which was also used as a background for the sample measurements. Different volumes of Port wine sample (2.5 ml, 4.0 ml, 5.0 ml, 6.0 ml and 7.5 ml) were transferred to a glass Petri dish (with a diameter of 4.0 cm) in order to measure colour at different depths (2.0 mm, 3.2mm, 4.0 mm, 4.8 mm and 6.0 mm). The measurements with Konica Minolta Chroma meter 400 were made with D65 illuminant and 2º angle observation, corresponding to the CIE 1931 colour space [4].
n =12
RSD < 78%
n =12
RSD < 65%
n =12
RSD < 51%
Sensorial assessment:
Twelve (previously untrained) panellists) were asked to assess the colour of Port wines samples. The sensory test consisted of placing the Petri dishes on an unstructured (1-meter) horizontal scale according to their hue using two “anchors” in the extremities of the scale (representing the lowest and highest values of H* obtained in the colorimetric readings). Plastic Petri dishes (6 cm of diameter) were used for this essay. Two sets of scaling test were made, one for Ruby styled wines and another for tawny styled wines. Each scaling test was performed with an established depth of 2 mm; 3.2 mm; 4mm; 4.8 mm and 6mm, in order to compare the results obtained in the colorimetric readings at the same depths.
Anchor
n =12
RSD < 83 %
n =12
RSD < 57 %
Anchor
Depth tested (Ruby and Tawny):
2mm;3.2mm; 4mm; 4.8mm; 6mm
Fig.2: Plots of correlation between Hue angle (H*) and sensorial scores by the panelists for Tawny Port wines at different depth. Standard deviation of sensorial scores is presented in each sample, as the maximum value of RSD of each plot.
Conclusions
Higher correlations (H* vs sensorial scores) were found at greater depths (4.8mm and 6mm) in Ruby Port wines. However, in Tawny Port wines it was found at shallower depths (2 mm to 4 mm). Yet, good correlations were found at all depths in all Port wines.
The panel was able to make a better distinction between the Tawny-styled wines than the Ruby-styled wines (as shown by the lower SD in the sensorial scores). In Ruby-styled wines, only at lower depths (2.0 to 4.0 mm) there was some consensus between panelists .
A linear correlation was observed for Ruby-styled wines at all tested depths; however, in Tawny-styled wines, a curved pattern was observed, meaning that the panelists used the scale in a non-linear manner for more aged wines (with higher H* values).
In general, sensorial results showed a better colour distinction on shallower depths (2mm; 3.2mm and 4mmm) for both styles of Port wine (Ruby and Tawny).
References
[1] Huertas, R. et al. (2003) Color Res Appl 28(6): ; [2] Martin, MLG-M et al. (2007) Food Qual Pref 18: ; [3] Sáenz Gamasa, C. et al. (2009) Eur Food Res Technol 229:263–276, [4] Konica-Minolta,
Acknowledgements
The authors wish to thank Rui Costa Lima for technical help. This work received financial support from FCT via project UID/Multi/50016/2013