Chromatic Characteristics (TypeI)
OIVMAAS211 Determination of chromatic characteristics according to CIELab
Type I method
 Introduction
The colour of a wine is one of the most important visual features available to us, since it provides a considerable amount of highly relevant information.
Colour is a sensation that we perceive visually from the refraction or reflection of light on the surface of objects. Colour is light—as it is strictly related to it—and depending on the type of light (illuminating or luminous stimulus) we see one colour or another. Light is highly variable and so too is colour, to a certain extent.
Wine absorbs a part of the radiations of light that falls and reflects another, which reaches the eyes of the observer, making them experience the sensation of colour. For instance, the sensation of very dark red wines is almost entirely due to the fact that incident radiation is absorbed by the wine.
1.1. Scope
The purpose of this spectrophotometric method is to define the process of measuring and calculating the chromatic characteristics of wines and other beverages derived from trichromatic components: X, Y and Z, according to the Commission Internationale de l’Eclairage (CIE, 1976), by attempting to imitate real observers with regard to their sensations of colour.
1.2. Principle and definitions
The colour of a wine can be described using 3 attributes or specific qualities of visual sensation: tonality, luminosity and chromatism.
Tonality—colour itself—is the most characteristic: red, yellow, green or blue. Luminosity is the attribute of visual sensation according to which a wine appears to be more or less luminous. However, chromatism, or the level of colouring, is related to a higher or lower intensity of colour. The combination of these three concepts enables us to define the multiple shades of colour that wines present.
The chromatic characteristics of a wine are defined by the colorimetric or chromaticity coordinates (Fig. 1): clarity (L^{*}), red/green colour component (a^{*}), and blue/yellow colour component (b^{*}); and by its derived magnitudes: chroma (C^{*}), tone (H^{*}) and chromacity [(a^{*}, b^{*}) or (C^{*}, H^{*})]. In other words, this CIELab colour or space system is based on a sequential or continuous Cartesian representation of 3 orthogonal axes: L^{*}, a^{*} and b^{*} (Fig. 2 and 3). Coordinate L^{* }represents clarity (L^{* }= 0 black and L^{* }= 100 colourless), a^{*} green/red colour component (a^{*}>0 red, a^{*}<0 green) and b^{*} blue/yellow colour component (b^{*}>0 yellow, b^{*}<0 blue).
1.2.1. Clarity
Its symbol is L^{*} and it is defined according to the following mathematical function:

Directly related to the visual sensation of luminosity.
1.2.2. Red/green colour component
Its symbol is a^{*} and it is defined according to the following mathematical function:
(I) 
1.2.3. Yellow/blue colour component
Its symbol is b^{*} and it is defined according to the following mathematical function:
(I) 
1.2.4. Chroma
The chroma symbol is C^{*} and it is defined according to the following mathematical function:

1.2.5. Tone
The tone symbol is H^{*}, its unit is the sexagesimal degree (º), and it is defined according to the following mathematical function:

1.2.6. Difference of tone between two wines
The symbol is ∆H* and it is defined according to the following mathematical function:

(I) See explanation Annex I
1.2.7. Overall colorimetric difference between two wines
The symbol is ∆E* and it is defined according to the following mathematical functions:

1.3. Reagents and products
Distilled water.
1.4. Apparatus and equipment
Customary laboratory apparatus and, in particular, the following:
1.4.1. Spectrophotometer to carry out transmittance measurements at a wavelength of between 300 and 800 nm, with illuminant D65 and observer placed at 10º. Use apparatus with a resolution equal to or higher than 5 nm and, where possible, with scan.
1.4.2. Computer equipment and suitable programme which, when connected to the spectrophotometer, will facilitate calculating colorimetric coordinates (L^{*}, a^{*} and b^{*}) and their derived magnitudes (C^{*} and H^{*}).
1.4.3. Glass cuvettes, available in pairs, optical thickness 1, 2 and 10 mm.
1.4.4. Micropipettes for volumes between 0.020 and 2 ml.
1.5. Sampling and sample preparation
Sample taking must particularly respect all concepts of homogeneity and representativity.
If the wine is dull, it must be clarified by centrifugation. For young or sparkling wines, as much carbon dioxide as possible must be eliminated by vacuum stirring or using a sonicator.
1.6. Procedure
 Select the pair of cuvettes for the spectrophotometric reading, ensuring that the upper measurement limit within the linear range of the spectrophotometer is not exceeded. By way of indication, for white and rosé wines it is recommended to use cuvettes with 10 mm of optical thickness, and for red wines, cuvettes with 1 mm optical thickness.
After obtaining and preparing the sample, measure its transmittance from 380 to 780 nm every 5 nm, using distilled water as a reference in a cuvette with the same optical thickness, in order to establish the base line or the white line. Choose illuminant D65 and observer 10º
If the optical thickness of the reading cuvette is under 10 mm, the transmittance must be transformed to 10 mm before calculating: L^{*}, a^{*}, b^{*}, C^{*} and H^{*}.
Summary:
Spectral measurements in transmittance from 780 to 380 nm 
Interval: 5 nm 
Cuvettes: use appropriately according to wine intensity: 1 cm (white and rosé wines) and 0.1 cm (red wines) 
Illuminant D65 
Observer reference pattern 10º 
1.7. Calculations
The spectrophotometer must be connected to a computer programme to facilitate the calculation of the colorimetric coordinates (L^{*}, a^{*} and b^{*}) and their derived magnitudes (C^{*} and H^{*}), using the appropriate mathematical algorithms.
In the event of a computer programme not being available, see Annex I on how to proceed.
1.8. Expression of results
The colorimetric coordinates of wine will be expressed according to the recommendations in the following table.
Colorimetric coordinates 
Symbol 
Unit 
Interval 
Decimals 
Clarity 
L^{*} 
0100 0 black 100 colourless 
1 

Red/green colour component 
a^{*} 
>0 red <0 green 
2 

Yellow/blue colour component 
b^{*} 
>0 yellow <0 blue 
2 

Chroma 
C^{*} 
2 

Tone 
H^{*} 
º 
0360º 
2 
1.9. Numerical Example
Figure 4 shows the values of the colorimetric coordinates and the chromaticity diagram of a young red wine for the following values:
X = 12.31; Y = 60.03 and Z = 10.24
L* = 29.2
a* = 55.08
b* = 36.10
C* = 66.00
H* = 33.26º
 Accuracy
The above data were obtained from two interlaboratory tests of 8 samples of wine with blind duplicates of progressive chromatic characteristics, in accordance with the recommendations of the harmonized protocol for collaborative studies, with a view to validating the method of analysis.
Colorimetric coordinate L* (clarity, 0100)
Sample Identification 
A 
B 
C 
D 
E 
F 
G 
H 
Year of interlaboratory test 
2004 
2002 
2004 
2004 
2004 
2004 
2002 
2004 
No. of participating laboratories 
18 
21 
18 
18 
17 
18 
23 
18 
No. of laboratories accepted after aberrant value elimination 
14 
16 
16 
16 
14 
17 
21 
16 
Mean value () 
96.8 
98.0 
91.6 
86.0 
77.4 
67.0 
34.6 
17.6 
Repeatability standard deviation (s_{r}) 
0.2 
0.1 
0.2 
0.8 
0.2 
0.9 
0.1 
0.2 
Relative repeatability standard deviation (RSD_{r}) (%) 
0.2 
0.1 
0.3 
1.0 
0.3 
1.3 
0.2 
1.2 
Repeatability limit (r) (2.8 x s_{r}) 
0.5 
0.2 
0.7 
2.2 
0.7 
2.5 
0.2 
0.6 
Reproducibility standard deviation (s_{R}) 
0.6 
0.1 
1.2 
2.0 
0.8 
4.1 
1.0 
1.0 
Relative reproducibility standard deviation (RSD_{R}) (%) 
0.6 
0.1 
1.3 
2.3 
1.0 
6.1 
2.9 
5.6 
Reproducibility limit (R) (2.8 x s_{R}) 
1.7 
0.4 
3.3 
5.5 
2.2 
11.5 
2.8 
2.8 
Colorimetric coordinate a* (green/red)
Sample Identification 
A 
B 
C 
D 
E 
F 
G 
H 
Year of interlaboratory 
2004 
2002 
2004 
2004 
2004 
2004 
2002 
2004 
No. of participating laboratories 
18 
21 
18 
18 
17 
18 
23 
18 
No. of laboratories accepted after aberrant value elimination 
15 
15 
14 
15 
13 
16 
23 
17 
Mean value () 
0.26 
0.86 
2.99 
11.11 
20.51 
29.29 
52.13 
47.55 
Repeatability standard deviation (s_{r}) 
0.17 
0.01 
0.04 
0.22 
0.25 
0.26 
0.10 
0.53 
Relative repeatability standard deviation (RSD_{r}) (%) 
66.3 
1.4 
1.3 
2.0 
1.2 
0.9 
0.2 
1.1 
Repeatability limit (r) (2.8 x s_{r}) 
0.49 
0.03 
0.11 
0.61 
0.71 
0.72 
0.29 
1.49 
Reproducibility standard deviation (s_{R}) 
0.30 
0.06 
0.28 
0.52 
0.45 
0.98 
0.88 
1.20 
Relative reproducibility standard deviation (RSD_{R}) (%) 
116.0 
7.5 
9.4 
4.7 
2.2 
3.4 
1.7 
2.5 
Reproducibility limit (R) (2.8 x s_{R}) 
0.85 
0.18 
0.79 
1.45 
1.27 
2.75 
2.47 
3.37 
Colorimetric coordinate b* (blue/yellow)
Sample Identification 
A 
B 
C 
D 
E 
F 
G 
H 
Year of interlaboratory 
2004 
2002 
2004 
2004 
2004 
2004 
2002 
2004 
No. of participating laboratories 
17 
21 
17 
17 
17 
18 
23 
18 
No. of laboratories accepted after aberrant value elimination 
15 
16 
13 
14 
16 
18 
23 
15 
Mean value () 
10.95 
9.04 
17.75 
17.10 
19.68 
26.51 
45.82 
30.07 
Repeatability standard deviation (s_{r}) 
0.25 
0.03 
0.08 
1.08 
0.76 
0.65 
0.15 
0.36 
Relative repeatability standard deviation (RSD_{r}) (%) 
2.3 
0.4 
0.4 
6.3 
3.8 
2.5 
0.3 
1.2 
Repeatability limit (r) (2.8 x s_{r}) 
0.71 
0.09 
0.21 
3.02 
2.12 
1.83 
0.42 
1.01 
Reproducibility standard deviation (s_{R}) 
0.79 
0.19 
0.53 
1.18 
3.34 
2.40 
1.44 
1.56 
Relative reproducibility standard deviation (RSD_{R}) (%) 
7.2 
2.1 
3.0 
6.9 
16.9 
9.1 
3.1 
5.2 
Reproducibility limit (R) (2.8 x s_{R}) 
2.22 
0.53 
1.47 
3.31 
9.34 
6.72 
4.03 
4.38 
Bibliography
 Vocabulaire International de l'Éclairage. Publication CIE 17.4. Publication I.E.C. 50(845). CEI(1987). Genève. Suisse.
 Colorimetry, 2^{nd} Ed. Publication CIE 15.2 (1986) Vienna.
 Colorimetry, 2^{nd} Ed. Publication CIE 15.2 (1986) Vienna.
 Kowaliski P. – Vision et mesure de la couleur. Masson ed. Paris 1990
 Wiszecki G. And W.S.Stiles, Color Science, Concepts and Methods, Quantitative Data and Formulae, 2^{nd} Ed. Wiley, New York 1982
 Sève R. . Physique de la couleur. Masson. Paris (1996)
 Echávarri J.F., Ayala F. et Negueruela A.I. .Influence du pas de mesure dans le calcul des coordonnées de couleur du vin. Bulletin de l'OIV 831832, 370378 (2000)
 I.R.A.N.O.R . Magnitudes Colorimetricas. Norma UNE 7203183
 Bertrand A. Mesure de la couleur. F.V. 1014 2311/190196
 Fernández, J.I.; Carcelén, J.C.; Martínez, A. III Congreso Nacional De Enologos, 1.997. Caracteristicas cromaticas de vinos rosados y tintos de la cosecha de 1996 en la region de murcia
 Cagnaso E.. Metodi Oggettivi per la definizione del colore del vino. Quaderni della Scuoladi Specializzazione in Scienze Viticole ed Enologiche. Universidad di Torino. 1997
 Ortega A.P., Garcia M.E., Hidalgo J., Tienda P., Serrano J. – 1995 Identificacion y Normalizacion de los colores del vino. Carta de colores. Atti XXI Congreso Mundial de la Viña y el Vino, Punta del Este. ROU 378391
 Iñiguez M., Rosales A., Ayala R., Puras P., Ortega A.P. 1995  La cata de color y los parametros CIELab, caso de los vinos tintos de Rioja. Atti XXI Congreso Mundial de la Viña y el Vino, Punta del Este.ROU 392411
 Billmeyer, F.W. jr. and M. Saltzman: Principles of Color. Technology, 2. Auflage, New York; J. Wiley and Sons, 1981.
Appendix 1
In formal terms, the trichromatic components X, Y, Z of a colour stimulus result from the integration, throughout the visible range of the spectrum, of the functions
obtained by multiplying the relative spectral curve of the colour stimulus by the colorimetric functions of the reference observer. These functions are always obtained by experiment. It is not possible, therefore to calculate the trichromatic components directly by integration. Consequently, the approximate values are determined by replacing these integrals by summations on finished wavelength intervals.

T _{(}λ_{) }is the measurement of the transmittance of the wine measured at the wavelength λ expressed at 1 cm from the optical thickness. 

_{(}_{}_{) }is the interval between the value of λ at which T _{(}λ)_{}is measured 

S _{(}λ_{)}: coefficients that are a function of λ and of the illuminant (Table 1). 

: coefficients that are a function of and of the observer. (Table 1) 
The values of Xn, Yn, and Zn represent the values of the perfect diffuser under an illuminant and a given reference observer. In this case, the illuminant is D65 and the observer is higher than 4 degrees.
= 94.825; = 100; = 107.381
This roughly uniform space is derived from the space CIEYxy, in which the trichromatic components X, Y, Z are defined.
The coordinates L*, a*^{}and b*^{}are calculated based on the values of the trichromatic components X, Y, Z, using the following formulae.
L* = 116 (Y / Y_{n})^{1/3} 16 
where Y/Yn > 0.008856 

L* = 903.3 (Y / Y_{n}) 
where Y / Y_{n} < ó = 0.008856 

a* = 500 [ f(X / ) f(Y / Y_{n}) 

b* = 200 [f(Y / Y_{n}) f(Z / Z_{n}) 

f(X / X_{n}) = (X / )^{1/3} 
where (X / X_{n}) > 0.008856 

f(X / X_{n}) = 7.787 (X / X_{n}) + 16 / 166 
where (X / X_{n}) < ó = 0.008856 

f(Y / Y_{n}) = (Y / Y_{n})^{1/3} 
where (Y / Y_{n}) > 0.008856 

f(Y / Y_{n}) = 7.787 (Y / Y_{n}) + 16 / 116 
where (Y / Y_{n}) < ó = 0.008856 

f(Z / Z_{n}) = (Z / Z_{n})^{1/3} 
where (Z / Z_{n}) > 0.008856 

f(Z / Z_{n}) = 7.787 (Z / Z_{n}) + 16 / 116 
where (Z / Z_{n}) < ó = 0.008856 

The total colorimetric difference between two colours is given by the CIELAB colour difference

In the CIELAB space it is possible to express not only overall variations in colour, but also in relation to one or more of the parameters L*, a* and b*. This can be used to define new parameters and to relate them to the attributes of the visual sensation.
Clarity, related to luminosity, is directly represented by the value of L*.
Chroma: defines the chromaticness.
The angle of hue: H* = tg^{1 }(b*/a*) (expressed in degrees); related to hue.
The difference in hue:
For two unspecified colours, C* represents their difference in chroma; L*, their difference in clarity, and E*, their overall variation in colour. We thus have:
Table 1.
Wavelength (λ) nm. 





380 
50.0 
0.0002 
0.0000 
0.0007 

385 
52.3 
0.0007 
0.0001 
0.0029 

390 
54.6 
0.0024 
0.0003 
0.0105 

395 
68.7 
0.0072 
0.0008 
0.0323 

400 
82.8 
0.0191 
0.0020 
0.0860 

405 
87.1 
0.0434 
0.0045 
0.1971 

410 
91.5 
0.0847 
0.0088 
0.3894 

415 
92.5 
0.1406 
0.0145 
0.6568 

420 
93.4 
0.2045 
0.0214 
0.9725 

425 
90.1 
0.2647 
0.0295 
1.2825 

430 
86.7 
0.3147 
0.0387 
1.5535 

435 
95.8 
0.3577 
0.0496 
1.7985 

440 
104.9 
0.3837 
0.0621 
1.9673 

445 
110.9 
0.3867 
0.0747 
2.0273 

450 
117.0 
0.3707 
0.0895 
1.9948 

455 
117.4 
0.3430 
0.1063 
1.9007 

460 
117.8 
0.3023 
0.1282 
1.7454 

465 
116.3 
0.2541 
0.1528 
1.5549 

470 
114.9 
0.1956 
0.1852 
1.3176 

475 
115.4 
0.1323 
0.2199 
1.0302 

480 
115.9 
0.0805 
0.2536 
0.7721 

485 
112.4 
0.0411 
0.2977 
0.5701 

490 
108.8 
0.0162 
0.3391 
0.4153 

495 
109.1 
0.0051 
0.3954 
0.3024 

500 
109.4 
0.0038 
0.4608 
0.2185 

505 
108.6 
0.0154 
0.5314 
0.1592 

510 
107.8 
0.0375 
0.6067 
0.1120 

515 
106.3 
0.0714 
0.6857 
0.0822 

520 
104.8 
0.1177 
0.7618 
0.0607 

525 
106.2 
0.1730 
0.8233 
0.0431 

530 
107.7 
0.2365 
0.8752 
0.0305 

535 
106.0 
0.3042 
0.9238 
0.0206 

540 
104.4 
0.3768 
0.9620 
0.0137 

545 
104.2 
0.4516 
0.9822 
0.0079 

550 
104.0 
0.5298 
0.9918 
0.0040 

555 
102.0 
0.6161 
0.9991 
0.0011 

560 
100.0 
0.7052 
0.9973 
0.0000 

565 
98.2 
0.7938 
0.9824 
0.0000 

570 
96.3 
0.8787 
0.9556 
0.0000 

575 
96.1 
0.9512 
0.9152 
0.0000 

580 
95.8 
1.0142 
0.8689 
0.0000 

585 
92.2 
1.0743 
0.8256 
0.0000 

590 
88.7 
1.1185 
0.7774 
0.0000 

595 
89.3 
1.1343 
0.7204 
0.0000 

600 
90.0 
1.1240 
0.6583 
0.0000 

605 
89.8 
1.0891 
0.5939 
0.0000 

610 
89.6 
1.0305 
0.5280 
0.0000 

615 
88.6 
0.9507 
0.4618 
0.0000 

620 
87.7 
0.8563 
0.3981 
0.0000 

625 
85.5 
0.7549 
0.3396 
0.0000 

630 
83.3 
0.6475 
0.2835 
0.0000 

635 
83.5 
0.5351 
0.2283 
0.0000 

640 
83.7 
0.4316 
0.1798 
0.0000 

645 
81.9 
0.3437 
0.1402 
0.0000 

650 
80.0 
0.2683 
0.1076 
0.0000 

655 
80.1 
0.2043 
0.0812 
0.0000 

660 
80.2 
0.1526 
0.0603 
0.0000 

665 
81.2 
0.1122 
0.0441 
0.0000 

670 
82.3 
0.0813 
0.0318 
0.0000 

675 
80.3 
0.0579 
0.0226 
0.0000 

680 
78.3 
0.0409 
0.0159 
0.0000 

685 
74.0 
0.0286 
0.0111 
0.0000 

690 
69.7 
0.0199 
0.0077 
0.0000 

695 
70.7 
0.0138 
0.0054 
0.0000 

700 
71.6 
0.0096 
0.0037 
0.0000 

705 
73.0 
0.0066 
0.0026 
0.0000 

710 
74.3 
0.0046 
0.0018 
0.0000 

715 
68.0 
0.0031 
0.0012 
0.0000 

720 
61.6 
0.0022 
0.0008 
0.0000 

725 
65.7 
0.0015 
0.0006 
0.0000 

730 
69.9 
0.0010 
0.0004 
0.0000 

735 
72.5 
0.0007 
0.0003 
0.0000 

740 
75.1 
0.0005 
0.0002 
0.0000 

745 
69.3 
0.0004 
0.0001 
0.0000 

750 
63.6 
0.0003 
0.0001 
0.0000 

755 
55.0 
0.0002 
0.0001 
0.0000 

760 
46.4 
0.0001 
0.0000 
0.0000 

765 
56.6 
0.0001 
0.0000 
0.0000 

770 
66.8 
0.0001 
0.0000 
0.0000 

775 
65.1 
0.0000 
0.0000 
0.0000 

780 
63.4 
0.0000 
0.0000 
0.0000 


Figure 1. Diagram of colourimetric coordinates according to Commission Internationale de l’Eclairage (CIE, 1976) 

Figure 2. CIELab colourspace, based on a sequential or 3 orthogonal axis continual Cartesian representation L*, a* y b* 

Figure 3. Sequential diagram and/or continuation of a and b colourimetric coordinates and derived magnitude, such as tone (H*) 

Figure 4. Representation of colour of young red wine used as an example in Chapter 1.8 shown in the CIELab three dimensional diagram. 