Application Note Determination of wine colour with UV-VIS Spectroscopy following Sudraud method IN VINO VERITAS. A very famous Latin R1 phrase becomes reality in case you prove the colour of the wine. R2 Wine is more or less natural product having all substances inside like sugars, wine acids and alcohol. Depending on the earth where it R3 was grown trace elements have their 0 influence. Other elements like potassium (K) R7 in combination with the graves will have influences on the colour. Colour can be white and red or different depending on theoretical R4 classification and practical subjective identification of human eyes. High K R6 concentration is combined with the red wine R5 because it exists an equilibrium between K, Fig. 2: Flavene is the base of the anthocyan structure, R1 to tartaric acid and the anthocyan pigments R7 represent organic groups which will generate the complex, which is responsible for the red difference among the anthocyanes colour. Wine Colour Determination [2] The definition of Wine Colour allows us to run analysis of absorption spectra of wine samples. Physically, the colour is a light characteristic, measurable in terms of intensity and wavelength. The human eye can reveal a substance as coloured due to two reasons: • absorption of all of radiation of the visible spectra and non-absorption of the colour under analysis; Fig. 1: Equilibrium between Anthocyan color and tartaric acid, • absorption of the complementary of K+ = Potassium, H2T = Tartaric acid, T= and HT- = tartaric the colour under test. acid salts [1] In the case of grapes and wine, we can approximately say they are RED, because The anthocyane is a natural colour which is the anthocyan pigments are absorbing in the found in plants like in leaves or in fruits like GREEN portion of the visible spectra, giving the grapes. From these anthocyan complexes to human eye the sensation of colour RED. are about 250 different structures known. They have partly in common the structure (Fig. 2) of the flaven molecule which will be substituted at 7 possible positions from simple -OH to complex sugar molecules. SCA_100_002 www.shimadzu.de The colour of wine can be defined by three Sudraud Method terms as follows: I = A420 + A520 1. Intensity or luminosity: related to the And “amount” of colour; T = A420 / A520 2. Tone or chromaticity: representing the wine colour shading off; We can observe the A520 becoming smaller 3. Brightness or purity: related to the as much as old the wine is. clearness. The tone is also varying and is below 1 for For better understanding the Wine Colour young wines, and greater than 1 when old; in analysis, have a look on one spectrum of it. particular, for red wines the colour is The methods to give results of chromatic changing from ruby red up to orange red. characteristics of wine are: T value can give some indication about the • tristimolous method: based on X, Y, Z age of wine, and if this is knew, on values, showing the RED, GREEN and preservation condition and if possible to be BLUE content to define colour aged again. (according to CIE); • Sudraud method: defining the Intensity I as the sum of absorbance measured at 420nm and 520nm and the Tone T as the ratio of a.m. absorbance, on a 1cm cell. Fig. 5: Result of Sudraud method in a UVProbe software table, sample see fig. 3. These values can be also used for determining the final colour of a red wine, especially when I is too weak (winery at high latitudes receiving few rays of sun). In fact, wines from southern countries are sometimes used for mixing (technically “cutting”) the same of the north. (This is possible when there’s no requirement of origin certification - DOC, DOCG, AOC, etc. - .) I has the property to be added to same value of another wine, Fig. 3: This is the absorption spectrum of a red Italian table so it’s easy to find the percentages. wine “colore rosso rubino” 10% Volume measured with UV- 1700. Literature: [1] Bruce Zoecklein, A review of potassium user. the for information technical as purely serve specifications The given Absorption spectra of three red wines bitartrate stabilization of wine, Publication No guarantee is given on technical specification of the described product and/or procedures. procedures. and/or product described the of specification on technical given is guarantee No 0.8 I-one year old 463-013, 1988, Virginia Cooperative II-10 years old 0.7 Extension Service ] III-50 years old D [ Notice the shift in [2] Emanuele Canu. Shimadzu Italy Milano, 0.6 y t i wavelength through aging. s II Wine Colour analysis, Shimadzu internal n 0.5 e d document l 0.4 a III c i t [3] Sudraud P., Ann. Tech. Agri. 7 (1958) 203 p 0.3 I o 0.2 Instrument: 0.1 UV-1700 and 1 cm liquid cell 350 400 450 500 550 600 wavelength [nm] Fig. 4: This is a wine and its variation while aging or oxidising [3]. Shimadzu Europa GmbH www.shimadzu.de Albert-Hahn-Str.6-10, 47269 Duisburg .