Analytica Chimica Acta 563 (2006) 229–237 Monitoring of the ageing of red wines in oak barrels by means of an hybrid electronic tongue Vicente Parra a , ´ Alvaro A. Arrieta a , Jos´ e A. Fern´ andez-Escudero b , Montserrat ´ I˜ niguez c , Jos´ e Antonio de Saja d , Mar´ ıa Luz Rodr´ ıguez-M´ endez a,∗ a Department Qu´ ımica F´ ısica y Qu´ ımica Inorg´ anica, University of Valladolid, E.T.S. Ingenieros Industriales, Paseo del Cauce s/n, 47011 Valladolid, Spain b Estaci´ on Enol ´ ogica de Castilla y Le ´ on, Rueda, Valladolid, Spain c Estaci´ on Enol ´ ogica de La Rioja, Haro, Logro˜ no, Spain d Department F´ ısica de la Materia Condensada, Facultad de Ciencias, University of Valladolid, Spain Received 28 July 2005; received in revised form 21 September 2005; accepted 22 September 2005 Available online 17 October 2005 Abstract A novel hybrid sensor array based on voltammetric electrodes has been successfully applied to monitor the ageing of red wines and to discriminate wine samples aged in oak barrels of different characteristics (wood origin and the toasting level). The hybrid sensor array is formed by three families of chemically modified electrodes, including polypyrrole sensors doped with a range of counterions, carbon paste electrodes modified with metallophthalocyanine complexes and finally, carbon paste electrodes modified with perylene imide derivatives. The diversity of the sensing materials has allowed obtaining a high cross-selectivity in the responses of the sensors forming the array. This voltammetric signals provided by the sensors have been used as data source for a principal component analysis (PCA) and soft independent modelling of class analogy (SIMCA) to confirm the high capability of discrimination and classification of the e-tongue. The array of voltammetric sensors has been able to follow the changes experienced by red wines aged in oak barrels after 3 and 6 months of ageing. In addition, the differences caused by oak barrels of different origins (French, Lithuanian and American) and toasting levels have also been discriminated. © 2005 Elsevier B.V. All rights reserved. Keywords: Electronic tongue; Sensor array; Carbon paste electrode; Polypyrrole; Phthalocyanine; Perylene; Wine; Oak barrel 1. Introduction It is well known that a red wine is a complex medium contain- ing a huge quantity of substances able to undergo a large number of changes throughout the oxidative ageing in oak wood. The physicochemical processes occurring during the ageing in bar- rels are directly responsible of most of the final organoleptic characteristics of the wines such as the colour [1]. In addition, a more complex aroma is attained due to extractions of volatile compounds from the wood matrix [2–4], and simultaneously the wine develops most of its sensory and palatable virtues [5–7]. Among the different factors affecting the maturation of red wines in oak barrels, the geographical origin of the wood is ∗ Corresponding author. Tel.: +34 983 423540/686 698080; fax: +34 983 423310. E-mail address: mluz@eis.uva.es (M.L. Rodr´ ıguez-M´ endez). of special importance since it is decisive for the structure and chemical composition of the wine [8,9]. Furthermore, issues like the toasting level [10] or the duration of the ageing [11] in the oak barrel also influence the composition and quality of wines. The majority of the works devoted to the study of the influ- ence of the oak wood in the chemical and sensory character- istics of wines are related to the analysis of particular families of compounds such as biogenic amines [12], monosaccharides [13], phenolic derivatives [8,14,15], etc., which are supposed to exhibit specific effects in the organoleptic characteristics of the red wines. Despite the usefulness of these analyses, they do not consider the global nature, harmony and chemical macro- equilibrium characteristic of wines. Besides, they usually are expensive and require long sample pre-treatments. Recently, a different approach for the evaluation and classi- fication of complex liquids has been proposed: the so-called “electronic tongues”. Such systems consist in the combina- tion of an array of sensors with pattern recognition software. 0003-2670/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2005.09.044