Electrochimica Acta 55 (2010) 6782–6788 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Application of an electronic tongue to study the effect of the use of pieces of wood and micro-oxygenation in the aging of red wine M. Gay a , C. Apetrei b , I. Nevares c , M. del Alamo d , J. Zurro e , N. Prieto f , J.A. De Saja f , M.L. Rodríguez-Méndez a,∗ a Department of Inorganic Chemistry, E.T.S. Ingenieros Industriales, University of Valladolid, Paseo del Cauce s/n, 47011 Valladolid, Spain b Department of Chemistry, Faculty of Sciences, European Excellence Research Centre for Environmental Problems, “Dun˘ area de Jos” University of Galati, Romania c Department of Agricultural Engineering, E.T.S.I.A., University of Valladolid, Spain d Department of Analytical Chemistry, E.T.S.I.A., University of Valladolid, Spain e Infirmary School Palencia, University of Valladolid, Spain f Department of Condensed Matter Physics, Faculty of Sciences, University of Valladolid, Spain article info Article history: Received 24 March 2010 Received in revised form 24 May 2010 Accepted 29 May 2010 Available online 8 June 2010 Keywords: Electronic tongue Wine Polyphenol Chips Phthalocyanine abstract The ageing of red wines matured in oak barrels and wines treated soaking pieces of wood of different sizes (chips or staves) in micro-oxygenated stainless steel tanks has been monitored periodically using an electronic tongue, chemical analysis and a panel of experts. The use of micro-oxygenation in stainless steel tanks, lets get wines with characteristics similar to wines aged in oak barrels. However, differences in the phenolic content and in particular in the anthocyanin levels are observed during the first steps of ageing and in the final product. In the early stages of ageing, Principal Component Analysis (PCA) and Partial Least Squares Discrimi- nant Analysis (PLS-DA) calculated from the electronic tongue outputs have permitted the discrimination between wines aged with traditional and alternative methods due to the faster rate of ageing caused by chips or staves. After 5 months of ageing, the use of alternative ageing methods cannot be longer detected. However, when the ageing continues in a reducing atmosphere (bottled wines), the electronic tongue has demonstrated a good capability to discriminate and classify bottled wines previously aged in oak barrels from those previously treated with oak chips and oak staves. The effect of the size of the pieces and of the type of wood can also be detected by the e-tongue. Using Partial Least Squares (PLS-1) good correlations have been found between the electrochemical signals provided by the array of sensors and the polyphenolic content parameters. Good correlations have also been established with the scores given by the panel of experts, in particular with the astringency. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Recently, alternative ageing methods have been developed that can simplify the traditional maturing of wines in oak barrels [1]. One of these techniques consists in adding small oak wood pieces (chips or staves) to wines kept in stainless steel tanks. A gentle oxidation of tanks is necessary to simulate the micro-oxydation that occurs in barrels due to the diffusion of oxygen trough the barrel pores [2–4]. The oxygen dissolved, promotes the oxidation of certain chemical compounds, resulting in wines with a high degree of similarity with wines aged in oak barrels. For this reason, there is a need to develop methods able to detect the use of such alternative ageing methods. The phenolic composition of wines is strongly influenced by the experimental conditions of the ageing. It is well known that the final ∗ Corresponding author. Tel.: +34 983 423540; fax: +34 983 423310. E-mail address: mluz@eis.uva.es (M.L. Rodríguez-Méndez). chemical and organoleptic characteristics of wines depend on the type of wood used (origin, drying and toasting of the wood), con- tact time with wine, temperature etc. In the case of treatment with pieces of wood additional parameters such as the size or the con- ditions of the micro-oxygenation have also an important influence in the phenolic spectrum of the final product [5–9]. For this reason, the phenolic composition can help to characterise and detect wine ageing styles. A promising approach to analyse wines consists in the use of electronic tongues [10–18]. Such systems are formed by an array of sensors where several sensing units, which exhibit different responses to various compounds, are coupled with signal pro- cessing methods based on pattern recognition or artificial neural networks. Our group has developed an electronic tongue dedicated to the analysis of red wines. It consists in an array of voltampero- metric sensors chemically modified with electroactive substances (phthalocyanines and perylenes). These materials are sensitive to 0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2010.05.090