La predicción del calibre del corcho al final del turno y su aplicación al muestreo de la producción

105 cork samples (20 cm x 20 cm) have been extracted from seven sites selected as representatives of the main cork oak production areas in Spain. Age, thickness and annual growth of cork have been measured on the transversal section of each piece. Thickness of cork one, two and three years before stripping has been calculated. Lineal regression analysis has been performed to obtain predicting equations for thickness at debarking time, where independent variables were thickness one, two or three years before stripping and growth rate at each moment. A set of equations was obtained, and regression coefficients varied between 0.9918 (the year before stripping) and 0.9182 (three years before stripping). Due to the sampling method, it is considered that these equations can be applied all over the cork oak distribution area in Spain. Best results can be obtained using the following equation: EF = 0.70021 + 1.05232 * Et–1 (EF: final cork thickness; Et–1: cork thickness one year before stripping) The results allow some changes in the current sampling methods, designed for owners assessment, as sampling in the field can be done the year before stripping. Due to the role of thickness in grading of cork planks, more 75 % of the production is not affected by these estimations, when thickness one year before stripping is used.Se ha tomado una muestra de 105 piezas de corcho en plancha de 20 por 20 cm de tamaño, procedentes de siete puntos de muestreo localizados en montes que se consideran representativos de las principales zonas españolas de producción de corcho. Sobre la sección transversal de cada pieza se ha determinado la edad, y se han medido el espesor, o calibre, y los crecimientos anuales para cada uno de los años del turno, calculándose para cada pieza el espesor y crecimiento medio anual que presentaban uno, dos y tres años antes del descorche. Se realiza un análisis de regresión lineal paso a paso para ajustar las ecuaciones predictivas del espesor del corcho al final del turno, en función del espesor y el crecimiento medio anual uno, dos y tres años antes del descorche. Como resultado se obtiene una serie de ecuaciones en las que los coeficientes de determinación oscilan entre 0,9918 (un año antes del descorche) y 0,9182 (tres años antes del descorche). Debido a la amplitud del muestreo realizado y a la calidad de los ajustes, se considera que estas ecuaciones pueden ser aplicadas en cualquier punto del área española de producción de alcornocal. Los mejores resultados se obtienen con la ecuación: EF = 0,70021 + 1,05232 * Et–1 (EF: espesor final del corcho; Et–1: espesor el año anterior al descorche) Las ecuaciones obtenidas permiten modificar los actuales métodos de muestreo para asesoramiento de los propietarios, al posibilitar la toma de muestras uno, dos o tres años antes de la saca del corcho. Debido al papel que el espesor, tiene en el proceso de clasificación, se estima que un 75 % de la producción no estaría afectada por los errores que se puedan cometer en la estimación si se utilizan las ecuaciones basadas en el espesor el año antes del descorche

Discriminant Analysis of Geographical Origin of Cork Planks and Stoppers by Near Infrared Spectroscopy

The objective of this study was to assess the potential of visible and near infrared spectroscopy (VIS+NIRS) combined with multivariate analysis for identifying the geographical origin of cork. The study was carried out on cork planks and natural cork stoppers from the most representative cork-producing areas in the world. Two training sets of international and national cork planks were studied. The first set comprised a total of 479 samples from Morocco, Portugal, and Spain, while the second set comprised a total of 179 samples from the Spanish regions of Andalusia, Catalonia, and Extremadura. A training set of 90 cork stoppers from Andalusia and Catalonia was also studied. Original spectroscopic data were obtained for the transverse sections of the cork planks and for the body and top of the cork stoppers by means of a 6500 Foss-NIRSystems SY II spectrophotometer using a fiber optic probe. Remote reflectance was employed in the wavelength range of 400 to 2500 nm. After analyzing the spectroscopic data, discriminant models were obtained by means of partial least square (PLS) with 70% of the samples. The best models were then validated using 30% of the remaining samples. At least 98% of the international cork plank samples and 95% of the national samples were correctly classified in the calibration and validation stage. The best model for the cork stoppers was obtained for the top of the stoppers, with at least 90% of the samples being correctly classified. The results demonstrate the potential of VIS + NIRS technology as a rapid and accurate method for predicting the geographical origin of cork plank and stopper

Classification of defects in cork planks using image analysis

Image analysis techniques were used on cork surfaces of transverse sections of planks and multivariate analysis was applied to differentiate pores (lenticular channels) from important defects such as nail (horizontal and vertical) and insect galeries. The discriminant analysis showed that the variables area, perimeter, specific length and width, diameters in the radial and in the tangential direction, as well as the optical density could be combined in three discriminant functions that could make the classification. Defect specific classification functions gave good results for the automatic classification of pores, insect galeries and horizontal nail (error <10%), and acceptable for vertical nail (20% error). © 1996 Springer-Verlag

Quality grading of cork stoppers based on porosity, density and elasticity

An objective control method for grading cork stoppers is presented using a cork stopper quality index based on porosity, density and elasticity, these being the properties which have the greatest influence on the closure capacity of the stopper. The elasticity of the cork stopper is measured through the relaxation ratio, which is defined by the relationship between the relaxation force exerted by the cork in the bottleneck and the compressive force exerted by a caliper to fit the stopper in the bottle. The relaxation ratio, defined in this way, represents the part of the compression force which is applied to the stopper on insertion and which is recovered in the form of the relaxation force to achieve closure. The calculation of the relaxation ratio involves the measurement of the relaxation force of the fitted stopper. This force has been measured rigorously and precisely using a device developed in the Cork Laboratory at the INIA-CIFOR and which is presented for the first time in this paper. © 2013 Springer-Verlag Berlin Heidelberg

Application of VIS/NIR spectroscopy for estimating chemical, physical and mechanical properties of cork stoppers

The aim of this study was to evaluate the potential of visible and near infrared spectroscopy (Vis/NIRS) in predicting the chemical, physical and mechanical behavior of single-piece natural corks stoppers used for sealing wine bottles. Two training sets of 90 and 150 cork stoppers were used to obtain four spectra per sample in different positions two of the stopper bases (transversal section) and two of the stopper sides (tangential section and radial section). The samples were scanned in the range of 400-2,500 nm using a Foss-NIRSystems 6500 SY II spectrophotometer equipped with a remote reflectance fiber-optic probe. On each training set, two-thirds of the samples were used to develop modified partial least square (MPLS) calibration equations, and the remaining one-third of the sample for the external validation of these MPLS equations. The best equations were obtained for the transversal section, which is the recommended one when applying Vis/NIRS technology to cork. The best results for the chemical composition were obtained for waxes and total polyphenols, showing coefficient of determination of the cross validation (r cv 2) values of 0.64 and 0.56 and coefficient of determination of the external validation (r EV 2) values of 0.53 and 0.55, respectively. The best equation for the physical and mechanical parameters was obtained for moisture content (r cv 2 = 0.86 and r EV 2 = 0.85), with somewhat lower results for density, compression force and extraction force (r cv 2 = 0.66, 0.72, 0.52 and r EV 2 = 0.52, 0.49, 0.51, respectively). The SECV (standard error of cross validation) and SEP (standard error of external validation) were similar for all the physical and mechanical parameters, thus confirming the robustness of the equations. MPLS model for moisture content fulfills the requirements for screening (RPD &gt;2.5), but MPLS models obtained for waxes, total polyphenols, density, compression force and extraction force are not good enough for routine analysis or quality control. The results obtained from the MPLS models based on Vis/NIRS technology would permit the continuous quality control of humidity in the production line as well as obtaining information about certain chemical components (extractives contents) and some physical and mechanical parameters (density, extraction force and compression force). © 2014 Springer-Verlag Berlin Heidelberg

Chemical characterization of reproduction cork from Spanish Quercus suber

The chemical composition of Quercus suber reproduction cork was studied in planks from three different trees at different stages of their industrial processing and in samples collected in seven locations in the three main Spanish production areas. Extracts in chloroform, methanol and water, neùtral and acid fractions of waxes, suberin, lignin, holocellulose and pentosans, and polyphenols (low molecular weight polyphenols and tannins), were quantified. Suberin was the main component in all the samples, followed by lignin and holocellulose in lower concentrations. The most affected variables throughout the industrial processing were lignin, chloroform and water extracts and the acid fraction of waxes. These variables did not allow one to distinguish the studied trees, which are differentiated by the percentages of methanol extracts, the tannic fraction of polyphenols, the free of suberin residue and the holocellulose content. Four variables were selected as those which provided the greatest discrimination among provenances methanol extract, low molecular weight polyphenols, desuberinized residue and acid fraction of waxes. However, the studied populations can not be clearly distinguished by their chemical composition and no relationship was found between geographical proximity of their provenances and chemical resemblance

Characterization of surface treatments of cork stoppers by FTIR-ATR

A general method is described for the identification of paraffin- and silicone-based surface treatments applied to single-piece natural and 1 + 1 (cork agglomerate with two natural cork disks) cork stoppers used to seal wine bottles. The method is based on Fourier transformed infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) analysis of ready-for-use stoppers. The absorbance in seven wavelength bands selected as the most characteristic (2916 and 2850 cm-1, for paraffins, and 2963, 1258, 1079, 1010, and 787 cm-1, for silicones) was measured for both kinds of stoppers. Univariate analysis of the results enabled identification of stoppers that had received surface treatment by measuring the absorbance in two of the selected bands, representing paraffins and silicones, respectively. The type of surface treatment used was identified by discriminant analysis. Using this technique, we constructed a mathematical model using the seven bands studied. The model correctly classified 100% of the stoppers used to construct it and 91.7% of the stoppers used for validation. © 2006 American Chemical Society