Corkage: Infrared clues

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  • Published: Nov 15, 2014
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Corkage: Infrared clues

Spanish wine uncorked

Application of VIS/NIR spectroscopy for estimating chemical, physical and mechanical properties of cork stoppers (Credit: David Bradley)

Researchers in Spain have demonstrated how infrared spectroscopy can be used to enhance the control of parameters that determine the performance of a wine cork in the bottle.

Cristina Prades, Isabel Gómez-Sánchez, Juan García-Olmo, Florentino González-Hernández, José Ramón González-Adrados, researchers at the Universidad Politécnica de Madrid, INIA-CIFRO and the Universidad de Córdoba, Spain, have been evaluating whether or not visible and near infrared spectroscopy (Vis/NIRS) would be useful tools for determining the future chemical, physical and mechanical behaviour of wine corks. Writing in the journal Wood Science and Technology they explain how they used two training sets of 90 and 150 wine corks 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). They then used the spectral data to obtain calibration equations that allow them to predict the properties of the corks quicker than is possible using conventional analytical methods.

Billions upon billions...

Cork is the main non-timber forest product in the Mediterranean region and has been used to stopper wine bottles for centuries. This tradition underpins the conservation of thousands of hectares of cork oak in southern European and Maghreb countries, sustaining the itinerant eco-systems and environmental conditions of those regions. Many wine connoisseurs prefer their bottles to have natural cork stoppers, but modern market pressures have led to the plastic wine "cork" being used by bottling plants more frequently in the last decade or so. The plastic cork offers homogeneity and consistency of product and precludes the possibility of the wine becoming "corked".

However, the romance of a natural cork is lost with plastics and so winemakers and wineries hoping to maintain and offer a traditional and perhaps better-received product live in hope of the emergence of tools to ensure greater consistency of cork stoppers. Sustainability and technical drawbacks associated with synthetics (such as premature oxidation and the absorption and transfer of aromas or strange flavours to wine) are helping natural corks to maintain their leadership.

Cork is a tissue (phellem) comprising the bark of the cork oak tree, Quercus suber L. As an entirely naturally sourced product, there is variability from cone batch to the next because of the different conditions in which the trees grow, the nutrients they absorb and the year on year weather conditions. Today, wine corks are already subjected to a wide range of control processes including physical, chemical, microbiological and organoleptic parameters and classification by image analysis and traceability. These various tests are expensive and technical skills are required that are also costly to the producers. Given that some 12 billion corks are produced each year, there is a growing need to automate the quality control processes.

...of corks

The team has now demonstrated that Fourier transform infrared spectroscopy (FTIR-NIR) can be used to easily determine the composition and the dosage of surface treatments applied to a wine cork, given that corks might be treated with paraffin and/or silicone before use in order to improve their surface properties, specifically their coefficient of friction (for grip and ease of opening) and capillarity (to decrease wettability).

The researchers have applied Vis/NIR spectroscopy for the determination of the geographical origin of the raw material as well as the physical, chemical and mechanical properties of the corks. They suggest that their results show the feasibility of this technique to improve the traceability as well as the control of some essential properties such as the humidity content, density or resilience after compression.

Prades told Spectroscopynow that, "Our latest research is focused on improving the accuracy and precision of the equations obtained as well as to extending the study to other cork products such as cork granulate and cork discs." She adds, "The last quantitative calibrations obtained for moisture content have a high predictive capacity and are suitable for use in routine quantification."

Related Links

Wood Sci Technol 2014, 48, 811-830: "Application of VIS/NIR spectroscopy for estimating chemical, physical and mechanical properties of cork stoppers"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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