Elemental characterization of sparkling wine and cork stoppers

Abstract

The variations of the elemental concentrations in sparkling white wine and respective cork stoppers throughout 18 months of storage time were determined with the PIXE (Particle-Induced X-ray Emission) technique. Three portions of the cork stoppers were analyzed: the top part (external layer), the inner part (bulk layer) and the bottom layer (which was in contact with the sparkling wine). Elements such as Na, Mg, Si, P, S, Cl, K, Ca, Mn, Fe, Zn and Rb were determined for both cork stoppers and sparkling wine samples. Similar concentrations of Si, P, S, Cl and Ca were found in the external and bottom layers of the corks. Distinct behaviors of the changes in the elemental concentrations as a function of the time were observed for cork stoppers and sparkling wines. The concentrations of Mg, S, K, Ca, Cu, Sr and Ba increased in the bottom layer of the cork as a function of storage time. On the other hand, concentrations of Al, Si, Cl, Ti, Zn and Br proved to be invariant, while the concentrations of P and Fe showed a slight decrease. Concerning the sparkling wine, an increasing trend of elemental concentrations was observed for most elements throughout the storage time. A diffusion mechanism of elements in the cork and the role of the secondary fermentation in the bottle are discussed.

Keywords: Cork stopper; Elemental analysis; PIXE; Sparkling wine; Wine aging.

Graphical abstract

Fig. 1

Pristine cork stopper (left panel) made of two disks of natural cork (bottom) and agglomerated cork (middle and top portions). The right panel depicts the used corks. The external and bulk layers had no direct contact with the wine, while the bottom layer was in direct contact with the wine during the storage time. The oval dashed lines are used for better visualization of the structures under discussion. The red arrows indicate the direction of the proton beam during the PIXE analysis. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

X-ray spectra of bottom (black line), bulk (red line) and external (blue line) layers of pristine cork stoppers belonging to G1 group as a function of the X-ray energy. Each spectrum represents an average of 5 measurements. All spectra are normalized by the charge accumulated during the experiments. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3

Concentrations of Mg, S, K, Ca, Cu, Sr and Ba in the bottom layer of the cork stopper along 18 months of storage time in steps of 3 months. G1 group represents those corks which did not interact with the sparkling wine, i.e. equivalent to zero months of storage time. The values stand for the mean of five samples per group, while the uncertainties are represented by the standard deviation. Magnesium was not detected in G1, G3 and G4 groups, while Sr and Ba were absent from G1 samples.

Fig. 4

X-ray spectrum of sparkling wine belonging to G1 group as a function of the X-ray energy. This spectrum represents an average of 5 measurements. The spectrum is normalized by the charge accumulated during the experiments.

Fig. 5

Sodium concentration as a function of the storage time. The straight line is the result of a linear regression analysis of the data (black dots). The population slope was tested with the F test with a level of significance of 0.05.