Does the winemaking process influence the wine 87Sr/86Sr? A case study

To evaluate the roles of the soil composition and vinification process on the wine strontium isotope ratio 87Sr/86Sr, two different wines (one red table and one fortified wine) from the Douro Portuguese wine-district were selected. The ratio 87Sr/86Sr was determined in the provenance soil, in the grape juices (prepared in the laboratory) and in the wines. Total strontium concentration was determined in the grape juices, skins and seeds and in the samples collected in the different steps of each winemaking process and respective produced wines. All analyses were performed by inductively coupled plasma mass spectrometry. The total strontium concentration increased during the vinification processes. The increase was attributed to the element liberation from grape seeds and skins (richer in strontium than the pulp) during the initial mechanical pressing and fermentation. The 87Sr/86Sr values were statistically identical in the provenance soil, respective grape juice and wine, which indicates that 87Sr/86Sr is a suitable tracer of the origin of the studied wines. The study deserves to be extended to many more wines/provenance soils in order to validate the suitability of that parameter as a tool for the identification of wine provenance region.