Abstract
The measuring of 87Sr/86Sr in wine, grape and bioavailable soil fraction samples with the same uncertainty of geological materials allows to fully compare the whole wine-production chain with the peculiar geochemical isotope signature of any geographic area. Indeed, this signature is the same that the final product inherited by the soil bioavailable fraction and, in turn, by the geological substratum of the vineyard. On the other hand, the few data available in literature referred to white wines cast doubts for the use of this geographic tracer due to the common use of geological-derived additives, such as bentonite, in the white wine-making procedure, which may overprint the original geochemical signature of the vineyard substratum. To tackle this issue, we analysed the Sr-isotope compositions of four white wines produced over a period of almost 10 years in a high-quality organic farm, located on the volcanic units of the Vulsini Volcanic District (southern Tuscany, Italy). The 87Sr/86Sr values of rock, soil, grape, grape juice, must, and wine were compared among them and furtherly weight against the isotope fingerprint of the bentonite and yeast employed during the wine-making process. The 87Sr/86Sr values from the entire white-wine production chain reveal that no variations are observed from the signature imprinted by the original geological substratum (rocks and soils), suggesting that no further contribution is given by the addition of bentonite and yeast to the white wine Sr-isotope values. On the other hand, intermediate 87Sr/86Sr compositions are found when grapes from different vineyards are used for making multi-cultivar wine blends. Indeed, the experimental data clearly show that the Sr isotope composition is maintained through the wine-making process for white as well as for red wines. Both grape and final wine preserved the isotope signature inherited from the labile fraction of the soil where the vines are farmed. Our data thus confirm, also for white wines, the robustness of Sr-isotope tool in studies where it is important to define terroirs and geographic provenance.
Highlights
In the last years the mass spectrometry analytic techniques were improved, allowing the researchers to perform Sr isotope measurements on samples of grape, must, wine, and soil with the same analytical precision of that obtained for geologic materials, enabling the comparison of the Sr radiogenic isotope composition in red wines to their own terroir of geographic provenance (e.g., Boari et al, 2008; Marchionni et al, 2013, 2016; Tescione et al, 2015; Durante et al, 2016, 2018; Vinciguerra et al, 2016; Braschi et al, 2018; Epova et al, 2019)
Among previous studies, the few dealing with white wines missed either to consider the full wine-making production chain (Petrini et al, 2015) or just considered a geographical areas where the isotopic variability was not large enough to discriminate among different substrata (Vorster et al, 2010)
In this paper we present a detailed experimental study applied of the 87Sr/86Sr signature along the whole oenological foodchain from the grape, through the must to the final product, the wine to test the suitability of radiogenic isotopes as tracers for provenance and authenticity to white wines
Summary
The adoption of isotopic ratios of heavy radiogenic elements (i.e., Sr and Nd) as possible geochemical tracers of food provenance is gaining scientific consensus within the scientific literature (e.g., Horn et al, 1993; Martin et al, 1999; Roβmann et al, 2000; Barbaste et al, 2002; Kawasaki et al, 2002; Fortunato et al, 2004; Kelly et al, 2005; Voerkelius et al, 2010; Bong et al, 2012; Durante et al, 2013; Marchionni et al, 2013, 2016; Song et al, 2014; Medini et al, 2015; Petrini et al, 2015; Coelho et al, 2017; Tescione et al, 2018; Tommasini et al, 2018).Preliminary studies using Sr isotopes as possible fingerprint for deciphering the geographic provenance in high quality wines provided questionable results essentially due to the analytical uncertainty of 87Sr/86Sr measurements reported, which were usually larger than the Sr-isotopic variability shown by most of the rocks/soils on Earth (e.g., Horn et al, 1993; Almeida and Vasconcelos, 2003, 2004; Vorster et al, 2010; Di PaolaNaranjo et al, 2011). The study of Petrini et al (2015) focused on the comparison between the isotopic composition of the grape components (skin, grape, seeds, and must) used for Prosecco white wine and that of the labile fraction in soils (i.e., bioavailable). They observed a statistically significant correspondence between must and soil but the whole isotope range given by the must was so large that encompassed most of the isotopic compositions of the rocks present in the restricted investigated area. Both these studies did not demonstrate the applicability of this tracing technique to white wines and did not solve the question if the use of bentonite may overprint the Sr isotopic signature acquired by the soil and rocks of the substratum of the vineyard
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