A comparative 87Sr/86Sr study on Red and White wines to validate its use as geochemical tracer for the geographical origin of wine

The wine geographical traceability has gained importance in the modern society producing the need of valid scientific protocols able to trace geographic provenance of wines. A strict correlation does exist between the wine and its terroir. Stable isotopes of light elements are nowadays widely used to detect aroma and flavor sophistications in wines, but it now is clear their little reliability for defining exactly and directly the geographic traceability of wines because of their strong dependence upon local climatic and anthropic factors. In the last decades, isotopic ratios of heavy elements of geological interest, such as 87Sr/86Sr, have gained interest in tracking regional provenance of foods and especially of wine. Recently high precision 87Sr/86Sr analyses have shown that Red wines keep the isotopic values of the vineyard substratum. Indeed, neither biological nor winemaking and aging processes are able to change the 87Sr/86Sr values through the oenological food chain from grapes to Red wine. In addition, 87Sr/86Sr of Red wines and those of rocks from the geological substratum of their vineyards correlate directly. Little isotopic studies were performed on white wines that might show minor sensibility to geographic traceability using 87Sr/86Sr due to their more complex wine-making procedure in which some geological additives are used to stabilize and clarify the final product. To fill this experimental gap 87Sr/86Sr has been determined for the entire production chain, from terroir to final product, of Red and White wines from the same winery. Sr-isotope data were also determined for the young pyroclastic rocks of the geological substratum, and the soil of the vineyards to disambiguate the original contribution to the 87Sr/86Sr values of wines. Further Sr-isotope data have been determined on additives used for fining the White wine. Our data further confirm that Sr-isotopic ratios of Red wines i) are constant through the different harvest years; ii) are not influenced by winemaking processes; iii) are strongly related to those of the geological substratum. The 87Sr/86Sr on White wines is showed, analogously to Red wines, that the winemaking process and the use of geologic additives, like bentonite, in the wine stabilization, and chalk in wine clarification and fining do not alter the Sr isotopic ratio acquired from the soil, confirming the applicability of the technique also on White wines.