87Sr/86Sr in wines, grapevine sap, soils, and bedrocks: an experimental study on geologic and pedologic characterisation using radiogenic isotope of heavy elements

An experimental study to define the Sr-isotope from bedrocks to soil and its uptake by the vine roots to the biological live of the plant then to the wine, was made on micro-vinifications of grape-bunches from one of the main high quality wine area of Chianti Classico Consortium (the Barone Ricasoli Winery). The experimental work was carried out with a deep control of the boundary conditions (i.e., type of geological substratum, soil, and ground water supply etc.) on 11 sampling points distributed on a relatively small but geopedologically variegated area. From each sampling point, grape-bunches were harvested from single vine-plant over a period of four consecutive harvest years. Sr-isotope was also determined on grapevine sap, on the bio-available fraction of the soil, on bulk soil and on the rocks of the substratum. No significant Sr-isotope variability was observed among wines obtained through micro-vinification from different harvest years, suggesting that the Sr uptake process from the grapevine roots to its final product is time independent even at a very small scale (single vine). A significant Sr-isotope variability is detectable among wines obtained by micro-vinifications of grapes growing on vine plants from different soils type. Each harvest point is characterised by a specific Sr-isotopic value related to its substrata. The Sr-isotopes of each single wine batch matches those obtained from the sap of the corresponding grapevine plant. In addition these data correlate with the bioavailable fraction of soils collected on which the plant grown. All Sr-isotopic data obtained fall well within the range found for bedrock. A mismatch was observed, however, between the Sr-isotope signature of micro-vinifications and the corresponding whole soil. Decoupling of Sr-isotopes between soils and bedrocks has also been found, and attributed to differential behaviour of minerals in response to pedogenetic and weathering processes, which are controlled essentially by the mineralogy of bedrock. The findings of our experiments confirm the evidence that the biological activity of the vine is not able to change the original 87Sr/86Sr up-taken from the bio-available fraction of the soil, and that the 87Sr/86Sr signature of wines is thus an unadulterated feature of the inorganic Sr component achieved by the terroir. Eventually, the recurrent small-scale 87Sr/86Sr value differences may support the possibility to typify the cultivation suitability of single cru apt to yield wines of the best quality by isotopic monitoring, combined with other important parameters such as best exposure, less water stress etc.