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grapegrowing However, feldspar and the other geological minerals common in vineyards, such as calcite and quartz, have virtually no ability to do this swapping. They have little cation exchange capacity (CEC). Some clay minerals, however, with their large surface-volume ratios and electrostatically negative surface charges, are able, on their extremities, to loosely hold cations that can be interchanged with those in the adjacent pore water. So the feldspar has to weather to a clay, normally by water slowly forcing the rearrangement of its constituent elements. Clays such as sericite or kaolinite usually result, depending on circumstances. However, both of these forms also have a relatively low CEC, so a good improvement in cation availability requires further reactions to produce higher CEC clays, such as illite or montmorillonite. The particular reaction routes taken by the degrading feldpsar through all this depends on a host of varying factors such as chemical environment, time, temperature, moisture content and pH. Additionally, the extent to which the CEC is actually triggered depends on the vine metabolism driving the expulsion of exchangeable protons from its roots and appropriate gradients being set up in the soil. Ionic transport from the clay surfaces to the vine roots, involving advection or diffusion through those soil pore-throats that are suitably interconnected, also depends on variable chemical and hydrostatic gradients, as does the extent to which the transported ions actually pass into the vine roots. It is all very intricate and changeable. The above is a terse outline of one example, but it hints at the complexities and the variables that are involved in making a constituent element of a geological mineral available as a nutrient mineral to vine roots. It glimpses the detachment between the two different kinds of minerals. indirect relationship with the vineyard geochemistry.1 This disconnect is magnified during vinification.2 For example, fermentation can remove mineral nutrients such as zinc, copper and barium from the must while adding others, such as aluminium, calcium and iron. Fining and/or filtering can remove yet more, and elements may be added where geological materials such as diatomite (kieselguhr) and bentonite are utilized. Stabilization3 and aging can increase copper, iron and manganese whereas calcium, aluminium and chromium are removed along with precipitates such as potassium tartrate.4 Consequently, the proportions of mineral nutrients in the finished wine bear only a complex, indirect and distant relationship with the geological minerals in the vineyard. (Incidentally, this is why it has proved so difficult to use inorganic analysis to chemically fingerprint the provenance of a wine. Attempts have had to resort to trace elements, isotopes, sophisticated statistics, etc. Although most conclude with some "potentially promising" correlations, those high-end © 2012 StaVin Inc. Twenty years ago, we opened our doors for business. And while some years have been better than others, we can't complain. Our innovations have far exceeded our original hopes and changed for good the way winemakers approach their craft. But that's not what we're most proud of. It's the people who work with us. They've bought their own homes, sent their kids to college and genuinely love coming to work. Which, in our book is what you'd call a dream come true. Disconnect between vineyard and wine chemistries This disassociation in the vineyard soils between the geological and nutrient minerals increases within the vine itself, where metabolic processes determine how much of the nutrient ions absorbed by the roots are actually loaded into the vine xylem and then in what proportions they are distributed around the various components of the vine. Even within the berries themselves, differing ratios of nutrients reach the skins, seeds and juice. Hence, in normal circumstances, the inorganic chemical profile of the grape juice bears only a distant and ® StaVın Inc, P.O.Box 1693, Sausalito,CA 94966 (415) 331-7849 f (415) 331-0516 stavin.com pr actica l win ery & vin e ya rd MAY 20 13 65