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grapegrowing distinctive "gooseberry" flavor of this variety are now known to be various mercaptans and methoxypyrazines. In marked contrast with inorganic minerals, humans can detect and recognize these at extremely low concentrations. For example, 2-methoxy-3-isobutyl pyrazine can be sensed "even at low parts per trillion levels," and 4-mercapto4-methyl-4-pentanone has an aroma threshold of a mere 0.0001–0.005 ppb.6 These concentrations are more than a million times less than the taste thresholds for elements such as calcium, copper and zinc. Quite simply, these easily experienced, volatile aromatics produced during vinification totally drown the inorganic mineral nutrients, which are virtually tasteless anyway. Any semblance of flavor that the tiny amounts of inorganic elements might have in this environment will simply be swamped and lost. True, there are wines that have anomalously high concentrations of nutrient minerals—above the taste threshold— but these are seen as bad wines. Almost invariably contamination has been involved, such as pollution or overuse of agrochemicals in the vineyard or reactive plumbing in the winery. Such wines can be problematic for the winemaker, through hindered fermentation and haziness (ferric and copper casse), and, in line with the taste of metals in water, they are reported as tasting bitter and insipid. In other words, wines with potential taste concentrations of minerals are to be avoided! There may even be a risk to public health. It is revealing to note that the obvious question regarding the detection thresholds of inorganic elements actually in wine seems unresearched. The reason may be the potential health issue. The concentrations needed to be added in order to bring the minerals up to detectable levels would almost certainly make the wine toxic. Geological metaphors Many wine enthusiasts have tried to explain what the word minerality means to them. Not surprising—given the nature of the word—most of these efforts involve comparisons with geological materials. In fact, this in itself might be subliminally reinforcing the idea of a direct inter-relationship between vineyard geology and minerality. However, while these analogies might be useful in providing tasting cues or metaphors, they have no literal, direct bearing on the genesis of minerality in a wine. 68 p r acti c al w i ne ry & v i n e yard MAY 20 13 Flinty taste/smell, or flintiness Minerality is compared by many writers to a flinty taste. It sounds fun, but the idea presents scientific problems. Geologically, flint is a form of silica, silicon dioxide, one of several natural forms such as quartz, agate and chert. In all of them, the silicon and oxygen atoms are locked in an efficient three-dimensional crystalline framework that makes the materials tough, insoluble and virtually inert. That is, they lack any taste or odor. Indeed, it is because of these properties that silica is used for glass, and hence for the very bottles and glasses that contain wine. Consequently, it does seem odd to say that a wine that was stored in a glass bottle (silica, tasteless) and is now tasted in a drinking glass (silica, tasteless) has the flavor of flint (silica, tasteless) that somehow was derived from the vineyard. However, another repercussion of the efficient crystalline framework of silica is its tendency to break unevenly with irregular, concave surfaces (just like glass). Intersections of these fractures give sharp edges and points, leading to the well-known archaeological applications of flint in cutting tools. Perhaps we therefore mentally associate flint with edges and sharpness, and hence, metaphorically, with very dry, acidic wines. Minerals in the geological sense are almost all compounds, and usually complex ones at that. And they are insoluble, which is significant as vines can only take up dissolved matter. Could it be that instead of reporting a sharpness or tartness in wine, some writers like to refer instead to flintiness? It sounds more refined! In line with such a thought, some authors find it even nicer to use instead the French equivalent of flint: silex. Curiously, although most geological and wine-tasting terms have their direct equivalents in other European languages, of these the French word for flint virtually alone finds its way into tasting notes. Vine roots cannot take up the inert, insoluble silica. If sharpness or metaphorical flintiness is seen as at least some component of minerality, it cannot be derived from flint or related materials in the vineyard. This is borne out, for example, by the fact that Chablis wines— to many the epitome of flintiness—come from vineyards that lack silica and are dominated by calcium carbonate. Gun-flint aroma, struck flint and matches Some writers compare minerality with flint not as a taste but as an aroma. Here the comparison is with the smell of striking a flint or what is sometimes called a gun-flint odor. The smell of a struck match is commonly mentioned also. These odors come about because of a phenomenon properly called pyrophoricity. That is, certain solids in the presence of oxygen are capable of spontaneously bursting into flames—autoigniting. They are pyrophoric. Sodium, potassium and calcium, for example, are extremely pyrophoric, which is why they are not found in nature. The phosphorus used in matchheads needs the addition of a little heat to ignite, such as from the friction of striking a match. A few metals such as iron, aluminium and magnesium can be pulverized such that the surface area of each tiny particle becomes exposed to sufficient oxygen for it to auto-ignite, making a spark. A spark is a speck of burning material, usually producing an associated smell as it vaporizes. Our ancestors discovered back in prehistoric times that fragments of iron could be induced to spark. They would strike the metal sharply against some fine-grained, tough substance—and their favorite was flint. Later on, this became the basis of the flintlock mechanism in early firearms, and the smell became known as gun-flint. However, note that the aroma is coming not from the flint, which is acting purely as an inert anvil, but from the burning particles of pyrophoric iron. (Modern firearms and lighters, incidentally, employ "flints" made of a synthetic alloy of cerium and iron.) The smell of a struck flint or of gun-flint is an illusion. It is actually the smell of burning iron or steel. In any case, although these odors may be well-known and helpful in trying to explain what minerality tastes like, clearly the processes involved have nothing to do with what happens in vines and vineyards. Earthy smell We like to talk of earthy smells, and these are sometimes compared with minerality. Some think of earthy as the odor of mushrooms or decaying leaves in the fall; others are reminded of freshly tilled earth. But the aromas are coming from organic matter in the soil; as we have seen,