ON VINEYARD GEOLOGY AND “MINERALITY” IN WINE

Most writings on wine and geology are descriptive, with a connection between the two being supposed but rarely analysed. This is especially true of wine taste. Examination of the role of geology in wine flavors shows that any linking mechanisms must be far more indirect than commonly presumed. An example of the difficulties is provided by the fashionable tasting term “minerality”. While poorly defined, the word now appears widely in taste descriptions, where it is generally taken to be a direct expression of the vineyard geology, by the vines absorbing minerals from the vineyard soils to be transmitted through to the finished wine. The idea is romantic and highly useful commercially but it is scientifically untenable.

The degree to which the geological minerals of the vineyard substrate yield “minerals” (i.e. inorganic ions or nutrients) and the extent to which they are taken up by the vine roots both depend on complex and variable physical, chemical and microbiological factors. Those ions that are absorbed are apportioned differentially around the growing vine. Thus there is a decoupling between the vineyard geochemistry and grape juice composition and this is magnified during fermentation, fining, filtering and maturation. Consequently the inorganic profile of the finished wine is normally unrelated to that of the vineyard. Moreover – and crucially – the ionic concentrations in wine are far below the human taste threshold, even in distilled water. Almost all inorganic ions are virtually tasteless. Their very low vapour pressures contrast with the easily sensed, aromatic volatile organic compounds that do give a wine its flavors. Hence modern treatises on the science of wine flavour disregard the inorganic components. Those few wines in which inorganic ions actually reach discernible levels (usually because of contamination) are problematic, throwing hazes and tasting flawed.

Minuscule amounts of inorganic ions might conceivably have indirect roles in grape development and vinification, through acting as catalysts, enzyme cofactors, etc., and these could turn out to be important. But at present this is purely speculative. The widely cited direct, literal connection between vineyard geology and wine taste seems scientifically impossible. Whatever “minerality” in wine is, it is not the taste of vineyard minerals.