What is Minerality? | A Little Lesson in Chemistry
Jane Masters MW is Opimian’s Master of Wine
Minerality is increasingly sought by winemakers and used as a wine descriptor. But what do we actually mean by minerality? There are many different minerals, but who knows what each smells and tastes like?
The tastes of mineral waters vary according to their natural composition of calcium, magnesium, potassium, sodium, bicarbonate, iron, zinc and other minerals. Wine contains low quantities of these same minerals, so it may sound logical that these contribute to a wine’s taste. However, wine is a far more complex matrix, containing many hundreds of compounds in an essentially acidic alcohol solution. Wine is acidic due to the natural presence of tartaric acid in grapes. Alcohol from the alcoholic fermentation gives a sweetness and viscosity. Some wines have residual sugars, glucose and fructose, adding sweetness; red wines contain tannins coming from grape skins, seeds or maturations in oak, which add bitterness and structure. It is the interaction of all of these aspects and their relative proportions that together make up a wine’s taste.
Certain flavours are attributed to particular grape varieties. For example, blackcurrants are associated with Cabernet Sauvignon, gooseberries with Sauvignon Blanc. Specific compounds responsible for these flavours have been identified and are naturally found in wines and in the fruits. Using them as descriptors makes sense.
It is much less clear which compounds are responsible for conferring mineral characters in wine. Wines can be said to have a flinty or wet stone character. Some wine professionals purvey the idea that this comes from minerals present in a vineyard’s soils and bedrock, which are absorbed by the vines to directly influence a wine’s flavour. Certainly, winemakers find that certain soils produce specific flavour characteristics; however, there is no scientific evidence to support the assumption that a soil’s minerals are directly responsible for flavour.
Minerality is often attributed to wines from cooler climates with naturally higher acidity levels. Chablis wines are said to have a taste of gunflint, sometimes described as steely. The Chablis appellation is certainly defined by its Kimmeridgian clay limestone soils, but also by its northern location. Attractive struck flint or matchstick characters sought by winemakers are attributed to volatile sulphur compounds. If these same compounds are present in high levels, the wine is faulty. As Riesling wines age, they can develop a diesel or mineral character due to 1,1,6 trimethyl-1,2-dihydronaphthalene known as TDN. In young Riesling wines, TDN is bound in a non-aromatic form. As the wine ages, the aromatic form with a sensory threshold of 2 micrograms/litre is released. In old Rieslings, TDN levels can reach over 25 times that amount. TDN has also been found to be present in wines made from Chardonnay, Sauvignon Blanc, Pinot Noir, Cabernet Sauvignon and Cabernet Franc at levels close to the sensory threshold. While less distinguishable, it is likely to contribute to the flavour of these wines. The appealing smell of fresh rainfall is due to geosmin, an organic compound which has an aroma of freshly tilled soil and an earthy flavour like beetroot. In wine, this is actually considered a fault.
Essentially, I suggest considering minerality as a generic term—the anthesis of fruitiness, which adds another dimension to a wine. Whatever the component responsible, it should not dominate but should add to a harmonious whole, making it more interesting.