The most over-used word in the world of wine is the ill-defined term “minerality.” I have mentioned it before in this column when talking about tasting terms but it deserves closer scrutiny.

Although talk of minerality has wide appeal for producers, wine merchants, wine critics and sommeliers, and is often seen as a mark of quality, it’s a relatively new wine term, having arisen in the 1990s. There is no entry for it in Ann Noble’s wine aroma wheel or Emile Peynaud’s classic text, The Taste of Wine. (Though the latest edition includes a note on it and there is a new entry in the fourth edition of The Oxford Companion to Wine.) There is, however, no agreement on its meaning, or which wines show the most minerality and certainly no basis to the claim that we can taste the soils of the vineyards.

In a 2013 article in the Journal of Wine Research, geologist Alex Maltman looked at the influence of minerals on wine and found it lacking. It would take crushed rocks weathered by rain to add anything to the vine and we don’t find these buried near the roots of the vine. Besides, what do slate or stone taste of? Nothing, says Maltman. When we speak of smelling wet stone what we are actually smelling is the humus of organic matter on the stone’s surface released by the added moisture. Thus whatever producers and sommeliers mean by gunflint in a Sancerre, or oyster shells in a Chablis, it is not the terroir they are tasting. As Maltman points out, there is actually more iodine—though still in minuscule amounts—in Australian Chardonnays than in Chablis.

So what are wine professionals talking about when they say a wine has good minerality? It generally suggests quality and distinction. They know that minerality is often confined to white wines. But beyond that point there is little else they agree upon.

At a recent seminar on minerality at the Institute of Masters of Wine, we were invited to take part in a blind tasting of the wines used in two studies, one by Jordi Ballester on Chablis and one by Wendy Parr on Sauvignons. Attendees had to record their verdict on each wine, rating them on a seven-point scale between no minerality and intense minerality. We had then to vote for which wine we thought showed the greatest minerality. There was no agreement whatsoever.

Undoubtedly, there are flavours we’re tasting that we are inclined to think of as minerals. But what are they? For some, minerality is a mouthfeel: chalky, slaty. (Have you ever licked slate? You will have a very dry tongue.) Others incline to odours like shell fish, or gunflint. To recognise the latter, as Maltman points out, you will need to have encountered an antique musket. Then again there are tastes like salinity or acidity; the latter gives the wine a freshness. So is minerality a smell, a taste or a feel? Of course, it could be a complex, multi-sensory interaction between all of these things, only some component of which is spoken about by those who experience it.

But what about the lack of agreement? Well, perhaps there is a glimmer of hope to be found in a PhD thesis I recently examined on minerality. Heber Rodrigues Silva, a student of Jordi Ballester and Dominique Valentin at the Centre des Sciences du Goût et de L’Alimentation in Dijon, reports on a study conducted among Chablis producers tasting a number of premier Crus. The producers all agreed the wines on the left slope of the river Serein showed good minerality, while the wines from the right slope showed little. There are marked chemical differences between wines from each slope, with those from the left having high levels of methanethiol, which suppressed the fruity and floral aromas shown in wines from the right bank, which had higher levels of copper and norisprenoids. Is this a breakthrough? It may reveal a mineral flavour in a Côte de Léchet, but not as we know it. Good minerality? More methanethiol anyone?