The mystery of minerality

In the July edition of Societynews we answered a member’s question on the term ‘minerality’. Here Master of Wine and scientist Caroline Gilby examines the subject in more detail

Back in the late 1990s, I recall doing some translation work for a Chablis producer when I insisted that ‘the typicity of the minerality’ was a meaningless phrase in English. The word ‘minerality’ barely appeared in wine language back then and it didn’t appear in Emile Peynaud’s legendary wine tasting bible The Taste of Wine published in the 1983. Today, though, you won’t read many wine descriptions before the words ‘mineral’ or ‘minerality’ crop up (‘mineral’ appears more than 50 times if you do a search on The Wine Society website, for example). It’s usually a positive cue for a quality wine with a sense of place or terroir and often linked closely to a specific soil or rock type.

> Classic 'mineral' wines to taste

But does minerality come from the soil?

There is an implication that this mineral quality must somehow come from the vineyard and the soils or bedrock, but try as they might scientists cannot find any sort of mechanism for this. The thing is that plants are very good at absorbing what they need and nothing more. And it’s important to understand that in fact what they take up from the soil through the roots has to be dissolved in water, meaning very simple ions, and these have no taste at the levels measured in wine. There’s a good paper by Alex Maltmann of Aberystwyth University on this for anyone wanting to delve deeper. It makes no difference whether a calcium ion, for instance, comes from chalk, limestone, clay or any other sort of bedrock – it’s still the same tasteless cation. And there’s no mechanism for complex or crystalline minerals to be taken up by plant roots and end up in the grapes.

At this point it’s worth a couple of definitions. The International Mineralogical Association definition is ‘A mineral is an element or chemical compound that is normally crystalline and that has been formed as a result of geological processes.’ It is also naturally occurring (so not man made), inorganic, solid with a definite chemical composition and ordered internal structure. In contrast, rocks are disordered and are a mixture of minerals. Examples of minerals include things like calcite (that is important in limestone rock), halite (rock salt) and sulphur, while rocks include chalk, slate, shale, basalt and many more.

Distinctly different: halite (rock-salt) is a mineral not a rock

Distinctly different: halite (rock-salt) is a mineral not a rock

Do we all mean the same thing when we use the term ‘mineral’?

The use of the word ‘mineral’ has become so widespread that various researchers have tried to identify if there is a detectable cause in wine and indeed if there is any unity between tasters in what the concept of ‘mineral’ or ‘minerality’ means. One recent paper by Parr et al in New Zealand tested two groups of tasters from France and New Zealand respectively to identify mineral characters in samples of sauvignon blanc. Descriptors like citrus, flinty and chalky were linked to minerality in both groups while tropical notes like passion fruit were negatively linked to minerality. Interestingly, in this group the French tasters relied more heavily on the nose to evaluate wines than the New Zealand ones though there was largely agreement about key descriptions. Parr has also pointed out that the rise of the term ‘minerality’ has also been paralleled by the rise of screw cap use in New Zealand.

Are some grapes more likely to be described as ‘mineral’?

Chardonnay, one of the grapes more prone to show mineral characteristics Chardonnay, one of the grapes more prone to show mineral characteristics

If you ever get the chance to do a horizontal tasting across wines from different soil types from a single producer, it’s clear there are differences and therefore also clear that there’s a gaping chasm between the art and scientific understanding of this aspect of wine. But scientists are working hard to try and tackle this. A recent study in Spain (by Outlook Wine and Excell Iberica) entitled Minerality in Wines found that the chemical composition of wines and perception of mineral characters are not linked to minerals in vineyard soil. The team also looked at the sensory basis for mineral character in wine and came to some conclusions. They found that certain grapes are more prone to showing mineral character including chardonnay, chenin blanc, albariño and sauvignon blanc, and in reds syrah and pinot noir with cabernet franc, nebbiolo and cabernet sauvignon to a lesser extent.

Cool climate means more incidences of ‘minerality’?

There was also an association with expressing ‘minerality’ if grapes had been grown in cold or cool climates; harvested earlier rather than fully or over-ripe; if the wines showed high acidity/low pH and had been made using reductive techniques (ie minimal exposure to oxygen) and had higher levels of free sulphur dioxide. They also found that there had to be an absence of highly aromatic compounds, particularly terpenes (responsible for key aromas in lemons, lavender and pine, for instance) and fruity esters. The researchers also found the presence of higher levels of an acid called succinic acid (which is produced by the yeast metabolism during fermentation) and has a salty taste is directly associated with the concept of minerality in some wines. However, careful research to define a group of wines as ‘mineral’ and then to analyse them, did not find any single compound consistently linked to this characteristic.

Vineyard characteristics could have some influence

What is clear is that this is a complex picture and there are almost certainly links with what is going on in the vineyard and its soils, even if the soils are not involved directly. For instance, stress in the vineyard caused by lack of water (on sandy, gravelly or rocky sites, for example) can cause changes in juice composition that may lead to ‘mineral’ characters. Another soil factor is that infertile soils with low nitrogen (limestone soils are often low in fertility, for instance) may mean low nitrogen in the juice which can force yeast to metabolise more sulphurcontaining compounds, leading to more reductive, struck-match/flinty characters associated with ‘mineral’ descriptions. This suggests that geological/climatic factors are involved but doesn’t show any firm link with an identifiable chemical. The process of fermentation plus clarification and stabilising wine also affects the composition of wine and thus its final taste and possible perceptions of ‘minerality’ too.

Stress in the vineyard due to lack of water may lead to ‘mineral’ characters (Rocky vineyard, Croatia)

Stress in the vineyard due to lack of water may lead to ‘mineral’ characters (Rocky vineyard, Croatia)

So, the answer doesn’t just lie in the soil then?

So it appears that the phenomenon of ‘minerality’ is complex and most likely to be an indirect effect of grape growing and also winemaking. But it is not in any provable or literal way a taste of actual rocks or minerals found in a vineyard. Nonetheless, the word ‘mineral’ has become very fashionable and a handy shorthand for implying quality, elegance and provenance. I don’t see the word going out of fashion anytime soon.

Caroline Gilby: Master of Wine

Caroline Gilby MW Caroline Gilby MW:
Master of Wine

Caroline Gilby is a Master of Wine and a scientist by training. She is a wine writer with a passion for the wines of Central and Eastern Europe and contributes to several wine books, magazines and websites.

> Classic 'mineral' wines to taste

> Winemaking: The Importance of the Soil

> Read other articles by Caroline Gilby MW

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