Exploring minerality

‘Wine producers like to kneel in their vineyards and scoop up a handful of dirt for you to admire. “See this gneiss (or schist, or limestone)” they’ll say. “Minerality. You can taste it in the wine”.’

The idea that the rock type that a vineyard’s soil is based on can affect the flavour of a wine, giving it so-called minerality, has been knocking around for a long time. It is certainly a romantic thought that you can go into a vineyard, look at the soil and be able to ascribe certain aromas and flavours in the wine to it. There is something about the sensory nature of soil – you can see, touch, smell and even taste it – that makes it easy to apportion wine flavour to. But is this idea of minerality really accurate, or is it just a romantic notion used by marketeers to add to wine’s mystique?

The thorny topic of minerality formed the basis of a recent seminar held by the Institute of Masters of Wine and aimed to shed light on these questions. By the end of it would a room full of MWs be able to agree on what minerality is? We were about to find out.

 

IMW Minerality seminar

 

The first part of the presentation was hosted not by a wine professional, but by geology professor Alex Maltman from the University of Aberystwyth and was titled ‘Why ‘Minerality’ is not the taste of vineyard minerals’. So, stating his position very firmly then.

Thus followed a quick chemistry class in minerals, how they are formed from constituent elements and how they are bound in rocks, followed by the disconnect with how vines take up nutrient elements from the soil to grow. Essentially, geological minerals are made up of compounds formed of eight elements. These minerals bind with each other to rigid aggregates aka rocks. Over a long time rocks can be weathered to sediment, which mixes with moist humus (organic matter) and water and becomes soil. Vines need 14 essential nutrients to grow which they can take up from soil when dissolved in water. So, on the surface it sounds like:

Elements combine → minerals which then combine → rock.

Rock weathers → soil → vines uptake minerals from soil.

But herein lies the disconnect: just because some geological minerals are in the soil, it doesn’t mean that they are able to be taken up by the vine. And on top of that, weathering is such a slow process that it cannot provide all of the nutrient elements that a vine needs. Instead, these nutrient elements come from the humus – the recycled organic matter in the soil (dead leaves etc). On top of that, the three main essential nutrients that vines need are sodium, phosphorus and sulphur and these can only come from humus, not weathered geological elements.

So Professor Maltman proved quite succinctly that minerals in the rock are not taken up by vines – let alone find their way into grapes and onwards into your glass. He then went further, arguing that beyond the geological arguments, you simply can’t taste minerals themselves. He gave the example of flint, a wine descriptor that often occurs in so-called mineral white wines. Flint itself is silica which is flavourless, odourless and tasteless. The aroma we link to flint is actually the smell of flint being struck – striking flint releases sulphur and iron impurities into the air, giving a distinctive smell. It is not, however, the smell of flint itself. Professor Maltman concluded by noting that minerality is a metaphor – you have to be alluding to something else. ‘Whatever minerality is, it’s not the taste of vineyard minerals’.

So, if minerality is not from vineyard minerals then what is it? What does it mean?

Well, in the words of pre-eminent viticulturist Dr Richard Smart, ‘Minerality as a wine descriptor is a nonsense…..I think that it is a deliberate method to mystify wine by wine writers’.

So, is mineral a term used by wine trade but not understood by consumers? The final two speakers, wine sensory scientists Dr Jordi Ballester and Dr Wendy Parr, were on hand to share their research on what minerality means to people.

Dr Ballester’s research asked people simply to define minerality. Perhaps unsurprisingly the wine experts (Burgundian winemakers) came up with many descriptive words, all of which were positive – with the most used ones including gunflint, acidity and shellfish. On the other hand, consumers lacked any sort of consensus over descriptors and these were not always positive. This seems to indicate that whilst the wine trade knows what they mean by minerality, consumers do not – and aren’t sure if it is a good thing or not. The other result of note was the lack of consensus on descriptors from the wine experts – 34 people were surveyed resulting in 17 groups of words, including everything from gunflint to salty to flower. Not exactly a ringing consensus of what minerality means.

Dr Parr then expanded on this by talking about her research which looked at French and New Zealand Sauvignon Blanc producers to ascertain whether minerality is a specific character (or characters) in a wine – or if it is driven by expectation: the idea that you think something is mineral and therefore you taste it.  She found that the French and New Zealand producers could both smell and taste minerality and that there was cross-cultural consensus on what flavours were associated with minerality. Simply put, there was definitely something in the wine driving a description of minerality. And in general these wines tended to be more citrus/fresh with an absence of passionfruit and green characters. But, she also reported that the wines had been put through a rigorous chemical analysis and they didn’t find anything that ‘minerality’ can be attributed chemically.

This research seems to show that minerality as a concept does exist and can be tasted in a wine – but there is a lot of variability in terms of the actual descriptors used by different people. So, could a room full of MWs and their guests agree what minerality was? We were about to find out.

What followed was a blind tasting, first of 5 Chardonnays and then of 10 Sauvignon Blancs. We had to taste each wine and score it on a scale of 0 (no minerality) to 10 (high minerality). Easy, you might think. Well, the results were fascinating.

 

Minerality

 

This graph shows the results for the Chardonnays and the number of attendees who scored each wine as ‘the most mineral’. As you can see there wasn’t much consensus! There was a similar result for the Sauvignon Blancs, leading Dr Parr to comment ‘the notion of mineral doesn’t tell us a lot’.

An open discussion with the room then asked what we mean when we say mineral. The comments included chalky, acid, salty, palate weight, lack of sweetness, hardness, tension and friction amongst others – an interesting mix of true flavours, textural ideas and even more semantic concepts.

So if a group of MWs can’t agree on what minerality is, means, or tastes like – what hope do consumers have?

Indeed, Dr Parr ended up by arguing that minerality is an umbrella term with many aspects to it and that we as wine professionals should be more specific when describing mineral aspects in a wine. So just as using the descriptor ‘fruity’ is very generic and can be broken down into the type of fruit, whether they’re ripe or unripe, fresh or cooked – so minerality should be dissembled and wines should be described as salty, stony or steely – or any of the many other descriptors out there. Not only would that be more understandable for consumers it would also open up the world of minerality further and shed light on what we are really describing in a wine.

So, if minerality can be tasted in a wine but it does not come from vineyard soils – where does it come from? That sadly is a question still to be answered – quite simply, the research hasn’t yet been done. Professor Maltman commented that there is a possibility that geology could influence soil bacteria somehow – which then might have some effect on the vine and resulting wine. Certainly, the microbiology of soil in vineyards is a topical subject at the minute and might shed some light. Or perhaps it is some climatic influence happening at a local level.

For now we simply don’t know what causes minerality in a wine. It will just be another one of wine’s mysteries until the right research happens.

Emma

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