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23-01-2019 15:21

“Wijn is geen terroir”

We hebben geoloog prof Alex Maltman eerder aan het woord gelaten over zijn opvatting dat terroir niet voornamelijk bepaalt hoe een wijn z’n karakter krijgt. Hij gelooft niet in de leer van de ‘terroiristen’ en legde in Decanter nog eens uit waarom niet.



“Professor Alex Maltman questions the new orthodoxy that vineyard geology is of overriding importance to a wine's character, and highlights some factors that may have been overlooked....

I should be jumping for joy. For years I’ve taught, researched and generally enthused about geology and its importance, and now my subject is making headlines in the world of wine.

‘Soil, not grapes, is the latest must-know when choosing a wine,’ Bloomberg tells me, for example. So why am I not full of joy? Well, because as a scientist I have to follow the evidence, and this leads me to query this new pre-eminence of vineyard geology.

Of course, a link between wine and the land has long been treasured as something special. It even survived the discovery of photosynthesis – that vines and wine are not made from matter drawn from the ground but almost wholly of carbon, oxygen and hydrogen, abstracted from water and the air.

The rocks and soils in which the vines grow are certainly still part of the scientific picture, but this pre-eminent role is something new.

Today there are restaurants with wine lists organised not by grape, wine style or country of origin, but by vineyard geology.

Alice Feiring’s book The Dirty Guide to Wine urges drinkers to choose their wines by ‘looking at the source: the ground in which it grows’. There’s a consortium of growers from such diverse places as St-Chinian, Alsace, Corsica and Valais that claims commonality of its members’ wines simply because their vines are growing on schist – even though schist and the soils derived from it are incredibly varied. The same could be said about the very fashionable idea of (so-called) volcanic wines.

Yet in none of this are we told what the geology actually does; how a particular rock brings something special to the wine in our glasses.

And our present scientific understanding makes it difficult to see how this might happen. The fact is that the claims are largely based on anecdote: the science suggests that the vineyard rocks and soils have more modest roles.


Questionable claims

So what are their effects? Well, quietly in the background the bedrock geology sets the context by determining the physical landscape. The resistance of different rocks to erosion governs where hills and plains develop, where we get favoured sites for vineyards such as hillsides and river valleys. But the major direct contribution of geology, consistently confirmed by research in various parts of the world, concerns water supply: providing decent drainage for the vines while storing sufficient water for dry periods. It’s pivotal to how grapes swell and ripen.

However, many different kinds of geological materials fulfil this – gravels in Bordeaux, for example, granite soils in the northern Rhône, chalk in Champagne.

Moreover, growers routinely attend to any shortcomings by inserting drains and, in most parts of the world, irrigating. That is, the role of the natural geology is overridden.

How the vine roots are warmed by the soil plays a role, but a particularly popular claim is that the rock of some particular vineyard provides an advantage through being heated during the day and re-radiating warmth to the grapes at night.

However, the scientific data show that this capacity varies little between differing rock types – all of them do it, provided the ground is bare – and that it’s not a very great effect anyway.

It’s probably only significant in some cool-climate areas where the grapes are trained close to the ground. And anyway, there is a school of thought that finer grapes are produced where night-time temperatures are markedly cooler than during the day.

The feature of vineyard geology most often mentioned relates to it supplying the nutrition needed by growing vines.

It’s often made to sound as though vines simply soak up whatever nutrients the local geological materials yield, and these are then conveyed through the vine to the eventual wine.

We read, for example, that ‘the vine transmits its nutrients all the way from the stony soils to the final wine’ and ‘the vines sip on a cocktail of minerals in the vineyard soil, for us to taste in our wineglass’.

Some statements even suggest that the rocks themselves are making it through to the wine, as in ‘the weathered Devonian slate is right there in your glass’.

Sadly – I suppose – scientific understanding of how vines grow means this kind of thing just doesn’t happen. To explain, let’s look at some aspects of how vines and soils work.