Mechanisms
of terroir
As
more new world producers start to take an interest in terroir,
scientists are turning their attention to defining it and
explaining how it affects a wine. Jamie Goode investigates. (This
feature was originally published in Harpers
Weekly, September 12th 2003)
‘Terroir’
is currently an in vogue concept. Once almost exclusively the
preserve of the old world, it’s now a talking point in the new
world, too. The traditional, old world definition of terroir is
quite a tricky one to tie down, but it can probably best be
summed-up as the possession by a wine of a sense of place, or
‘somewhereness’. That is, a wine from a particular patch of
ground expresses characteristics related to the physical
environment in which the grapes are grown. But why the sea-change
in the new world, where for so longer the job of grape growing was
seen merely as a mundane prelude to the work of the all powerful
winemaker?
Even fairly recently, the new
world response to ‘terroir’ was that it was a last ditch
marketing ploy by European winegrowers who were panicking about
their increasing loss of market share. This turn-around is because
new world wine growers have realized that one of the keys to wine
quality is starting with grapes that show homogeneous (even)
levels of ripeness, and the recognition of the role that natural
variation within and between their vineyards plays. With the
increasing adoption of technique known as precision viticulture,
vineyards are commonly broken up into sub-plots sharing similar
characteristics (known as natural or basic terroir units) so that
vineyard interventions can be precisely targeted to where they are
needed. But you don’t have to look too far below the surface to
see that there are subtle but important differences between old
world and new world notions of terroir. Speaking generally, in the
old world terroirists aim to make wines that express the typicity
of the specific vineyard site, whereas in the more pragmatic new
world, understanding terroir is seen as a route to improved
quality.
A
taste of the soil?
The notion of terroir is fundamental to the wine industries
of old world countries such as France, Italy and Germany. It’s a
philosophical framework within which wine growers work. Local wine
laws are built around the concepts of appellations, which lend
official sanction to the idea that a combination of certain
vineyard sites and grape varieties creates unique wines that
faithfully express their geographical origins.
Correspondingly, many old world
growers feel they have a duty to make wines faithful to the
vineyard sites they are working with. These growers will commonly
make associations between properties of the wines and the soil
types the grapes are grown on. In some cases these putative
associations are quite specific: people will talk about mineral
characters in wines and associate them with the minerals in the
vineyard, taken up by the roots of the vines.
There’s even a French
expression, goût de terroir, that is used to describe
this. Do chalk, flint or slate soils impart chalky, flinty or
slate-like characters to wine? As a scientist who has a working
knowledge of plant physiology, I find this notion, which I call
the ‘literalist’ theory of terroir, implausible. Yet I can’t
get away from the fact that an overwhelming majority of the
world’s most compelling and complex wines are made by people who
hold the notion of terroir as being critical to wine quality.
Thus the goal of this feature is
to explore the mechanisms of terroir, focusing specifically on
soils. Just how do soils affect wine quality? Is it a direct or
indirect relationship? What are the scientific explanations for
terroir effects?
Randall’s
Rocks
In fact, the inspiration for this article came from a
characteristically wacky experiment conducted by Randall Grahm, of
California’s Bonny Doon. Even though he’s from California,
Grahm is actually one of the most eloquent proponents of terroir,
and he had the unusual idea of bypassing the vine and adding rocks
directly to wine, to investigate their influence on flavour.
‘Our experiments were incredibly
simplistic and gross in comparison to the very subtle chemistry
that occurs in mineral extraction in real soils,’ explains
Grahm. ‘We simply took interesting rocks, washed them very well,
smashed them up and immersed them in a barrel of wine for a
certain period of time, until we felt that the wine had extracted
some interesting flavours and we were able to discern significant
differences between the various types.’
Surely, this is taking the
literalist notion of terroir – that flavour compounds are
translocated from the soil to the developing grapes through the
vine roots – to its extreme. Grahm continues, ‘We initially
screened a number of different rocks with bench trials and
ultimate decided on a few for larger scale experimentation - rip
rap (granite), Noyo cobble stone, black slate and Pami pebbles.
We certainly took the extraction way too far as we ended up seeing
pH rises of 0.5–0.7 units, i.e. from 3.5 to 4.1 or 4.2, which is
clearly beyond the pale for most wines. Obviously the big pH
shift and the lowering of the acidity caused major changes in the
texture and mouthfeel of the wine, but we also observed dramatic
differences in aromatics, length and persistence of flavour.’
Grahm is convinced of the
importance of mineral flavours in wine. ‘In every case, low
doses of minerals (before we really overdid it), added far more
complexity and greater persistence on the palate.’ His view is
that minerality in wines has important implications for wine
quality. ‘It is my personal belief that wines that are richer in
minerals just present way differently. I believe that in
general mineral-rich wines there is a suppression of obvious
fruit. What is most striking to me though about wines that
have higher levels of minerals is that they seem to have a certain
sort of nucleus or density around their centre, they are gathered,
focused, cohered the way a laser coheres light. It is a
different kind of density relative to tannic density, somehow
deeper in the wine than the tannins. In any event, I am
utterly convinced that minerality is the one true key to
ageability in wines and that everything else—tannin, acidity,
sulphur dioxide—plays a far more secondary role.’
It is unlikely that adding rocks
to wines will ever become a common winemaking manipulation,
though. Grahm’s rock-infused wines ran into some trouble with
the regulatory body in California who were finding elevated levels
of nickel and antimony, among other things, so it looks like this
experiment won’t be repeated.
Scientific
views of terroir
While in some circles it is quite common to hear such literalist
explanations of terroir, they are treated with a degree of
incredulity by many new world viticulturalists. I asked
viticultural guru Dr Richard Smart what he thought of popular
notions of terroir which propose direct translocation of flavour
molecules from the soil to the grapes, and hence the wine. ‘This
is an absolute nonsense’, he replied. ‘I have never heard
this, yet you say it is popular. Who on earth postulated this?’
Dawid Saayman, a South African
viticultural expert known for his work on terroir, adds that, ‘I
don’t believe that the minerals taken up by the vine can
register as minerality in the wines. Minerality appears to me to
be more the result of absence of fruitiness.’ But it’s pretty
much a given that wines that made from grapes differing only in
the soil in which they were grown taste different.
So just what is the scientific
explanation for these terroir effects? It is an important
question, because providing a sound scientific footing for terroir
is a worthy cause. Not only will it lend credibility to the
concept in the eyes of sceptics, but it will also help the already
converted understand and therefore better utlilize terroir
effects.
If we are going to frame terroir
in scientific language, then we’ll need to start with some plant
physiology. The miracle of the plant kingdom is that these complex
organisms build themselves from virtually nothing: all a plant
needs to grow is some water, sunlight, air and a mix of trace
elements and nutrients. All the complex structure and chemistry of
an oak tree, a daffodil or a grapevine is fashioned from these
very basic starting ingredients. What do vine roots take up from
the soil? Primarily water, along with dissolved mineral ions.
It seems implausible that such a
complex structure as a vine is created from virtually nothing by
photosynthesis – the capture of light by specialized organelles
called chloroplasts, which turn light energy into chemical energy
that the plant can use—but that’s the way it is. As Richard
Smart emphasizes, ‘All flavour compounds are synthesized in the
vine, made from organic molecules derived from photosynthesis
ultimately, and inorganic ions taken up from the soil.’
Professor Jean-Claude Davidian
of the Ecole Nationale Supérieure Agronomique in Montpellier,
echoes these sentiments. ‘Nobody has been objectively able to
show any links between the soil mineral composition and the
flavour or fragrance of the wines’, he says. Davidian adds that
‘those who claim to have shown these links are not
scientifically reliable’.
on
to part two...
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