I wrote an article for Wine Technology magazine a couple of months ago that looked into the tangible effects of soil and geology on the quality of the fruit and resultant wine.
The piece itself was an ambitious undertaking and one where I barely scratched the surface, but it is a research area that I have a lot of interest in and I’ve attached the story below. The aim was to provide a brief overview of the topic, removing my romantic bias where possible, from a selection of sources that included professors, geologists and winemakers.
It’s worth mentioning here that, with the demise of NZ Grape Grower, Wine Technology is one of the few technical, industry-focused magazines left domestically and well worth getting hold of if you’re involved in the winegrowing sector (both winemaking and viticulture).
Soils, Geology - and Wine that Rocks
Grapegrowers like to preach about it, winemakers think they can taste it, and wine marketers write hyperbole about it, but is there really a tangible connection between the unseen, underground world of rocks and soil with the characteristics and qualities in wine?
There is considerable anecdotal and empirical evidence worldwide that would suggest a strong correlation between the type of soil grapevines grow in and the corresponding flavours, textures and aromatics of the wine, though little research has been conducted (partly due to the scope of such an undertaking) and there is certainly no scientific proof. Yet.
It’s the sort of topic that polarizes opinion and yes, before you start knowingly shaking your head, there is overlap to the terroir debate. There are Old World vignerons who swear on their ancestor’s graves that site specificity is real and you only have to walk their vineyards to actually see the change in soil type within identical blocks and then taste the difference in the wines they craft. On the flipside, a selection of wine scholars around the globe argue that soil plays only a secondary role, placing much more emphasis on climate and canopy management. They certainly lend no credence to the premise of geology having an impact, nor the notion of mineral characteristics or any such thing being derived from rocks.
Mike Weersing of Pyramid Valley Wines in the Waikari district of North Canterbury has had the privilege to work in vineyards and wineries all over the world. As a proponent of soils and geology having a strong influence on wine, Weersing has drawn on his experience to make some philosophical comparisons.
“Everything in the Old World from good producers is predicated to letting the soil speak, letting the soil show. In the New World, we say ‘yeh, but if you change winemaker, yield, viticulture, etc, the soil becomes such a small part that it’s probably meaningless’. I think that the single biggest difference – the reason why Europeans know and believe in the influence of soil – is based on their desire to express their sites. In the New World we want to express varietal character.”
“There are some very basic patterns; there are certain kinds of soil that have a consistent imprint on the wines grown from them. You can defy that imprint if you choose to. This is why most New World winemakers and grapegrowers think that soil has no impact; because it can be overridden. But that doesn’t mean it’s not there. The reason soil shows more precisely and convincingly in Europe is because that’s what they want to show.”
“I’ve worked around Europe with a lot of growers who emphasise terroir and who work deliberately to allow differences of site and soil to show in their wines. Patterns then emerge. From my time in the Mosel, Alsace and Burgundy, you see consistent soil types and consistent impacts on the soils grown from them. The European sensibility is that limestone provides structure – not just more tannin (though it can be), but a kind of density; a rigour that takes time to soften. There is absolute agreement that wines grown on limestone take longer to come round. They age better, or age longer, or require more time to show what they have. Pinot is a thin-skinned variety where the seed to skin ratio is tipped towards seed; because it makes light, perfumed wines, the extra structure that limestone confers is valuable.”
The idea of a winemaker’s will allowing the soil and geology to talk is an interesting one. This is the approach that Weersing takes, ensuring that his winemaking is invisible and transparent to fully expose the pure expression of place. It’s hard to ignore the fact that even though men like Weersing may comprise an overall minority, their products speak louder than words, with an uncannily high, exponential ratio for some of the most interesting wines in the world. Surely that must count for something; you think, you act, you are.
I spoke to Professor Robert White of the University of Melbourne; the author of “Soils for Fine Wines” and “Understanding Vineyard Soils”, hoping that he could shed some light on some of the more technical mechanics of what really goes on under the ground.
“We have the wine technical approach on one hand, and the wine marketing approach on the other. The more popular idea is that soils can influence wine character. There is quite a lot written by wine writers and vineyard managers/owners, but it’s usually not based on any scientific analysis; it’s usually based on their assessment of the flavour and aroma of the wines. I’m not an expert in that area – I don’t have very good sensory tasting and I’m no Master of Wine or anything like that – but people like Max Allen write quite confidently about the soil influence and the sense of place. I’ve been in correspondence with David Schildknecht, one of Robert Parker’s team, who certainly believes that there are soil influences on wine character in the Old World.”
“The reason why there isn’t a lot of progress lies with the abundance of variables and their interactions. If you want to look at a particular factor – like manganese, or calcium – you have to eliminate the other variables. This is easier said than done. I prefer, as a working hypothesis, that adverse mineral nutrition may give the wines different characters. I also support the French view that water in the soil – its rate of release and drainage – has a very important effect on the maturation of the grape and the character of the wine.”
This French view that White refers to has its roots with two French researchers some thirty years ago; Seguin and Pomerol, and more recently van Leeuwen. They concluded that the chemical properties of soil failed to demonstrate any links (though recent experiments show that soil chemistry can in fact trigger gene expression and hormonal responses in grapevines), but the physical properties – namely the structure and inherent hydrology of the soil – were determining factors across different vineyard sites. Countless papers over the past half century have been published that support this theory.
Thus, the geological influence is somewhat obscured and indirect because it acts through the soil forming process. David Farmer, a geologist who now lives in the Barossa Valley working in wine retail, presented some pragmatic arguments on the soil/geology dogma.
“The cornerstone of terroir is wrapped in soils, yet the connection is very vague and to date I have been unable to relate it back to geology. In all likelihood there is no connection to geology. I have wanted to believe otherwise but the science of my own observations has led me in the opposite direction.”
“What we can say is that the vine will produce finer grapes in this environment here, than that environment there. This relates to how the vine grows, so the soil texture and water access will play a role. You cannot say that if we have this bedrock with this soil we will get this taste (anywhere in the world). I actually think every vineyard area is unique. Some are so unique that the flavours make great wine.”
Farmer also added some sobering thoughts to the Old World and New World discussion,
“I find it helpful to imagine back to when vines were planted in new colonies with rootstocks from Europe. We planted in the regions where we settled and no thought was given to the climates or soils of the Old World. With today’s knowledge, if Australia was just being founded and we went rigidly with Old World data, some of our best regions would not be planted and we wouldn’t have Grange.”
“Now we can do the reverse and say if the New World was the Old World and we were now planting Europe for the first time, with all the knowledge we now have where would we go? In my belief it would be a long time before someone would suggest draining the cobbled marshes along the Gironde.”
“This reasoning is what makes me so enthralled by New Zealand. Before our eyes we have watched in the last 20 years as three or four world class areas have opened up. We have a tiny scrap of country deep down in a vast ocean making great wines. The soils are for the most part derived as glacial outwash and are young. There is no evidence of a geology influence and I argue much of it is an experiment - one step removed from hydroponic farming. The Gimblett Gravels are a very special case in point. For me, New Zealand explains very well the major reasons for complex grape flavours; major weather patterns and variable local patterns (such as heat traps like the Gimblett Gravels), rather than the soil.”
“So it’s how water is delivered to the plant that’s most important, and in some cases to do this in the most favourable way a slope is important (like in Burgundy). Not too much, not too little – it must be just right.”
The common theme here focuses on water within the soil profile; not only rates of water storage and drainage but how water moves – the effects of suction, gravity, porosity, permeability and so forth. So, does it then stand to reason that two soils with identical or very similar hydrology could have totally different mineral constituents and still engender wines of like characteristics? Whilst there is wide acceptance that hydrology is a determining factor, it’s but one piece of a larger puzzle affording only a glimpse of clarity for a question that may very well remain unanswered for the duration of our lives.
In closing, Weersing aptly summarizes the status quo and his desire to let sleeping dogs lie,
“There is no scientific proof that soil type or geology directly influences or impacts the way that a wine tastes or smells. In general when we talk about the influence that a soil has, we’re often talking about shape in the mouth, or architecture, or the ability of the wine to age. Nobody has made a massive effort to try and understand why a wine that grows on sandstone next to a wine that grows on limestone is so different (when the winemaking and viticulture are the same). We don’t know whether it’s vine physiology, whether its root physiology, whether it’s the chemical makeup of the soil, the physical structure of the soil, hydrology, or whatever. But it doesn’t really matter to me that we don’t understand why it happens – just because we don’t understand it, doesn’t mean that it doesn’t happen. It almost pleases me that there are still great mysteries in the world of wine.”
