Quantifying terroir with chemistry: still searching for the Holy Grail

It’s the Holy Grail of wine research: chemical proof of terroir. Though the quest has fallen out of favor with those who think that the Grail can never be found, or that it doesn’t exist, it should come as no surprise that many are still searching.

The most recent contribution: a team from France and Germany have used mass spectrometry to look for chemical differences among wines from four different vineyards — two in the Côte de Beaune, two in the Côte de Nuits — across the 2007, 2008, and 2009 vintages. Mass spectrometry* is in essence a way of separating out all of the chemicals in a sample by weight — each compound has a unique weight — and displaying what the sample contains by showing a blip on a graph for every unique compound. A sample containing only one compound will show only one blip, a sample containing two compounds will show two blips, and something as complex as wine will show — according to this study — up to 7016 unique blips. The researchers analyzed must, dried skins, and finished wine (fermented by the commercial winery) to come up with what is, essentially, a chemical fingerprint: a unique set of blips for each sample.

Think we know a lot about wine chemistry? These scientists could identify only about 5% of the compounds identified in their fingerprinting. If we ever wanted evidence that wine is more complex than current chemistry can explain, we have it here. We know about all of wine’s major constituents, and many of the minor constituents that affect flavor, color, and smell. But amongst all of those yet-unidentified minor components might be the explanations for any number of wine mysteries we can’t currently explain.

Even without knowing what all of the compounds are, though, we can still see their signature blips and make some generalizations about which wines are most similar based on the similarity of their fingerprints. No doubt the researchers hoped that the different wines would show nice, tidy similarities among wines from the same place and wines from the same year. They found similarities; they just weren’t tidy. The Côte de Beaunes wines weren’t as a group chemically distinguishable from the Côte de Nuits. And one of the Côte de Beaunes wines grouped more closely with the other vineyards’ 2007 vintages even in 2008 and 2009, though the other wines were roughly similar by vintage.

Maybe out of desperation — or maybe because it was part of the plan all along — the researchers fingerprinted the wines again in 2012, three, four, or five years after bottling for the 2009, 2008, and 2007 vintages, respectively. Encouragingly, the wines did group more closely after some age: both the regions and the vintages formed tighter clusters. The authors concluded that “this fundamental result highlights the fact that the terroir as a whole – i.e. that considers the vine-soil-climate-human ecosystem – definitely impacts the initial chemical complexity of a wine, but time – i.e. bottle ageing – might be required to fully reveal it through the in-bottle diagenesis of complex chemical signatures.” Diagenesis, by the way, is the process by which accumulating particles transform over time into sedimentary rock. It’s a geology term, though I can see the analogy here in how accumulating chemical changes can transform over time into something new with distinct properties.  This is taking things just a bit too far, I think. Their results from just-bottled wine aren’t convincing and, with their broad definition of terroir, they’re really saying nothing more than “different wines are different,” which isn’t very helpful. There’s also the problem that the vintages aged for different amounts of time, and that we only have two time points: some unspecified time very shortly after bottling, and three or four or five years later. In another five years, would the wines have grouped even more tightly? Or less so?

These scientists want their results to mean “that various and distinct chemical reaction pathways can actually exist in bottles, which provide after a few years of ageing an instantaneous picture of the chemical complexity associated with a specific terroir that could potentially be as small as the countless ‘climats’ of Burgundy.” I’ll grant them the point about chemical complexity, which is beautifully demonstrated in this paper even if it is something we already knew. The rest of their conclusions seem out of place. Disappointingly, they haven’t demonstrated that they can link that chemical uniqueness with individual vineyard plots. Not even close, I fear. First, their sample size is too small, looking only at four vineyards from two regions (with no mention of what the individual differences are between the vineyards in terms of soil, elevation, etc.). Second, the wines from each vineyard weren’t more similar to each other than to the other wines from the same year or the same region, which seems to quite clearly say that these chemical profiles can’t be used to distinguish local terroir. Again, all we can say with any confidence is that different wines are different.

The strength of this study lies in its being, with any luck a jumping-off point. Chemically fingerprinting terroir is a worthy goal, and if chemists analyze enough wines, they’ll eventually see useful patterns. I imagine these wine like stars in a crowded night sky. Amongst the billions of stars, if we isolate just four or six, we can say that some are closer together than others, or that they’re clearly different points in the sky. Ho hum. But if we look at enough stars, we can start to develop constellations — which, like terroir, are a story, a tool we use for understanding the world. And if we look at enough stars with the right kind of instruments, maybe we can start to develop even more useful tools for thinking about them.

I suppose, then, that the Holy Grail is still out there, amongst the stars.

*A more complicated explanation of the kind of mass spectrometry that these researchers used, along with a lovely explanatory video, is here, courtesy of the Johnson lab at Yale

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5 thoughts on “Quantifying terroir with chemistry: still searching for the Holy Grail

  1. Pingback: The Science of Terroir Has a Long Way to Go | Edible Arts

  2. Pingback: “Does bottle age reveal terroir ?” A discussion. | Noble Route

  3. Hi Erika – Thanks for the article. I have posted a response on my blog, as the article you discuss is of particular relevance to me since I have recently begun an internship in the lab responsible for this study. I find your post well-written and carefully considered, but I have chosen to post my response directly on my blog to go into a bit more detail than I will here! http://wp.me/p1JBUd-nT

    • Alissa, thanks very much for the conversation. I’ve left my thoughts on what you’ve said as a comment on your post. Allow me to reiterate here, though, that I’ll agree wholeheartedly that the knowledge generated through a journal publication is a very different animal than the knowledge held by people in the lab responsible for the publication (part of my PhD studies; raise your hand if you’ve heard of Latour). I’m actually a bit sorry that you focused so much on critiquing the article (and my comments on the article) rather than putting the article in the broader context of the lab!

      • A great suggestion, and hopefully something to come. I’ve only been in the lab for a couple of weeks, and as my project is a bit different from the work published in the article, I am not familiar enough with their total body of knowledge to be sharing at this point. There is also, as another unfortunate consequence of the present scientific system, the question of confidentiality, as there are, of course, more recent results that give deeper insight into this work that are in the pipelines of publication, but which I do not have authorization to make public. Alas… limited by the structural restraints of the system, this interesting question of differences between published knowledge and knowledge actually possessed by researchers is a difficult one to get around. But maybe someday…

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