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

Are wine drinkers healthier than beer drinkers? Not so fast…

Yet another study was published this month showing that habitual wine drinkers are, all things considered, healthier than habitual beer drinkers. This one was about Dutch people — part of a national dietary survey — but similar findings have come out of the United States and other parts of Europe. We can draw all kinds of conclusions from such data, some of them plausible, but many of them ill-advised. Let’s jump to some conclusions and see where they take us.

1. Wine is better for you than beer – Maybe. Let’s say that you’re a marathon runner who runs the eight miles each way to work every day, teaches yoga in the evenings, eats salads for breakfast and lunch and half a pizza for dinner most nights. Your next-door neighbor drives to his desk job, gets winded walking up the stairs, and eats stir-fried tofu and veggies for dinner most nights. A study could conclude that you, the pizza-eater were healthier than your neighbor, the stir-fry eater, but that wouldn’t mean that pizza was healthier than tofu. Clearly, other lifestyle choices are contributing to your difference in health. The same is true for studies of habitual wine or beer drinkers: wine drinkers may be likely to make healthier choices in general.

In fact, this study came to exactly that conclusion: wine drinkers ate more fruits and veggies and less red meat, soda, margarine, and snacks than beer drinkers. We clearly can’t ascribe the health difference between the two groups just to their choice of beverage. That said, the study found that when the effects of several other health behaviors were accounted for — that is, when we measure and remove the effect of total calorie consumption, or smoking — wine drinkers were still healthier. Moreover, this study looked at healthy lifestyle habits, not at  measures of the participants physical health other than body mass index, and measuring healthfulness by weight-to-height ratio alone is pretty simplistic. This study gives support, then, for the idea that wine might be healthier than beer, but doesn’t give us enough information to reach that conclusion.

2. People who want to be healthier should start drinking wine – Maybe but, again, not supported by this study. We’ve already concluded that beverage alone isn’t responsible for the health difference between wine and beer drinkers. There’s no reason to believe that starting to drink wine, or switching from beer to wine, will help you eat more veggies.

3. Wine drinkers are better educated than beer drinkers – Yes, actually. Among the four groups considered in this study — wine drinkers, beer drinkers, spirits drinkers, indiscriminate drinkers with no preference, and alcohol abstainers — wine drinkers were most likely to have university degrees.

4. Wine drinkers tend to have healthier lifestyles than beer drinkers – Yes. This is the study’s primary conclusion: “alcoholic beverage preference was associated with dietary habits in The Netherlands.” On average, wine drinkers eat more healthfully, consume fewer calories, are less likely to smoke, and tend to have a higher socioeconomic status (which is itself strongly correlated with healthful habits) than beer drinkers. But we don’t know why this is true, though we can say that socioeconomic status and education have a lot to do with it.

So, we can fairly say that regular wine drinkers tend to live healthier lifestyles than regular beer drinkers in the Netherlands. Generalizing these findings to other countries is dangerous. Similar studies in other northern European countries (Denmark, for example) and the U.S. have come to similar conclusions. No surprise: any American could probably guess that American wine drinkers in general tend to be better educated and wealthier than beer drinkers. But that’s a cultural phenomenon. In Italy and Spain, where regular wine drinking in volume is a habit of the old guard, wine consumption doesn’t necessarily go hand-in-hand with healthy eating or other markers of a healthy lifestyle.

The conclusion? Studies such as this are interesting. Maybe they help the medical profession get a better picture of who to target with healthy lifestyle interventions (though education and socioeconomic status do most of the work here). But they tell us nothing at all about whether wine is good for you.

What I’ve been reading

I’ve just added a page (linked at the right) entitled “What I’ve been reading” where I’ll keep short notes on books and articles that I’ve been reading of late, mostly about wine, science, and rhetoric (and sometimes about other things). I hope that some of these may spark your interest, too.