Last week the University of California at Davis announced its latest research into terroir, that elusive concept that says wine profoundly reflects the place where the grapes it's made from grew. And now we're all trying to figure out what it means. So, I should add, are the scientists who did the study.
Prof. David Mills analyzed the mix of fungi and bacteria in crushed grapes from widely spread vineyards in Napa, Sonoma and Central Coast. By sequencing genes in 273 different lots over two vintages, he and his colleagues found that the microbe communities fell into distinct and predictable patterns depending on their location and grape variety. Intriguingly, the communities in Sonoma looked very different from those in Napa, and Sonoma showed more similarities to Central Coast than it did to Napa.
The big question is what this means for wine.
It's pretty clear that geography, geology and climate affect the character of the wine made from a specific place. Now there's the tantalizing suggestion that microbes could be in play as well. So far, that's all it is, a possibility. Nowhere in Mills' research does he connect these microbes to the qualities of the wine actually produced from the vineyards.
That hasn't stopped commentators from taking it for granted, however, that whatever it is that makes the wine from a certain vineyard distinctive depends on the microbes in the soils and on the grapes.
Tempting as it is to say that this study proves it's the microbes that make terroir apparent in the finished wine, we don't know that yet. We know that certain geographic, geological and climate conditions demonstrably influence various elements of the wine (aromatics, flavors, structure, etc.). These same environmental factors could simply encourage a certain mix of microbes, which in turn could have no identifiable effect on the finished wine. We just don't know.
This would be easier to talk about if we could all agree on just what terroir is. Unfortunately, everyone seems to believe in a different concept. Some focus on soil, others on climate. Some include the natural yeasts that cling to the grapes. Those who follow the precepts of biodynamics speak of the life in the soil, not just microbes but insects too. I've even heard some definitions that include local winegrowing traditions.
Exactly how all these affect wine is also a matter of some conjecture. It's possible to discern differences in wines from different regions of Europe, though how much is due to grape variety, grapegrowing and winemaking practices (usually not included in a reasonable definition of terroir), and how much to the environment (a pretty good one-word definition), has yet to be settled.
Then again, what is it in the wine that specifically can be attributed to terroir? Texture, as in a tendency toward certain kinds of tannins? That can be affected by viticultural practices and winemaking processes. Fruit and spice character? Picking dates and clonal selections can define those. Other flavor notes? Fermentation yeasts and winemaking techniques can produce those.
These are some of the things that make terroir so hard to define. And don't get me started on how easy it is for us to find specific indications of terroir in the wine we're drinking when we know who made it and where it came from, thus setting up specific expectations. If we can't taste it in the glass when we taste it blind, is it really there?
In the end, however, I do believe terroir exists, but as a set of potentials, not predefined flavor or texture profiles. Every vineyard has certain tendencies—particularly tannic wines, a characteristic cherry flavor, certain floral notes—some more noticeably. These microbes are just another tantalizing factor that might, just maybe, if we can prove it, help explain why certain vineyards (or regions) do seem to make wines distinct from others.