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On terroir, and the vine’s microbiome



Doesn’t it seem to you like these stories lately about microbes in soil affecting wine are making the concept of terroir even more complicated than we thought it was? We used to think terroir was a matter of the physical structure of the soil and the climate, or meso-climate, of the vineyard. John Winthrop Haeger, in his encyclopedic “North American Pinot Noir,” interpreted the soil part to include “orientation and aspect,” and possibly the “chemical composition.” But he said nothing about microbes.

Emile Peynaud, the great French enologist, in “The Taste of Wine” similarly referred to terroir’s “combination of site and soil,” and while he differentiated between “surface soil [and] subsoil and its water content,” he, like Haegar, has nothing to say about microbes. (For the record, as I’ve pointed out before, Peynaud takes note of the hand of man in crafting wine’s qualities in introducing the word “cru” to denote the combination of terroir and human intervention.) Even as hardcore a scientist as Clark Smith, in “Postmodern Winemaking,” refers to no fewer than “sixty five data dimensions” in soil analysis, but they have to do with structure, chemical composition and water content—not microbes.

So if this new report on the “wine grapevine’s microbiome,” published by the American Society for Microbiology and widely reported in scientific media, is true, we’re looking at a vastly more complex explanation of terroir than anyone has envisioned up to now. The study looked at “how different bacteria colonize these plants [i.e. grapevines] and also how those microbes might ultimately contribute to the wine’s sensory properties.” The study found a very close connection—almost an identity—between the “bacterial species found in the plant [and] the soil it was growing in.”

While one of the scientists who conducted the study, Jack Gilbert, conceded that “We don’t have evidence that bacteria are specifically contributing to terroir,” he firmly concluded that “those bacteria are affecting the chemistry of the plant,” which seems to pretty conclusively state that the microbes are, in fact, impacting terroir, since the chemistry of the plant obviously plays a large part in the qualities of the wine made from it.

The thing that puzzles me is this statement from Gilbert, which really requires more explanation than I’ve been able to find. “No matter where you are in the world, the types of bacteria growing on or in Merlot grapes are quite similar.” Gilbert looked at Merlot grapes or wine from Long Island, Bordeaux and California and found “similar bacteria species” in them all. Several things are unclear. Were the Merlot microbes also found in lab specimens of other grape varieties and wines? Were the Merlot bacteria substantially different from the bacteria associated with other varieties? Why should plants growing as far apart as California and France all possess similar bacteria? Does this suggest that Merlot itself can only thrive in the presence of certain bacteria?

I hope the scientists do a lot of followup work in these areas. This entire conversation about terroir has been stuck in a ditch for decades, and important new discoveries in the vine’s microbiome may help to push it forward. It will certainly give wine writers a whole new area to write about.

  1. Bill Haydon says:

    That’s all very interesting, but I still think that the presence of these bacteria amount to their being a contributing factor rather than a definitive factor. Chemical compounds in the soil, climate, exposureet et al will all have as great if not greater impact on the final expression of terroir.

    Here’s the best scientific study that I’ve read to date that looks more at chemical composition of the soil rather than bacterial presence.

  2. Bob Henry says:

    From New York Times
    (November 25, 2013):

    “Microbes May Add Special Something to Wines”


    By Nicholas Wade

    Terroir is a concept at the heart of French winemaking, but one so mysterious that the word has no English counterpart. It denotes the holistic combination of soil, geology, climate and local grape-growing practices that make each region’s wine unique.

    There must be something to terroir, given that expert wine tasters can often identify the region from which a wine comes. But American wine growers have long expressed varying degrees of skepticism about this ineffable concept, some dismissing it as unfathomable mysticism and others regarding it as a shrewd marketing ploy to protect the cachet of French wines.

    Now American researchers may have penetrated the veil that hides the landscape of terroir from clear view, at least in part. They have seized on a plausible aspect of terroir that can be scientifically measured — the fungi and bacteria that grow on the surface of the wine grape.

    These microbes certainly affect the health of grapes as they grow — several of them adversely — and they are also incorporated into the must, the mashed grapes that are the starting material of winemaking. Several of the natural fungi that live on grapes have yeastlike properties, and they and other microbes could affect the metabolism of the ensuing fermentation. (Several species of microbes are available commercially for inoculation along with yeast into wine fermentations.)

    But are the microbial communities that grow on the grapes of a given region stable enough to contribute consistently to wine quality, and hence able to explain or contribute to its terroir?

    Such a question would have been hard or impossible to address until the development of two techniques that allow the mass identification of species. One is DNA bar coding, based on the finding that most species can be identified by analyzing a short stretch of their genome, some 250 DNA units in length. The other is the availability of machines that can analyze prodigious amounts of DNA data at a reasonable cost.

    Armed with these new tools for studying microbial ecology, a research team led by David A. Mills and Nicholas A. Bokulich of the University of California, Davis, has sampled grape musts from vineyards across California. Grape varieties from various wine-growing regions carry distinctive patterns of fungi and bacteria, they reported Monday in The Proceedings of the National Academy of Sciences.

    They found, for instance, that one set of microbes is associated with chardonnay musts from the Napa Valley, another set with those of a must in Central Valley and a third grouping with musts from Sonoma. They noticed a similarly distinctive pattern of microbes in cabernet sauvignon musts from the north San Joaquin Valley, the Central Coast, Sonoma and Napa.

    The discovery of stable but differing patterns of microbial communities from one region’s vineyards to another means that microbes could explain, at least in part, why one region’s zinfandel, say, tastes different from another’s. The links between microbes and wine-growing regions “provide compelling support for the role of grape-surface microbial communities in regional wine characteristics,” the researchers conclude.

    “The reason I love this study is that it starts to walk down a path to something we could actually measure,” Dr. Mills said. “There are high-end courses on terroir, which I think are bunk. Someone has to prove that something about terroir makes it to the bottle, and no one has done that yet.”

    Microbes are deposited on the grape surface by wind, insects and people, and may fail or flourish because of specific local conditions such as the way the grape vines are trained. And there may be genetic affinities between particular microbial species and each variety of grape, the researchers say.

    Even if Napa’s chardonnay grapes, say, carry a distinctive pattern of fungal and bacterial species, the Davis scientists need still to prove that these microbes affect the quality of the wine. Microbes could exert an influence both during the lifetime of the grape and during fermentation, when they may add particular ingredients to the wine. “We will look at how overall microbial communities correlate with quality traits in the wine, and whether you can predict quality from the microbes present,” Mr. Bokulich said.

    Thomas Henick-Kling, a professor of oenology at Washington State University, said it was plausible that microbes are a component of terroir. “Unripe grapes taste the same the world over,” he said. It is known that single strains of yeast can have a strong effect on a varietal’s flavor, he continued, “so it’s likely that microbes play a larger role than presently known and are probably a part of the regional differences that we recognize.”

    While Dr. Mills said that “I make fun of terroir all the time,” he believes that regional distinctions between vineyards do exist and that microbes have a role in creating them. If the specific links between microbes and the sensory properties of wine can be identified, growers will be able to take a savoir-faire attitude to terroir instead of a je ne sais quoi shrug.

    On the other hand, he added, pinning the qualities of wine on bacteria and fungi may spoil that frisson of enchantment for some connoisseurs. “Many people don’t want this figured out,” he said, “because it demystifies the wonderful mystery of wine.”

  3. Bob Henry says:


    From UC Davis
    (November 25, 2013):

    “Sequencing Study Lifts Veil on Wine’s Microbial Terroir”


    It’s widely accepted that terroir — the unique blend of a vineyard’s soils, water and climate — sculpts the flavor and quality of wine. Now a new study led by UC Davis researchers offers evidence that grapes and the wines they produce are also the product of an unseen but fairly predictable microbial terroir, itself shaped by the climate and geography of the region, vineyard and even individual vine.

    Results from DNA sequencing revealed that there are patterns in the fungal and bacterial communities that inhabit the surface of wine grapes, and these patterns are influenced by vineyard environmental conditions. The findings appear online this week in the Early Edition of the Proceedings of the National Academy of Sciences.

    “The study results represent a real paradigm shift in our understanding of grape and wine production, as well as other food and agricultural systems in which microbial communities impact the qualities of the fresh or processed products,” said Professor David Mills, a microbiologist in the Department of Viticulture and Enology and Department of Food Science and Technology.

    He noted that further studies are needed to determine whether these variations in the microbial communities that inhabit the surface of the grapes eventually produce detectable differences in the flavor, aroma and other chemically linked sensory properties of wines.

    The study co-authors suggest that by gaining a better understanding of microbial terroir, growers and vintners may be able to better plan how to manage their vineyards and customize wine production to achieve optimal wine quality.

    Sequencing grape microbes

    To examine the microbial terroir, the researchers collected 273 samples of grape “must” — the pulpy mixture of juice, skins and seeds from freshly crushed, de-stemmed wine grapes.

    The must samples were collected right after crushing and mixing from wineries throughout California’s wine-grape growing regions during two separate vintages. Each sample, containing grapes from a specific vineyard block, was immediately frozen for analysis.

    The researchers used a DNA sequencing technique called short-amplicon sequencing to characterize the fungal and bacterial communities growing on the surface of the grapes and subsequently appearing in the grape must samples.

    They found that the structure of the microbial communities varied widely across different grape growing regions. The data also indicated that there were significant regional patterns of both fungal and bacterial communities represented in Chardonnay must samples. However, the Cabernet Sauvignon samples exhibited strong regional patterns for fungal communities but only weak patterns for bacterial communities.

    Further tests showed that the bacterial and fungal patterns followed a geographical axis running north-south and roughly parallel to the California coastline, suggesting that microbial patterns are influenced by environmental factors.

    Taken together, these and other results from the study reveal patterns of regional distributions of the microbial communities across large geographical scales, the study co-authors reported.

    They noted that it appears that growing regions can be distinguished based on the abundance of several key groups of fungi and bacteria, and that these regional features have obvious consequences for both grapevine management and wine quality.

    Collaborating with Mills were graduate student Nicholas Bokulich of the UC Davis Department of Viticulture and Enology; John Thorngate of Constellation Brands Inc.; and Paul Richardson, CEO of MicroTrek Inc., a company founded to provide microbial mapping services to help vintners understand this phenomenon.

    Constellation Brands Inc. provided in-kind support for the study through sample and metadata collection.

    Funding for the study was provided, in part, by the American Wine Society Educational Foundation Endowment Fund, the American Society of Brewing Chemists Foundation and the Wine Spectator.

  4. “The grape is the same – it all in the ground”
    I have seen it on the mBiosphere the other day.
    Is it the hen or the egg? To me this is what I allways have been thinking about the Terroir-thing. Im sure everything is connected.

  5. Bob Henry says:

    An update on microbes:

    “Microbes in Pressed Grapes Before Fermentation May Predict Flavor Metabolites in the Finished Wine”


  1. March 27, 2015 | Microbiome Digest – Bik's Picks - […] On terroir, and the vine’s microbiome – Steve Heimoff […]

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