Yeasts Gone Wild: Part 1.

October 12th, 2008

Yeast gone wild.  Composite from http://exploration.nasa.gov and other images available on the web.

Yeast gone wild.

“There are no wild yeasts, only feral ones” Bruno D’Alfonso once told me bluntly. I had been probing the winemaker about notions in the wine loving and wine writing spheres about what is and is not excessive intervention and manipulation in modern winemaking.

Recalling my undergraduate and medical school microbiology, I had some understanding of yeasts and concepts of their utility in winemaking. Bruno’s argument made sense to me, and it affected my thinking about wine yeasts going forward.

After a recent increase in blog chatter about natural wines and the aversion some writers and critics have to cultured yeasts, I wanted to revisit this topic. Obviously, there is a disconnect between what the winemakers know and what some writers and critics believe. It seems to me, though that getting hung up over the use of inoculated yeasts as an inherently bad thing is misguided.

This is the first in a series of three posts that look at the idea of wild yeasts.

First, a little background.

What we commonly think of as yeasts, is a group of microorganisms (categorized as fungi) capable of carrying out fermentation. In this group, there are some like Brettanomyces, Dekkera and Kloeckera which can ferment wine grapes but are thought of as spoilage yeasts because they tend to produce off aromas (which result from the chemical byproducts of these yeasts’ fermentation). If those are undesirable yeasts, there is one desirable species: Saccharomyces cerevisiae. This particular yeast has had a very positive relationship with humankind for a very long time.

To get a sense of the history of this relationship, I recommend reading the shaded area (“Box 1″) in Robert K. Mortimer’s article about the evolution of the genome of Saccharomyces cerevisiae. (Dr. Mortimer is Emeritus Professor of Molecular and Cell Biology at UC Berkeley. Thanks to Larry Brooks for sharing this article with me).

Wine Myths Abound.

Lisa Van de Water, a microbiologist specializing in fermentation problems, calls it a “romantic myth” to believe that, somehow, the micro-environment of vineyard and winery select yeast strains that settle on the grapes and winery surfaces and make their way into the vineyard and, if allowed to, can result in complex wines.

Napa winemaker, Philippe Langner, echoes this, saying:

“There is always an assumption that using wild yeast produces better wines. In the imagination of some people, letting nature follow its course is best. Sometimes this works, often it doesn’t. Some wild yeast fermentations produce beautiful results but I’m sure that many more produce faulty wines and you never hear about those.

Additionally, there is a notion of local or regionally native yeasts being somehow part of terroir or “best” for a given grape variety. Jerry. D Murray, winemaker at Oregon’s Patton Valley Vineyard, expands on this aspect of the “native yeast mythology” by saying:

“Another thing I find fascinating is the assumption that ‘native’ or ‘wild’ yeasts are somehow more ‘varietaly’ correct than cultured.  That if I am making pinot noir and using cultured yeasts then I should be using a Burgundy yeast. Why, if I am not making Burgundy?  And that if I grow pinot noir and employ spontaneous ferments that it somehow enhances varietal character; as if the yeast cares about what varietal [sic] is being fermented.”

It is important to remember that cultured S. cerevisiae used in winemaking is not a genetically modified organism. It is not recombinant. Nobody has “tweaked” its DNA. Cultured yeasts come from wineries, not labs. They are selections collected and grown on a nutrient-rich medium to increase their numbers. This does not result in homogeneity of organisms in the culture because a single winery is home to numerous distinct strains of S. cerevisiae.

This brings us to the idea of “natural” and “unnatural”. Many people do not understand that a human guiding hand is only a small factor. An organism’s inherent characteristics (their “nature”) are not altered when a yeast selection is made. Larry Brooks puts it this way:

Natural does not always mean good. There’s a reason that we have selected certain tomatoes, for instance, over others and the same holds true for yeast. It is a truism that there is a range of performance for all organisms – ourselves included – if you can have organisms at the top of their range, why not? For example we do not use wild grapevines for winemaking – with good reason. And the same holds true for yeasts.

Wine is artificial in the best way – in the sense of artifice.”

The truth is out there (but is it in the vineyard?).

While numerous yeasts may grow naturally on grapes in a vineyard, Saccharomyces cerevisiae makes up a tiny minority of these microorganisms. It does not spread by airborne means like other yeasts and molds so it can’t leave the fermenter and winery surfaces and waft into the vineyard.

It has been demonstrated, that S. cerevisiae is present on surfaces in the winery and that it is carried into the vineyard from the winery by personnel, insects and on pomace used as fertilizer. However, its optimal environment is grape juice. Larry Brooks points out that the vineyard “…is not a particularly hospitable environment for them [yeasts] except during the harvest period. The grape juice itself is where they thrive.”

That S. cerevisiae is not indigenous to the vineyard has been demonstrated scientifically. In a presentation she gave in 2002 at a microbiology seminar, Van de Water said:

“…research in the past decade has shown that Saccharomyces, the yeasts used by winemakers for fermentation, are rare in the vineyard. Grape samples taken directly from the vineyard hardly ever contain any Saccharomyces yeasts at all.” (Thanks to Philippe Langner for this resource)

So the S. cerevisiae coming into the winery on fruit during harvest is not likely to be “wild” but “feral” as Bruno D’Alfonso called them. Arcadian‘s winemaker Joe Davis explains his skepticism of “wild” yeasts:

“I am always amazed at the interest in local yeast and wonder how many actually culture and identify them [the yeasts] at the time of fermentation. I often hear other winemakers talking about using only indigenous yeast and my immediate response is how do you know? Were you able to identify them and if so what were they specifically?  Could it be yeast from a previous fermentation in your cellar from last week, or even last year? I have yet to have any winemaker answer that question. Too many assumptions are made that prove to be incorrect.”

Josh Hermsmeyer of Capozzi Winery, recently wrote about genetic typing of yeast species and strains at vineyards contracted by Ravenswood. Over several vintages, this identified about 30 yeast species and strains. The majority were S. cerevisiae but there were other species as well, he says.

The investigation showed that four strains of S. cerevisiae prevailed in the subsequent fermentations. I have no information, though, how these prevailing strains compared with the domesticated strains already present in the winery. Knowing that would shed more light on the origin of these yeasts.

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In the next installment: “Wild-Domesticated-Feral.” and “What’s the Deal?”. Coming this Wednesday.

 

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8 Responses to “Yeasts Gone Wild: Part 1.”

  1. wine sooth » Blog Archive » Yeasts Gone Wild: Part 2. Says:

    [...] wine sooth searching for truth in wine « Yeasts Gone Wild: Part 1. [...]

  2. Jerry D. Murray Says:

    Arthur,

    I do want to go on the record as being a winemaker that employ’s spontaneous fermentations. It works well for me ( in Pinot Noir ). My issue arises from critics ( I use the term loosley ) that dismiss wines because they were made from cultured yeasts. I won’t second guess a winemaker that avoids spontaneous fermentations, we all have our own level of risk we are comfortable with.

  3. Josh Says:

    Great series Arthur!

    Just wanted to note that Joel conveyed to me that the yeast identified in the vineyards was distinct from those they had used in the winery in the past.

    I was – and am still – thrilled that Joel was kind enough to allow me to share Ravenswood’s research. Really good stuff.

  4. wine sooth » Blog Archive » Yeasts Gone Wild: Part 3. Says:

    [...] is the third post in a series of three that look at the idea of wild yeasts. (See the first post here and second post [...]

  5. Bench Grafts: What I’m Up To Says:

    [...] over at Wine Sooth has posted an exhaustive three part series on wild wine yeasts dubbed “Yeasts Gone Wild.” He even has a scandalous pic [...]

  6. Nick Says:

    In Principles and Practices (Boulton, Singleton et al.), the concurring opinion to yours was published back in 96. This is (was?) a principle text used for teaching at UCDavis, and though published in 96, has no information (on our yeast topic) newer than 90. Professor emeritus Mortimer, a yeast geneticist from UC Berkeley, concluded a study of uninoculated fermentations in 93 or 94 I think. He found that: Almost all of the vineyards he looked at had S. cereviseae on the grape surface. The yeast doing the fermenting were the same as those found on the grapes. The average number of different S. cereviseae strains per fermentatuion was four. Each strain dominated a different part of the fermentation.
    No contention was made vis the flavor contribution from these yeasts. The study was contributing information to the possible source of the yeast, and the number of different strains present.
    What any decent UC VEN student can tell you is that the S. cereviseae hanging out on the grape skin is biding its time: They are metabolising aerobically, taking one six carbon sugar and producing 32 ATP, and doing this very slowly, very stingily, making the most of a very scarce resource. When a grape skin is compromised and abundant six carbon sugars become available, S. cereviseae switches its metabolism to fermentative, and though only making 2 ATP per six carbon sugar, quickly overwhelms all other microoganisms by dint of sheer reproductive rate.
    That there are very few S. cereviseae on the grape surface proves nothing. They are fully capable in such small numbers to outcompete the competition. Not that I’m taking sides.
    I have more on this. Does anyone have any further info on Mortimer’s research and any follow up studies?

  7. Bill Edinger Says:

    First, I’d prefer that this not be published, but I have a couple of corrections to make: Lisa van de Water does not have a doctorate, and she is not associated with Fresno State. As someone who is a lecturer in that department (I’m standing next to Jim Kennedy in the website photo), I can say this with some confidence.
    Otherwise a nice posting.

  8. Arthur Says:

    Thank you for the clarification, Bill

    At the time of publication, this posting had a link to Lisa van de Water’s bio. Since that page is no longer there, I have removed the link.

    Additionally, at the time of posting, I understood van de Water to hold a doctorate. Upon checking, I cannot verify this so I have edited the “Dr.” out.

    Thank you for the clarification.


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