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11.07.2008

Semi-Debunking Wild Yeast Fermentation in Wine

If you've read many wine labels, especially those of wines that cost more than $25, you've almost certainly seen on that contains the phrase "fermented with wild yeasts" or "native yeast fermentation." This indication that the winemaker has not used a so-called "commercial" yeast is often a telltale clue as to the overall philosophy of the winemaker. Making wine without commercial yeasts can be more difficult, more unpredictable, and more risky than some are willing to accept. Those who do eschew commercial yeasts often do so because they are committed to making what they believe is a more natural wine, both for its lack of "intervention" by the winemaker, as well as because the yeasts that do end up driving the fermentation are believed to be from the vineyard and part of its ecology.

Without a doubt, making wine without commercial yeasts represents a more traditional method of making wine, but apparently the more we learn about yeasts and winemaking the less it seems that there actually is any such thing as a wild yeast fermentation.

A recent thread on the Mark Squires bulletin board addressed this very topic, and I highly encourage anyone who is interested in the subject to check it out. The discussion ranges across a number of different issues regarding yeasts, often getting quite technical, but the gist of it can be boiled down to a simple set of arguments.

First, it is clear that there are yeasts on the skins of the grapes out in the vineyards, and that when no commercial yeasts are added (and sometimes even when they are) some these yeasts can also be found working away in fermenting grapes in the winery.

However, it is also true that most of the time the yeasts that do the most work in fermenting the grapes in the winery are very different yeasts than are found in the vineyard. Which begs the question where, exactly, did they come from?

The answer, according to a lot of winemakers and researchers, is from within the winery itself. No matter how well a winery is sanitized, it tends to harbor all sorts of biological elements, including complex "cultures" of yeast that breed, mutate, and even evolve in the little ecosystem that is the winery.

If the winery ever has used commercial yeasts, this local culture will most certainly include some of these commercial yeasts. And if it hasn't it will likely include yeasts that were brought into the facility on humans, pets, equipment, insects, and more.

All of which is a long-winded way of saying that the decision to not use commercial yeasts to ferment the wine doesn't really mean that what you're getting instead is some natural cocktail of yeasts that are specific to a vineyard. A native fermentation it may be, but the yeasts that are chowing down on the grapes are much more likely to be native to the winery building than they are the vineyard, and in many cases they may include commercial yeasts as well.

I'm certainly guilty of romanticizing native yeast fermentations as a writer. Along with the decision not to fine or filter the wine, this decision generally says something to me about the quality of the wine. The fact that winemaking yeasts aren't entirely wild doesn't necessarily undermine that meaning, but it certainly does call into question just how much justification there might be for prejudice against commercial yeasts as somehow "unnatural." Biodynamic winemaking, for instance, clearly proscribes use of commercial yeasts as yet another unnatural intervention in winemaking.

The process by which grapes ferment involves sometimes 80 or more different kinds of yeasts, the actions of which are affected by pH, temperature, sugar levels, and thousands of compounds in the grapes, not to mention anything we humans might do. We're still trying to figure out just exactly how it all comes together.

As intrigued and excited as I am about the degree to which science is gradually deepening its understanding of what wine is and how it comes to be, I also love the fact that it's so complex that we've still got a long way to go.

Mystery is a good thing. It means we need to keep drinking.

Read the yeast discussion on the Mark Squires board.

Thanks to Jack at Fork & Bottle for pointing me to the discussion.

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