Wild Yeast Fermentation

Wild or native yeasts, according to a general definition, occur naturally in the air or on surfaces. While the word, ‘wild’ might give the romantic impression that winemaking’s native yeasts come from the grapes in the vineyard, it’s just as likely a wild ferment is the result of yeast from winery equipment or even the floor.

Commercial yeasts, on the other hand, are cultured in laboratories and turned into powders or liquid cultures. Winemakers can select a particular commercial yeast strain from dozens of options in catalogues. When they want fermentation to start, they simply add the yeast to the must either by sprinkling it into the must, or by adding water to rehydrate the yeast culture and pitching it into their juice – a process called inoculation. With a wild ferment, on the other hand it’s a bit like magic: You crush the grapes and just wait until fermentation happens.

Wild Versus Commercial

A simple analogy might help explain the difference between commercial and wild yeast fermentations. Picture two suitors: A successful accountant and a gifted artist. Choosing the accountant is like choosing the commercial cultured strain. These monocultures can be selected, not only for the style of wine they make, but for their tolerance of specific temperatures, alcohol and sugar levels. Their fermentation speed is also known, so is how they interact with other organisms in the juice. Everything is in place for a planned, predictable and successful fermentation. For good reasons, many commercial winemakers in the United States and around the world use commercial yeasts. Users include winemakers who like having as much control as possible over the winemaking process. For example, big wine companies sourcing grapes from all over the world and making massive volumes of wine which needs to have a consistent profile tend to use commercial strains as a rule.

Choosing the artist, on the other hand, leaves you more open to possibilities. Likewise, with a wild yeast fermentation there’s more unpredictability during the winemaking. There’s a higher chance of something going wrong, but there’s also an opportunity to create something unique.

Supporters of wild ferments tend to be smaller, more experimental winemakers who have less inclination to intervene in the winery and a close relationship with their vineyards, such as winemaker Antoine Favero from Mazzocco Winery, in Sonoma, California. He’s used wild yeast ferments for 25 years and says they create greater complexity in the wine.

“Generally speaking I have found that native yeast fermentations tend to have a tapestry of aromas, textures and tastes that are much more multi-dimensional and complex than utilizing cultured yeasts,” said Favero.

Sometimes there is crossover between how native and commercial yeasts are used in the winery. Not everybody who uses native yeasts waits for a ferment to happen. Some winemakers create cultures of a winery’s more successful native yeasts so that they can use them each year. For example, Ponzi Vineyards in Sherwood, Oregon, has used a ‘house’ yeast for more than two decades. The yeast, a closely guarded proprietary secret, is used for their Pinot Gris, Pinot Blanc, and Chardonnay.

Mazzocco Winery is in the process of isolating a yeast strain in their Smith Orchard used to make their Zinfandel. And if you thought all wild yeasts have trouble at high alcohol levels, you’d be wrong — this Zin reaches 16% ABV.

Wild Yeast Research

Linda Bisson is professor and geneticist from the Department of Viticulture and Enology at the University of California-Davis. Wild yeast is at the heart of her current research exploring what causes slow or stuck fermentations. Bisson’s work will help winemakers decide scientifically whether they can opt for a wild fermentation by identifying the types of wild yeast that contribute off characters to the wine.

“The goal here is to be able to tell people if you’ve got this particular inhibitory flora then maybe you want to inoculate commercially; and, if you don’t have it, then you’re okay, or maybe you want to adjust the amount of sulfur dioxide you’re using,” said Bisson. Her team is also looking at other organisms on the surface of grapes that cause problems for Saccharomyces yeasts.

Dr. Bisson says wild ferments are more likely to be successful if, like Ponzi and Mazzocco wineries, the source of the grapes is well known.

“You’re not going to have as many problems as you would if you have completely unknown fruit that you’re buying on the bulk market or getting from a winery that you’ve never worked with before,” she explained.

However, the professor says a winemaker’s decision to use wild ferments is less about risk factors and more about the sort of wine he or she wants to make.

“It really depends on the goals of the winemaker and what they’re trying to showcase,” she said. Wild yeasts, she explained, do add complexity to fruit flavors and contribute other nuances as well. Commercial yeasts, on the other hand, tend to highlight varietal character.

Favero says his well-regarded Zinfandels owe a lot to his wild ferments. “Each yeast places an imprint in your wine creating unique tastes, aromas and mouthfeel.” He says they bring out a sense of place for each vineyard site.

JP Pierce, Assistant Winemaker at Ponzi Vineyards agrees. “What Luisa [Luisa Ponzi, Head Winemaker] is definitely trying to capture is what the vineyards are bringing out,” said Pierce. “I think the end result is that wild yeast produces a really unique product with some unusual aromatics and unique character,” he said.

Cellar Vall Llach is a Spanish winery in the Priorat region. The winery, located in the town of Porrera, was founded in the 1990s by a local singer-songwriter. “I never use yeasts other than wild ones,” affirmed owner and winemaker, Albert Costa. The town was once regarded as the most rebellious in the region, so together with his winery’s rock star roots, Costa’s wild ferments seem appropriate.

“About 70% of my yeast comes from the grapes and 30% lives at the winery, making my wines more unique than using commercial yeast,” he added.

Wild Risks

‘Unique’ is a descriptor that comes up frequently when you talk to vintners about their wild ferments. Dr. Bisson says many winemakers believe native yeasts are advantageous.

“They’re [commercial yeasts] not necessarily the best fermenters and they’re not necessarily the most aromatic because when they’re produced commercially they have to be able to be active dried and then rehydrated.”

However, like any winemaking process, there are risks associated with using wild yeast.

“Wild yeast can be so dangerous,” said Costa. One danger, he says, is when the fermentation gets stuck before all the sugar is gone which can cause the volatile acidity (VA) to go up.

“Lactobacillus is your greatest enemy when doing native yeast fermentations,” said Favero. “Because my primary fermentations are generally slow, averaging approximately one month to complete, bacteria such as Lactobacillus can at times increase in population and compete with the yeast, producing acetic acid which can be quite toxic to yeasts and arrest primary fermentation,” he said.

One solution is to learn what level of sulfur the native yeast strains can tolerate. Favero uses 40 ppm sulfur dioxide additions at the crusher, usually enough to deal with spoilage bacteria like Lactobacillus.

“It would have to be a drastic situation for us to use sulfur at the press” said Ponzi’s assistant winemaker. “So when the fruit comes in, our idea is to maintain a cold temperature so that we don’t have ferments getting started. That way we don’t have to use sulfur on it and when ferments do get going they don’t have sulfur there to inhibit them,” he said.

Slow fermentations are common with wild yeasts, but stuck fermentations, at least according to the experienced winemakers consulted for this article, are rare.

Mazzocco’s winemaker says his slowest fermentations have produced his best wine, but he has had a  stuck fermentation or two. “I’ve had to do a re-start fermentation utilizing a Saccharomyces [cerevisiae var.] bayanus yeast,” he said.

In Spain, Costa’s wild yeast fermentations are much shorter. “My red wine normally takes 15 days at between 20 and 30 °C (68 to 86 °F) My white takes 15 days too, at between 10 °C and 18 °C (50 to 64 °F).”

But at La Clarine Farm, in the foothills of California’s Sierra Nevadas, Winemaker Hank Beckmeyer sometimes needs a lot of patience. He’s had to wait six months for a fermentation to finish. “It is a little nerve wracking,” he admitted. “But the wine finished up fine.”

La Clarine’s vines are farmed biodynamically and Beckmeyer believes in making wine with minimal intervention and no chemicals. “I don’t use any sulfites at crush at all because I want all those diverse species in my must.” He says sulfites kill off the good organisms.

Generally, says Beckmeyer, funky smells and most other spoilage issues tend to sort themselves out, at least in his experience.

There is a scientific basis for wild yeast ferments resolving their own problems says Dr. Bisson. “Many times the yeast will subsequently reuse that compound during their fermentation so they might not stay there in the end.” But she says the fermentations are riskier because, depending on your Saccharomyces strain, the juice can experience a negative impact that sticks around. For example, wild yeasts may produce off-odors by metabolizing substrates into stinky compounds, and may not ferment to dryness.

Pierce at Ponzi Vineyards says using wild yeasts does mean that you have to watch your fermentation more closely, including factors like temperature and Brix levels.

“There are different characteristics for fermentation every year. Some years we find we constantly have to keep heat on them in order to get the initial portion of fermentation going and then some years we find that we’re having to keep cooling on the ferments to keep them from overheating,” he said.

Mazzocco’s Favero checks his fermentation daily under a microscope looking for spoilage microorganisms.

Biodiversity in the Wine

Another difference between commercial and wild yeast ferments is the number of fermentations going on. Commercial yeasts are designed to take over the fermentation so any other resident yeasts don’t get much chance to influence the flavor because they’re quickly denied access to sugar and nutrients. Winemakers who employ wild ferments say there are often several yeast strains acting on their must throughout fermentation.

“Those [commercial] yeast packets are pure, they’re single strained and my whole point is I want more than that,” said Beckmeyer. “I want that whole progression of different yeasts that come into play.

Beckmeyer says, after eight years of wild ferments, he has a good resident yeast population acting in combination with several others, some from the grapes, others in the air. He hasn’t tested to find out what they are exactly, in part because he believes they mutate each year, changing his wines’ flavors.

“The flavor profile could be smokier one year and the next year a little more fruit forward. They kind of swim around this central pole and it’s fairly consistent,” he said.

Pierce compares Ponzi’s wild fermentations to a relay. He says they start with native populations from the vineyard and finish with a dominant in-house fermenter, the result of many years of mutations that might have originated on the grapes.

Pierce explained that these yeast strains vary from year to year but behave consistently during any single year. “If one year we’re baking cakes then we’re going to be baking cakes all year long,” said Pierce.

Winemakers also talk about wild yeast having a multidimensional effect on the flavor profile of the wine.

“What I see in our Pinots, especially with fruit that comes from better vineyard sites, is that there tends to be a blend of flavors, where it  transitions instead of being choppy,” said Ponzi’s Assistant Winemaker. “You can see characteristics go from currant to cherry fruit, to maybe more earthy characteristics and there’s a smooth transition between those,”  he explained.

There’s also an effect on mouthfeel. Dr. Bisson says wild yeasts are particularly good at contributing “a coating, a fullness and a silkiness.” Favero and Beckmeyer both highlight this factor when they talk about their favorite wines.

So what makes better wine? A superb wild yeast mixture or an excellent commercial strain?

Dr. Bisson says that choosing between a wild or commercial yeast is a trade-off. “You get complexity [using wild yeast] but you don’t necessarily get varietal complexity,” she said.

The truth is, yeasts of all kinds might have been studied since the great French microbiologist Louis Pasteur, but there’s still a lot we don’t understand. That’s pretty clear when The Yeast Handbook, a scientific series that covers current research, throws its metaphorical hands in the air and admits, “so much of present yeast biodiversity and ecology is unknown.”

Nick Smith, Enology Outreach Specialist at the University of Wisconsin, says the topic area he gets most questions about is yeast. “The challenging part,” he said, “is scientists trying to figure out what exactly their influence is.”

Some scientists are more confident in wild yeast fermentations than others. According to the late wine journalist Robert Lawrence Balzer, a study of yeast strains by a French enologist in 1939 concluded: “Wines of fine quality can only be made by relying upon the natural mixed flora of the grapes — that the use of single, selected yeasts tends to produce wines of uniform flavor.”

Smith isn’t so confident. “It’s hard to tell if the wild yeast is actually the one doing it.”

In fact, one recent study was  very loudly trumpeted in some wine media as suggesting that wild yeast aren’t doing anything. Research from University of British Columbia found  that, unknown to the winemakers, native yeasts at three different  wineries were being dominated and squeezed out during fermentations by commercial inoculations.

However, winemakers who use wild yeast fermentations are often well aware of the dangers of a commercial strain dominating their ferments, so they do their best to prevent them entering the winery.

“I never use yeasts other than wild ones,” said Costa. “That’s so important because if one day I used a commercial yeast, this yeast is going to be in the building for much longer than one year!”

However, even if the science is still playing catch-up, many winemakers are confident that wild yeast plays a significant role making their wines more complex, and yes, unique.

Wild Ferments At Home

So, should you try a wild fermentation in your hobby winery?

First off, wild fermentations are only possible if you are working with grapes, or fresh must/juice that is pressed for you and has not been treated with SO2. Kit wines, too, are out — they will not ferment unless you add yeast as kit companies removed living organisms from the must to ensure shelf-stability.

Second, a wild fermentation is not a completely hands-off approach. As the pros in this article have detailed, the wines that are best suited to wild fermentations are those that are made in the vineyard — that is, grapes that you know to have been harvested with the right Brix, pH, and acid. That said, you also have to be willing to take the risk on a batch of good grapes. If you have a reliable supply of grapes and don’t mind taking a chance, go for it. If you can’t afford (financially and/or psychologically) to experiment (and possibly lose) a carboy of wine, however, wild ferments aren’t for you. As I said at the beginning of this article, wild ferments are more of a risk because you do not know what flora exist on the grapes, and therefore cannot predict fermentation results.

As for wild yeast winemaking technique, this is something you will have to work on in your own winery. A great experiment to start out with is to ferment only a small portion of your must with a “wild” ferment and simply see how it goes. Best case scenario you get an interesting wild-fermented wine that you can drink as-is, or something that you can blend with a portion of your commercially-inoculated wine (blends like these are done in commercial wineries as well). Worst case scenario: You have to dump out a few gallons (liters) of bad wine and try it again next harvest.

Third: Keep in mind with wild fermentations that your home winery is not akin to an Old-World Burgundian winery. A commercial wild ferment is not left to chance. Jeff Chorniak, in a 2005 article on wild yeast for WineMaker summed up the differences when he said, “Over decades of growing and fermenting (often the same grape), and dumping the old pomace and yeast sludge back into the vineyard, an accumulative buildup of particular yeast strains tend to dominate the region. They blow in the wind, cling to the winery walls, stick to equipment, on hands and feet and clothing and lodge themselves in the wood grain of barrels. The grapes themselves are covered with the same dominant micro-flora year after year. Decade after decade. Century after century. The result is every harvest spontaneously ferments the grapes with the same “native” strain(s) of yeast. No inoculation is necessary. The entire appellation has been permanently inoculated over generations.

Unless your vineyard and winery has that consistency of wild yeast that has built up over generations, chances are your wine will not have the same reliable or predictable results.”

Go Wild

You might summarize the differ-ences between the fermentation approaches this way: Wild yeasts are unpredictable and can make complex wine with unique local character. Commercial yeasts are predictable and can make quality wine with classic varietal character. It’s difficult to say if growing numbers of commercial winemakers are using wild ferments. In California, Dr. Bisson says there’s an even split between the numbers of new winemakers using wild versus commercial yeasts. Beckmeyer does think interest is growing, but mainly among smaller more experimental winemakers.

More than twenty years ago, in the same article where he referenced the French enologist’s study, Robert Lawrence Balzer described a Chardonnay made at Franciscan Estate by the late Greg Upton. He said it had, “singular, almost haunting excellence.” Quoting Alexander Dumas, Balzer added, “It should be drunk bareheaded and kneeling.” The wine was the first Napa Valley Chardonnay fermented with wild yeast. If that’s an indication of what wild yeast can inspire, bring it on!


• “A Wild One: Franciscan Winery Goes With Natural Yeasts and Gets Choice Chardonnay,” Robert Lawrence Balzer, September 17, 1989, LA Times

• “Study Indicates Commercial Yeast Strains Take Over Fermentation,” Andy Perdue, Aug 2013, Wine Business Monthly