Growing & Winemaking


Upsides of Wild Fermentation

April 2012
by Jean L. Jacobson
    Smelling for ethyl acetate and H2S

    Winemaker Antoine Favero of Mazzocco Winery has been using wild fermentations for 15 years. Being very conscientious both in and out of the vineyard, Favero counts an “incredibly low” number of stuck fermentations and says he has never lost a fermentation. He makes SO2 additions at the crusher and post-secondary fermentation.

    “During native fermentations, I’m typically looking for an evolution of aromas,” he said, adding that it’s OK to smell ethyl acetate for the first two or three days. “However, if the ethyl acetate does not disappear by the end of the third day, replaced by fruity aromatics, then I may do an intervention in the form of yeast addition.” Favero said he does not encourage co-fermentations—especially with Zinfandel. Sometimes the secondary fermentations go native, but he said there are years when he doesn’t inoculate.

    Leo Hansen of Stuhlmuller Vineyards checks daily for off odors—“mainly H2S if a lot needs aeration or potential lack of nutrients.” Any suspicious fermentation is sampled and sent to the lab for analysis.
During the second weekend in January, the winery and lodging association Wine Road held its 20th anniversary event, “Winter Wineland 2012,” in northern Sonoma County, Calif. With more than 140 participating wineries to choose from, I opted to stop at wineries I had never visited but knew by reputation for the quality of their Zinfandels. The time flew quickly, but the wineries I did visit were well worth the effort.

As a former winery lab manager and current winemaking consultant, I was particularly interested in hearing the winemaking stories, especially when the subject of wild fermentations came up (OK, I brought it up.) My focus was whether winemakers used commercial cultured yeast, and if they have tried the new yeast products cultured from “wild” non-Saccharomyces yeast or Saccharomyces hybrids. The majority of these new yeast products are cultivated from Torulaspora delbrueckii and are used in sequential inoculations with Saccharomyces cerevisiae.

Nature harbors a plethora of wild yeast species and subspecies, both Saccharomyces and non-Saccharomyces. The mix is different from vineyard to vineyard and year to year, depending on the soil pH and nutrients, altitude, moisture content, sulfur use, etc., plus the aggressiveness and population of the dominant yeasts. Non-Saccharomyces yeasts include Pichia, Kloeckera, Candida, Zygosaccharomyces, Dekkera, Hansenula, Torulaspora, Brettanomyces and Hanseniaspora. In addition to yeasts, incoming fruit also will carry molds, Lactobacillus and Acetobacter.

In Thomas Ulrich’s June 2011 article “The Secret Life of Feral Yeast,” he refers to University of California professor and geneticist Dr. Linda Bisson’s comments about wild yeast populations. According to Dr. Bisson, the yeasts Kloeckera apiculata and Hanseniaspora uvarum are the most common yeasts found on incoming grapes at concentrations of 65% to 80% of the total yeasts isolated. Pichia and Candida yeast species have been shown to be approximately 10%, while Saccharomyces yeast populations are far fewer, numbering approximately 1 in 10 million yeasts.

Ulrich quotes winemaker Greg La Follette as saying that Kloeckera, Hanseniaspora and Candida dominate the early stages of fermentation, and Pichia drives the fermentation when the ethanol concentration reaches 3% to 4%. La Follette said at the time, “The finishing yeast is always S. cerevisiae, which can tolerate higher concentrations of alcohol.”

It seems to me that a winery having great wild fermentations would benefit from knowing the types of yeasts that drive their fermentations. Acorn Winery owner and winemaker Bill Nachbaur in Healdsburg, Calif., has had great success with his wild fermentations but said he is not in a rush to identify the yeast. He related a story he heard about an Australian winery that had strong, vigorous and fast fermentations. Since the winery did only wild fermentations, they were curious and had their wild yeasts identified; tests identified S. cerevisiae as the predominant yeast. The cultured yeast was being introduced into the winery by bees carrying it over from the neighboring winery on their bodies. Evidence of previously used cultured yeasts can frequently be found in wineries regardless of the level of sanitation.

Wherever the yeasts come from, the vineyard or winery, a growing number of winemakers feel strongly that wild fermentations are the only way to go. Conversely, many winemakers feel just as strongly that a wild fermentation is much too risky. What are the major issues?

The downside of wild fermentations
I believe the foremost downside is time—time involved in the primary and secondary fermentation process and the time and labor to care for those fermentations. Dealing with sluggish or stuck fermentations and fermentations that are going badly requires extra work.

The low populations of wild yeast coming in on the grapes take time to multiply. Finally, S. cerevisiae eventually will multiply to sufficient numbers and go on to complete the fermentation. Wild secondary fermentation can coincide with primary fermentation or start at the end of primary and be very slow. The rate of fermentation for both depends on fermentation conditions such as nutrients, temperature, pH, population and SO2. Wild primary and secondary fermentations can take months to complete, and each year is different.

Larger wineries need to turn over tanks and/or barrels to accommodate the volume of wine produced, and most often they use a controlled fermentation using pure cultured S. cerevisiae yeast, of which some strains will begin to ferment within hours. These inoculated fermentations can proceed quickly, with completion within a week or two. Following primary fermentation the wine is inoculated with Oenococcus oeni to complete secondary fermentation within weeks.

Wild fermentation can go bad in a very short time. Low Saccharomyces population in the wild mix may result in a stuck fermentation once the alcohol level is high enough to eliminate alcohol-sensitive wild yeast. Wild yeasts are nutrient-sensitive, and if the nutritional requirements are depleted or not being met, the yeast population will fail. A stuck fermentation can be difficult to restart, and in some cases it may require the addition of cultured Saccharomyces yeast to kick-start it and allow the fermentation to complete.

The real trick is to get the fermentation going quickly before other microbes jump in to take over while the protective barrier of carbon dioxide produced during fermentation drops. Prior to the advent of modern winemaking methods, the annual losses of wine due to failed wild fermentations were commonly 20% or more. Dr. Peter Salamone, North American technical manager for winemaking supplier Laffort USA, said, “One man’s diversity is another man’s spoilage.”

Unfermented sugars and the lack of competing viable yeasts encourage Lactobacillus (LAB) and Acetobacter growth. In stuck fermentations, Acetobacter aceti (which produces acetic acid, or vinegar) can soar if not detected early. Nutrient-deficient fermentations, LAB and some yeasts can produce high levels of hydrogen sulfide H2S (rotten egg smell), which can be corrected if caught early in the fermentation.

Close watch on every tank
The success of a wild fermentation is keeping a close watch on every tank and/or barrel until fermentation is complete to head off any problems that may be developing. “I observe, smell and look under the (micro)scope every day…primarily (for) Lactobacillus,” said Antoine Favero, winemaker and general manager at Healdsburg, Calif.-based Mazzocco Winery, which produces approximately 25,000 cases of wine using wild fermentation, predominantly Zinfandel.

For larger producers, “scoping” fermentations daily would overwhelm the staff. The normal protocols to monitor fermentations consist of daily monitoring of Brix levels and tasting/smelling. If a problem is detected, microscopic evaluation is performed to detect microbes such as Acetobacter, LAB and unwanted yeasts such as Brettanomyces. Testing yeast viability and Oenococcus counts also may be performed.

Wild fermentations can produce a wonderful wine one vintage and a completely different wine the next. Wild fermentations in barrels most often have barrel-to-barrel variation due to different yeast populations in each barrel. Larger wineries want vintage-to-vintage continuity for their brand identification with the public and choose the cultivated yeast fermentations to maintain the profile.

As smaller wineries grow, it may become more important for them to shorten fermentation time, reducing the time required to care for their wild fermentations and shifting their focus to faster controlled cultured fermentations.

The upside of wild fermentations
Many winemakers say that some problems can be dealt with in the vineyard, and the rest can be headed off by vigilance and quick reactions. These winemakers feel the risk is minimal and worth the reward.

Leo S. Hansen, winemaker for Stuhlmuller Vineyards of Healdsburg, Calif., for nearly 10 years, produces approximately 14,000 cases of wine per year using only wild fermentations—both primary and secondary. Chardonnay, Cabernet Sauvignon and Zinfandel are the primary varietals. He also bottles his own brand, Leo Steen Wines, and produces a dry Chenin Blanc. Hansen wants to showcase the vineyards and strongly feels that wild yeast fermentation best expresses the terroir. “Commercial yeasts were too big,” he said, “and took away from the character of the terroir and varietal.”

The wines Favero produces are vineyard designates, and he wants to emphasize each vineyard by accenting the terroir and capturing the varietal character, aromas, flavors and mouthfeel that a wild fermentation provides. The variation of different yeasts found year to year in the vineyard “does change the wine, but there is a common thread. “It is just different,” Favero said. “I welcome it.” Comparing a wild fermentation to a cultured yeast fermentation, he said, is like “a painting of multi colors instead of a black and white.”

Hansen believes you must know the vineyard you are working with and watch the fermentations very closely. “I like lower pH and higher acid (fruit). Since we are an estate, it depends on the vintage and/or how early I pick. Healthy fruit/juice with higher acid and natural, balanced nutrients seems to be the happy scenario to begin fermentation.”

At harvest, Hansen will add some SO2 at the juice stage for whites, evaluate the red fruit quality and may not add until spring, when secondary fermentation is complete. “Every lot is treated, as needed, from crusher to spring,” he said. “I even wait until summer if it is a cold spring.” On average, 10% of the fermentations will stick, and Hansen will inoculate with a low dose of Saccharomyces, with the exception of the past two years, when the fermentations have completed on their own.

Wild fermentations have been reported to reduce the percentage of alcohol at the beginning of fermentation, reduce VA, partially break down malic acid and lower tannins in red wine.

Both of these seasoned winemakers believe that vineyard management, picking at the right time, keeping on top of the fermentations and slow and constant fermentation rates are key to producing an ultra-premium, world-class wine.

What if…
What if there was a way to get some of the benefits of wild fermentation while keeping the stability, continuity, timeliness and repeatability of a cultured Saccharomyces fermentation? I presented this question to Hansen and Favero. Hansen answered that he would always use wild fermentation, though he would consider conducting a trial. Such a product could be of benefit if production would double, he said. Favero said he could see this type of product being useful, but not at the ultra-premium level. If production increased dramatically, he said, and a cultured Saccharomyces fermentation is needed, “It would at least give more dimension.”

During the past few years several majo r producers of cultured yeasts have been dedicating their efforts to research and the development of a wild yeast product for the winemaking market. It has been a task to isolate a wild yeast strain that enhances the wine without adding possible faults, can be successfully propagated and has sufficient quality to ensure good multiplication when added to juice. It is not surprising that some of these products cost twice as much as S. cerevisiae.

Anchor’s Exotics SPH utilizes a non-GMO hybrid between Saccharomyces cerevisiae and Saccharomyces paradoxus. S. paradoxus has the ability to partially break down malic acid as well as pectinolyic activity (assist with clarity and filterability)—traits not found in S. cerevisiae. This product has been shown to increase glycerol production, lower potential alcohol, enhance secondary fermentation and expand aromatics. It is recommended for white and red wines.

Begerow’s SIHAFERM Pure Nature, Lallemand’s Level²TD fermentation kit, Chr Hansen’s Prelude and Laffort’s Zymaflore AlphaTD n.sacch. are produced with the yeast species Torulaspora delbrueckii (TD). The TD products are intended to be used in a sequential inoculation with S. cerevisiae. TD is added first with addition of S. cerevisiae as follows: Prelude at 5%-6% alcohol; Alpha at 24 hours for reds and 72 hours for whites; Level²TD when Brix levels drop 1.5°-3°, and Pure Nature when Brix levels drop 3°-4°. Level2TD and Pure Nature come in a kit with both the TD and the S. cerevisiae included. Nutrient additions also are recommended.

Laffort’s technical manager, Dr. Peter Salamone, has degrees in microbiology, enzymology and genetics. He explains that TD was chosen as the target non-Saccharomyces yeast because, “There are no organoleptic faults in strains analyzed.…There is a neutral impact on varietal character,” and the natural positive traits included aromatic purity and complexity, improved mouthfeel, low VA production (especially in high-Brix grapes and wine), negative phenolic off flavor (POF-such as 4-EP), excellent fermentative capacity, better SO2 tolerance and low ethanol and ethyl acetate production—making TD the best choice to date. The average fermentation time using the Alpha is approximately 2 to 3 days longer than using S. cerevisiae alone.

Laffort’s studies show an increase in fruitiness, thiol expression (especially grapefruit, tropical fruits and passion fruit aromas), less vegetal character and more complexity—especially in Sauvignon Blanc, with similar improvement in other high-thiol wines such as Semillon, Riesling and Gewurztraminer, with Chardonnay showing improved mouthfeel. Fruit-forward red wines like Pinot Noir and Zinfandel are accentuated and show improved mouthfeel—as do Merlots and Cabernets. According to Salamone, the use of Alpha in Tempranillo has been very successful.

Salamone said Alpha has been used and studied in red and white varieties worldwide, and he hopes to have more information about new yeasts coming in early summer.

Trials with Chardonnay
Andrew Brooks, assistant winemaker at Bouchaine Vineyards in Napa, Calif., has used Laffort’s Zymaflore Alpha and conducted trials for the past two vintages. It was “recommended we try it in 2010 for a Chardonnay-based dessert wine that had historically produced elevated levels of VA during fermentation,” he said, adding, “We liked the results and used TD-Alpha again this year in greater quantity.”

Brooks said, “There’s a little bit more work involved in essentially preparing two inoculums, but it’s a trivial amount of extra effort.…We didn’t see any consequential difference in fermentation speed or completion rate as compared to the non-TDA (TD Alpha) control lots.”

The fermentations were monitored via daily Brix checks. As far as the results, Brooks said, “In the dessert wine, we definitely saw a significant reduction in the VA.…We also noticed some increase in body in the still wines. In 2010 we preferred the aromatic/fruit character of the Saccharomyces-fermented control wine…but the difference was small, and we liked the mouthfeel enough to use TDA again—this time in about 25% of our Chardonnay. A single data point isn’t really enough evidence to make a judgment about aromatic impact.”

Bouchaine is happy with the performance of the Alpha and recommends its use. For vintage 2011 Bouchaine put the Alpha wines through secondary fermentation and tried two different base yeasts and is anticipating the results.

Having no experience in wild fermentations except from a lab perspective, I look forward to this new generation of yeast products. For fellow winemakers wanting to capture some of the positive nuances of a wild fermentation without the time commitment, stress and possible loss of wine or quality, these new yeast products just may be the ticket.

Jean L. Jacobson is a consulting winemaker in Sonoma County, Calif., a writer and author of “Introduction to Wine Laboratory Practices and Procedures,” a book published by Springer Publishing. Jacobson has 15 years of experience in winemaking.

Currently no comments posted for this article.