Wild Yeast in Winemaking

For many years, a group of California winemakers have been practicing a fermentation technique known as “indigenous yeast” fermentation and making consistently excellent wine. Why all of a sudden has this technique become a buzzword in the wine press and why have other winemakers recently begun experimenting with this technique?
Alan Tenscher, Senior Winemaker at Franciscan Vineyards comments, “I see a trend toward a more natural way of making wine which starts in the vineyard with organic grapegrowing and extends to minimal handling of the wine. The use of wild yeast, from one perspective puts one in that same camp. But on the other hand, there is a group of winemakers out there who are looking for any technique that will help them improve wine quality. The use of wild yeast is a tool to create complexity.”

The trend Tenscher observes has been popularized by influential wine critics who are proponents of wines made with more natural, less interventionist techniques. Indigenous yeast fermentations fall into this category because the vineyard’s native yeast start the fermentation naturally in contrast to the common California, and in recent years European, practice of adding yeast to start the fermentation.

Fining and filtration are other examples of ‘interventionist’ techniques that these critics object to because they perceive them as excessive manipulation which compromises wine quality. This view is contradicted by assertions from top California winemakers that a properly carried out fining or filtration can improve the quality of some wines. Nonetheless, the success Robert Parker—a skilled writer and passionate advocate of wine quality—has had in molding consumer opinions and buying habits has reached the point where some winemakers—well aware that favorable Parker reviews sell wine—are actually shaping their wines to suit his taste. This is where John Williams, Owner and Winemaker of Frog’s Leap draws the line: “When I see people making good wines change what they’ve believed in for a long time just to satisfy the latest craze, I have to scratch my head.” Another outgrowth of the traditional methods “fashion,” is the familiar winemaker refrain that, ‘I never fine/filter/inoculate’, when in private, many—including some of Burgundy’s most highly regarded producers—admit to the use of these practices. What role then, should the wine writer have in the winery? Williams sees a limited one, “Wine writers do have a place in the cellar—reflecting on and communicating the vision of the winemaker. To me, the most interesting wines are those made with conviction based on the personal experiences of the winemaker. That conviction can change, that’s how wines get better, but it should not shift with the wind.”

To be fair, most winemakers using wild yeast are looking less at the marketing dividends and more at the potential for enhancing wine quality. This article will compare wild yeast fermentations with inoculated fermentations, how each affect quality and why some of California’s top winemakers use wild yeast and others do not.

Inoculated Fermentation

Fermentation is a vitally important stage in winemaking. The yeast not only convert sugar to alcohol but also produce esters and other compounds, which contribute to the wine’s fruit aromas. Extraction of flavor and color from the grape skins (for red wines) also occurs during fermentation. For larger production, less expensive wines, a yeast strain is chosen to get the job done as expediently as possible—converting all of the sugar to alcohol and freeing up the tank for the next load of crushed grapes. Some yeast produce a heavier sediment which settles more quickly after fermentation making racking and clarification easier. For smaller producers, varying the yeast strain as well as the temperature and duration (maceration) of fermentation can enhance the wine’s aromatic and flavor characteristics.

The common practice in California is to add a sufficiently large dose of a single strain of yeast (Saccharomyces cerevisiae) to the grape juice to start the fermentation. A few commonly used strains are Prise de Mousse, Montrachet and Champagne. The yeast is selected for its ability to quickly (in a few hours) start the fermentation and to tolerate the increasing alcohol levels enabling it to ferment all of the sugar while producing minimal amounts of undesirable by-products such as volatile acidity and sulfides. Volatile acidity is acetic acid or vinegar. Sulfides are compounds, which at thresholds levels may be desirable but in higher concentrations smell like rubber or rotten eggs (hydrogen sulfide) or worse. Inoculated fermentations can, in certain circumstances, produce objectionable amounts of volatile acidity and/or sulfides and even worse “stuck” fermentations. Winemakers get nervous if for some reason the fermentation stops or before all the sugar has been consumed. A stuck fermentation is difficult to restart and dangerous because once the yeast stop growing, the protective layer of carbon dioxide is removed. The door is open for spoilage yeast and bacteria (Brettanomyces, lactobacillus and acetobactor) to consume the remaining sugar in turn producing vinegar, earthy, barnyard or sauerkraut aromas.

The Nature of the Yeast

An indigenous yeast fermentations starts by itself when wild yeast strains – originating in the vineyard—start fermenting. Wild yeast can take up to a week to begin the fermentation because their initial populations are small compared to an inoculated fermentation. But there is strenuous debate as to whether the wild yeast come in from the vineyard or are already present in the cellar on winemaking equipment.

A proponent of the vineyard theory is Robert K. Mortimer, Professor emeritus of Molecular and Cell Biology at UC Berkeley who has worked closely with several California winemakers studying the role of yeast in natural fermentations. He and others have shown that Saccharomyces cerevisiae is on the grapes but only on about 1 in 1,000 berries. Saccharomyces cerevisiae is referred to as the “true” wine yeast because its alcohol tolerance enables it to ferment up to and beyond 13% alcohol. Also on these grapes are other species of wild yeast, bacteria and mold. Generally, Saccharomyces cerevisiae is the least prevalent of these microbial species. When the grapes are crushed, all of these organisms enter the fermentation, whether inoculated or non-inoculated. For the first one to three days of a natural fermentation, the wild yeast predominate. As alcohol levels reaches 3-4%, the wild yeast give way to the increasing numbers of alcohol tolerant Saccharomyces so that by two to five days this yeast predominates. At the end of a natural fermentation usually only Saccharomyces cerevisiae is present. Professor Mortimer has shown that there is a multiplicity of strains (as many as 16) of this yeast in such fermentations. Whereas in inoculated fermentations, Saccharomyces cerevisiae predominates from beginning to end because of the high level of inoculum. The end result of what also may be referred to as a sequential fermentation is a wine believed to have added texture and finesse. Proponents claim that red wines are lower in tannin. This extra degree of complexity is subtle and owes itself in part to the array of by-products from the different native yeast strains as well as the longer lag period prior to the start of fermentation.

But there are situations when even devoted followers of wild yeast would opt for an inoculated fermentation. Rain at harvest washes off the native yeast, reducing their populations. The ensuing rot contains bacteria and mold which can, during the longer lag phase of a native yeast fermentation, proliferate and ruin the wine. Large winery size is another deterrent to the use of wild yeast. The irregularities of natural fermentations require closer monitoring of individual barrels, which may be impractical on a large scale.

Danger Lurks

Despite the proven successes of native yeast fermentations (Kistler, Ridge, Ravenswood, Sterling, Signorello, Marcassin, Chalk Hill, Frog’s Leap, Franciscan), little is heard about the quantities of wine sold-off in bulk due to failed wild yeast fermentations. Linda Bisson, Yeast Geneticist and Enology Professor at the University of California at Davis believes that, with the exception of a few wineries, the success of native yeast fermentations is anything but “proven” and supports the Department’s recommendation against the practice of uninoculated fermentations. She states, “I do not endorse this practice for several reasons. First, most wineries can ill afford to lose 10-20% of their production. In contrast to other techniques, a bad natural yeast fermentation leads to a wine that is not merely low in quality, but unmarketable. Recommending this technique is equivalent to endorsing Russian roulette, the economic consequences of your luck running out are deadly and unacceptable.” Bisson points out that must pH is a crucial factor. Wineries have had bad experiences with native flora fermentations of higher pH musts because they favor the growth of spoilage bacteria. Bisson continues, “Second, the positive natural yeast characteristics are relatively short-lived and are not detectable after six or more months of aging. However, the negative characteristics persist for longer than this. Finally and most importantly, over the years we have conducted numerous unbiased, blind tastings of commercial wines comparing native fermentations to inoculated ones. Panelists have been professional winemakers, knowledgeable consumers and novice tasters. The naturally fermented wines have never been preferred by any group. Experience has taught us to take such results very seriously.”

Tenscher comments on why winemakers are interested in experimenting with native yeast fermentations, “I think a lot of people tried it, some people use it, some don’t. Is it necessary to make a great wine, probably not, does it make some very interesting wines, it sure does. I don’t think it is an integral part of a great wine, but I do think there are some definite marketing advantages to having the ability to say that a wine was made with traditional methods. By themselves, these methods guarantee nothing; they are part of the bag of tricks winemakers can pull from to help craft more complex and distinctive wines.”

Tenscher acknowledges the potential for disaster, “It’s a high risk way of making wine because you’re going to fail from time to time.” Comparing the use of wild yeast for small versus large-scale production wines, “We use a small percentage of wild yeast in the Estancia Chardonnay. We don’t have the option on the entire blend because I wouldn’t want to put that magnitude of financial investment on the line. For 1,000 cases of Cuvee Sauvage, it’s one thing; for the much larger quantity of Estancia Chardonnay, it’s just not a risk we can afford to take.”

Franciscan produces ‘Cuvee Sauvage’ its premium Chardonnay, with 100% wild yeast. Tenscher explains, “For us, wild yeast fermentations are sluggish getting going, then they may really rock ‘n roll or just poke along. You don’t have a highly predictable fermentation so each barrel stands a greater chance of being different. With the different yeast strains involved, we get a diversity of components that help us create a wine with more interest—different textural elements brought out by the longer fermentations in addition to desirable aromatic and flavor profiles.” Tenscher uses wild yeast for a small quantity of red wines, but gets different results, “We don’t find the effects as powerful in red wines as we see it in white wines. In a Bordeaux style blend it is not going to make a world of difference because the added maturation time and oak influence overwhelm the positive impact from the native yeast”.

Don’t Worry, Be Happy

Williams of Frog’s Leap is a long-time user of wild yeast and feels that the risks Tenscher is worried about may be valid, but his experience has shown them to be overstated. He says, “You bring grapes into a winery and you’re faced with risks. I don’t think those risks are substantially increased by using natural yeast fermentations and that is 20 years experience. I don’t want to say that we’ve never had fermentation problems, that is not true, we have. But I think there may be some benefits to an overall program of using natural yeast that come with it—the wines are more harmonious, more knit and reflect their vineyard character more closely.” Williams adds that if the must is deficient in a nutrient required by the yeast, there will be problems regardless of the fermentation method used.

Williams came to be a believer in wild yeast by accident. He recalls, “Back East in my first year at Glenora (1977) we were in a start-up situation and I just didn’t get yeast in time from the companies, so some of my first fermentations started naturally. I had great results—the wines turned out beautifully; the fermentations went slower but we seemed to have very few sulfide problems.” Williams moved on to Spring Mountain in the early 1980’s and recalls inoculating some of the first fermentations there, “The Montrachet yeast had so many problems with sulfides and stuck fermentations that wild yeast fermentations soon became routine practice at Spring Mountain and later on at Frog’s Leap.” Williams does not consider wild yeast to be the secret sauce, “It’s just another way. The benefits do not far outweigh the risks. One chef stirs the soup one way, another stirs it another way—each will swear his is the right way. If you’re not comfortable with it, I wouldn’t do it. I think the risks are overemphasized but I think the benefits are probably overemphasized as well.”

Bill Dyer was Winemaker at Sterling for 19 years and for the last three vintages fermented everything with wild yeast. He explains the transition, “I had a dissatisfaction with cultured yeast. Prise de Mousse was giving me fast, high temperature fermentations, especially in barrel with no temperature control.” High temperatures make a winemaker nervous—they lead to volatilization of desirable components and possibly stuck fermentations. He continues, “We experimented with other yeast strains and found the results, while at times favorable, were not repeatable. The wild yeast fermentations were slower and the wines were richer on the palate and more complex. All the fears and negatives—elevated VA (volatile acidity) levels, stuck fermentations,—we didn’t get.” Dyer explains a situation where he has backed away from using wild yeast, “It does take a longer time for the fermentation to start up when dealing with large tanks (versus barrels). I dedicate the barrel for the whole harvest to a single wine but I want to turn the tank over a few times during harvest which is difficult given the longer duration of the wild yeast fermentations.”

Terry Adams, Winemaker at Sonoma-Cutrer Vineyards comments on the wild yeast trend, “There is a continuum, 10% of the wines I think are excellent and 10% I think should be sold in bulk and there are wines in the middle. I do about 10–15% of the wine that way because I like the complexity. But I like the clean fruit characters that I get from cultured yeast. I continue to work with it because I think it’s fun and exciting, but it just doesn’t work for me the way it seems to work with other people. I think it’s a great philosophical approach; I just don’t know that everyone has the same indigenous yeast. We’ve decided which yeast we like and they work well for us.”

Wild vs Inoculated

For inoculated fermentations, the size of the inoculum which yeast manufacturers recommend adding is large enough to insure that the fermentation starts rapidly and is therefore dominated by this single strain. Adams inoculates with a considerably smaller dose of yeast and feels he derives some of the benefits of a wild yeast fermentation. The result is a longer, slower fermentation, giving a toehold for native yeast to have an influence on the fermentation.

Adams describes the experiments he conducted to establish his cautious but enthusiastic approach. “One year, every lot of Les Pierres we pressed, we took off some must and sent it to barrels uninoculated. So I had matched pairs of every block in Les Pierres. Every barrel turned out different. So I went through and selected the barrels I liked and put them into the final blend—but that was only about 10-15% of the whole production. The uninoculated barrels I liked better were cleaner and had fresher fruit. I didn’t like the heavier, almost musty, ‘composty’ characteristics. So after an additional three months I went through those barrels that I liked and selected five barrels that I especially liked and put them into the Founder’s Reserve bottling—and everybody loves it! So I know it can be done and it can be wonderfully interesting, but what happens to all those barrels that I didn’t care for? I wasn’t willing to change the whole Sonoma Cutrer style just to satisfy the current trend.”

The attitude at Acacia Winery, according to former Winemaker, Dave Lattin, is to encourage wild yeast where possible through what is called a ‘cold soak.’ He explains, “We routinely inoculated 2-3 days after crushing so that we get a build up of wild yeast. Frequently, there will be some activity with those yeast, particularly if you don’t add sulfur. Three days later, we hit it with a yeast we know will ferment. If we’re dealing with a part of a vineyard that has never been particularly complex or has very aggressive tannin, then why not try an uninoculated fermentation to build in more softness and complexity, but I would never advocate going into it 100%, Lattin says. But he says the practice is different with their best vineyards, “with St. Clair and Beckstoffer, we attempt to let them go without inoculating. Sometimes they take off and sometimes we have to inoculate because nothing happens. These vineyards have low pH, high acidities and lots of tannins, which have inhibitory effects which make for a sound wild fermentation. On the other hand, there is another vineyard which produces high pH, low tannin fruit—you just look at it and it gets funky.” Lattin is referring to the fact that high pH’s leave a wine unprotected. During the longer start-up period for an uninoculated fermentation, the door is open for bacterial growth (acetobacter, lactobacillus) which can produce stinky aromas.

David Ramey, Winemaker at Rudd Estate, traces his involvement in wild yeast, “When I came back from France after spending the harvest of 1989, I found myself thinking about why it had been so common for so many years in Europe and not used at all in California, so I was inclined towards experimentation. And shortly after that I tasted some experiments done by Bill Dyer who was then at Sterling and by Helen Turley at Peter Michael and found the same kind of things I later found in my experimentation—texture, subtlety and finesse.”

At the time, Ramey was making wine at Chalk Hill Winery and each vintage from 1990 to 1995 he conducted trials comparing Chardonnay fermented with wild yeast versus inoculated and concluded, “I have always found the wild yeast to be more complex aromatically and on the palate both more delicate and yet richer and rounder.” When asked why, Ramey is less certain, “It’s hard to tell, I think it’s the multiplicity of yeast strains, but it’s speculation.” Given the various ways a winemaker can influence wine quality, he regards the use of wild yeast as, “A small part; it’s a tool, suitable in some circumstances, perhaps not in others.”

Traditional Practices or “Man as Maker”?

Bordeaux and much of Europe practice inoculated fermentations. The exceptions are some of the small estates in Burgundy and the Rhone who use native yeast in most years. For these smaller domaines, science and technology take a back seat to tradition, or ‘doing it how my father did it.’ While California winemakers have embraced many traditional French winemaking techniques, natural yeast fermentations have caught on only in the last ten years or so. One reason some feel is because graduates from the Department of Viticulture and Enology at UC Davis, while receiving what many consider to be the finest training in the world, are not trained in traditional winemaking. The Davis approach, based upon technological advances, reflects the belief that an inoculated fermentation—where the winemaker exerts greater control—is a more responsible approach to winemaking.

One outspoken critic of the “man as maker” approach to winemaking is Paul Draper, Winemaker at Ridge Vineyards, who has used natural yeast at Ridge for virtually 100% of the fermentations for 28 years. What interests Draper—a Philosophy graduate turned winemaker—is the natural process. “Originally, we did it because philosophically, it allows us to step out of the way and guide the development of the wine instead of thinking of ourselves as creators. You are allowing the wine in a sense, to make itself. To me, that’s more fun, more interesting and has more meaning. Winemaker is a bad phrase; it doesn’t exist in French or Italian because it implies that we are the creators, and we are not; at least not with fine wine that comes from a distinctive vineyard that can be kept separate. He continues, “It is tragic that a lot of winemakers come out of school being taught that you are supposed to manufacture the wine. So Parker and those guys are simply passing on—sometimes a bit wrong-headedly—the fact that these traditional methods are more interesting. But just because you used natural yeast and didn’t filter your wine, there is no guarantee that you’re going to make a better wine—it may be lousy. One the other hand, you may get a really lovely wine from someone who has used an inoculated fermentation, has watched his wines and maybe even sterile filtered the wine.”

Draper stresses the importance of the vineyard, “It’s almost as though you need a distinctive quality and character in a vineyard for the use of native yeast to be worthwhile. Low pH’s, sound ripeness, good tannin and high acidity give you the natural protection you need to succeed far more often with natural yeast. Conversely, the more average the quality of the vineyard, i.e. where the vineyard is clearly going to be for use in blending and not in single vineyard wines and in warmer regions with higher yields, the natural yeast do not seem to work as well. It’s certainly less clear that an inoculated fermentation wouldn’t do as well.”

As for problems with volatile acidity and stuck fermentations, Draper comments, “Almost never have I seen elevated VA’s, certainly that could be traced to the natural yeast. For us, wild yeast have actually performed better than the typical winery using cultured yeast.” He cites the one exception, “In years where rain has reduced the yeast population or caused rot, I may want to add an immediate, large inoculum of yeast to be able to ferment as quickly as I can and get the grapes off the skins on which there are various forms of fungus and rot. A long drawn out fermentation would be too risky.”

Draper alludes to the labor intensive aspect of this process, “Part of what fine winemaking takes and certainly natural yeast winemaking, is that you watch the tanks, not just let them ferment and come back in a few days or let someone pump them over who may or may not know what he’s looking for. You have to taste them and smell them every day. They are virtually never off but if they are you know it and you can intervene. Anyone who has never done it before should move very slowly.”

Without complete certainty, Draper attributes the added subtlety and complexity to a combination of a lower level of inoculum, a slower fermentation and the multiplicity of yeast. He is however, like Bisson, certain that the benefits of natural yeast fermentation become less clear with age, “Once the wines age beyond 6-12 months, it becomes more and more difficult to see the exact character that the yeast gave the wine. But the fact that you vastly prefer one wine to another when it’s young, convinces me that you’re starting with more elements and more subtlety with the natural fermentation.”


Wild yeast is not the secret, indispensable answer to making great wine. Rather, it is a piece of the puzzle—one in a number of ways to develop complexity in wines, even if this added complexity is short-lived. This quality factor, coupled with the fact that the majority of winemakers feel these methods make their craft more interesting and challenging assures that the use of wild yeast will continue to grow in the production of super premium wines. By matching the right grape varieties to the right growing regions, winemakers will be working with high acid, low pH fruit, reducing the risks of wild yeast fermentations.

Wine & Vines, September, 1997