Brettanomyces: Science & Context

Thank God for TCA.

It may be the source of significant irritation and occasional heartbreak, but at least we can all agree to hate it. Unfortunately, in the discussion of wine flaws, that is where consensus ends. Some crave reduction in their Chardonnay, while others decry it as distracting; many enjoy the oxidative edge of extended barrel aging; and while volatile acidity gives a certain population of drinkers pain between the eyes, more than a few praise its lifting abilities. There are others, of course, but Brettanomyces, with its attendant earthy aromas that range from spicy to putrid, seems to be the most polarizing “flaw” of them all.

First of All, What is Brett?

Like its more famous cousin Saccharomyces, Brettanomyces is a yeast. And like Saccharomyces, Brett feasts on sugars, converting them to alcohol, carbon dioxide, and a range of compounds that can influence the aroma and texture of wine. But while the compounds created by Saccharomyces, the dominant agent of wine fermentations, are widely viewed as positive, those produced by Brett are a bit more divisive. Common descriptors include clove, barnyard, Band-Aid, and leather, but vomit and sewage are also a part of the tapestry.

Beyond their aromatic signatures, the two yeasts also differ in terms of their growth patterns. Saccharomyces multiplies rapidly in a must, devouring all available glucose and fructose, and expiring when either the food runs out or the alcohol content gets too high. Brettanomyces, on the other hand, grows slowly, which is part of the reason it rarely presents until several months after fermentation. Brett is also able to feed on a wider range of substrates, and while residual glucose and fructose are its favorites, this enterprising yeast happily snacks on a wine’s “un-fermentable” (i.e., non-six carbon) complex sugars as well as oak sugars. Because of this, though previously used barrels are a common source of Brett infection, new barrels—especially heavily toasted ones—may have the sweetness to support a much larger Brettanomyces population than their neutral counterparts.

Being a yeast, Brettanomyces is also technically a single-cell fungus. Most fungi go by two scientific names, one for the sexual (i.e., spore-forming) version and one for the non-sexually reproducing form. For Brettanomyces, the spore-forming version is known as Dekkera, but this is rarely seen in wine. Under the Brettanomyces and Dekkera umbrella are five known species and a potentially infinite number of strains. ETS Laboratories in Napa Valley has isolated at least 70 of these, and was surprised to discover that they displayed less genetic variation than expected, considering the yeast’s wide range of aromatic expressions.

From left to right, Brettanomyces colonies at 12x magnification, at 400x magnification with Phase Contrast Illumination, and 400x magnification with Nomarski Illumination. Images courtesy of ETS Laboratories.

Being a microscopic and versatile little critter, Brett can thrive pretty much anywhere, and it is widely found in both vineyards and cellars. On account of its ambient nature, some claim it to be an element of terroir, or at the very least part of a given house’s signature style. Others point to the often domineering nature of its aromatics and classify Brett as a flaw. This debate is a lively one, with solid points on either side, and seems unlikely to be resolved any time soon.

How Does Brett Express?

The primary aromatic compounds produced from Brettanomyces’ metabolic processes are 4-Ethylphenol and 4-Ethylguaiacol, commonly shortened to 4-EP and 4-EG. Both vary sensorially, but in general, 4-EP is responsible for scents ranging from Band-Aids to manure, while 4-EG accounts for the more traditionally pleasant aromas of clove and spice. These two compounds are synthesized over the course of several months from coumaric and ferulic acid—polyphenols found in grape skins. Such polyphenols are far more common in red varieties than white, which is a big part of the reason that Brett is most often found in red wines (other factors are that red wines tend to have higher pHs and spend more time in barrel). Of all the microorganisms that play a role in the fermentation and aging of wine, only Brett is capable of synthesizing significant levels of 4-EP and 4-EG. 

It is estimated that most people will start to describe a wine as “Brett-like” when the 4-EP level reaches between 300 and 600 micrograms per liter (ppb), and the more volatile 4-EG hits at around 50 micrograms per liter. Of the two compounds, 4-EP is generally far more prevalent. A ratio of 8 parts 4-EP to 1 part 4-EG is standard, but anything from 2:1 to 30:1 has been found, and the timbre of the Brettanomyces expression relates to both the absolute and relative concentrations of these two compounds. Interestingly, 4-EG seems to determine the aromatic intensity, as, given two wines with the same 4-EP reading, the one with twice the 4-EG will smell twice as “Bretty.” But this concept of “Brettiness” is fluid, as not only do people have different levels of sensitivity but grapes have different levels of congruity. One need only look at UC Davis’ Brettanomyces aroma wheel and consider the typical bouquets of Syrah and Mourvèdre to understand how Brett might be obscured by the natural countenance of certain varieties.

UC Davis Brettanomyces aroma wheel. © 2017 American Society for Enology and Viticulture. Catalyst 1:12-20.

“There is this false idea that there are good Brett strains and bad Brett strains,” Gordon Burns of ETS Labs tells me, explaining the regular requests he gets to isolate and disseminate some kind of mythical benevolent Brett, one that steers more toward leather and less toward latrine. “But it’s not as simple as that. The same strain of Brett will perform differently under different circumstances.” His colleague Dr. Richard DeScenzo outlines a recent study he performed, wherein a wine made from a German variety registered a 4-EP/4-EG ratio of 1:2. “We took that same strain and put it in Cabernet, and the ratio completely changed.” Additionally, they maintain that the same strain in the same wine can also vary dramatically by vintage. “Brett is impossible to control,” Burns explains. “You can have the same grapes from the same vineyard, vinified in exactly the same fashion with the same strain of Brett two years in a row, and you’ll have a distinctly different sensory outcome. This has been demonstrated time and time again.” The reason for this is that Brett’s expression depends entirely on what it had to eat, which has everything to do with what happened in the vineyard that year. In that sense, Brett’s reaction is a kind of super exaggerated look at the unseen forces that shape a vintage.

Those same Brett lovers that inquire over cultivating a friendly strain might have considered simply adding 4-EP and/or 4-EG to an otherwise clean wine, but as with everything with Brett, the reality is far more complicated. “If you were to take a wine and add a squirt of 4-EP and 4-EG, would it smell like Brett?” Burns asks. “The answer is no. It might be vaguely evocative, but there are perhaps hundreds of compounds that Brett produces that present sensorially. And it’s not the sum of the individual compounds but the way they interact that impacts a wine.” One of the most distinctive of those other compounds is isovaleric acid, infamously evocative of vomit. 

But Brett not only adds to a wine, it also subtracts. According to Dr. Jamie Goode’s The Science of Wine, Brett produces enzymes that break down esters in wine, diminishing the impression of fruitiness. And it can also affect texture. By feeding on residual, un-fermentable, and oak sugars, Brett can reduce the cushion and mouthfeel of a wine, rendering the acidity more angular, the tannins more gruff.

The Sommelier Response

“I’m case-by-case when it comes to Brett,” explains Michael Madrigale, Consultant at Sanroc. “Usually, I don’t love it in high doses. In fact, I opened a bottle of 1982 Château Bourgneuf when I was watching the Super Bowl and it had heavy Brett, so much that I couldn’t drink it. There was another sommelier with me who had no problem with it and drank the bottle by himself.” , the former head sommelier of Saison and soon-to-be proprietor of WesternStates, also assumes a central position. He considers Brett in musical terms. “Brett is like distortion. It turns an otherwise sine wave of a wine into a square wave. Distortion isn’t a bad thing; it’s the amplification of certain natural frequencies. However, it can and does get overused.” He adds, “Nobody wants to drink a wine that tastes like Nine Inch Nails.”

These positions seem representative of the general sommelier response to Brett. None that I polled were either completely for or against its presence in wine, but all took a strong stand somewhere in the middle, each with an elaborate list of when, where, and in what context Brett was acceptable.

Raj Vaidya, Head Sommelier for The Dinex Group, allows, “Brettanomyces can be pretty interesting in certain applications in wine. I think it’s less so for more delicate and expressive varieties and more interesting in robust or tannic varieties.” He also posits that some wines can be improved by the presence of Brett. “I am not offended by some Brett in Châteauneuf-du-Pape. In fact, the squeaky-clean style that I associate with Janasse is not my favorite.” , MS, Vice President of Wine and Beverage Experiences for Cooper’s Hawk Winery and Restaurants, agrees. “To me, Brett really stands out in places like Burgundy. Because of the transparency of Pinot Noir, you really can’t hide anything.”

Even critics are open to Brettanomyces on occasion. "I do not consider Brett to be a positive attribute in a wine,” says Antonio Galloni of Vinous. “However, there are cases in which Brett lies below detectable thresholds or is present in such a small way that it does not detract meaningfully from a wine's overall quality. Brett does seem to be less intrusive with some grapes [and] regions, including Bordeaux, Barbera, and Sangiovese in Italy, and old-school California Cabernet.”

Galloni is not alone in his regional bias. Madrigale believes that Brett is perfectly fine in certain parts of the world. “I’m more tolerant of Brett in the Southern Rhône and Southern Italy, as it adds to the perceived funk and soul that the regions are known for, whereas in Northern Rhône, Piedmont, and Bordeaux, I’m much less tolerant. In my opinion, Brett doesn’t play well with wines known for pure aromatics and elegance.”

For , Sommelier at Le Bernardin—and Madrigale’s Super Bowl drinking buddy—his admittedly high tolerance of Brett is directly related to the meal in front of him. “Let’s say I’m drinking Beaujolais and eating charcuterie—a little barnyard doesn’t bother me. Funkiness in context can be a very good thing. But Brettanomyces doesn’t have a place alongside fine cuisine. Beef shanks or oxtail, okay. But with a delicate or light fish, a Bretty wine just won’t work.”

For many sommeliers, cost plays an important role in determining their level of Brett-love. Madrigale says, “There’s nothing more disappointing than opening a bottle of Gentaz or Verset, i.e., expensive wine, and Brett is the overpowering ingredient.” Wines, who is not particularly enamored of Brett, agrees. “I find it really disappointing when an expensive wine is flawed.”

MS , a vocal advocate of the so-called natural wine movement, is acutely aware of the complexities surrounding Brettanomyces. “Brett represents such a wild spectrum of aromas and flavors, you can’t simply say you are against it. It’s not black and white. It’s a scale of gray.” Having said that, she’s not universally for it, either. “Brettanomyces can add value to a wine, but the question is, how much? Is it still in balance with the rest of the wine?" 

Over the years, Lepeltier has found that a good proportion of her clientele enjoy a bit of Brett in their wine. A recent experience working with a perfume maker has her considering whether there might be an underlying psychological factor. “A couple of years ago, I had a super cool experience with a perfume maker. We were walking in the city on a hot day in August, describing the smell of the city in the summer. We ended up in the Central Park near all the horses and their manure. I told her, ‘You know what is extraordinary? The wines I have the most success with at the restaurant have these aromas.’ She then explained to me that in the world of perfume, there is a similar musky note that they put in very specific perfumes because it triggers a sexual response, a kind of primal bestial reaction."

Lepeltier also contends that a drinker’s age and culture might influence their appreciation of Brett. “I grew up in France, so I grew up with that taste,” she confesses. “And I also think that, for the public, there are some categories of people that will like it more. For example, you have some older drinkers who enjoy the classics of old Bordeaux, old Châteauneuf, old Napa, where there is often a bit of Brett. And then you have a generation who grew up with more technical wines, and Brett might be a problem for them. And then you have this new generation of drinkers, the Millennials, who are very interested in natural wine, and they are comfortable with things like Brett and VA and might even want to seek those qualities out.”

Our Evolving Awareness of Brett

To Lepeltier’s point, Brett has been indelibly associated with certain wineries (Beaucastel), regions (Rioja), even eras in winemaking (pre-2000s Bordeaux) over the course of history. And within these categories are some of the world’s most widely worshiped wines. And yet, though Brett has likely been a part of wine since the dawn of fermentation, we have only recently begun talking about it. 

Christopher Howell, Winemaker and Vineyard Manager for Cain, worked in Bordeaux from 1982 to 1984 and returns regularly. “When I came to Napa in 1984, everyone was already talking about Brett. This was shocking, because in Bordeaux, no one ever discussed it, even though so many of the wines clearly showed its presence. If you asked a producer, they would simply tell you that that was their terroir, or maybe that the wine was reduced.” The turning point came later. “It wasn’t until Dr. Pascal Chatonnet from the University of Bordeaux began running tests that clearly showed the presence of Brett in the early 1990s that the conversation began.”

Chatonnet remembers that time well. “In some châteaux, the Brett character was present every year, [so] the producers were convinced that it was an original part of the style of the place, and so a signature of the terroir.” As a trained scientist, he knew otherwise. “We published serious papers in between 1989 and 1992 on this topic, with the last putting on the table all the critical points to understand the origin of the ethyl phenols responsible for the Brett taint and the fundamental point to control the development of Brett.” And yet, at the time, producers showed limited interest.

Unlike our equivocating sommeliers, Chatonnet believes strongly that Brett is a flaw. “I think that tiny amounts of ethyl phenols are not negative when you can’t smell them, but when you reach the perception threshold, you are obviously losing immediately all the fresh, typical fruit and the originality of the wine. If we let Brettanomyces grow in every red wine, whatever the variety and the geographic origin, all the wines will smell the same.” Chatonnet preached endlessly for good hygiene in the winery, a more efficient use of sulfur dioxide, and better management of wine pH. 

Slow though it may have been to change, Bordeaux eventually cleaned up its act (mostly), and many other regions followed suit. However, just as the collective wine world was understanding how to detect and control Brett, winemaking trends moved in a direction that encouraged its proliferation.

The “international style” that began in the late 1990s and early 2000s was characterized by higher alcohols, greater extraction, and often a good amount of new oak. And though Brettanomyces is tolerant to a wide range of pHs, it thrives in the lower acidity of super-ripe wines. In a similar vein, though elevated alcohol levels can inhibit its development, the oft-accompanying residual sugar of such blousy wines provides Brett with a powerful food source, which is compounded by the presence of new oak. And greater extraction means more polyphenols—that is, the precursors to Brett’s signature stink. Interestingly, the natural wine movement, which is thought to be at least in part a reaction against this international style, also encourages Brett. Here, the primary point of entry is low sulfur levels.

The Winemaker Response

“What’s my relationship to Brett?” Randy Dunn repeats my question out loud in the dining room of his Howell Mountain home. “I mean, I have one, certainly, but we try to keep it long-distance.”

Father-and-son team Randy and Mike Dunn are the winemakers behind Dunn Vineyards, one of Napa Valley’s most celebrated brands, and formerly one of its Brettiest. “We had Brett,” Randy allows, “but honestly, everybody did back in the day. A lot of what we in the Napa Valley used to call ‘bottle bouquet’ or even ‘terroir’—in hindsight, I think a lot of that was Brett.” The Dunns first realized they had a problem in the early 2000s, right after the 1998 vintage was released. As Mike recalls, “We bought some bulk wine for the 1998 Napa Valley blend and didn’t test it for microbial activity. It smelled okay but bloomed in the bottle. After that, we had all the old vintages tested, and we were right at threshold for all except 1998 and 2000.” The elevated Brett levels of those two vintages was compounded by the fact that they were lean years: without the typical Napa ripeness, the Brett signature was amplified.

The relatively high pH of their mountain fruit and Randy’s insistence on low sulfur levels had rendered them vulnerable. But Mike took a course on Brett management in 2002 and began changing some of their cellar practices. All old barrels were replaced, sulfur dosage was marginally increased, and they banished the then-common practice of using a small batch of the previous year’s wine to inoculate for malolactic fermentation. They also began sterile filtering at the bottling line. “We didn’t sterile filter in the 1990s on account of it was a pain in the ass,” Randy tells me. “You can really mess up a wine if you filter incorrectly.” For much of the past two decades, though, they have relied on cross-flow filtration but estimate they lost about a barrel a year through dripping—a high price to pay just to manage Brett. Happily, they’ve recently switched to a new lenticular pleated membrane system that is far more efficient. “No drippy drippy,” Randy says with a wide smile.

Mike and Randy are committed to keeping their Brett levels as low as possible, but they have also come to terms with the fact that it is simply a part of their lives. “I haven’t gotten rid of it entirely, but it’s the lowest it’s ever been,” Mike says. “2012 was clean as a whistle, though ’13 had a little bump.” That said, they remain impressed with how well-received their Brettier vintages continue to be, and how much they themselves like drinking them. “Brett adds a cool, savory quality, almost like an early aged aspect to our wines,” Mike continues. “And most importantly, we find that a lot of our clients like and have come to expect at least a little mark of Brett.” 

But while Mike and Randy Dunn seem to have successfully domesticated the Brett beast, a good proportion of winemakers live in fear. Mac Forbes of his self-named winery in the Yarra Valley of Australia explains, “We work with a range of really terrific old vineyards, and we are focused on trying to retain the freshness and purity and expression of those vineyards. Whether it’s new oak or some microorganism, we don’t want anything to dominate that.” At some point in the past, Forbes discovered the presence of Brett in his wines and winery and worked swiftly to eradicate it. “We pick a bit earlier than most, so our pHs are pretty good, which helps. But we’ve cut back on buying secondhand barrels, and when we do, we buy used white [wine] barrels. We also sulfur quite early after malo and monitor cell counts.” Like many winemakers, Forbes is open to drinking wines with background levels of Brettanomyces, but is not interested in making wines with such a mark. “We work too hard farming to let some bug come in and take over.”

Nicolas Géré spent a year with Jean-Louis Chave before returning to Bordeaux. In 2016, he took over winemaking for the Teycheney group, which currently owns three wineries in Bordeaux including Châteaux L’Étampe and Fleur de Lisse in Saint-Émilion. When I ask him about Brett, Géré asserts, “Brett is a hard subject to understand. Sometimes you visit a cellar that looks so dirty and it doesn’t have Brett. Then you visit the cleanest cellar and they do have Brett.” For his wines, Géré is absolutely against any Brett expression, even though he is committed to biodynamic farming and native yeast fermentations. Toward this end he harvests early, is extremely hygienic in the winery, keeps the cellar cool, racks regularly off the lees (“Brett lives in the lees,” he assures me), and is fanatic about monitoring his levels of free SO2. But it is just prior to harvest when he takes the greatest care. “I want to work with the natural yeasts in the vineyard, but I don’t want Brett. So one week before harvest, I pick fruit from each of my blocks and let it ferment. I then send these samples to a woman named Margarethe Chapelle, who works with many of the top estates in France. She performs a crystal analysis.” Chapelle’s unorthodox testing method indicates the health and range of the microbes in a given must or wine. Based on her recommendation, Géré will harvest a certain area, ferment the fruit, and use that as an inoculum for the rest of that year’s crop. “I understand that wine, especially natural wine, is alive and there are no rules, but for me, it is important to always be clear in the bottle.”

At the other side of the Brett spectrum is Christopher Howell, who went so far as to try and cultivate an active Brett population at Cain in the 1990s. Howell is a thoughtful, philosophical man who constantly questions the perceived norms and standard practices of winemaking. “Who am I to say that wine fermentations can and should only be carried out by Saccharomyces?” Howell posits. “I don’t think that any winery should have a signature based simply on their microbiology. But there are many wines that I fell in love with that had Brett, and if they didn’t exist I would miss them.” He adds with a smirk, “But that doesn’t mean I want every wine to smell and taste like Brett.” 

Howell is both comfortable with and fascinated by the level of Brett in his wines. “People act as if grapes are sterile,” he explains, “and I’m sure that many winemakers wish that they were. But really, they are covered in microbial life, and when you crush them, you are introducing a substantial inoculum. Not as large as a commercial yeast add, but still.” We walk through his cellar and sample barrels from the 2016 and 2017 vintages, some Bretty, some clean. “I believe in wine beyond fruit. In my view, fermentation is about transformation, not preservation. You expect the wine to be transformed, not just preserve its fruit. That is certainly true of cheese.” Howell pauses, drawing a sample. “And so, by extension, having more than one fermentation is interesting.” Howell also believes that people’s positions on these matters are very much the stuff of trends. “In the mid-1980s, when malolactic fermentations in white wine were less common, some wineries actually defined their Chardonnay by having undergone ML. We used to think that buttery diacetyl scent was a positive. We loved it. And then we learned not to love it.”

Though today Howell attempts to control the Brett in his winery by tracking residual sugars and sulfur levels and relying on ozone to clean barrels, he seems as content as ever to live alongside the yeast, so long as it doesn’t dominate. “Bottle blooms are the biggest issue. In the 1990s, we began to think of Brett as having a moment of fermentation, either in the barrel or in the bottle. And they are not the same.” In response to this, he attempted to actively maintain a Brettanomyces culture in the winery. The thinking was that if they were going to have Brett, they might as well inoculate for it and get the fermentations out of the way before bottling, but the notoriously fickle yeast refused to cooperate. “People are more or less equivocal about wine flaws, but no matter, wine changing in the bottle is confusing. For the most part, when you are selling the wine, you don’t want it to be in action.” They then tried to predict the bottle blooms, which was also unsuccessful, though they did notice the half bottles tended to go off first. “At some point, we stopped trying to get rid of the bottle blooms, so now when we see them, we just stop shipping that wine until it’s over.” Even so, the ever-open-minded Howell’s stand on bottle bloom is beginning to shift. “Now I’m starting to think that fermentation in the bottle can be interesting. Look at Champagne!” Howell pauses, seemingly running the logistics of deliberate bottle blooms in his head. “If only we could control it.”

I Have Brett. What Happens Now?

Brett is tenacious and extremely difficult to kill. It can lie dormant for long periods of time and subsist on relatively little, and it is virtually impossible to eradicate from a barrel once it’s in the wood. And often, once you can smell it, the infection has already reached the tipping point. Assuming you don’t want it in your wine, the best way to beat Brett is through early detection.

For a long time, the only way to test for Brett was through plating, i.e., smearing your wine on some agar and seeing what grows. This strategy was never foolproof for, as Burns at ETS explains, Brettanomyces can exist in a range of states, not all of which will multiply in on a culture plate. “Brettanomyces is not always either just alive or dead; there is a continuum in between in which the cells are viable but not culturable. The reason for this is usually exposure to SO2, which doesn’t kill the cells, but does enfeeble them.” These shrunken husks can survive in stasis indefinitely, until the molecular sulfurs drop below a certain threshold, or heat or oxygen is introduced. Then they spring back to life, get munching, and return to the business of smelling up your wine.

Later, it was discovered that the presence of Brett could be determined by measuring the levels of 4-EP and 4-EG. But again, this was an imperfect approach, as all it really did was measure the history of Brett in a wine. That is, it proved that Brett had at one point been active, but didn’t necessarily tell you whether the population was still present or viable. Both approaches, plating and ethyl phenol analysis, are forensic in nature in that they aim to answer the question what went wrong with this wine?

Client report data, courtesy of ETS Laboratories.

Actual preemptive detection wasn’t commercially available until around a decade ago, when scientists at ETS devised the Scorpion panel. A Scorpion assay uses microbiology to provide a real-time cell count of all the organisms in a wine. “We can now see the beginnings of an ‘infection,’ which allows people to take non-draconian steps to get it under control,” says Burns.

Client report data, courtesy of ETS Laboratories.

Once Brett has been identified in a wine, what recourses are available to the winemaker? In talking to Burns, it seems there is little point in trying to remove or kill the Brett prior to bottling, as there are too many opportunities for re-infection during élevage. As such, the best methods are those outlined by the winemakers above. Specifically, maintaining a low pH, minimizing residual sugar, general cellar hygiene, low cellar temperatures, and staying on top of sulfur levels. Racking is a double-edged sword in that it is good to get a wine off its lees if Brett is a part of the yeast population, but any introduction of oxygen can give Brett a boost. The same holds true for the use of micro-oxygenation and lazy topping practices.

The goal of the above listed strategies is to keep Brett in a weak enough state so that it is not producing 4-EP, 4-EG, and their companion compounds. Once those aromatic markers are in a wine, they are difficult to selectively remove. Dr. DeScenzo admits, “You can throw some carbon in there also to diminish their impact, and many have tried to use reverse osmosis to remove the 4-EP and 4-EG. The problem with that is, there’s no truly selective way to remove only those compounds. Besides, they are only part of the spectrum. You might reduce the imprint of smoke and barnyard only to,” he pauses, splaying his palms for emphasis, “bring forth the vomit.”

At the point of bottling, there are only three fool-proof ways to get rid of Brett for good: pasteurization, the addition of Velcorin, and sterile filtration. Pasteurization has the obvious drawbacks that come with super-heating a wine, and Velcorin is equally controversial. Known in scientific circles as DMDC, or dimethyl dicarbonate, Velcorin is toxic to humans if consumed shortly after application, but is widely used in the fruit juice and sports drink industries. It works by inhibiting certain enzymes within the cells that eventually cause death. That said, Velcorin only works to a point. “Velcorin is a great tool for winemakers, but it is only guaranteed to be effective up to 500 cells per milliliter. And that count is not just Brettanomyces. It includes any other microbes that might be living in the wine,” explains Dr. DeScenzo. 

“Velcorin is fine if you need to get a wine quickly to market, but if you are going to bottle age, filtering is better,” explains Mike Dunn. Burns elaborates, “Filtering, specifically sterile filtering, is one end of the spectrum of fining. The other end is time.” By this he means that they are all nothing more than the removal of solids from wine. Fining generally involves adding a substrate to a wine that will bind with the larger molecules and settle them out of solution. Filtration is a mechanical process wherein wine is passed through or across a filter, and tends to be more invasive. Different levels of filtration are available to winemakers, from the fairly gentle “bug catcher” with its 10-micron pores, down to sterile filtration, which features holes only 0.45 microns in diameter. As there is no machine that can puncture such microscopic holes, electric sparks are employed. “One micron is really sufficient to remove most Brett,” says Burns, “but some enfeebled, desiccated Brett cells might be able to squeeze through, which can cause problems with bottle bloom and therefore bottle variation down the line. This is why we recommend absolute sterile filtration.”

This may seem like a lot of hoops to jump through for such a tiny little thing, but Brettanomyces and other microorganisms can be pernicious, and not even time can tame them. “I’ve opened 30-year-old wines before and, because I’m a microbiologist, I plated them,” Dr. DeScenzo remarks. “And even after all those years, there were still things living in that wine.” As Nicolas Géré noted, wine is very much alive. The question is, how lively do you want it?

A Quick Checklist of Brett’s Biggest Myths
Brett can’t infect a white wine. Brett absolutely can infect a white wine, it just tends not to. And as an extension, Brett can also be present in used white wine barrels, though this is far less common than for red wine barrels. Because the precursors are different for white wines, Brett tends to express more on the smoky/spicy/vinyl side of the equation, though there is some debate as to whether certain floral or minty aromas can be ascribed to Brett. We are still waiting on the white wine Brett aroma wheel.

Bone dry wines won’t get Brett. Brett is rather omnivorous and can subsist on very little for a very long time. Research indicates that as little as 0.5 grams per liter of residual sugar can support a robust enough population of Brett to reach above-threshold levels of ethyl phenols. By comparison, many winemakers consider 2 grams per liter of residual sugar to be technically dry.

Brett prefers high alcohol. Alcohol is a source of stress to Brett just like any other yeast. It’s just a little bit tougher, so it can take it better than Saccharomyces!

Sulfur dioxide kills Brett. Sulfur dioxide only weakens Brett. Only Velcorin (when used properly) and pasteurization can kill it, and only sterile filtration can remove it from a wine.

Brett diminishes with time. While the aromas created from 4-EP, 4-EG, and the other aromatic compounds may evolve and quiet with time, Brett cells can live in a wine bottle for an indeterminate number of years. Cells in stasis can cough back to life under a variety of circumstances. Sulfur breaks down over time, which can be sufficient to wake Brett up, but heat is also an instigator. This is why Brett blooms are more prevalent in warm places or under poor storage conditions. The wine you drink in Miami may be wildly different than the wine you drink in Stockholm if there is Brett involved!

Bibliography

Joseph, C.M. Lucy, Albino, Elizabeth, and Linda F. Bisson. 2017. "Creation and use of a Brettanomyces aroma wheel." Catalyst 1, no. 1 (February 2017): 12-20. http://www.asevcatalyst.org/content/1/1/12.article-info.

Goode, Jamie. The Science of Wine. Oakland, CA: University of California Press, 2014.

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  • From my own experience cellaring wine, I was under the impression that Brett, like VA sometimes greatly increases over time.  I remember one Northern Rhone Syrah that I bought five cases of and had a pleasant leathery Brett note that after 4 years in the cellar was like drinking bandaids and I had to write off as a loss.  Now I have to wonder if I didn't store that wine at a cool enough temperature or it wasn't sulfered heavily enough.

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