August 2008 issue


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PAGES (66-70) August 2008

Wine Flaws: Brettanomyces Jamie Goode

Of all wine flaws, Brettanomyces is one of the most complex, yet also one of the most fascinating, partly because it is one of those “faults” that can sometimes be regarded as positive (see my earlier article in this Sommelier Journal series, on reduction, in the 2008 Premiere Issue). Indeed, there are many highly sought-after, expensive wines that owe some of their character to Brettanomyces, usually referred to simply as “brett.” But it’s a controversial topic; some winemakers and other experts argue that brett is to be avoided at all costs, while others think a less dogmatic approach is in order.

First, some basics. Brettanomyces is a genus of yeast, also known as Dekkera (a technical point: the yeast can exist in two states, and the latter name is used for the sexual, spore-producing form). Although several species names are commonly used, the current classification lists the wine-relevant brett as just two species, B. bruxellensis and B. anomala, with the former by far the most important. Brett was first discovered by the brewing industry as an important component in British and Belgian beer styles in the early 20th century. When the first single-culture Saccharomyces cerevisiae yeasts (the species used in making wine) were introduced to make British beers, people noticed that something was missing: the imprint of brett, which in the context of a good bitter, can add real interest. Curiously, brewers often refer to brett character in beer as “vinous.”

Brett is annoyingly resilient. It sits around, biding its time, and then grows in conditions where virtually nothing else can. In practical terms, this means that it does its real damage after the normal alcoholic fermentation and malolactic conversion have been completed. Brett is slow-growing and tough, and it doesn’t need much to feed on. Rarely found in white wines, it is predominantly a red-wine problem. And the reason it is such a problem is that it produces distinctive flavors that, at higher levels, can ruin a wine.


The sensory effects of brett are many. The first sign is a reduced varietal character, followed by the degradation of certain fruity aromas by the esterases contained in this yeast. Esterases are enzymes that cause the breakdown of esters, a chemical group important in conferring fruitiness. Pinot Noir, for example, is particularly impaired by brett because it loses its bright cherry and violet notes; this loss of fruit can be an early indication of the presence of brett while the wine is still in barrel. Next, hints of smoke and spice begin to appear, the chief culprit being a compound called 4-ethylguaiacol (see table). As the infection progresses, the wine starts to smell and taste medicinal (largely due to 4-ethylphenol), and it loses its fruity flesh, exposing the structural bones of the wine. Typically, the acid and tannins will stick out. Finally, the wine begins to smell of barnyards, horses, animal sheds, and Band-Aids.

It’s difficult to teach people how to spot brett, because its manifestation will vary depending on the substrates that were initially available to the yeast cells as they multiplied, the precise strain of brett involved, and the context of the other flavors present in the wine. As the combination of spoilage compounds produced and their relative concentrations differ, the overall effects of brett will differ. I’ve experienced some bretty wines that were earthy and spicy, while others have been more at the fecal-animal end of the spectrum.


How common is brett as a wine flaw? The only thing we can say for certain is that it is far from rare in red wines. Wine scientist Pascal Chatonnet, who was responsible for much of the groundbreaking research on this subject, surveyed the incidence of brett in a variety of red wines some years ago and found that a little less than a third had 4-ethylphenol levels of more than 600 micrograms per liter. This compound, which is only found in wines infected by brett, is used as a diagnostic indicator; most people can spot it at around 420 micrograms per liter, but that sensitivity varies with the style of wine. Chatonnet says that the incidence of brett is probably higher today than it was at the time of his study.

Consultant winemaker Sam Harrop, for his Master of Wine dissertation, presented 25 of the world’s leading Syrah-based wines in a blind tasting, then asked those present to comment on whether they detected brett. He sent samples of the same wines to be analyzed for 4-ethylphenol. A striking number of them, including some famous names, showed above-threshold levels of the compound.

A further clue is provided by data from the International Wine Challenge, the world’s largest blind tasting, where brett consistently makes up around a third of all wine flaws recorded (typically, about 15,000 bottles of wine are tasted each year, with some 5-7% of these deemed faulty). Over the last three years, brett has shown signs of being an increasing problem, as Chatonnet suggests.

There’s a widespread misconception that brett contamination is a hallmark of wineries with poor hygiene. “Brett can occur in the cleanest cellars,” says New Zealand winemaker Matt Thomson, who is an expert on the subject. Brett has been identified in every wine region where people have looked for it. Thomson thinks that oak is largely to blame: “If you use new oak, you will get brett. It is not something you can associate just with a dirty cellar.”

Brett likes oak. It particularly likes toasted, new barrels, because it can also feed off a compound called cellobiose, which is formed when barrels are toasted. But Thomson observes that brett is associated not only with new oak, but also with old barrels. It has been found at depths of more than a quarter-inch in staves, which makes it nearly impossible to remove by steam or ozone cleaning. Because it is such a resilient yeast, it is difficult to eradicate.

Thomson agrees that brett is a growing problem. “I am convinced that in large numbers of wineries in both the New and Old worlds, brett is a new thing,” he remarks. He has a theory that there has been a change in the way oak barrels are produced in the relatively recent past: “Something happened with the huge demand for new oak in the 1980s. Coopers had a boom period and started doing something different, and there was a change.”


What can be done to stop brett? This is where things get interesting, because many of the steps that need to be taken to ensure clean wines run counter to the winemaking approach you’d want to follow to make interesting wines.

The simplest solution is to avoid oak altogether. Stainless steel can be cleaned properly, which vastly reduces the risk of brett. If you really need barrel aging to make good wine, however, you should try to prevent cross-contamination. When taking samples, Thomson uses a plastic barrel thief once, then sterilizes it before using it again. He also avoids a “rack and return” method, in which the wine from several barrels is mixed in a tank before going back into barrel; instead, each barrel is racked separately to tank and returned, and the tank is cleaned before the procedure is repeated with the next barrel. I don’t know of many winemakers who are this careful.

Another way to fight brett is to keep pH levels low, either by acidifying or by harvesting earlier. Because brett is so widespread, you want to make your wine an uninviting habitat for its growth. Low pH is important for two reasons: First, brett doesn’t like more acidic media; second, at lower pH levels, any doses of sulfur dioxide will be much more effective, because more of the SO2 will be in its active (free) form.

It’s also important to keep the period from the end of alcoholic fermentation to the end of malolactic conversion as short as possible. Since SO2 levels have to be low to facilitate the malolactic, this is a risky time in terms of potential brett growth. Therefore, it’s advisable to inoculate for the malolactic conversion, and after it is complete, to add a whack of SO2 to protect the wine for the rest of its time in the barrel or tank.

Other preventive steps include restricting the amount of lees aging, keeping barrels topped up, keeping cellar temperatures low, avoiding temperature changes, and aggressively cleaning both new and used barrels.

If brett has already been at work on a wine, there are two ways a winemaker can deal with the problem. The first is to strip out the remaining brett cells, either by filtration or by using a chemical called DMDC (dimethyl dicarbamate, also known by its trade name Velcorin). This is extremely toxic to microbes, but it breaks down into harmless products once it has done its job. The wine will still have the impact of the compounds associated with brett, but at least it won’t get any worse, and it will be stable in the bottle. The second approach, once the wine is stable, is to use modern crossflow-filtration or nanofiltration technologies to remove compounds such as 4-ethylphenol selectively. These processes are still new, however, and they haven’t yet been widely adopted.


So we come back to the initial question: Is brett always a problem, or are there contexts in which it is acceptable? If you were a winemaker, you’d probably want to eliminate it completely because it is so difficult to control. Still, whether through luck or design, some wines seem to work well even though they have noticeable brett. These tend to be red wines from warmer climates, where the sweetness of the fruit can be complemented by the earthy, spicy funk of the brett.

Unlike many other wine flaws, then, brett becomes a matter of personal preference. Some people find it objectionable no matter what the context. And that creates a problem when it comes to restaurant service. If a sommelier tries a wine and notices brett, should it be pointed out to the customer? Probably not, because the customer may think the wine is perfectly acceptable. If a customer refuses a wine because it is bretty, however, then the wine must be considered faulty. Perhaps the safest course is to warn customers of the implications of ordering wine from a producer whose house style involves a significant imprint of brett.

Brett is an issue the entire wine trade should become more aware of. “Lots of winemakers still haven’t grasped the complexity of Brettanomyces,” says Thomson, “and there’s still a bit of denial out there.” But it is also something that he thinks everyone can understand: “All decent tasters can pick up the nuances of brett once you tune into it.”

I suggest that we need to recognize the problems associated with brett, while keeping an open mind about wine styles in which it adds complexity. We shouldn’t become brett policemen who are always trying to spot it in whatever wine we’re tasting.