June-July 2014

On the Track of BRETT
By: Jamie Goode, Ph.D.
Of all wine faults, Brettanomyces is one of the most complex — and also one of the most fascinating, partly because it is one of those “faults” that in some contexts can be regarded as a positive. Indeed, there are many sought-after, expensive wines that owe some of their character to Brettanomyces (usually referred to simply as “brett”). It’s also a controversial topic, with some arguing that brett is to be avoided at all costs, while others think a less dogmatic approach is more in order.

First, some basics. Brettanomyces is a genus of yeast, also known as Dekkera (the yeast can exist in two states, and this latter name is used for the sexual, spore-producing form). While several species names are commonly used, the current classification has 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 important component in British and Belgian beer styles in the early years of the 20th century. Indeed, when the first single-culture Saccharomyces cerevisiae yeasts (the species of yeast used for making wine) were used 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.

The reason brett is a problem in winemaking is that it is annoyingly resilient, sitting around, biding its time, and then growing in conditions in which virtually nothing else can. In practical terms, this means that it does its real damage after the regular alcoholic and malolactic fermentations are complete. Brett is slow-growing and tough, and doesn’t need much to feed on. While it is seen in white wines (albeit very rarely), it’s predominantly a red wine problem. And the reason it is such a problem is that it produces some distinctive flavours that, at higher levels, can ruin wines.

Recognizing Brett

What are the key characteristics of this wine fault as it might be encountered in wine? The first sign is reduced varietal character, followed by the degradation of certain fruity aromas by esterases present in this yeast. Esterases are enzymes that cause the breakdown of esters, important in conferring fruitiness. Pinot Noir, among other grape varieties, is particularly badly hit by brett, because it loses its bright cherry and violet characters. Then, hints of smoke and spice begin to appear, with the chief culprit here being a compound called 4-ethylguaiacol. As the infection progresses, the wine will begin to smell and taste medicinal (4-ethylphenol is largely responsible for this), and it will lose its fruity flesh, exposing the structural bones of the wine. Finally, the wine will begin to smell of barnyards, horses, animal sheds and Band-Aid.

t’s difficult to teach people how to spot brett, because the characteristics of bretty wines will vary depending on the substrates that were initially available to the brett cells as they multiplied, the precise strain of brett involved and also the context of the other flavors present in the wine. Depending on the combination of spoilage compounds produced and their relative concentrations, the overall effects of brett will differ.

The Prevalence of Brett

How common is it? It’s hard to be sure, but at least we can say 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 just under a third had levels of 4-ethylphenol above 600 μg/litre (4-ethylphenol is used as a diagnostic indicator for the presence of brett; most people can spot it at around 420 μg/litre, but this will vary with the style of wine). He says that he thinks the incidence now will be higher. For his Master of Wine (MW) dissertation, consultant winemaker Sam Harrop did a study in which he presented 25 of the world’s leading Syrah-based wines in a blind tasting, and asked those present to comment on whether they detected brett or not. He then sent samples of these same wines away for chemical analysis for 4-ethylphenol. A striking number of these wines showed above-threshold levels, including some famous names.

How It Happens, and Why It Is Increasing

So what causes this problem? There’s a misconception that brett contamination is solely 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. It has been identified in every wine region where people have looked for it. Thomson thinks that oak is largely to blame for many infections, because brett can live in the oak and it is almost impossible to get out by cleaning. “If you use new oak, you will get brett: It is not something you can associate just with a dirty cellar.”

Brett particularly likes toasted new barrels, and has been found eight millimeters deep in staves. This makes it very hard to remove by steam or ozone cleaning. It can feed off a compound, cellobiose, formed when barrels are toasted. Thomson goes further, suggesting that brett is not only associated with new oak, but also that he has identified specific coopers who have a problem with bretty barrels. Brett is also associated with old barrels. Because it is such a resilient yeast, it will survive most cleaning attempts. What can be done to avoid brett, according to Thomson? This is where things get interesting, because many of the steps that need to be taken in order to ensure clean wines run counter to the sort of winemaking approach you’d want to take to make interesting wines.

The first is to avoid barrels. Stainless steel can be cleaned properly, which vastly reduces the risk. Second, you need to avoid cross-contamination. When taking barrel samples Thomson uses plastic barrel thiefs that are used just once, and then sterilized. He also avoids doing rack and return where the wine would go from several barrels to be mixed up in one tank: instead, each barrel is racked separately to tank and returned, and the tank cleaned before the procedure is repeated with the next barrel.

The next stage is to keep pH low, either by acidifying or harvesting earlier. This is crucial in the fight against brett. Because brett is widespread, make your wine an uninviting habitat for its growth. If you make your wine in the sort of place where brett is happy growing, it will. Low pH is important for two reasons. First, brett doesn’t like more acidic media. Second, at lower pH any sulphur dioxide (SO2) additions will be much more effective, and more of the SO2 will be in the active (molecular) form.

Another important prevention measure is to keep the time from the end of alcoholic fermentation to the end of malolactic fermentation as short as possible. SO2 levels have to be kept low in order to facilitate the malolactic fermentation, which makes this a risky time in terms of potential brett growth. Other preventive steps include avoiding lees aging, keeping barrels topped up, keeping cellar temperatures low, avoiding temperature changes and aggressively cleaning new and used barrels. If brett has been at work on a wine, there are two ways that a winemaker can deal with the problem. The first is to strip out the remaining brett cells by either filtration or the use of a chemical called DMDC (dimethyl dicarbamate, also known by its trade name of Velcorin). The wine will still have the impact of the compounds associated with brett, but at least it won’t get any worse, and will be stable in bottle. The second approach, once the wine is stable, is to use modern cross-flow filtration or nanofiltration technologies to remove compounds such as 4-ethylphenol in a selective manner. This is quite new, and hasn’t yet been widely adopted.

Is Brett Always a Problem?

So we come to the thorny question: Is brett always a problem, or are there contexts in which it is acceptable? If you are a winemaker, you will probably want to avoid it altogether because it is so difficult to control. But, perhaps through luck, some wines seem to work even though they have noticeable brett. Unlike many other wine faults, which are more clear-cut, it becomes a matter of personal preference. Some people find brett objectionable no matter what the context. This makes brett a problematic wine “fault” when it comes to restaurant service. If a sommelier tries a wine and finds some brett, should he or she point it out to the customer? Probably not, because the customer may find the wine to be perfectly acceptable. If, however, a customer refuses a wine because it is bretty, then in this context the wine is faulty.

Brett is something that the trade needs to 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.” It’s also something that he thinks everyone can get. “All decent tasters can pick the nuances of brett once you tune into it.” In conclusion, I’d suggest that we need to become more aware of brett, while keeping an open mind about wine styles where it adds complexity, and not becoming brett policemen who are always trying to spot it in whatever wine we’re tasting.

Some Compounds Produced by Brettanomyces
COMPOUND SENSORY IMPACT
4-ethylphenol
4-ethylguaiacol
isovaleric acid
4-ethylcatechol
4-ethylphenol
2-phenylethanol
guaiacol
ethyldecanoate
trans-2-nonenal
isoamyl alcohol
ethyl-2-methylbutyrate
4-ethylphenol
spicy, smoky, phenolic, cloves
sweaty, rancid, cheesy
medicinal, stables
honey, spice, lilac
smoky

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