How do you react when Brett comes up in a conversation about wine?
Some may wonder why bread appears in the discussion — the resemblance goes no further than the sound of the word. What drifts from the glass is a distinctive smell rarely encountered in everyday wine.
Soapy, slightly animal, yet somewhere spicy, with a floral quality reminiscent of roses or violets. That is Brett. It shares a superficial direction with familiar wine aromas, but closer inspection reveals a different character altogether. Its unfamiliarity is precisely what makes it conspicuous.
Open any technical reference and Brett appears under off-flavors and taints. Wine school tasting courses teach the same classification. Among producers, the dominant view is that Brett represents absolute contamination. Yet a competing position treats it as a contributor to complexity, and both coexist.
Competition results make this division concrete. A Brett-affected wine may be eliminated before judging as a defective entry, or the same nuance may earn a top award.
What Brett Is
Brett in wine is sometimes called phénolé in French. The responsible compounds are volatile phenols. Two aromatic compounds carry the central role: 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG).
4-EP and 4-EG are not present in grapes directly. Grapes contain hydroxycinnamic acids — the precursors from which these volatile phenols are formed. The yeast Brettanomyces converts these organic acids into volatile phenols with exceptional efficiency. Because the character derives from volatile phenols produced by Brettanomyces, it carries the name Brett.
Brettanomyces is not specific to wine; it is said to occur wherever fermentation takes place. It was first identified in beer. Later isolations came from cheese and fermented dairy. Several species exist within the genus, but in wine, strains of Brettanomyces bruxellensis are reported to be the most consequential.
In the wine context, Brettanomyces enters the winery via grapes. Heard this way, it sounds no different from any other wild yeast — not inherently problematic. In practice, however, judgments about this organism divide sharply by region.
Regional Differences in Reception
One axis of difference in how Brett is perceived is geography. In what is broadly called the Old World, both producers and consumers are said to hold a more favorable view.
Appellations such as the Médoc, Rhône, Cahors, Chianti, and Piedmont are considered to have a high affinity with Brett. In these regions, the character is relatively often framed as part of terroir or as desirable complexity.
New World regions take the opposite stance. Brett is classified as absolute contamination and treated with strong aversion.
One reason for this regional divergence lies in differences in cultural convention.
The Learned Structure of Acceptance
Attitudes toward Brett are not innate. They are shaped by acquired learning and experience. Training that frames Brett as a natural expression of terroir tends to produce positive associations; training that frames it as absolute contamination tends to produce negative ones. This distinguishes Brett from compounds such as volatile acidity (VA), which trigger aversion through physiological, intuitive responses.
One reason attitudes toward Brett are susceptible to learning is that its sensory detection threshold and preference threshold nearly coincide. The detection threshold for 4-EP is approximately 600 μg/L; for 4-EG, approximately 100 μg/L. These concentrations are also close to the preference threshold. The concentration at which Brett becomes detectable is thus nearly the same as the concentration at which rejection occurs. Exposure to Brett in a training context readily reinforces the link between detection and rejection.
Training has been reported to shift attitudes toward Brett measurably. More extensively trained assessors show a lower preference threshold — they reject Brett at lower concentrations. Training at formal institutions assumes concentrations above the detection threshold; sub-threshold concentrations are not included in off-flavor training to begin with.
Producers and consumers without direct training are not exempt. Indirect learning, mediated through assessors, produces comparable effects.
In regions where Brett has historically been embedded in regional style, Brett-affected wines enter commercial distribution without issue. Here, traditional practice rather than critical evaluation functions as the criterion for market access. In regions without that traditional context, wine distribution tends to depend more heavily on competition results and critic evaluations. The assessors operating in those systems have largely been trained to reject Brett. Where Brett directly translates into commercial disadvantage, wineries develop a bias toward treating it as something to be eliminated. The selective pressure exerted by assessors thus functions as indirect learning, even for producers and consumers who have never attended a formal tasting course.
Is Brett Terroir?
The premise that Brett constitutes wine character rests on the idea that it is one element of terroir. Brettanomyces does arrive in the winery on grape surfaces as a wild yeast, and in that respect it does not depart from the context of spontaneous fermentation.
A fact worth establishing here: among non-Saccharomyces yeasts — those outside the genus responsible for primary fermentation — many are classified as spoilage organisms and targeted for removal during winemaking. Brettanomyces is not uniquely singled out among wild yeasts.
The reason Brettanomyces is targeted for removal is that its presence suppresses fruitiness and gradually homogenizes the aromatic profile across different wines.
At high concentrations, 4-EP produces Brett’s characteristic barnyard, horse sweat, and leather notes; 4-EG produces medicinal and Band-Aid-like odors. These are off-odors — recognized as defects beyond the threshold of character. This holds even in regions that display relatively tolerant attitudes toward Brett.
Below the preference threshold, Brett adds nuances to wine that are absent from typical expressions — spicy and floral qualities among them. At these concentrations, Brett does not necessarily constitute an off-odor. This is the basis for treating it as a contributor to complexity.
At the same time, wines lose their individual identity and converge toward a uniform Brett character. Fruitiness is the first casualty — Brett attenuates it strongly. It is because Brett strips wines of place-specific character, and because fruitiness has become increasingly central to contemporary wine style, that current wine education positions Brettanomyces as a target for elimination and Brett as an off-flavor.
This logic, however, only holds because Brett has spread across wine regions worldwide. When wine production was confined to a few regions, before modern distribution, when consumers had access only to nearby producers — with limited points of comparison, the argument that Brett makes everything taste the same could not stand. And if fruitiness is not the defining axis of wine style, its attenuation is not a significant defect. That Brett-inflected wines established themselves as a natural regional style is, on these terms, entirely coherent. This is the logic on which traditional regions base their acceptance of Brett.
Research has reported that Brettanomyces, once established in a winery, may persist for decades. A contaminated cellar is therefore likely to produce wines carrying Brett character across vintages, regardless of the harvest. If Brett’s presence is not recognized as contamination, and the same nuance appears consistently year after year, it is likely to be recognized eventually as a traditional regional style and become established as such.
Brett can become tradition — and terroir — within an environment shaped by human practice.
From an Era of Unavoidability to an Era of Choice
The principal tools for controlling Brettanomyces activity are sulfur dioxide addition and filtration. In cellars operating under a natural wine philosophy, neither is applied, or both are used at levels insufficient to suppress Brettanomyces. Beyond natural wine producers, contemporary winemaking broadly trends toward minimizing intervention. Measures adequate to eliminate this yeast from tank or bottle are frequently absent. Against this backdrop, the proportion of wines carrying Brett is expected to increase.
Why Brett has been discussed as an element of terroir and, in some cases, tolerated, is understandable from a historical perspective. With contemporary technology and equipment, managing Brettanomyces to a level that does not compromise wine quality is achievable. Complete elimination, however, is not straightforward. At earlier levels of technical capacity, it was even less so. That era was also one in which what we now call natural winemaking was standard practice. Just as medieval public health cannot be judged by contemporary standards, the historical period when Brett was a routine presence in wine is straightforwardly understandable.
The question concerns the present. Brett strips wines of regional and varietal character. Preserving that character is the defining aspiration of mainstream contemporary winemaking. Precisely because this has become the standard, the risk of producing undifferentiated wine — one indistinguishable from the majority — emerges. Standing out by the absence of what is expected can function as a marketing advantage. Whether finding value through the loss of terroir to Brett — after considerable effort — is a desirable outcome is a question worth revisiting.
Defect and Character: Separate Judgments
Brett at concentrations above the preference threshold is an off-odor and a defect. The contested zone is the concentration range below that threshold. In this range, “is it a defect?” and “is it character?” function as separate questions requiring different criteria.
“Is it a defect?” varies with the cultural and educational background of the recipient. For someone trained to treat Brett as something that should not exist, it may represent an absolute defect. For someone without that training, the same wine registers as an impressive one with an unfamiliar nuance. There have been recent observations that evaluative attitudes toward volatile phenols have become excessively negative. Given the historical record of traditional acceptance, the argument that treating any detectable Brett as an automatic defect goes too far carries some validity.
“Is it character?” requires a different axis of judgment. Brett can function as legible differentiation. But if that differentiation arises from reversing the homogenization Brett itself causes, it cannot constitute character. For today’s consumers with access to wines from across the world, the nuance will eventually be identified as Brett. What is present is not each wine’s specific character but the homogenizing action of Brettanomyces. An element that produces the same result regardless of who makes the wine or how it is made cannot be the source of character. Uniformity is a criterion that belongs to industrial production.
“Is it a defect?” and “is it character?” should be asked independently, each according to its own criteria. The diversity of positions around Brett cannot be captured by placing these two questions on the same axis as opposing poles.
