Brettanomyces

Brettanomyces (commonly called “Brett”) is a type of yeast that can grow in wine, causing distinctive flavor and aroma compounds:

• Brettanomyces bruxellensis and B. anomalus are two species of Brettanomyces yeasts—wild yeast strains that produce volatile phenols, particularly 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG). There are different strains and species of Brettanomyces, each with unique characteristics.
• These compounds can be present in large amounts and at different levels and different ratios, creating aromas often described as barnyard, band-aid, leather, smoky, medicinal, or horse blanket. The sensory impact depends on the specific strain and environmental conditions.
• Brett thrives in environments with residual sugars, high pH levels (above 3.5), and lower sulfur dioxide levels. Higher pH increases the risk of Brettanomyces growth, while lower pH inhibits it. Winemakers need to monitor pH, sulfur dioxide, and sanitation to control Brettanomyces growth.
• It can live in barrel wood, winery equipment, and grape skins, and can originate from the vineyard and even persist in vineyards. Grapes are a source of Brett precursors, and vineyard conditions can influence its presence.

Brettanomyces is considered a wine fault when present at high levels, as it can spoil wine and produce volatile acidity as a byproduct. While most commonly associated with red wine, white wine and white wines—especially varieties like Chardonnay and Riesling—can also be susceptible. Cabernet Sauvignon and Syrah are red varieties often discussed in relation to Brett, and Chardonnay is a white variety that can be affected. Brettanomyces is also important in the production of certain beers, such as Belgian ales. To control Brett, winemakers may use a sterile filter before bottling to create a clean wine. Brett is a frequent topic in winemaking courses.

Where is it Most Common?

Brett contamination is more prevalent in certain winemaking contexts:

• Red wines, such as Cabernet Sauvignon and Syrah, are particularly susceptible due to their grape composition and aging practices—especially those aged in oak barrels for extended periods.
• Regions with warmer climates—where higher pH wines are more common; high pH increases Brett risk, while lower pH can help inhibit it.
• Old World wines—including many wines from Bordeaux What is a Bordeaux Blend? Bordeaux blend… More, Burgundy, and the Rhône, as well as different wines from other regions, particularly traditional French wines (some Rhône, Burgundy, and BordeauxBordeaux is one of France’s most famous … More producers).
• Natural wine production and minimal intervention winemaking, where winemakers may accept or even encourage Brett presence, and where minimal sulfur dioxide is used.
• Older, used barrels and extended ageing or aging in barrels can increase the risk, where Brett can establish itself in the wood pores.

White wine and white wines, including varieties like Chardonnay, can also be affected by Brett, though less commonly than red wine. Brett can originate from the vineyard and vineyards, and grape skins provide precursors for Brett compounds. All the wines in a cellar or region can be at risk if Brett is present, and many wines worldwide have shown Brett character. Drinking wines with Brett in small doses can offer a diversity of consumer experiences, from appreciation of complexity to avoidance due to spoilage notes.

Is Brett a Wine Fault?

This is controversial and depends on concentration and perspective:

Arguments: It’s a defect:

• At high levels, Brett overwhelms fruit character and diminishes the fruitiness and palate texture of the wine
• It can indicate poor winery hygiene or cellar management
• Many modern winemakers actively prevent it
• Brett produces flavor and aroma compounds, including off-flavors described as band aids, which are considered a wine fault by many

Arguments: It’s a characteristic:

• At low levels, some believe it adds complexity and “terroir”, with some winemakers and wine drinkers finding the bretty, spicy, or savoury flavour profile interesting, especially at lower levels
• Traditional in some classic wine regions
• Some consumers specifically enjoy these flavors
• Part of the signature style for certain prestigious wines; in certain courses on winemaking, Brett is discussed as both a flaw and a contributor to unique wine character

The wine industry is divided – many consider any Brett presence a flaw, especially when large amounts are present, while others see subtle Brett as adding character and influencing how the wine is tasted and perceived on the palate.

How Does it Affect Wine?

Sensory impacts:

• Creates distinctive “funky” aromas and flavors, including savoury, spicy, and band aid notes that can be present at different levels depending on the Brettanomyces strain and species involved
• Can mask fruit character and reduce the fruitiness and freshness on the palate
• Adds earthy, savory, or animal notes and can introduce spice or spicy elements to the flavour profile
• At extreme levels, it makes wine unpalatable

Chemical changes:

• Produces volatile phenols from naturally occurring phenolic acids and volatile acidity, which can contribute to wine faults and spoilage
• Can continue developing in the bottle as Brettanomyces growth may persist during aging, especially if large amounts of residual sugarResidual sugar (often abbreviated as RS)… More are present
• May increase over time if not controlled, with different ratios of 4-EP and 4-EG leading to a range of Brettanomyces characteristics in different wines

Market impacts:

• Heavily Brett-affected wines, or those with high levels of bretty, band aids, or savoury notes, often receive lower scores from critics.
• It can reduce wine value and consumer acceptance.
• Some niche markets specifically seek subtle Brett character and find these wines interesting, especially when tasted alongside many wines in a region.

Winemakers must balance the risk of Brettanomyces growth with the potential for added complexity, and drinking wines with subtle Brett can be a unique experience.

Detection and Diagnosis

Finding and figuring out Brettanomyces in wine is like being a detective! It’s both an art and a science that can challenge even the most experienced winemakers and wine lovers. Brett can be sneaky, sometimes showing up as subtle earthy or barnyard smells that are easily mixed up with other wine problems or even mistaken for good complexity in certain red wines.

The first weapon in a winemaker’s arsenal is often their nose and tongue. Winemakers and wine pros use their sense of smell and taste to catch those classic Brett warning signs—think sweaty horse saddle, barnyard, or earthy notes. But here’s the tricky part: how sensitive people are to these smells and flavors can be totally different from person to person, and even from wine to wine. What one taster finds interesting and complex, another might think is clearly spoiled. This makes it super important to combine nose-and-tongue testing with more scientific methods.

Lab testing is an amazing tool for proving that Brettanomyces is really there. By measuring specific compounds like 4-ethylphenol and 4-ethylguaiacol (the troublemakers responsible for those characteristic Brett smells), winemakers can get a much clearer picture of what’s happening in the bottle. Techniques like gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) are commonly used, though they can cost quite a bit of money. It’s also important to know that treatments like sulfur dioxide, often used in winemaking to control other tiny organisms, can sometimes hide the presence of Brett, making detection trickier!

Microbiological testing gives another layer of certainty that’s pretty impressive! By growing yeast from wine samples and using molecular techniques like PCR, winemakers can identify Brettanomyces strains directly. While this approach is highly accurate, it can take a long time and specialized equipment, making it harder for smaller wineries to use.

Understanding how the wine was made and the wine’s history is also crucial for diagnosing Brett problems. Wines that have gone through malolactic fermentation, been aged in new barrels, or been bottled with higher levels of leftover sugar are at much greater risk for Brett growth. Environmental factors, like warm or humid cellars, can further encourage Brett cells to multiply, especially in red wines that are aged for long periods in barrels.

In regions like Australia, where Brettanomyces has caused significant headaches for many red wines, winemakers are taking a smart, proactive approach. They combine nose-and-tongue testing with lab work, innovative strategies using yeast strains that can outcompete Brett, or adding compounds that stop its growth. Sterile filtration is also used to remove Brett cells before bottling, helping to make sure the wine stays clean and will age beautifully.

Interestingly, having Brett at low levels isn’t always seen as a bad thing! Some winemakers and wine drinkers actually appreciate the added complexity and savory character that small amounts of Brett can bring, especially in big, bold red wines. However, when Brettanomyces growth gets out of control, the resulting flavors and smells can completely take over the wine, leading to spoilage and a loss of lovely fruit character.

In the end, effective detection and diagnosis of Brettanomyces requires a combination of sensory skill, scientific testing, and a deep understanding of how wine is made! By staying alert and using all the tools available, winemakers can manage Brett problems and make sure their wines hit the perfect balance between complexity and cleanliness.

Conclusion

Brettanomyces represents one of winemaking’s most debated topics. While modern enology generally treats it as a preventable contamination that diminishes wine quality, context matters. Trace amounts in certain traditional wines might be considered part of their authentic character, but noticeable Brett typically indicates a winemaking issue. The key is control – winemakers who understand Brett can make informed decisions about prevention through proper sanitation, sulfur dioxide management, and careful barrel maintenance. For consumers, whether Brett is acceptable comes down to personal preference and the wine’s style and context.