What Is Brettanomyces in Wine?

Quick answer

Brettanomyces is a wine-associated yeast, particularly the species Brettanomyces bruxellensis, that can grow during winemaking, maturation or storage. It can produce volatile compounds that alter a wine’s aroma and flavour.

Depending on the wine and the level present, Brett character may smell medicinal, like a bandage or antiseptic; smoky or spicy; leathery and earthy; or animal-like, sometimes described as “barnyard”, “horse” or “stable”. It may also do something less obvious: suppress the wine’s fruit, making it seem dull, muted or less fresh.

Is Brett always a fault? No. Brettanomyces is generally treated as a spoilage organism, especially when it dominates the wine or obscures its intended character. However, low levels may be tolerated or even appreciated by some drinkers in some styles. There is no single point at which every wine and every person will judge it in the same way.

What does “Brett” mean?

“Brett” is informal shorthand, but it can mean several related things:

• the Brettanomyces yeast;
• the compounds produced by the yeast;
• the sensory character those compounds create; or
• a suspicion based on how a wine smells.

These are not identical. Calling a wine “Brett-like” is a sensory description, not laboratory proof that the yeast is present. Similar earthy, leathery, smoky or savoury notes can have other causes, including reduction, oxidation, smoke taint or normal development with age.

What can Brett smell and taste like?

The most useful way to think about Brett is as a range of possible characters rather than one unmistakable smell.

A wine affected by Brett may show:

• medicinal, pharmaceutical or antiseptic aromas;
• bandage-like or “band-aid” notes;
• smoky, spicy or clove-like character;
• leather and earthy aromas;
• barnyard, horsey, stable-like or animal notes;
• sweaty or savoury impressions.

The profile depends on the yeast strain, the wine’s composition and the concentration of the compounds produced. One wine may seem mainly medicinal; another may show leather and savoury notes. A heavily affected wine may simply seem to have lost its bright fruit.

This is why the word “barnyard” should be treated as a clue, not a diagnosis. Tasting vocabulary helps us describe what we notice, but it does not identify the cause with certainty.

What compounds cause Brett character?

Brettanomyces can transform naturally occurring compounds in wine into volatile phenols—aroma-active compounds that are easier to smell.

The two most discussed are:

• 4-ethylphenol, often associated with medicinal, pharmaceutical, bandage-like or animal aromas;
• 4-ethylguaiacol, often associated with smoky, spicy, clove-like or savoury aromas.

Other compounds can contribute too, so Brett character cannot be reduced to one chemical or one smell.

The amount that a person notices varies with the wine. Alcohol, acidity, tannin, oak, grape variety, other aromas and the drinker’s own sensitivity can all affect perception. A level that is noticeable in a light, delicate wine may be masked or interpreted differently in a fuller wine.

Is there a Brettanomyces threshold?

Research reports sensory thresholds for individual compounds, but these figures vary according to the wine, the testing method and the people taking part. A chemical result also does not perfectly predict what a drinker will notice.

So there is no universal Brett threshold that applies to every wine or every palate. It is better to ask:

• Has the wine lost its fruit and freshness?
• Do the medicinal, smoky or animal notes dominate?
• Do they fit the wine’s intended style?
• Do you find the wine enjoyable?

A laboratory analysis can help a winery investigate a problem, but a consumer cannot definitively diagnose Brettanomyces from one aroma descriptor.

Is Brett a fault or a style?

Brettanomyces is commonly discussed as a wine fault because it can overwhelm fruit character and make a wine seem unbalanced. At pronounced levels, many drinkers would consider medicinal, animal-like or heavily leathery character undesirable.

At lower levels, opinions can differ. Some people may accept or enjoy a subtle earthy, leathery or savoury contribution, particularly in a wine where that character does not dominate. Others may notice the same character immediately and dislike it.

The important distinction is between a character that adds complexity without overwhelming the wine and spoilage that masks the wine’s fruit and structure. Neither “Brett is always bad” nor “Brett is always desirable” is a reliable rule.

Where can Brettanomyces occur?

Brettanomyces can be relevant during production, maturation and storage. It may persist in winery environments, equipment and porous wine-contact materials such as barrels. Wine conditions can also influence whether the yeast survives or grows.

For wineries, control is mainly a matter of hygiene, monitoring and managing wine-contact materials and conditions. It is not something a producer can sensibly judge only after a bottle reaches the customer.

Australian Wine Research Institute material recognises Brettanomyces as a wine-management issue across Australian wine regions. That does not mean a particular region, grape variety or producer has a special Brett problem. Brett is a wine-production challenge, not a useful basis for stereotyping Australian wine.

What should you do if you suspect Brett?

First, smell and taste the wine carefully in a clean glass. Avoid deciding from one word such as “leather” or “barnyard”, because those notes can have several causes.

If the wine seems clearly unpleasant or significantly different from what you expected:

1. Keep the bottle, closure and proof of purchase where practical.
2. If possible, compare it with another bottle of the same wine.
3. Contact the retailer or producer and describe the problem.
4. Explain the aromas you noticed rather than insisting on a diagnosis.

Decanting, chilling or leaving the wine open may change how it smells temporarily, but these actions do not reliably remove established Brett character. Consumers generally cannot reverse the underlying condition at home.

Brettanomyces compared with other wine faults

• Cork taint: commonly associated with musty, mouldy or damp-cardboard aromas and suppressed fruit. It is a different problem from Brettanomyces.
• Oxidation: can produce bruised-apple, nutty, stale or cardboard-like character after excessive oxygen exposure.
• Reduction: may produce struck-match, rubber, cabbage or rotten-egg-like aromas. It is chemically distinct from Brett.
• Volatile acidity: may smell vinegary or solvent-like. It can be associated with microbial activity, but it is not the same diagnosis as Brett.
• Smoke taint: may show ash, burnt or campfire-like character and can overlap with some smoky Brett descriptions.

Sensory overlap is real, which is another reason not to diagnose Brett from one aroma alone.

Frequently asked questions

Is Brettanomyces the same as cork taint?

No. Cork taint and Brettanomyces can both suppress fruit, but they have different causes and commonly produce different sensory patterns.

Can you smell Brett in every affected wine?

No. Brett character varies. Some wines show obvious medicinal or animal notes, while others mainly seem less fruity or less fresh.

Is Brettanomyces only found in red wine?

No universal claim like that is supported. Brett can be relevant to wine production more broadly, although its sensory expression depends on the wine.

Can aeration cure Brett?

No. Aeration may temporarily change perception, but it does not reliably remove the compounds or eliminate the underlying issue.

Is a wine with Brett automatically unsafe?

The research supplied for this guide supports treating Brett primarily as a quality and enjoyment issue. If a wine seems faulty, contact the retailer or producer rather than relying on a home diagnosis.