Brettanomyces (Brett)
A wild yeast (Brettanomyces bruxellensis) that can colonise wine and produce distinctive compounds giving barnyard, leather, smoke, and medicinal aromas — considered a complexity-adding character at low levels and a fault at high levels.
In depth
Brettanomyces (often shortened to "Brett") produces several compounds that dramatically alter wine's aromatic profile. The main ones are: 4-ethylphenol (barn, leather), 4-ethylguaiacol (smoke, cloves, spice), and isovaleric acid (cheese, sweat). At low levels, Brett adds an earthy, leathery, smoky complexity that some winemakers and critics find appealing — particularly in traditional red Burgundy and some Rhône and Bordeaux wines. At high levels it is widely classified as a fault.
Brett thrives in conditions of: low sulphur dioxide, higher pH, residual sugar, and warm temperatures. It is particularly common in wineries that use used oak barrels (which can harbour Brett in the staves). Cellar hygiene is the primary preventative measure.
The debate over Brett is genuinely contested among wine professionals. What one person calls "farmyard complexity" another calls "sweaty saddle." Exam questions at Level 3 typically ask candidates to: name Brett, describe its aroma characteristics, and explain why it is controversial rather than universally classified as a fault.
Related exam topics
Frequently asked questions
- Is Brettanomyces always considered a wine fault?
- Not universally. At low levels, Brett adds earthy, leathery, smoky complexity that many wine lovers and winemakers appreciate — particularly in Burgundy, Rhône, and Bordeaux. At high levels, the barnyard, band-aid, and medicinal notes dominate and are widely considered a fault. Whether Brett is a fault or a feature depends on concentration, wine style, and personal preference.
Practise questions on this topic
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