Wine · Terminology

Brettanomyces

A spoilage yeast that gives wine barnyard, plaster and smoked-meat aromas — a fault in quantity, a signature in trace.

Brettanomyces — Brett to everyone who deals with it — is a genus of yeast that can survive in wine after fermentation is over. Feeding on trace sugars, it produces volatile phenols whose aromas are described as barnyard, horse blanket, sticking plaster, smoked meat, leather and clove.

Whether that is a fault or a feature is the oldest argument in the tasting room. At trace levels many drinkers read it as savoury complexity; above threshold it buries the fruit and makes every affected wine in a cellar smell the same.

In practice

  • Lives in oak barrels, especially old ones — the pores are impossible to sterilise completely.
  • Thrives where sulfur is low, pH is high, and residual sugar lingers after a slow or stuck ferment.
  • Controlled by hygiene, sulfur dioxide, low pH, sterile filtration and — the blunt instrument — replacing infected barrels.
  • Affects reds far more than whites, which are usually more acidic and more protected.

Where you'll meet it

  • Traditionally in the southern Rhône, older-style Bordeaux and Rioja — much less so today.
  • In low-intervention and natural wine, where sulfur is minimal by design.
  • On every exam list of common wine faults.

Judging it

Brett is a spectrum, and the same wine reads differently to different noses — sensitivity to 4-ethylphenol varies several-fold between individuals.

Level Impression
Trace Savoury lift, spice, "old-school" complexity
Moderate Leather and farmyard clearly ahead of the fruit
High Plaster, mousey, medicinal; fruit gone

The practical test is the same one used for volatile acidity: is the fruit still there? If Brett is the loudest thing in the glass, it is a fault.

The exam angle

  • Name it as a fault: "Brettanomyces — animal, plaster and clove notes" — and say whether it masks the fruit.
  • Know the control measures, since production questions ask for them: cellar hygiene, sulfur management, avoiding high-pH musts, careful barrel selection.
  • Brett is not the same as reduction (struck match, rotten egg) or oxidation (bruised apple). Examiners look for tasters who can separate the three.

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