🍷 Brettanomyces

Brettanomyces is a yeast commonly found in wineries that can cause significant spoilage in wine by producing volatile phenols, in particular 4-ethylphenol (4EP), 4-ethylguaiacol (4EG) and 4-ethylcatechol (4EC). They are associated with "Band-Aid", "medicinal", "horsy" and "barnyard" characters, collectively known as "Brett" character. According to the Australian Wine Research Institute (AWRI), it can be found across all Australian wine regions.

Growth is strongly favoured by residual sugar and by high pH, mainly because pH determines how effective SO2 is. The risk is highest at the end of malolactic fermentation, when wines are usually at their highest pH and lowest SO2. Hazy wines are at higher risk, and wine used for topping barrels can be a source of contamination.

The AWRI says control needs a multi-faceted approach: sanitation of equipment, tanks and barrels, minimising residual sugar, and a single large SO2 addition soon after malolactic fermentation (only about 35 to 40% of added SO2 becomes free SO2). For contaminated barrels it recommends hot water of at least 70 C for 30 minutes or 85 C for 15 minutes. Well-performed filtration is preferred to the risk of spoilage after bottling, and DNA-based tests can detect the yeast before volatiles pass the sensory threshold. Reverse osmosis can remove up to 7% of 4-ethylphenol per pass.