Brettanomyces bruxellensis is a wild yeast known for its significant impact on fermented products. While it can sometimes contribute desirable characteristics, it is often considered a spoilage organism, particularly in beverages. This yeast is widely distributed and can lead to a range of aromatic changes, which are frequently viewed as flaws in the final product.
Unique Biological Traits
Brettanomyces bruxellensis is an ascomycete yeast that primarily reproduces through budding. It adapts well to challenging environmental conditions, including high ethanol concentrations, low pH, and limited nutrient availability. As a facultative anaerobe, it can metabolize in both the presence and absence of oxygen.
Its distinctive metabolism allows it to utilize various carbon sources, producing acetic acid and carbon dioxide as dominant fermentation end products. Compared to other yeasts, Brettanomyces bruxellensis has a slow growth rate. This slow growth, combined with its resilience, enables it to persist in environments inhospitable to many other microorganisms.
Where It Thrives
Brettanomyces bruxellensis is commonly found in natural environments and is strongly associated with industrial fermented products. In winemaking, it is a significant concern, often isolated from wineries and persisting in cellars. Red wines are particularly susceptible.
This yeast thrives in low-oxygen conditions, fermenting small amounts of sugar even with minimal oxygen. It tolerates high ethanol concentrations and low pH levels. Its ability to form biofilms on surfaces, such as stainless steel, contributes to its persistence and resistance to cleaning agents in production facilities.
Its Impact on Sensory Qualities
The impact of Brettanomyces bruxellensis on sensory qualities comes from its production of volatile compounds, especially volatile phenols. Two common examples are 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG), synthesized from cinnamic acid precursors in grapes. 4-ethylphenol is often described with aromas of “barnyard,” “band-aid,” “antiseptic,” or “horse stable.”
4-ethylguaiacol is associated with “spicy,” “smoky,” or “clove” notes. While usually present in lower quantities than 4-EP, 4-ethylguaiacol is more volatile and has a lower sensory threshold. The combined concentration and ratio of these compounds influence the overall “Brett” character. Brettanomyces bruxellensis can also produce medium-chain fatty acids like isovaleric acid, which may contribute “rancid” or “sweaty saddle” notes.
Controlling Its Presence
Managing or preventing Brettanomyces bruxellensis in production environments involves several strategies. Proper sanitation and hygiene are foundational, as this yeast forms persistent biofilms on surfaces. Stronger cleaning methods, such as foaming caustic soda and peroxide solutions, are often effective.
In winemaking, sulfur dioxide (SO2) is a common preservative used to inhibit microbial growth, though some strains show tolerance. Filtration techniques physically remove yeast cells. Temperature control, by maintaining temperatures at or below 15°C, also helps limit spoilage. Regular monitoring of products for volatile phenols can track yeast activity and the effectiveness of control measures.