Ensuring the continued efficacy of Brettanomyces control strategies for avoidance of spoilage
Brettanomyces yeast cause wine spoilage by producing 4-ethylphenol and 4-ethylguiacol which are responsible for ‘phenolic’, ‘leather’, ‘sweaty’ and ‘medicinal’ aromas (collectively known as ‘Brett’ character). Although wine spoilage from this yeast was a major issue in Australian red wines produced during the late 1990s and early 2000s, the risk of ‘Brett’ spoilage is now commonly managed via a multi-faceted strategy developed by the AWRI, enabling winemakers to significantly decrease levels of ‘Brett’ spoilage compounds in finished wines. Yet, Brettanomyces has not been eliminated from Australian wineries, and loss of wine value still occurs. To ensure Australian winemakers’ continued ability to manage Brettanomyces in a cost-effective manner, the control strategy must be future-proofed against market pressures to minimise levels of sulfite in wine, and augmented with rapid detection methods.
The potential for emergence of sulfite-tolerant Brettanomyces strains
In order to determine if the genetic plasticity exists within Brettanomyces for it to become resistant to current control measures, several different environmental lineages of Brettanomyces bruxellensis have undergone long-term growth experiments under ever-increasing amounts of sulfite. Populations evolved from all of the different strains of Brettanomyces were shown to possess the ability to adapt to increased levels of sulfite, with many showing a doubling of their original levels of sulfite resistance. In addition, for many of these populations this resistance was stably inherited, ever after long-term growth in the absence of the selective agent. Genomic analysis of these populations and individuals from these populations, is now under way in an attempt to associate specific genetic alterations with these resistant phenotypes. Once established, these differences will provide genetic markers that maybe used as an early alert mechanism to determine if resistance is developing in the field before problems with the control of Brettanomyces are encountered by winemakers.