Sequencing the genomes of hundreds of strains of the wine yeast¹ S. cerevisiae has revealed little genetic² diversity and high levels of inbreeding. In many cases, yeast strains sold by different companies were almost genetically⁴ identical. The results, published in the April issue of G3: Genes⁵|Genomes|Genetics, a publication of the Genetics Society of America, suggest that winemakers attempting to develop improved wine yeasts⁶ will need to look to creating hybrids⁷ with more exotic strains. "It takes a tough yeast to ferment⁸ wine," says lead author Anthony Borneman of the Australian Wine Research Institute. "Wine yeast need to be far more stress tolerant than strains used in brewing⁹ or baking, for example, to cope with the very high sugar and acidity¹⁰ levels of grape juice. Our results show that only a limited branch of the yeast evolutionary¹¹ tree is currently used in winemaking."

 

Yeast contributes to the flavors of wine, and may even provide a component¹² of a wine's "terroir," the local conditions that give a wine its unique flavor. Traditionally, wine has been fermented¹³ by naturally occurring yeast, but this can deliver inconsistent results from vintage to vintage. To yield more predictable results, most winemakers now use pure active dried yeast starter strains that have been produced by commercial suppliers.

 

Scientists at the Australian Wine Research Institute are developing new strains of yeast that contribute different flavor profiles during wine fermentation, including boosted floral aromas¹⁴. To better understand the genetic diversity available for breeding new yeast types, the authors of the study sequenced 212 strains of the yeast Saccharomyces cerevisiae. This included commercial wine and brewing starters and strains isolated¹⁵ from natural fermentations of wine and other alcoholic¹⁶ beverages¹⁷.

 

The results showed that virtually all the wine yeasts were closely related and carry only a tiny fraction of the overall pool of S. cerevisiae genetic diversity. For example, most of the strains from the Prise de Mousse collection of champagne¹⁸ yeasts carry almost identical gene³ variants¹⁹. These yeasts likely arose from a single ancestor, or from an inbred ancestral population. In fact, dozens of strains sold by different companies are, genetically speaking, almost completely indistinguishable.

 

None-the-less, subtle genetic distinctions were often detected between strains, which may be responsible for their unique fermentation and flavor properties. There were also a few cases of major differences. For example, four strains carry a unique set of genes involved in producing a class of aromatic²⁰ chemicals. In another example, several commercial strains seem to be derived²¹ by hybridization with non-wine yeast strains, and contain a gene cluster typically associated with ale yeast.

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