20 AUGUST 2009 - Scientists from the University of Auckland have discovered a unique group of New Zealand yeasts involved in wine production, and have begun to identify the origins of the local yeast strains - with surprising results.
The researchers examined Saccharomyces cerevisiae wine yeast from a spontaneous ferment at Kumeu River winery. "We identified almost a hundred different strains in the ferment" says lead researcher Dr Mat Goddard "and many of them were genetically distinct from S. cerevisiae found elsewhere in the world."
Spontaneous fermentation relies on the yeasts that are naturally present rather than the addition of an commercial yeast preparation from overseas, and Kumeu River in West Auckland is one the New Zealand wineries that employs this process. While spontaneous fermentation has been used throughout winemaking history, and is often associated with premium wines, until now the origins of the yeast involved has been a mystery.
"The Kumeu River yeast population was surprisingly diverse and distinctive, and we wanted to know where the strains came from," says Dr Goddard. Further genetic analyses indicated that the Kumeu population comprised six different but interbreeding groups. "None were related to commercial yeast strains, so they couldn't have 'escaped' from a local winery. Nor could we detect any S. cerevisiae in the winery before harvest, so the yeast must have come from an outside source."
Following this reasoning, the scientists took samples from nearby Matua Valley vineyard and showed, for the first time, that some of the strains in a spontaneous ferment were derived from yeasts inhabiting local soil, bark, and flowers.
A linking step was required however, as the yeast could not travel between sites, and grapes from Matua Valley were not carried to Kumeu River for processing. Further research showed that one if the ways it dispersed was with insect assistance, catching a ride on honey bees moving around the area.
A new oak barrel imported from France proved to be yet another source of yeast involved in the ferment, harbouring a population of yeasts that was very closely related to one of the sub-groups in the Kumeu ferment. This provides the first direct evidence that wine yeasts may be found in new barrels and shows that humans, like honey bees, distribute yeast inadvertently.
"Our results indicate that geography is a major determinant of the biology of wine microbes, and that New Zealand has a unique population of wine yeasts," says Dr Goddard. "A lot more research is needed, but ultimately we would like to learn more about the characteristics these yeasts impart to New Zealand wines, and how they could be harnessed in future."
"The use of New Zealand-specific wine yeasts may prove a powerful tool to further differentiate New Zealand wine and they certainly more faithfully reflect the New Zealand sense of place (the meaning of the French term 'terroir') than using overseas wine yeasts."
Dr Goddard hopes to be able to reliably harness these New Zealand yeasts and provide them to local winemakers.
The current research has been published online in the journal Environmental Microbiology.
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