New Zealand scientists and winemakers are trying to solve part of the puzzle of terroir by researching yeast varieties indigenous to one West Auckland winery.
A study by Auckland University scientists at Kumeu River Estate has uncovered close to 100 new varieties of wine yeast, each of which is specifically indigenous to the greater Kumeu wine region and unlike any other strains of yeast in the world, according to lead researcher Dr. Mat Goddard.
He believes this scientific breakthrough could have wide-ranging benefits. "The use of New Zealand-specific wine yeasts may prove a powerful tool to further differentiate New Zealand wine," said Goddard. "They more faithfully reflect the New Zealand sense of place than overseas wine yeasts."
The use of so-called wild versus cultured strains of yeast is a long-running debate for winemakers. Yeasts, the single-cell fungi that ferment grape sugar into wine, come in hundreds of different varieties. Some winemakers prefer to buy commercially cultivated strains and inoculate the grape must with them. The advantage is that these strains usually work efficiently and don't break down in the middle of fermentation.
But other winemakers prefer the yeast strains that enter a winery on the grape skins themselves. While they're more unpredictable in the vat, these yeasts have evolved in the vineyard and produce distinctive local flavors, argue these winemakers. What's more, indigenous yeast advocates believe commercially cultivated strains produce uniform flavors in all the wines they're used in. Winemakers can request yeast strains that will produce particular flavors or aromas. Inevitably, multiple yeast strains end up taking part in a fermentation.
The Auckland study has helped Kumeu River Estate Wines winemaker Michael Brajovich understand the unique microbial world of his vineyards and winery, but the results won't change the way he goes about crafting his wines. Brajovich has long been a believer in using wild yeasts for his winemaking. After becoming disillusioned with commercial strains while studying winemaking in Australia during the early 1980s, an eye-opening vintage in St.-Emilion prompted Brajovich to forgo the use of commercial yeasts from the 1986 vintage on.
And his wines have never tasted better, he says. He believes a commercial yeast strain tends to dominate a ferment, which often leads to a lack of varietal definition and lessens the expression of the vineyard. But subtle wild yeasts seem to let the geography show, he says.
"With wild yeasts, the yeast character retreats a lot, allowing the expression of variety and vineyard," he says. "This makes the wine much more expressive of it's place. It allows the vineyard to show better. That, and because the yeasts are unique to us, which has been shown through DNA analysis, they are, arguably, part of the terroir."
The recent study also uncovered similar, related indigenous yeasts at nearby Matua Valley, five miles up the road. Since yeast cannot travel unassisted, this proves the yeast has been moved via either human contact or bees, he says.
"This proves that the population is not static," Brajovich says. "There is always new generic material coming through."
For Goddard, the ever-increasing quantity of indigenous yeast strains places a greater emphasis on the need for study. "A lot more research is needed," he said. "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 the future."