Microbes’ role in a wine’s ‘terroir’

New Zealand and British scientists say they have discovered the first direct evidence of a fungus that helps provide wine with a distinctive bouquet and flavour linked to a certain district, a concept known to wine lovers by the French word “terroir”.

Debate has ranged over whether winemaking is an art or a science and just what is creates a unique vintage. Geographic differences in wines have been attributed to plant genetics, local soil and climate, and farming methods.

But the new study, published in Nature, has found a type of yeast called Saccharomyces cerevisiae, makes a “small but significant” contribution to a wine’s taste.

While the scientists have caught up, it is something Australian winemaker, Oakridge chief executive David Bicknell, told Cosmos late last year when we took a close look at the science of winemaking. He has been making distinctive wines based on exposing his fermentation to wild yeast strains for years.

He swears by the difference in flavour and bouquet.

“With commercial yeast you get certainty – you can sleep at night. But how do you make wine more interesting? You exploit the metabolic processes of different yeast species.”

The recent study backs Bicknell up, with the researchers saying the findings provide the first direct, experimental evidence the fungus contributes to “terroir”.

“I was surprised that we detected any signal at all from these geographically different yeast populations in the aroma profile of the wine – I thought we would not,” the study’s co-author Associate Professor Matthew Goddard of the University of Lincoln, told ABC news. “The signal is small, but detectable.”

The scientists identified genetic differences between different populations of S. cerevisiae found in sauvignon blanc grapes in six major wine-growing regions of New Zealand. They found that about half of the chemical compounds that determine a wine’s characteristics came from yeast during fermentation.

“Most of the ‘fruity’ notes in wine are in fact derived from yeast not the fruit,” Dr Goddard was quoted as saying.

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