Being a winemaker is a specialised calling, requiring intimate knowledge of soil composition, seasons and weather, chemistry, flavour, even marketing and sales.

Yet the distinctive bouquet and flavour of a Chablis or chardonnay could not be achieved without the input of a brainless, single-celled organism, said a study on Thursday.

The previously overlooked vintner, a type of yeast called Saccharomyces cerevisiae, makes a “small but significant” contribution to a wine’s flavour and taste, scientists reported in the journal Scientific Reports.

This makes the fungus a key to that enigmatic wine concept “terroir” – everything from the soil, topography, climate and agricultural processes that go into producing your favourite Bordeaux.

“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,” co-author Matthew Goddard of the University of Lincoln in England told AFP.

“The signal is small, but detectable,” he said by email.

Geographic differences in wines were previously ascribed mainly to plant genetics, local soil and climate, and farming methods.