There is no such thing as terroir yeast, contrary to what winegrowers think

Terroir’ yeast does not exist. Neither do bacteria. This, at least, is the belief of French researchers. Admittedly, Saccharomyces cerevisiae occur in vineyards, but in minute quantities. “In fact, they are rare, about one berry in 1,000 hosts a strain of Saccharomyces cerevisiae. A winemaker can select and multiply it to carry out fermentation. However, the concept of a 'terroir yeast', in the sense of a yeast that occurs exclusively in a particular block or in a particular vintage, has not been scientifically proven”, claims Isabelle Masneuf-Pomarède, oenologist and professor at Bordeaux Sciences Agro. So why are so many producers convinced otherwise? “It's through of a lack of scientific knowledge, which is partly our responsibility, because we have not publicised our research results enough. I am sure that winegrowers who say they use terroir or local yeasts are sincere”, says Patrick Lucas, professor of oenology at the Vine & Wine Science Institute (ISVV).

On 9 November, the two scientists held a conference about the controversial issue at the Cité du Vin, during the ‘Vendanges du Savoir’ event. According to Masneuf-Pomarède, the concept of terroir yeasts appeared at the end of 2013 following the publication of a scientific article by David A. Mills, professor at the University of Davis in California, and his team. “He is a renowned researcher in wine microbiology. He studied the population of microorganisms in 273 samples of must from three different regions, the Central Coast, Sonoma and the Napa Valley, over three years. He showed that depending on the production area, the microbial communities were different. He hypothesised that this could have consequences on the characteristics of the wines”, explained Masneuf-Pomarède. In 2014, a second study from the University of Chicago supported this idea. “Its authors speculated that the microorganisms occurring in the soil and on the plant play a significant role in the sensory characteristics of the wine”.

Among the studies that contradict American research, Patrick Lucas cited that by Jackson Peter of the University of Strasbourg published in 2018. “This researcher studied more than 1,000 strains of Saccharomyces cerevisiae from several vineyard sites in Europe, North America and Asia. His study shows that there is no difference between the strains based on their geographical origin”, summarised Lucas, who noticed the same result for the lactic acid bacteria Oenococcus oeni. “Fermentation microorganisms are not immobilised in one region. We have recently seen how quickly a virus can be transported around the world... Well, the same is true for yeast and bacteria. The entire European scientific community agrees with us”, he added.