When Duccio Cavalieri’s grandfather went to work in the fields of Tuscany, caring for Sangiovese vines, the hornets buzzing about the vineyard were a regular presence. These days, Cavalieri works in the same fields, collecting scientific data. And his findings suggest those hornets are a winemaker's best friend.
Thanks to that data, Cavalieri, director of computational biology at the Edmund Mach Foundation at the Institute of San Michele all'Adige, and a team of colleagues at the University of Florence, have produced a portrait of the ecology of the wild yeast species used in winemaking and beer brewing. Their findings, published July 30 on the website of the journal Proceedings of the National Academy of Sciences, identify European hornets as a natural reservoir for Saccharomyces cerevisiae, or brewer’s yeast, in Tuscany. The findings suggest that wasps living among the vines may be responsible for some of the terroir we taste in wines.
Winemakers have known for more than a century that Saccharomyces cerevisiae is behind most wine fermentation. In recent years there has been a debate about whether the best wines are made by cultivated strains of the yeast that winemakers add or by the yeasts already present in the winery and on grapes. But no one understood where these ambient yeasts were coming from. Were they present in the vineyard or just strains lurking in the winery?
Previous experiments have found Saccharomyces in the stomach of wasps, bees and hornets, but Cavalieri and his team are the first to prove that the hornets retain the yeast throughout the year and pass the yeast down to their offspring. Genetic analysis found that the yeast survives the winter by living in the wasps, and that yeast used to produce Tuscan wine shares a common ancestor with the Saccharomyces varieties found in the hornets. When the grapes are ripe, wasps bite them, leaving the yeast behind and giving fermentation a head start.
“It’s the first time we’ve shown the role of insects in harboring the same exact microbe that you find in the first five days of a wine’s fermentation,” Cavalieri told Wine Spectator. “There are strains that come into the wine from the wild, from the hornets. The role of the hornet in providing the natural biodiversity is crucial. In our opinion, it’s really part of the terroir.”
“I wish someone would do this exact study in the U.S.,” said Katie Hyma, a research associate at Cornell University who also studies grapes. “I was at a talk at the N.Y. wine industry workshop, and they were talking about culturing yeast strains typical in the vineyard for use in inoculation.”
Additionally, Cavalieri believes the hornets do more than protect the yeast from the winter. The precise mixture of yeast varieties that survive in the hornets provide a microbial terroir that effects the final flavor of the wines inoculated by the hornets.
“There is a story we currently don’t tell, and it’s the story of what happens to the grapes in the first five days," he said. "Many of the yeast species we find in the first days provide aromatic traits that are unique. And that’s enough to make the difference between one wine and another."
Cavelieri may be getting ahead of himself by claiming that hornets and their yeast affect the flavor of wines fermented with cultured yeast, however. “We know for sure that there are flavor and aroma differences between these strains,” said Hyma. “But the direct connection between the yeast surviving in the wasps and the yeast biodiversity in the vineyards will need to be explored a little further.”