To connoisseurs of fine wine, terroir is that ineffable quality produced by a vineyard’s unique location. In a crowded €220 billion industry, the concept of terroir helps vineyards carve out an identity and market share – consider the example of champagne, which is nothing more than sparkling wine unless it comes from the narrowly defined and jealously guarded Champagne region of France.
Terroir is part of a worldwide debate on appellation of origins, in which traditional growers and makers defend their unique right to call their products feta cheese, Parma ham or tequila – it’s simply not the same if it comes from anywhere else.
Beyond the strain of grapes used, experts say climate, weather and farming practices play a role in a vintage’s terroir – but is there a biological signature in the soil that stamps a vineyard’s grapes with a particular taste?
New research, published in March in Communications Biology, lays the groundwork for understanding how a vineyard’s soil microbiome affects the character of the wine. With soil samples from four continents and 13 countries, the study is the first to establish a rough global map of microbial terroir.
Two hundred vineyards, but fewer glasses of wine
Alex Gobbi, a postdoctoral researcher at the University of Copenhagen’s Department of Plant and Environmental Sciences and first author of the study, knows good wine. Raised near Verona, Italy, Gobbi has studied wine microbiology for half a decade. “Apart from the economic thing, wine is very much cultural for many countries, including mine,” Gobbi says.
A high-quality wine starts from the ground up, and a vineyard’s soil teems with microscopic life. Research in other plants has demonstrated that root systems can selectively recruit microbes that can improve the plant’s health – some bacteria play important roles in the nitrogen cycle, while fungi work to break down organic matter into a form that roots can absorb.
To conduct the study, scientists and partners in industry scooped up topsoil samples from 200 vineyards across the world. Many of the samples were collected through an EU-wide research collaborative called MICROWINE, which aims to explore the role of microbes in wine-making from seed to fermentation.
The researchers found that vineyard managers were eager to participate in the project, according to Lars Hestbjerg Hansen, Professor of Microbial Ecology and Biotechnology at the University of Copenhagen and principal investigator for MICROWINE – and that isn’t always true for the farming industry. “I think part of the charm of the terroir and the mystery of wine is that if we can demonstrate that a vineyard has a specific set of microbes, their wine is special in some way,” he explains.
How to pinpoint a vineyard’s microbial terroir
Then researchers sequenced microbial DNA from each sample and compared it with a genetic database of bacteria, fungi and protist species. Gobbi and his team identified some species common to virtually every soil sample – not just in vineyards – and determined that a vineyard’s climate was the best predictor of its fungal diversity. But by analysing proportions of the less frequently observed species, the researchers were able to identify location-based microbial fingerprints with more spatial resolution than they expected.
In broad strokes, the further the distance between two vineyards, the more distinct the communities of soil microbes, the researchers say. Using deep learning to identify patterns in the data, the team developed a predictive model that could “trace back a sample of soil [to its country of origin] without knowing anything else but its microbial composition,” Gobbi says.
“We can actually predict, just by the pattern with this data set, where a random, double-blinded sample comes from,” Hansen explains. The model can predict a vineyard soil sample’s country of origin with an accuracy of over 80%, Gobbi adds.
But how precisely could they pinpoint a specific vineyard’s microbial terroir? To tease out finer-scale differences, the data set included 84 vineyards in Spain, from Álava in the far-north Basque country to the Balearic Islands off the eastern coast. The pattern held, and vineyards from the same region were significantly more similar to each other than to more distant vineyards.
These smaller-scale differences were “even more noteworthy” than the intercontinental and international differences, the study authors wrote, and could one day form a legal foundation for appellations of origins. The soil microbiome could be used to establish terroir units, “the smallest area for which it is possible to objectively describe the effect of the environment on plant physiology and agricultural production,” the article reads.
A drop in the barrel
But what does Gobbi’s microbial map tell us about how the tiny creatures living in the soil influence the flavour profile of wine?
“This is basically the microbial potential in the soil,” Hansen explains – the full universe of microbes in the soil that could play a role in shaping what ends up in your cup. “What is recruited by the roots and directly affects the vines is not known at present.”
“Finding the real correlation between that specific taxa of bacteria, fungi, whatever it is and that specific character in the wine – that takes other studies,” Gobbi adds. Unfortunately for the researchers, there wasn’t an official taste-testing component for this research. “Let’s just say that we sampled wine in many places, but not for the project,” Gobbi says.
Although total clarity on terroir is many years away, Gobbi and Hansen say the lessons learned in research into vineyard microbiomes can be easily transferred to the study of other crops. Hansen heads a project called MATRIX, funded by a grant from the Novo Nordisk Foundation, that aims to explore the relationship between plants and microbes that occur above ground.
The MATRIX will “use the same methods that we applied and developed for the wine project” to study the microbes found on the leaves of wheat plants, Gobbi says, and hopefully obtain insight into how they affect industry targets such as sustainability and crop yield.
“We have to realise that the complexity of soil microbiology is so massive that this study is, well – no pun intended – just scratching the surface,” Hansen says.