What can the microbiota of grapes tell us about the wine’s terroir?
Does the microflora of a bunch of grapes have an impact on the wine-making process and enhance a vintage? That’s what the authors of a study, published in Plos One, suggest.
It’s a known fact: wine quality depends on the grapes it comes from, the environmental conditions they grew in, and the fermentation stages. However, we don’t know much about the impact of microbial diversity in vine stock on the wine-making process or the microorganisms involved.
To better understand, Italian researchers analyzed the bacteria and fungi present in grapes and grape must (grape mash obtained after pressing bunches of grapes, in this case to produce Italian Cannonau – the local name for the Grenache grape variety). The wine is cultivated in Sardinia, a region where the terroir characteristics (temperature, humidity level, oxygen, and carbon dioxide) vary from one locale to another. The scientists took samples from mature bunches from four geographically distinct vineyard plots, before moving through the successive steps of the wine-making process in a single wine cellar (the place where wine is made from must), without any additional yeast or chemical treatment.
Analysis revealed that some of the bacterial makeup was common to all samples, and some of it was specific to each plot of origin. The fact that most of the bacteria from the original bunch persist in the must (supplemented by new species, probably from the wine cellar) is both the vineyard’s signature and the reflection of the environmental conditions of the wine-making process. The researchers conclude that the grape’s microbiota brings certain qualities to the wine, such as its appearance, aroma, and sourness, but it is also a rich source of microorganisms involved in alcoholic fermentation and the construction of the wine’s aromatic complexity. Extending the microflora analysis to the entire vine stock could identify new bacterial species with oenological properties likely to improve the quality of the wine and reduce the need for chemical products, say the authors.
Mezzasalma V et al. (2017) Grape microbiome as a reliable and persistent signature of field origin and environmental conditions in Cannonau wine production. PLoS ONE 12(9): e0184615. https://doi.org/10.1371/journal.pone.0184615