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"The study results represent a real paradigm shift in our understanding of grape and wine production, as well as other food and agricultural systems in which microbial communities impact the qualities of the fresh or processed products," says David Mills. (Credit: Niall Kennedy/Flickr)

grapes

Grape microbes add to wine’s distinctive terroir

The microbial communities living on the surface of grapes may shape a wine’s terroir—the unique blend of vineyard soil and climate of every winegrowing region.

Results from DNA sequencing reveal patterns in the fungal and bacterial communities on grapes and these patterns in turn are influenced by vineyard environmental conditions. The findings appear in the Proceedings of the National Academy of Sciences.

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“The study results represent a real paradigm shift in our understanding of grape and wine production, as well as other food and agricultural systems in which microbial communities impact the qualities of the fresh or processed products,” says Professor David Mills, a microbiologist at the University of California, Davis.

He says further studies are needed to determine whether these variations in the microbial communities eventually produce detectable differences in the flavor, aroma, and other chemically linked sensory properties of wines.

By gaining a better understanding of microbial terroir, growers and vintners may be able to better plan how to manage their vineyards and customize wine production to achieve optimal wine quality, the study authors say.

Chardonnay vs. Cabernet Sauvignon

To examine the microbial terroir, the researchers collected 273 samples of grape “must”—the pulpy mixture of juice, skins, and seeds from freshly crushed, de-stemmed wine grapes.

The must samples were collected right after crushing and mixing from wineries throughout California’s wine-grape growing regions during two separate vintages. Each sample, containing grapes from a specific vineyard block, was immediately frozen for analysis.

The researchers used a DNA sequencing technique called short-amplicon sequencing to characterize the fungal and bacterial communities growing on the surface of the grapes and subsequently appearing in the grape must samples.

They found that the structure of the microbial communities varied widely across different grape growing regions. The data also indicated that there were significant regional patterns of both fungal and bacterial communities represented in Chardonnay must samples.

However, the Cabernet Sauvignon samples exhibited strong regional patterns for fungal communities but only weak patterns for bacterial communities.

Further tests showed that the bacterial and fungal patterns followed a geographical axis running north-south and roughly parallel to the California coastline, suggesting that microbial patterns are influenced by environmental factors.

Taken together, these and other results from the study reveal patterns of regional distributions of the microbial communities across large geographical scales, the study co-authors report.

They note that it appears growing regions can be distinguished based on the abundance of several key groups of fungi and bacteria, and that these regional features have obvious consequences for both grapevine management and wine quality.

The American Wine Society Educational Foundation Endowment Fund, the American Society of Brewing Chemists Foundation, and the Wine Spectator supported the project.

Source: UC Davis

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