Soil-based bacteria key to wine style?

Soil-based bacteria – not soil type – may be key to understanding why certain sites produce specific wine styles, according to research published yesterday.

Soil-based bacteria affects wine style and vine disease resistance, according to a new study. Picture credit: Horticulture Week

In a paper posted on 24 March in mBio, the online open-access journal of the American Society for Microbiology, it was noted that bacterial communities from vineyard soils were found on a vine’s grapes, and that such communities on the berries “have the potential to influence the organoleptic properties of the wine, contributing to a regional terroir”.

In essence, the study showed that it is the soil that serves as a vital source of vine-associated bacteria, and that it is both the nature of the soil, and its management, that affect the character of the bacteria on the berries – otherwise known as the vine microbiome.

Consequently, it has been suggested that by managing the soil in a particular manner, it could be possible to influence the flavour of the wine, or create a specific terroir.

Indeed, Dr Paul Chambers, the research manager in biosciences at The Australian Wine Research Institute, says that the role of the microbiome could be crucial to understanding the influence of site specifics on wine flavour, although he adds that the science is currently poorly understood.

“If a viticulturist can shape the style of wine in a controlled manner by managing the microbiome of her or his vineyard in a targeted way, it opens the way for winemakers to more effectively shape their wines to meet market demands,” he said.

The research also showed that “Vine-associated bacterial communities may play specific roles in the productivity and disease resistance of their host plant”.

As a result, Jack Gilbert, a microbial ecologist at the Argonne National Laboratory in Illinois said, “Just the same as the human biome plays a role in health, bacteria have intricate associations with plants that affect disease resistance, stress tolerance and productivity.”

Indeed, earlier this year db broke news of a trial at Reims University that sees bacteria used to stimulate the vine’s defence mechanisms to a botrytis infection by thickening the plant’s cell walls.

The same university is also investigating a technique called “biocontrol” which sees the application of natural beneficial micro-organisms that can be taken up from the roots and diffuse in the vine to help it protect itself against diseases, as well as stimulate growth.

Nevertheless, when it comes to the role of soil in grape berry development, and subsequently wine flavour, the major influence stems from the water holding capacity of the soil – which can benefit berry maturation by allowing for rapid drainage in wet areas, or storage in dry climates.

However, the findings published in mBio endorse a move by quality-minded producers to nurture soil-based organisms to enhance site-specific characters in their wines. For example, Olivier Humbrecht MW told db back in 2011 that it was beneficial micro-organisms in the soil which help the roots break down and take up minerals in the surrounding soil, contributing to a clearer expression of vineyard terroir in his Rieslings.

The research:

The team of researchers, which included winemaker Gilles Martin, looked at four closely related Merlot plants growing in five different vineyards across a small stretch of the North Fork region of Long Island, New York.

For each location, they sampled the soil, roots, leaves, flowers and grapes throughout a growing season. Then, the team used shotgun metagenomic sequencing to characterize all the bacterial species found on each part of the grapevine.

Next, the team compared the New York grapes’ microbiome to those associated with Merlot grapes from Bordeaux, France, and crushed Merlot grapes from California. All three hosted similar bacteria species.

To see the paper, click here.