Study reveals soil health's impact on wine flavour profiles

Source: Supplied | Controlled Grazing in Vineyards at Hartenberg. ©Heni Andrag

In the modern era, Hartenberg first introduced cattle to the property in 2017 and soon found that these ruminants significantly impact soil health. Their presence has proven to be an invaluable asset to the general health and well-being of the property.

Over the past seven years, the farm’s biodiversity has blossomed with the arrival of an abundance of inexplicable new fauna and flora, including nine new species of mushroom, many new grass species - like the appearance of Medics (a legume plant) - and dung beetles that gather around the cowpats.

While these changes above ground are easy to track with the naked eye, soil is slightly more secretive. So, to determine the impact of the cattle on soil health, Hartenberg viticulturist Wilhelm Joubert started taking soil samples and using nematodes - microscopic roundworms that feed on plant roots - as bio-indicators of soil health.

The tests showed that as soon as the animals were introduced, the nematode diversity increased, the ratio of non-harmful to harmful nematodes improved considerably and no single group of nematodes dominated.

What does this mean for the wine?

“In the first year since we brought animals into the vineyard, we were impressed by the rapid improvement in the measured soil biodiversity and -health,” says Hartenberg cellar master, Carl Schultz. "The question was: What happens to the grapes from vineyards where cattle graze as opposed to the vineyard without cattle? We had to think about what it meant for the wine and if this would display noticeable differences."

To answer this question, in 2022, Schultz and Joubert divided a vineyard parcel into two portions and then picked separately. High-density, controlled grazing took place in one portion (the 'ruminant portion'), while the other served as a control without any grazing. This process was replicated a year later in September 2023.

Vineyard observations

Although the control block yielded slightly more bunches per vine, the ruminant parcel produced a noticeably different wine, displaying brighter fruit on the bouquet and greater elegance on the palate.

Schultz says: "In the ruminant portion, there were slightly fewer bunches per vine and the berries were smaller too. This means production per hectare could be marginally less (but expressed as such, only at this juncture), but smaller berries naturally result in greater concentration of fruit."

"We also achieved physiological ripeness at lower sugar levels. If I can achieve physiological ripeness at a Balling or two lower, the resultant alcohol will also be lower," adds Joubert.

The proof is in the tasting

Once harvested, the grapes were handled separately in the cellar, but the winemaking process was meticulously similar, as only one parameter was being trialled.

Although Schultz is adamant that it is still too early to make definitive inferences, there is a clear indication that the two portions are producing markedly different wines; where the wine from the grazed portion of the vineyard block is elegant, fresh, and red fruit-driven, the control is weightier and more structured perhaps with hints of darker berry fruits and riper top notes.

"Winemakers will tell me it’s not the same wine, but the irony is that it is," says Schultz. "Both are super, but they are different. That means you are giving the winemaker another colour on his palette with which to paint, or another building block in a blend, which is a good thing."

Soil health still top priority

While the study provides a fascinating comparison, Schultz and Joubert emphasise that, ultimately, the goal remains to improve soil health and carbon levels, especially in the light of climate change and global warming.

"Our soil, environment and people are our biggest assets and neglecting to foster and nurture them will make running a successful wine farm increasingly difficult," concludes Schultz. "Western Cape agriculture will have to develop innovative solutions timeously, addressing the following question: how do we maintain steady production in a warmer, drier future with less water?

"Carbon sequestration is one of those ways and this can only be increased by techniques like covered soils, no-tillage, etc. We believe, however, that real measurable difference occurs once ruminants are re-introduced to, in our case, the vineyards. The science tells us that elevated levels of carbon in soils greatly increase the drought resistance of those soils.”

"Creating a superb wine is a fortunate byproduct, but we feel we have not just a sustainable future responsibility, from both an ecological and a business point of view, but the need to regenerate, rejuvenate the still little understood life forces of our terroir – i.e. one step beyond."

As Einstein once said: "Look deeper into nature, to gain a better understanding of life."