In most winegrowing countries, organic viticulture is gaining more and more importance. However, in most non-European countries organic viticulture is still in the initial stages.
Organic cropping systems are considered more sustainable than conventional cropping systems from an environmental standpoint. Reganold and his colleagues have reported that organically farmed soil had significantly higher organic matter content, less erosion, larger topsoil depth, showed increased biological activity, lower bulk density. Another team of researchers led by Mader showed that organic farming systems promote efficient resource utilization and enhance floral and faunal diversity. However, until recently, it was not clearly established what effects these alternative farming systems have on vine, grape and wine parameters.
Impacts of organic viticulture
In an attempt to determine the best mechanisms for attaining sustainability (through soil improvement, pesticide reduction, increased vineyard biodiversity,etc..), Cassandra Collins and her colleagues led a six year long study on a 20 year-old Cabernet Sauvignon vineyard in Australia. The researchers compared four management systems: organic, biodynamic and conventional (low-input and high-input). For each season, yield and pruning weight were compared with berry pulp and skin composition (total anthocyanin and phenolic levels). Small lot wines were made from all treatment replicates for sensory analysis by an expert winemaking panel through blind tasting for each wine.
During the last four seasons, the researchers found that vine vegetative and reproductive growth was lower for organic and biodynamic practices compared to conventional farming practices. At the fruit level, no significant differences were found between treatments for traditional berry pulp composition. However, skin composition did vary between treatments. Organic and biodynamic wines were described as richer, more textural, complex and vibrant than wines from conventional farming. These findings suggest that organic and biodynamic vineyard management are sustainable systems and may lead to improved wine quality.
In Germany, a team of researchers led by Döring have investigated variations in vine performance and fruit composition under different management practices (organic, biodynamic and conventional). Authors compared plant physiological performance and resistance to disease over 3 consecutive seasons with Riesling. Their results showed that organic and biodynamic treatments significantly lower growth and yield in comparison to conventional treatments. By measuring pre-dawn water potential and leaf gas exchange (for carbon assimilation and transpiration), the authors demonstrated that vine physiological performances were significantly lower under organic and biodynamic treatments. Such physiological decline reduced growth, cluster weight and therefore induced lower yields. Furthermore, yields under organic and biodynamic treatments partially decreased due to higher disease incidence of downy mildew.
The unsolved linkage between sustainability and quality
These contrasted results illustrate the effects of local growing conditions at driving the success of alternative strategies. Interactions between farming strategies and local conditions are complex and make it difficult to predict the impact of practices on fruit and wine composition. However, an interesting question remains: what could explain improved wine sensorial perception under organic and biodynamic farming strategies?
The scientific results we reported suggest that our current analytical methods fail. We are unable to really explain why a panel of Australian winemakers is able to systematically detect an improvement of wine quality under such practices for 4 consecutive years! Perhaps this is partly due to the exquisite sensitivity of our human palate, which is not matched by the most advanced sensing technologies. In fact, research on wine sensorial properties constantly reveals new aroma compounds not previously identified (like pepper nuances from rotundone or mint nuances from piperitone). In this context, we can not expect to explain easily why organic and biodynamic wines are preferred.
That said, the research on flavor impacts of organic viticulture is worth pursuing and interesting insights may come from tomatoes. A team of researchers led by Oliveira tested the hypothesis that tomato fruits from organic farming accumulated more phenolics, as a consequence of the stressing conditions associated with farming system. Authors found that under organic farming, tomatoes total phenolic content was almost 140% higher than under conventional farming. Furthermore, this result was consistent with a higher activity of phenylalanine ammonia lyase observed throughout fruit development under organic farming. (ie. the same enzyme active in grape berry). This result combined with other observations suggests that fruits from organic farming experienced stressing conditions that resulted in oxidative stress and the accumulation of higher concentrations of phenolic compounds.
Tracking time variations of phenolic compounds during maturation could help understand and maybe better predict how different growing conditions can affect fruit and wine sensorial properties. Last, to anticipate the effect of farming strategies on vine growth decline, which may appear after two years of treatments, it is useful to quantify the variations of dry wood biomass accumulation after the seasons.
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