An overview of the impact of clone, environmental factors and viticultural techniques on rotundone concentration in red wines

Abstract

Context and purpose of the study – Rotundone is the main aroma compound responsible for peppery notes in red wine. This positive and very potent molecule has an odor threshold of 8 ng/L in water and 16 ng/L in red wine. It has been detected in several grape varieties with some of the highest concentrations recorded in Syrah, Duras, Tardif and Noiret, an interspecific hybrid grown in the North-East of the USA. If several winemaking practices have been identified to lower rotundone in wine, up to date, no enological solution has proved its efficiency to maximize it. This means that efforts to produce high rotundone wines must be undertaken in vineyards. This work provides practical ways that can be used by winegrowers to modulate rotundone levels in their wines.

Material and methods – Several field trials have been conducted for more than ten years in the southwest of France on Duras to investigate the impact of environmental factors and viticultural practices on rotundone concentration. This grape variety only grown within the protected designation of origin Gaillac was selected as it is known to exhibit substantial and regular levels of rotundone. These experiments were carried out using, in most cases, randomised complete block design with three replications per treatment. This research includes the study of the effect of clone, disease, ripeness, irrigation, defoliation, grape thinning, and the key factors driving the variability in rotundone concentrations between sites. Rotundone was quantified indirectly in wines fermented under microvinification conditions (1 L Erlenmeyer flask).

Results – Our results highlighted that certified clones had an impact on rotundone concentration in wine. The production of rotundone by the plant could be a response to biotic stress as a significant and positive correlation was established between rotundone concentrations and the severity of powdery mildew (Erysiphe necator) on bunches. On the opposite, Botrytis cinerea had a negative impact on rotundone in wine as a likely consequence of the activity of its polyphenol oxidase. Rotundone accumulation was also affected by abiotic factors, rising in concentration with an increase in water supply and radiation, while temperature elevation had a depreciative impact. The molecule was not impacted by grape thinning, suggesting the absence of translocation and a likely in situbiosynthesis. Harvesting date, irrigation, defoliation were identified as leverages to manipulate rotundone levels in wines.