Impact of anti-hail netting on secondary metabolites of Nebbiolo grapes and on wine quality

Abstract

Current climate change-related challenges are increasingly exposing grapevines to abiotic stresses, such as extreme heat and intense solar radiation, particularly during the ripening period. These conditions increase the risk of sunburn damage, leading to negative organoleptic changes in the berries and wine produced1.

The effect of the use of anti-hail nets on polyphenolic and aromatic composition of Nebbiolo grapes was investigated, in two consecutive years with different meteorological trend. Anti-hail nets covered the bunch zone from shoot removal until harvest in the covered thesis, whereas control vines remained uncovered from veraison until harvest. Grapes were harvested and vinified separately.

Analytical determinations in grapes and wines were performed using Gas Chromatography coupled to Mass Specrtrometry (GC-MS), to assess the aromatic composition, while polyphenols were analyzed through spectrophotometry and HPLC. Chemical-physical determinations were carried out according to OIV methods and sensory evaluation was conducted by a trained panel.

Generally, sugar contents were similar between treatments, while malic acid was higher in the must from covered grapes in 2025. Polyphenolic indices were lower in the net covered grapes in both years (in both skins and seeds). Lower flavonol contents were observed in grapes covered with anti-hail nets in 2025, due to significantly reduced concentrations of quercetin glucoside. Aroma precursors in grapes showed no significant differences between treatments in the rainy 2024 season. In contrast, significantly higher concentrations of norisoprenoids were observed in grapes grown under anti-hail nets during the hottest and dry 2025 season. 2025-wines produced from covered grapes showed lower total polyphenol and anthocyanin indexes as well as reduced wine color intensity if compared to the control wine. Although the fermentative aromatic composition remained largely unchanged, sensory evaluation highlighted a broader aromatic intensity across nearly all descriptors for the anti-hail wine, especially for raspberry, jam, and herbaceous notes.

Meteorological conditions during the last phase of ripening are crucial in determining grape and wine quality2. Sustainable mitigation strategies, such as the installation of anti-hail nets in vineyards, represent promising solutions to protect grapes from sunburn while preserving aroma precursors, thereby maintaining wine aromatic quality and a delicate profile.

References

1. Gambetta J. M., Holzapfel B. P., Stoll M. and Friedel M. (2021) Sunburn in Grapes: A Review. Frontiers in Plant Science, 11:604691. https://doi.org/10.3389/fpls.2020.604691
2. Asproudi A., M., Petrozziello, M., Cavalletto, S., & Guidoni, S. (2016). Grape aroma precursors in cv. Nebbiolo as affected by vine microclimate. Food Chemistry, 211, 947–956. https://doi.org/10.1016/j.foodchem.2016.05.070