Prié blanc sparkling wines from Mont Blanc: Altitude effects on the physical- chemical characteristics during second fermentation and ageing

Prié blanc is an ancient white grape variety (Vitis vinifera L.), native to the Aosta Valley alpine region in North- West Italy, growing own-rooted in heroic viticulture at altitudes between 900 and 1200 m asl where it can ripe properly with short growing seasons. This linkage between grape variety and terroir gives a strong identity to the wines produced. To date, no study has been published on the characterization of sparkling wines produced from Prié blanc grapes. Therefore, the first aim of this research was to determine physical-chemical characteristics of this unique sparkling wine. During second fermentation and ageing, the altitude impact was also evaluated. The effect of atmospheric pressure with increasing altitude can influence the fermentation process in bottle, yeast autolysis, and therefore volatile organic compounds. The base wine was submitted to second fermentation at two different altitudes on the glacier of Mont Blanc (923 and 2173 m asl), and then aged also at 3462 m. The sparkling wines were analyzed at 6, 12, and 24 months from the end of second fermentation for technological parameters, color traits, phenolic composition, volatile compounds, and bubble pattern. Sensory differences were evaluated at each sampling point using a duo-trio test. The results showed that the performance of Saccharomyces cerevisiae starter culture and fermentation kinetics were not influenced by altitude. During ageing, Prié blanc sparkling wines exhibited a reduction in total polyphenols and an increase in b* color component. After 24 months, significantly higher b* values were observed for the wines aged at 2173 m. Wines aged at 3462 m showed a better preservation of (+)-catechin, (–)-epicatechin, and resveratrol. Volatile compounds were influenced by both altitude and ageing time. Fruity fermentation esters were higher at lower altitude, whereas ageing-related compounds accumulated more at higher altitude. Norisoprenoids and volatile phenols achieved the highest values after 24 months, particularly at 2173 and 3462 m. The greatest altitude gave wines with the lowest concentrations of ketones, confirming their better preservation against oxidation. Regarding the bubble pattern, the only observed effect concerned the reduction in foam thickness over time, which decreased with increasing altitude. Sensory significant differences were found at 6 months of ageing between the wines produced at different altitudes, but the effect decreased with extended ageing.