WINETECH Technical Yearbook 2021

FIGURE 4. Principal component analysis indicating the positive association between lower Cold Night Index (lower minimum temperatures in the month prior to harvest) and aromatic precursors.

28% (figure 1), characterised by greater number of bunches per vine (+255%) and fewer berries per bunch (-32%). Mean date of harvest in MP was also delayed by nine days compared to VSP. AROMATIC PRECURSORS Berry size in MP was significantly lower (-31%) (figure 2) compared to VSP and this is perhaps the main driver to explain the effect on the aromatic precursor composition. Clearly, the concentration of aroma precursors increases with decreasing berry size. Thus, grapes from MP are generally richer in most compounds tested, mainly those from the group of C13-norisprenoids, C6 compounds and aromatic alcohols (figure 3). However, the total amount of aroma precursors per berry, remained unchanged, indicating

no influence of MP on the biosynthesis of these precursors per se. VINTAGE The amount of precursors per berry was very different depending on the vintage (2011 > 2013 > 2010 > 2014) showing that vintage was the main factor determining the aromatic potential of grapes, regardless of training systems. This vintage effect was not due to water status of the vines since irrigation was applied according to strict leaf water potential threshold values. The potential of the year compared to the amount of aroma precursors is mainly explained by the thermal conditions; in this case ripening conditions expressed with the Cold Night Index (Tonietto & Carbonneau, 2004) indicated a positive effect of low night temperatures during the last month

FIGURE 3. Concentrations (µg per kg of grapes) of the four families of grape aromatic precursors (C6 compounds, monoterpenes, aromatic alcohols and C13-norisoprenoids) as influenced by training system (* indicate statistical significance).

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