Maturità fenolica del Nebbiolo in Valtellina: effetto dell’annata e del sito.

Nebbiolo is the dominant variety in Valtellina. The wide environmental variability, due to differences along the vineyard belt in elevation, slope and orientation angles, and to the ahead orographic profile, determine differences in thermal and radiative fields, which affect the technological and phenolic grape maturity. The course of grape ripening has been monitored during the 2001-2003 three year period in eight vineyards representative of the variability in the thermal and radiative availability of the vineyard belt. In the relatively normal years (2001-2002) the thermal resources seems to be the limiting factors the anthocyanin accumulation. The effect seems to be due either to the veraison precocity and to the thermal course during ripening with a greater effect of the temperature of September in respect of the temperature of October. On the contrary, the exceptionally high 2003 temperature was evidence for a negative effect of the excessive thermal availability on the anthocyanin accumulation. The simulation of the temperature effect on anthocyanin accumulation, based on the expected physiological effect, improved the understanding of the relationships among thermal status and phenolic maturity.