Influence of the year and the environmental factors on condensed tannins from Cabernet franc grapes

The composition in condensed tannins of the grape berries is essential for the quality of the harvest. Proanthocyanidins have a significant influence on the organoleptic properties of the red wines.
The influence of the environmental factors on the Cabernet franc composition in condensed tannins was studied in Saumurois and Touraine. For 3 years, a network of 14 plots was conducted in an identical way in terms of viticultural management. The biochemical composition of the berries was analysed, in particular for the condensed tannins, by RP-HPLC after fractionation and thiolysis.
The results showed that the type of soil did not discriminate the plots. However, the quantity of tannins was influenced by the climatic variables except for sunshine. The duration of the vegetative cycle and its precocity had a significant influence on the percentage in prodelphinidin. The average degree of polymerization was correlated with the delta C13 and with rainfall between flowering and ripening. This study showed a year effect on the content of tannins, expressed in g/kg, the DPm and the percentage in prodelphinidin. The proportion in galloyled units was correlated with the water stress during the period previous veraison and by the vigour of the vine.