Quantity and quality of flavonoïds in grape berries are important parts of their global quality. Several studies had shown that tannins are responsible for some major flavour properties of red wines such as colour, bitterness and astringency. Nevertheless, their synthesis and properties are still misunderstood. Some studies had suggested that the tannic pool was set before veraison. Thus, the comprehension of the relations between environment and setting of this tannic pool, up to the harvest, is not sufficient.
This paper describes the relation between the environmental factors of the terroir system, in particular soil moisture, plant response in term of precocity and vigour, and the setting of tannic pool. We had also studied the effect of viticultural management, in interaction with milieu, in the setting of these compounds.
Study of the flavan-3-ols was done on Cabernet franc in 2004 and 2005 from a network of 14 experimental plots. In 2005, each plot was monitored twice, according to a standard viticultural management and a dedicate one, chosen by the viticulturist.
The berries were sampled at the pre-veraison stage and harvest. Soil moisture was described by a two-dimensional soil resistivity profile and by measurement of the soil water reservoir. The vine water status was determined through leaf water potentials until mid-veraison, and with DeltaC13 discrimination between veraison and maturity. Analysis of these flavonoids were performed on berry skin. The composition in procyanidins of skin and seeds were determined by HPLC reversed phase.
Results showed that the period before veraison was important to understand the harvest quality. The quantity and the quality of the condensed tannins were in relation with the vine water status, in interaction with precocity. The interest and limit of the soil description is discussed in the point of view of a terroir characterisation. The influence of the dedicate agricultural management is also pointed out. The relation with the biosynthesis of the procyanidins and berry development kinetics is considered and discussed.
Authors: Yves CADOT, Nicolas BOTTOIS, Gérard BARBEAU, Étienne GOULET, Maria Teresa MIÑANA CASTELLO and Réjane CHAMPENOIS
Keywords: flavan-3-ols, terroirs, precocity, water status, Vitis vinifera