The search for an "ideal" leaf to fruit ratio
Structured, well-balanced wines require the production of healthy, concentrated grapes. At Couhins the ideal yield is around one kilo of grapes per two square meters of leaf area. This is adjusted depending on grape variety and soil characteristics. The control of yields involves numerous operations. First, there is pruning which, if carried out systematically, enables an approximate determination of the yield. Adjustments are then made with a series of operations that favour the ripening process (removal of non-fruiting buds, removal of excess growth at the base of the vines, and the removal of unwanted shoots). Leaf removal is moderate, so as not to expose the bunches to the rays of the setting sun that could burn the grapes. The removal of green grapes provides a final means of controlling the yields. The main value of this last procedure is to ensure well-spaced, regular distribution of the bunches on the vines.
Like several properties in Pessac-Leognan, Couhins' terroir is complex due to features of the terrain and the variable composition of its soil. The vines develop differently in this heterogeneous environment and this is reflected, for example, by variations in the vines' vigour*, a key parameter in the ripening of the grapes. Our objective to adapt all our interventions to these variations. To achieve this, we assess the vines' vigour, plant by plant, using a new technique developed by Inra. By crossing this information with other parameters observed over several years (resistivity of soil **, ripeness tests, etc.) we can determine homogeneous areas. *vigour: the vines' vegetative growth **measuring the resistivity of soil gives an initial indication of the presence of water and therefore clay, information that is then verified by taking samples.
Evaluation of vigour using the "GreenSeeker"
Since 2007, we have been able to map the vines' vigour with a precision of one square metre by means of a sensor ("GreenSeeker") combined with a GPS. It analyzes the light reflected by the leaves - the reflectance - in red and near infrared frequencies and enables us to calculate a vegetation index (NDVI) which correlates strongly with the vines' vigour. (Château Couhins and Château Cheval Blanc are the two first vineyards in Europe to use this technique)
We can thereby identify areas with homogeneous profiles and adjust the quantities of fertiliser, grass cover crop and canopy management. This precise knowledge of the vineyard has also enabled us to refine measures taken against parasites. Finally, we harvest the grapes and make the wine in a specific way for each zone.