Sometimes you can see people in the vineyard, stripping off the leaves around the grapes. Why that? In fact, this action can have a direct influence on rott development, grape colour, quantity and quality of tanins, as well as on grape aromas.
After removal of the leaves, air circulates better inside the grape vine’s canopy. This may slow down development of Botrytis, a fungus responsible for grape rot. In addition, all spraying agents, chemical, biological and biodynamic, are more effective because they reach the inside of the vines, as well as the the grapes.
Exposing grapes directly to the sun can also change their composition and thus their taste. The synthesis of phenols (natural colour, tanins) as well as some flavors are directly connected to heat and light. In general, grapes develop more fruit aromas and taste less green, while red grapes show more color, as well as a higher content of mature and savory tannins.
Defoliation can be carried out manually or mechanically. In general, it is done after véraison (which indicates that the ripening process has started) and can even take place a few days before harvest in rainy harvest years. However, care should be taken to ensure that the grapes are not sun burned when exposed to much to the sun and heat. Therefore, only one side of the vine is defoliated in most cases, the one pointing towards sunrise or to the north.