Shades of shading: chemical and sensory evaluation of riesling grown under various shading techniques

Climate change constitutes an enormous challenge for humankind and for all human activities, viticulture not being an exception. Long-term strategic changes are probably needed the most, but growers also need to deal with short-term changes: summers that are getting progressively warmer, earlier harvest dates and higher pH in musts and wines. In the last 10-15 years, a relevant corpus of research is being developed worldwide in order to evaluate to which extent extreme canopy management operations, aimed at reducing leaf area and, thus, limiting the source to sink ratio, could be useful to delay ripening. Although extreme canopy management can result in relevant delays in harvest dates, longer term studies, as well as detailed analysis of their implications on carbohydrate reserves, bud fertility and future yield are desirable before these practices can be recommended.

In grape berry pedicel, xylem hydraulic conductance can be impaired by blockage deposition in the lumen of xylem elements. However, the varietal difference of the interruptions has not yet been characterized. In this preliminary work, we utilized synchrotron x-ray computed microtomography experiments performed at MOGNO beamline (LNLS – Brazil) to identify possible blockage sites in natural grape pedicel xylem. For this, we imaged dehydrated pedicel’s stem portion from the Niagara Rosada variety in three different phenological stages (Pre-veraison (PreV), veraison (V) and post-veraison (PostV). The reconstructed tridimensional images with a voxel size of 1.16 µm were segmented for the identification of xylem vessel lumens. After analysing one pedicel stem per stage, we identified 658 vessels without occlusion throughout his axial plane and 41 in which we could identify possible interruptions.

To our knowledge all the studies about laccase kinetics and its inhibition have been performed with substrates and conditions very different from those of real grape juice. Moreover, none of these researches really measure enzymatic browning, since they have not taken into account what happens after the oxidation of o-diphenols in o-diquinones and their subsequent polymerization to form melanins1. For that reason, the aim of this research was to develop a new model to measure the kinetics of browning caused by Botrytis cinerea laccase under conditions much closer to those of grape juice and using the substrates naturally present in it.

Constitue une appellation d’origine “la dénomination géographique d’un pays, d’une région ou d’une localité servant à désigner un produit qui en est originaire, et dont la qualité ou les caractères sont dus exclusivement ou essentiellement au milieu géographique, comprenant les facteurs naturels et les facteurs humains …”

We tried to give a part of the answer to this question by monitoring glutathione during winemaking and storage. The novelty of our approach is to quantify simultaneously the three known forms of glutathione: free glutathione (GSH), oxidized form (GSSG) and glutathione-S-sulfonate (GSSO3H).