Understanding sweetness of dry wines: first evidence of astilbin isomers in red wines and quantitation in a one-century range of vintages

Water status impact in viticulture has been widely explored, as it strongly affects grapevine physiology and grape chemical composition. It is considered as a key component of vitivinicultural terroir. Most of the studies concerning grapevine water status have focused on either physiological traits, or berry compounds, or traits involved in wine quality. Here, the response of grapevine to water availability during the ripening period is assessed through non-targeted metabolomics analysis of grape berries by ultra-high resolution mass spectrometry. The grapevine water status has been assessed during 2 consecutive years (2019 & 2020), through carbon isotope discrimination on juices from berries collected at maturity (21.5 brix approx.) for 2 Vitis vinifera cv. Pinot noir (PN) and Chardonnay (CH). A total of 220 grape juices were collected from 5 countries worldwide (Italy; Argentina; France; Germany; Portugal). Measured δ13C (‰) varied from -28.73 to -22.6 for PN, and from -28.79 to -21.67 for CH. These results also clearly revealed higher water stress for the 2020 vintage. The same grape juices have been analysed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and Liquid Chromatography coupled to Mass Spectrometry (LC-qTOF-MS), leading to the detection of up to 4500 CHONS containing elemental compositions, and thus likely tens of thousands of individual compounds, which include fatty acids, organic acids, peptides, phenolics, also with high levels of glycosylation. Multivariate statistical analysis revealed that up to 160 elemental compositions, covering the whole range of detected masses (100 –1000 m/z), were significantly correlated to the observed gradients of water status. Examples of chemical markers, which are representative of these complex fingerprints, include various derivatives of the known abscisic acid (ABA), such as phaesic acid or abscisic acid glucose ester, which are significantly correlated with higher water stress, regardless of the variety. Cultivar-specific behaviours could also be identified from these fingerprints. Our results provide an unprecedented representation of the metabolic diversity, which is involved in the water status regulation at the grape level, and which could contribute to a better knowledge of the grapevine mitigation strategy in a climate change context.

Labor shortage is one of the most crucial issues in current viticulture. Mechanized approaches are helpful in reducing production costs and increasing vineyard efficiency but their effect on grapes and wines needs evaluation. This work assess the results of combined mechanical pruning and shoot thinning with deficit irrigation strategies to reduce management costs but not quality of production.

It is well-known that there is a relationship between the “terroir” and the characteristics of grapes and quality of wines. However, adequate grape variety and other cultural factors should be also taken into account

A worrying drop in the acidity of wines has been observed in many wine regions, such as Bordeaux (Merlot), Burgundy (Pinot Noir), Côtes-du-Rhône (Grenache) or Rioja (Tempranillo). This lack of acidity is particularly marked in the Midi-Pyrenean vineyards of the Côtes du Frontonnais (Tournier, 1993). However, the acidity of a wine is one of the main factors of its quality, in fact, a low acidity combined with an insufficient tannic structure leads to rapid oxidation of wines and makes them age prematurely.

To be accepted by the market and consumers table grapes need to meet certain requirements in terms of physical and chemical quality parameters.