Discrimination of white wines by Raman spectroscopy coupled with chemometric methods

Agriculture is one of the largest contributors to environmental pollution and causing significant impacts on human health, ecosystems, and resource availability.

Aim of the study was to investigate the metabolomic differences between Chilean Cabernet Sauvignon wines, divided according to their quality in two main groups: “Varietal” and “Premium”, and to point out metabolites tentative markers of their chemical signature and sensorial quality. Initially, 150 (50 x 3 biological replicates) experimental wines were produced by the same semi-industrial process, which covered 8 different Chilean valleys. The wine classification made by experts, divided the wines into two major groups (“Varietal” and “Premium”) and four subgroups (two for each major group). All the samples were analyzed according to a robust LC-MS based untargeted work-flow (Arapitsas et al 2018), and the proposed minimum reporting standards for chemical analysis of the Metabolomics Standards Initiative (Sumner et al 2007)

Bentonite fining is widely used to prevent protein haze in white wines. Most wineries use laboratory-scale fining trials to define the appropriate amount of bentonite to be used in the cellar. Those pre-tests need to mimic as much as possible the industrial scale fining procedure to determine the exact amount of bentonite necessary for protein stability. Nevertheless it is frequent that, after fining with the recommended amount of bentonite, wines appear still unstable and need an additional fining treatment. It remains a major challenge to understand why the same wine, fined with the same dosage of the same bentonite, achieves stability in the lab, but not in the cellar.

Several Uruguayan wineries have begun to produce wines with minimal intervention, to increase the sustainability of their vineyards and wines. These wines are characterized by the minimum intervention in the management of the vineyard, its harvest, vinification, conservation and aging1,2. Sulfur dioxide (SO2) is not used or is used in reduced doses, although chitosan can be substituted or supplemented1. The objective of this research is to evaluate SO2 reduction or replacement options adapted to the production of Tannat red wines with minimal intervention. Vinification of the Tannat grapes with autochthonous yeasts (LN) was carried out during the 2023 vintage.

In red wines the post-MLF SO2 addition is an essential event. It is also the case for the “mutage” during the elaboration of the “liquoreux”. At these moments SO2 plays an antimicrobial action and an antioxidant effect. But at current pH of wines, ensuring a powerful molecular SO2 has become very difficult. Recent work on Brettanomyces strains have also shown that some strains are resistant up to 1.2 mg / L of molecular SO2. It’s also the case of the some Saccharomuces or Zygosaccharomyces strains suitable to re-ferment “liquoreux” wines after the “mutage”.