LARGE SURVEY OF THE CHEMICAL COMPOSITION OF WINES RESULTING OF THE PRESSING OF RED WINE MARC. FIRST RESULTS

Abstract

In the Bordeaux vineyards, press red wine represents about 15% of the volume of wines. Valuing this large volume of press wine is necessary from an economic point of view, of course, but also because of their organoleptic contribution to the blend. Nevertheless, there is a lack of recent knowledge on the composition of press wines. This work aims to establish an initial assessment of their composition (aromatic and polyphenolic) and to set up hypothesis on to the links with their sensorial identity.

Measurements and dosages were done in 50 press wines and their associated free-run wines. Wines are monovarietal batch from: cabernet-sauvignon and merlot from Saint-Estèphe, Médoc, France. The vintage is 2021. The production of wines was done in the estate to the classical process. The grapes, picked up and harvested by hand, were destemmed, sorted using an optical sorter and crushed. During vinification, extractions were adapted to each batch by daily tastings. Maceration did not exceed 21 days. After pressing, the wines were kept in oak-barrels. Three months after pressing, all the wines were tasted and were categorized according to their aptitude to be incorporated in the blend of the premium wine. Samples were kept at 12°C in bottles.
For the study of the aromatic composition: dimethyl sulphide (DMS) and its precursors (HS-SPME-GC-MS); higher alcohols (GC-FID) and 33 esters (HS-SPME-GC-MS) were measured. Concerning the analysis of phenolic compounds: anthocyanin monomers (HPLC-UV) and flavonols (HPLC-fluo.) were determined. Indices such as IPT, CieLAB, pH, AT have also been measured.
As expected, the results showed a significant difference between the two grape varieties. For each grape variety, PCA suggest differences between the press wines and the drop wines for all compounds. For the aromatic compounds, total tannins and flavonols: the press wines are more concentrated than the free-run wines. There are no significant differences between the press and free-run wines concerning anthocyanins. More statistical analysis permits to highlight unexpected separation of compounds according to the pressing step. The data also highlight links between the composition and the sensorial categorization.
In conclusion, the study permits to propose a first molecular database and to explore the origins of the sensorial categorization of that wines.
The experiment is renewed during the 2022 harvest and new compounds are added to the database.