Chemical composition of press and free-run wines from three vintages and Bordeaux grape varieties. A comprehensive analysis

Abstract

Press wines play a crucial role in red winemaking, representing up to 15% of the final blend [1]. Optimizing their value is essential both economically and for maintaining wine identity, especially given evolving climatic and societal challenges. However, little recent research exists on their composition. This study provides an initial assessment of press wines’ chemical characteristics.

A total of 262 press wines and their corresponding free-run wines were analyzed from Cabernet-Sauvignon and Merlot across three vintages (2021–2023). General parameters, including pH, total acidity, volatile acidity, and total alcohol (TAV), were measured alongside color analysis. Volatile compounds (dimethyl sulfide, its precursor, and 32 esters) were analyzed via SPME-GC-MS. Phenolic content, including total tannins, total anthocyanins, anthocyanin monomers, and flavanols, was determined using spectrophotometry, HPLC, and UPLC techniques.

Results revealed significant compositional differences between press and free-run wines, influenced by grape variety and vintage. Principal Component Analysis confirmed distinct chemical profiles.

For Merlot, press wines had higher pH and lower TAV across all vintages. Esters were more abundant in free-run wines, while pDMS levels varied depending on the year. Press wines contained more tannins and flavanols, but total anthocyanin levels showed no significant differences.

For Cabernet-Sauvignon, trends were similar: press wines had higher pH and lower TAV, and free-run wines had higher ester concentrations. Press wines exhibited greater tannin and flavanol content, with no significant anthocyanin variation. Unlike Merlot, pDMS concentrations in Cabernet-Sauvignon remained stable in 2021 and 2022 but were significantly higher in free-run wines in 2023.

This study provides a foundational database on the aromatic and phenolic composition of press wines over three vintages. The findings challenge assumptions about their role, revealing significant chemical differences.

References

[1] Vivas, N. (2007). Les composés phénoliques et l’élaboration des vins rouges. Féret, 333p.