Within the circular economy framework, grape stems, a major winemaking by-product, are increasingly recognized for their potential to modulate wine composition despite some criticalities. This study aimed to investigate fresh and withered stems as both sources of compounds and adsorbents of off-odors. Corvina and Cabernet Sauvignon stems were tested under three conditions: fresh, and 20% and 40% weight loss. Over 14 days of maceration in red wine, the release kinetics of key enological parameters, including pH, ethanol, total phenolics, methoxypyrazines, and C6 alcohols, were investigated. Concurrently, the adsorption capacity for methanethiol was evaluated. Results indicated that stems significantly influence wine composition by increasing pH and phenolic content while reducing ethanol, with variability associated with the withering treatment. Withered stems showed reduced release of herbaceous pyrazines compared to fresh stems. Stems demonstrated a high affinity for methanethiol, resulting in a significant decrease greater than that observed with commercial enological tannins, known for their ability to reduce reductive mercaptans. This decrease was primarily driven by direct adsorption onto the solid stem matrix, with a secondary contribution from leached soluble compounds. This work provides new insights into the chemical interplay between grape stems and wine, highlighting their valorization potential as a sustainable tool to manage wine composition and mitigate sensory defects.
Luzzini et al. (Wed,) studied this question.