Grape- and fermentation-related volatile compounds involved in the chemical diversity of unaged monovarietal Grappa distillates

Monovarietal Grappa, a category within the Geographical Indication (GI) Grappa, is expected to express chemical features related to the grape variety used for its production. However, the extent to which cultivar-related signatures can be detected after fermentation and distillation, and the contribution of fermentation-related compounds to its volatile differentiation, remain poorly understood. This study investigated the contribution of grape and fermentation-related volatile compounds to the chemical differentiation of monovarietal Grappa produced from aromatic, semi-aromatic and neutral grape varieties, including Moscato Bianco, Glera, Nebbiolo, and Sangiovese as representative cultivars. Volatile compounds were characterized by solid-phase extraction-gas chromatography–mass spectrometry (SPE-GC-MS). The Kruskal–Wallis test and partial least squares discriminant analysis (PLS-DA) with variable importance in projection (VIP) scores were applied to assess differences among monovarietal Grappa distillates and identify discriminant compounds, respectively. Grappa from Moscato Bianco grapes was distinguished by its higher abundance of monoterpenes, whereas Nebbiolo- and Sangiovese-derived Grappa showed higher levels of sesquiterpenes. Fermentation-related compounds also contributed to sample differentiation, with white grape Grappa characterized by higher C6 alcohols and red grape Grappa by higher concentrations of fusel alcohols, medium-chain ethyl esters, and most fatty acids. PLS-DA models showed high classification performance, with permutation testing confirming model significance and VIP analysis identifying discriminant compounds, including potential cultivar-related markers. Overall, these findings indicate that the volatile fingerprint of monovarietal Grappa reflects the combined influence of grape and production-related characteristics, providing molecular insights that may support future approaches to authentication, traceability, and quality assessment of monovarietal Grappa.