Profiling the Aroma of Grape Spirits for Port Wine Using a Multi-Analytical GC Approach and Sensory Analysis

Port wine production involves the addition of grape spirit to halt fermentation and retain natural sweetness. This spirit, produced by distilling wine and its by-products, must comply with legal standards, including a mandatory sensory assessment. Because grape spirit influences Port wine’s volatile composition, this study investigated the odour-active compounds present in several grape spirits intended for fortification. Volatile compounds were extracted by liquid–liquid extraction, concentrated, and analysed using gas chromatography–olfactometry (GC-O) and gas chromatography–mass spectrometry (GC-MS). In GC-O, based on frequency detection, a panel of assessors sniffed the extracts to determine the presence of aroma compounds. The results revealed a wide range of odour-active compounds in grape spirits, belonging to several chemical families such as esters, alcohols, terpenic compounds and acids. These compounds exhibited both pleasant aromas, such as fruity, floral and caramel notes as well as undesirable ones like cheese and foot odour. Most of these compounds originate from the fermentation process and are also found in other unaged distilled beverages, including young Cognac, Calvados and fruit spirits. This research highlights the aromatic complexity of grape spirits and, for the first time, determined the aroma thresholds for 25 of 36 the compounds studied at an ethanol content of 20%.