# Volatile Composition of Fortification Grape Spirit and Port Wine: Where Do We Stand?
## 5 Grape Spirits' and Port Wines' Volatile Components and Their Potential Impact on Aroma Properties
Some esters, terpenic compounds, norisprenoids, and volatile phenols also have been reported to have sweet aroma descriptors. Their sensorial impact is quite diverse due to the wide range of reported olfactory thresholds that are associated with these compounds (also including compounds with no reported olfactory threshold), for instance: 10.3 \(\upmu\)g/L for guaiacol (sweet, smoke, medicinal aroma); 250 \(\upmu\)g/L for \(\upalpha\)-terpineol (lilac, floral, sweet, and anise aroma), 16 mg/L for 5-methyl-2-furfurral (almond, caramel, and burnt sugar aroma), or 1 g/L for monoethyl succinate (caramel and coffee aroma). Considering the spicy aromas (including cinnamon, anise, clove aroma), their sensorial impact is quite high, once the compounds that contribute with these aromas have low reported olfactory thresholds (most of them between 1.1 to 41 \(\upmu\)g/L). Few compounds have been reported to have olfactory spicy notes, e.g., ethyl cinnamate (cinnamon, balsamic, and honey aroma, 1.1 \(\upmu\)g/L), eugenol (cinnamon, clove and honey aroma, 5 \(\upmu\)g/L), or 4-ethylguaiocl (spice, clove, toasted bread, and smoky aroma, 41 \(\upmu\)g/L). Woody aromas, including vanilla, coconut, coffee, and toasted, are characteristic of volatile phenols and norisoprenoids. Indeed, volatile compounds such as \(\upbeta\)-ionone (0.1 \(\upmu\)g/L), \(\upbeta\)-methyl-\(\upgamma\)-octalactone (oaky, coconut and vanilla aroma, 54.5 \(\upmu\)g/L), and vanillin (vanilla aroma, 200 \(\upmu\)g/L) may have an important sensorial impact for woody aromas, while \(\upgamma\)-butyrolactone (caramel, sweet, and coconut aroma, 75 mg/L) and monoethyl succinate (1 g/L) require higher concentrations to be sensorially perceived. Seven volatile compounds from different chemical families may contribute to nutty aromas in Port wine, with sensorial impact differing according to the olfactory threshold. Indeed, sololon (nutty, spicy, perceived aged aromas) and 1,3-dimethoxybenzene (median and hazelnut aroma) have the lowest reported olfactory thresholds, namely 19 and 47 \(\upmu\)g/L, respectively, thus their sensorial impact should be higher than the one expected for benzaldehyde (almond, nutty, and smoky aroma), furfural (bread, almond, and sweet aroma) or 5-methyl-2-furfural, whose reported olfactory thresholds are 5, 15 and 16 mg/L, respectively. Most of the volatile components that contribute to sweet, spicy, woody and nutty aromas to Port wine are ageing-related compounds, belonging to the following chemical families: volatile phenols, lactones, furan derivatives, and/or norisoprenoids. Their concentrations and consequently their sensorial impacts are dependent upon the ageing conditions, particularly the length of ageing and wood type. Compounds such as eugenol might be the result of the thermal degradation of lignin, being posteriorly extracted from the wood during oak barrel ageing [111]. Wood-extracted compounds also include other volatile phenols, such as phenol, vanillin, 4-ethylphenol, and 4-ethylguaiacol, and lactones, particularly \(\upbeta\)-methyl-\(\upgamma\)-octalactone [39]. Moreover, furan derivatives, oxygen-containing heterocyclic compounds, can originate from carbohydrate degradation, non-enzymaticbrowning reactions, and aldehyde polymerization, with their content being linearly correlated with the duration of the wood maturation period [39; 108].