# 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
Additionally, some of the compounds that do not have reported olfactory thresholds were also included in Figure 5. It is important to point out that the matrix in which the olfactory threshold is determined has an impact on the obtained value, for instance, the ethanol and sugar content will influence the odor perception. Only three research papers have reported olfactory thresholds in Port wines [14,52,89]; therefore, it was necessary to expand the search for olfactory thresholds. Only the hydroalcoholic matrices, in which ethanol content varied between 9 and 14% \(v/v\), were selected from the reported literature (Table S2). Even though these ethanol concentrations are lower than the ones in Port wines (18-22 and 16.5% \(v/v\) for red and white wines, respectively [1,39]), they were the closest matching matrices, and only those were considered in Figure 5.  
Each aroma class (spicy, woody, sweet, fruity, nutty, and floral) included several other reported aromas associated with those; in this case, spicy aroma notes incorporated cinnamon, anise, clove; woody aroma notes also comprised vanilla, coconut, coffee, and toasted; sweet aroma notes covered honey, caramel, and cocoa; fruity aroma notes contained tree fruit, tropical fruit, berry fruit, and citrus; nutty aroma notes encompassed also almond; and floral aroma notes involved rose, lavelender, hyacinth, lilac, and orchid. Fruity is the aroma class with the highest number of volatile compounds, and their sensorial impact varies significantly, ranging from those with the lowest (0.06-10 \(\upmu\)g/L) to the highest (0.1-1 g/L) reported olfactory thresholds (Table S2), e.g., 5 \(\upmu\)g/L for ethyl hexanoate (banana and green apple aroma), 203 \(\upmu\)g/L for methyl octanoate (orange aroma), or 0.76 g/L for diethyl malate (over-ripe peach, prune aroma) Indeed, most of the fruity aromas arise from esters. Moreover, some ketones present fruity aroma notes, e.g., 2-hexanone (fruity, fungal, meaty, buttery aroma, 24 \(\upmu\)g/L). Figure 5: Organization of the VOCs using two main types of information: One side with the six valuable classes of aromans in Port wines (spicy, woody, sweet, fruitry, and floral notes), and the other side with the range of olfactory thresholds (Table S2). Each volatile component was distributed according to its aromans descriptor(s) and the respective olfactory threshold reported on Port wine (limited data are available for this matrix) or hydroalcoholic matrices, ranging from a few ug/L to g/L. VOCs considered potential contributors to these aromans, even without reported olfactory thresholds in ethanol/water matrix, were also included. Several chemical families may contribute to floral aromas; for instance, esters, alcohols, intergenic compounds, and norisprenoids, which have olfactory thresholds between 15 and 800 \(\upmu\)g/L, e.g., citronellol (rose aroma, 100 \(\upmu\)g/L), linalool ( floral, rose, lavender aroma, 15 \(\upmu\)g/L), or 2-phenylethylal acetate (floral and rose aroma, 250 \(\upmu\)g/L). Norisprenoids such as \(\upbeta\)-damascenone (cooked apple, floral, and honey aroma, 0.1 \(\upmu\)g/L) and \(\upbeta\)-ionone (violet, woody, raspberry, rose aroma, 0.1 \(\upmu\)g/L) have the lowest reported olfactory thresholds, therefore, the highest sensorial floral perception. On the contrary, alcohols have the highest reported olfactory thresholds, such as 2-phenylethylal (floral, rose and honey aroma, 12 mg/L) and 1-octanol (jasmine, rose, waxy, and soapy aroma, 10 mg/L). Esters, alcohols, and ketones that contribute to fruity and floral aromas may arise from yeast fermentation, e.g., from carbohydrate metabolism, from lipid oxidation, and/or from amino acid metabolism [39; 108]. Furthermore, terpenic compounds are varietal components once they are secondary metabolites from grapes, but they also can be biotransformed along with yeast fermentation [109; 110]. Norisprenoids are produced from the breakdown of carotenoids (present in grapes) [109]. Sweet aroma notes can be associated with furan derivatives and lactones.