## 3 Results
### Olfactometry of Hops vs. Sensory and Volatile Composition of Dry-Hopped Beers  
Gas chromatography coupled with mass detection and olfactometry was applied to assess the odour-active compounds in 15 Portuguese wild hop samples (from which four were selected for dry-hopping beers). A total of 42 odour-active compounds were identified, including three aldehydes described as green fruits and grassy, three fruity, rancid, and cheese-like carboxylic acids, eight fruity (non-citrus) esters, two higher alcohols (green grassy and earthy), the ketone diacetyl (rancid), three monoterenes (myrcene, limonene, and ocimene) and two monoterpoids (linalool and geraniol) presenting resinous, spicy, citrus and floral perceptions, 12 thioesters producing sulphurous (garlic, onion, and cooked vegetable) but also earthy and fruity notes, and eight sulphurous thiols/ sulphides (Supplementary Table S2). The observed duality between the undesirable and pleasant description of sulphur compounds agrees with previous reports [17]. The sums of odour intensities for each class of compounds were calculated for each hops sample and were used as variables for the PCA, since the compounds from the same chemical functional group described above presented similar odour descriptions. Therefore, a PCA was performed to join the olfactometry data of hops with the sensory characteristics and volatile compounds content of dry-hopped beers. The active variables were the olfactometry data of the four hops used for beer production, while the sensory attributes and volatile compounds content in the dry-hopped beers were supplementary (passive) variables and the olfactometry data of the other 11 hop samples were supplementary observations (Figure 4). The first two component factors explained 85.70% of the total variance in the relationship between the hops and the sum of odour intensities of the chemical classes of the odour-active compounds. Supplementary variables and observations were not used to calculate the coordinates and are displayed as a layer over the plotted correlation. According to the square cosine values (Supplementary Table S3), PT05 and PT11 hops and thiols/sulphides are best explained by the F2 axis. The hop samples PT14 and PT15, and the other eight classes of odour-active compounds, are best described by the F1 axis. PT14 hops presented the highest odour-intensities of esters, monoterpneoids alcohols, aldehydes, ketones, monoterpenes and carboxylic acids. PT11 and PT15 hops showed more odour-intensity of thioesters, PT11 of thiols/sulphides and both, plus PT05, presented more odour-intensity of higher alcohols. In addition, supplementary variables (sensory attributes and compounds quantified in beers) were used to understand how the chemical classes of hops' odour-active compounds connected to the sensory and composition analysis of respective dry-hopped beers (Figure 4). Taking into consideration the Pearson correlation coefficients, it was possible to identify the relationship between the odour intensity of monoterenoid alcohols and the citrus (r = 0.81) and non-citrus (r = 0.83) fruit sensations of beers, as well as with the concentration of linalool (r = 0.95). The odour intensity of the esters identified in olfactory of hops presented a positive correlation (r = 0.94) with the citrus characteristic of dry-hopped beers, while ethyl 2-methylpropanoate (r = 0.98), 3 MBZIP (r = 0.95), and 2 MBZIP (r = 0.98) were the esters that presented strong correlations. These results are in total agreement with previous reports, reinforcing the connection between monoterenoid alcohols and esters with citrus/fruity beer characteristics [11; 17; 22]. The odour intensity of thiol/sulphide compounds showed negative (r = -0.98) and positive correlations (r = 0.82) with spicy and non-citrus fruits, respectively. Data should be further investigated, since DMTS, the compound that showed an association (r = 0.98) with these results, is described as providing unpleasant sulphaurous (garlic, onion, cooked vegetable) effects on beer flavour [34; 35].