## 3 Results and Discussion
### Multivariate Statistical Discrimination of the Different Extraction Methods  
The VOC analysis of the four groups of filter coffee allowed the quantification of a total of 49 compounds, previously reported in Table 2. A chemometric tool has been applied to comprehensively assess if it is possible to discriminate the filter coffee extraction method from the aroma profile of the final product. The Partial Least Squared-Discriminant Analysis (PLS-DA) revealed discrimination in this sense (Figure 1A). A good grouping was obtained among the samples from the same group, underscoring the reproducibility of the extraction and the fact that each method allows for the extraction of a coffee with a specific aromatic profile. The FP and AP samples were farther apart than the replicates of the other two groups, revealing lower reproducibility of the extraction method. Manual turbulence as it is applied in FP and AP also has lower reproducibility where the coffee preparation processes involve a stirring/applied pressure step, but not in PB and V60. This parameter, together with the pressure, could be indicated as the main causes of the greater dispersion of AP and FP samples in the graph and therefore the lower reproducibility of these extraction methods, as they are strictly related to the operator's skills. The PB coffee samples, obtained using an espresso coffee machine, and the V60 ones, obtained using a pour-over method exploiting the atmospheric pressure, are not so much affected by the operator. Moreover, PB and V60 extractions share the same conical filter shape, while in FP and AP extractions, rounded filters are used. The obtained results led us to assess that the filter shape can influence the volatile profile of filter coffee samples more than the filter material. Indeed, AP and V60 extractions, which involve a paper filter, resulted in coffee samples clearly discriminated based on the volatile profile. At the same time, a good volatile profile similarity was found between FP and PB samples, which were extracted using metal filters. In the PLS-DA model, scores of VIP estimated the importance of each variable in the PLS projection [36]. Figure 1B represents the top 15 compounds with higher VIP scores, which fluctuated wildly among samples. In particular, nine of them reported a VIP score higher than 1.0, meaning they were important factors for the discrimination of filter coffee extraction methods based on the volatile profile. These VOCs belong to six different chemical classes: furans, aldehydes, ketones, pyrazines, pyridines, and phenolic compounds. The main factor influencing VIP was 2-furanmethanol, followed by furural and 2-acetylfuran. These molecules are associated with high olfactometric activity [29] and with candy, burnt, caramel, and sweet attributes. V60 samples reported a higher concentration of the first two compounds, while the third was mainly present in Pure Brew samples, followed by V60. The possibility to discriminate the extraction method of the analyzed samples based on their volatile profile was confirmed by the application of hierarchical clustering, and the results are shown in a heatmap in Figure 2. Good clustering was obtained among the four groups. First, clustering between PB and FP on the one hand and V60 and AP on the other was obtained. This was mainly due to the detected concentrations of the first seven features (red squared in the figure). These molecules were more present in filter coffees obtained from metal filter extractions. Analyzing the aromatic notes of this short list of VOCs, it can be seen that they are mainly related to malty, fruity, and nutty aromas. The following group of seven features characterize the V60 filter coffee samples, and they were mainly associated with sweet, earthy, and buttery oil aromatic notes (light blue squared). The next ten VOCs were highly concentrated in PB samples, resulting in roasted coffee, nutty, corn-like, and chocolate aromas (blue squared).