## 4 Conclusions  
HS-SPME combined with GC \(\times\) GC-TOFMS provides a suitable and sustainable approach to establish the volatile signature of grapes of different varieties. The SPME technique was optimized, and the only conditions that were considered sufficient to obtain a good extraction were a duration of 40 min and a temperature of 60 \({}^{\circ}\)C. The optimization of the modulation conditions was also crucial to guarantee the success of the analysis.  
Overall, seventeen monoterpenes, twenty-eight sesquiterpenes, and seven C\({}_{13}\)-norisopenroids were found. Compounds such as \(\beta\)-myrcrene, hotrienol, and \(\beta\)-citronellol are exclusive to the TB variety, while \(\beta\)-elemene, \(\alpha\)-cedrene, and aromadendrene are specific to the Sy variety. Isocaryophyllene, on the other hand, is solely found in the Trinc variety. In 2021, TB exhibited a higher relative area for the total sum of free varietal volatile compounds compared to the other varieties under study. In the year 2022, it was the Trinc variety that obtained a higher total relative area.  
The application of the LDA demonstrated statistically significant differences among the five varieties under study, both in 2021 and 2022.  
The work described herein marks the initial phase of a comprehensive study on varietal volatiles within selected grape varieties cultivated in Portugal. The subsequent phase will naturally involve analyzing bound varietal volatile compounds, as they constitute a reservoir of compounds that may be liberated into wine following hydrolysis during wine production processes.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/molecules29091989/s1](https://www.mdpi.com/article/10.3390/molecules29091989/s1)]([https://www.mdpi.com/article/10.3390/molecules29091989/s1](https://www.mdpi.com/article/10.3390/molecules29091989/s1)), Figure S1: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of Trincadeira grapes; Figure S2: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of Cabernet Sauvignon grapes; Figure S3: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of Tina Barroca grapes; Figure S4: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of Syrah grapes; Figure S5: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of Castelao grapes; Figure S6: Example of a contour plot obtained through GC \(\times\) GC-TOFMS analysis of a sample of CS grapes, region of (a) monoterpenes, (b) C\({}_{13}\)-norisopenroids, and (c) sesquiterpenes; Table S1: The results of ANOVA and MANOVA for the free varietal compounds.  
**Author Contributions:** D.F.: methodology, writing, and investigation; N.M.: resources and supervision; M.J.C. and R.G.: conceptualization, supervision, project administration, and writing--review. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by \"Vine&Wine-Driving Sustainable Growth Through Smart Innovation\" project (sub-project-BioGrapeSustain), \"Mobilizing Agendas for Business Innovation\" under the Recovery and Resilience Program. This work is financed by National Funds through FCT-Foundation for Science and Technology under the Project UIDP/05183/2020.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement**: Not applicable.  
**Data Availability Statement**: The data presented in this study are available on request from the corresponding author.  
**Acknowledgments**: The authors would like to acknowledge ALT20-03-0246-FEDER-000034. Metabolomica, ambiente e agricultura de regado, for the acquisition of the GC \(\times\) GC-TOFMS equipment.  
**Conflicts of Interest**: The authors declare no conflicts of interest.