## 5 Conclusions  
This review represents an overview of the main studies for the authentication and quality control of Gr and WB GIs over the last 10 years. The evidence that emerged is that the scientific literature relating to the authentication of these matrices is scarce compared to that for other categories of distillates such as whisky [94]. The studies presented in this overview highlighted that targeted methods, mainly chromatographic and hyphenated, are the most frequently adopted for the classification and quality control of these products. These techniques, coupled with suitable chemometric tools, have proven effective in discriminating Gr from other categories of spirit drinks, enabling the identification of distinctive chemical markers. The same techniques also showed good potential in discriminating Gr samples according to brand, origin of raw materials and aging conditions. For WB GIs, the literature is mainly related to the authentication of the aging processes, which are essential for developing the distinctive organoleptic characteristics of this distillate [95]. In this respect, chromatographic techniques appear to be effective approaches for discriminating WB GIs according to aging time and characteristics of the wood used for aging, including its seasoning and toasting. However, some of the main disadvantages of these techniques are the high costs and long analysis times. Another approach is based on spectroscopic methods, in particular IR (MIR and NIR) Raman and fluorescence spectroscopies, combined with chemometrics. Despite relatively few research works on Gr and WB samples, these techniques appeared very promising for both discrimination and for the detection of adulterations with low-quality spirits. These methods, generally, do not identify specific chemical markers but focus on particularly informative spectral regions and rely heavily on the use of chemometrics. Their main advantages are cost-effectiveness, reduced analysis time and ease of sample handling. Furthermore, a comparison of some of these methods with official analysis methods has shown comparable or even better results, although they have no legal value until they are approved as standard methods. A third analytical approach is a combination of the previous two. It involves the fusion of chromatographic and spectroscopic data into individual chemometric models. This multi-platform strategy, successfully carried out for discriminating Gr from other distillates, seems to produce better results and more information about the type of adulteration than single techniques, combining the advantages of chemical marker identification with the quickness of untargeted methods. Finally, among new technologies, sensor arrays have proven reliable for discriminating between WB samples according to alcohol content and brand name and for discriminating between adulterated and authentic WB GIs.  
Conceptualization, S.A. and F.C.; methodology, S.A.; validation, F.C.; data curation, S.A.; writing--original draft preparation, S.A.; writing--review and editing, F.C.; supervision, F.C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflicts of interest.