## 2 Analytical Strategies for Authentication and Quality Control
### Chromatographic and Hyphenated Techniques  
One of the most important parameters for evaluating the quality, safety and authenticity of alcoholic beverages is the content of volatile compounds, named congeners. These molecules are formed together with ethanol in the processes of fermentation, distillation and maturation. Chromatographic techniques, most commonly GC-FID and GC coupled to mass spectrometry (GC-MS), are the techniques traditionally used for the determination of these compounds. The European Commission Regulation n. 2870/2000 [18], which establishes community reference methods for the analysis of spirit drinks, provides a GC-FID method for the determination of acetaldehyde, higher alcohols, ethyl acetate and methanol, which are parameters that must be checked for compliance with the legal limits prescribed for the category of spirit drink by the European Regulation n. 2019/787 [5]. In accordance with the official method mentioned above, some authors [39] proposed a faster method with good accuracy and precision parameters to quantify 16 main volatile compounds, including acetaldehyde, ethyl acetate, methanol and propan-1-ol, by using Fast GC. Fast GC includes fast, direct heatin/cooling technology that reduces post-run cooling and steep temperature gradients in combination with a high-pressure operating column. According to the authors [39], this combination allowed them to achieve a total analysis time of 8 min instead of the 40 min of conventional GC-FID while improving analytical performance and achieving lower LOQ and LOD values. The Fast GC method was tested on eight different spirits (including brandy) and wines supplied by proficiency-testing providers or taken from the market. Another proposal to improve the official GC-FID method by using the ethanol already present in the sample as an internal standard instead of 4-methylpentan-2-ol (as indicated in the reference method) is reported in a more recent study [40]. The method, developed to quantify the 10 main volatile compounds subjected to regulatory limits, was tested on 25 samples of spirits (including Gr and WB) and, after validation, was compared with the official method with regard to parameters of precision. A comparison of the results obtained through the two methods displayed non-significant differences from \(-1.3\) to 0.9% at \(p\leq 0.05\). The advantages of using pre-existing ethanol as an internal standard are many. The European regulation, in fact, requires congeners concentrations to be expressed as mass of congener (in g) per 100 L of ethanol in the sample. This implies determining the density and the ethanol content for each sample by distillation and densitmetry, respectively. These sample preparation steps, combined with the addition of the internal standard, increase the measurement uncertainty as well as the time required for the analysis. With the proposed method the concentrations of the congeners are directly expressed in grams per 100 L of ethanol without any other analytical step, eliminating further sources of uncertainty and significantly shortening the analysis times. Another study [41] demonstrated the potential of GC-FID combined with LDA and PCA to verify the authenticity of Gr samples. The authors analyzed the content of the 10 main volatile substances mentioned above and the alcoholic strength of 123 spirit drinks belonging to different categories, including Gr, wine spirit, grain spirit and fruit spirit. The data were processed by LDA to develop a classification model in which to project two samples considered not compliant for flavor. The model, previously validated, provided a percentage of correct classifications higher than 97% in both cross-validation and external validation. To verify the assignment of the LDA model to the \"wine spirit\" category, the authors computed two one-class PCA models for the \"Grappa\" and \"wine spirit\" categories, finding that the suspect samples did not belong to any of the classes considered, as incorrectly predicted by the LDA model.