Brand authenticity is important to customers, as they prefer genuine and real products, and further research is needed to shed light on what underlies perceptions of authenticity and what may influence them in order to better theorise and operationalise authenticity in the field of marketing. Since authenticity was not found to be unidimensional, multidimensional scales were structured to explain brand authenticity, resulting in the 3-dimensional approach, which corresponds to the CBBA (Consumer-Based Brand Authenticity) scale in its improved form, which is the most appropriate for the beer product, since it has been used in studies related to the food and beverage industry, in addition to being used in Mexico. Nevertheless, the CBBA is not the only model that has been used, according to the literature review, three theoretical perspectives are used, in this case the subjective one is the most widely accepted among the models tested, as is the case of the CBBA. Therefore, the first purpose is to validate the authenticity factors that make up the CBBA (Consumer-Based Brand Authenticity) scale in three different brand beers: Tecate, Corona, and XX, and the second purpose is to explore consumers' perception of authenticity, through a longitudinal study applying a questionnaire in the northeast of Mexico (Victoria City, Tamaulipas) in two periods of time, being a non-experimental and descriptive investigation. The questionnaire was composed on 21 items, including nine questions for the quality commitment dimension, seven questions for the legacy dimension and five questions corresponding to the honesty dimension. It was applied with 5-point Likert scale. In order to answer both objectives, statistical analyses were carried out using SPSS software version 21 and R studio software version 1.3.1093 through several stages: First, an Exploratory Principal Component Analysis (PCA) was calculated, and at the same time the KMO (Kaiser-Meyer-Olkin), Bartlett's sphericity test, Sperman's rho and Cronbach's alpha were calculated. Then an exploratory factor analysis (EFA) was calculated. After the factor analyses, MIRT (Multidimensional Item Response Theory) was calculated and finally we used the Mann-Whitney U test, in two independent samples (174 people for each sample), which corresponds to a non-probabilistic convenience sample of 348 young consumers in total. The results indicate that the CBBA scale could be validated in two of its factors: quality commitment and inheritance, unlike previous research that considered three factors as quality commitment, sincerity and inheritance. Regarding the second objective, it was shown that for Mexican consumers, the authenticity of beer is perceived in terms of quality and the relationship between the brand and its history (heritage). The original contribution lies in the application of MIRT and the longitudinal scope of the study, while the results show that the exploratory factor analyses and the Mann-Whitney U test were consistent, but the application of MIRT was not favourable. The implications of the research include the construction of a scale to support the assessment, planning, understanding and testing of product authenticity and the analysis of its impact on the consumer. In addition to considering a prior diagnosis of the company in relation to the authenticity of the brand and its products. However, more attention should be paid to the variable of sincerity. As for future lines of research, more longitudinal studies should be conducted in Mexico and Latin America, since the responses per item of the scale tested were not consistent, in addition to considering different industries and cultures to continue testing the scale. analysed. Finally, the study is limited to one area and one product, the brands Tecate, Corona and XX, so it is necessary to continue the research in different industries and cultures. [ABSTRACT FROM AUTHOR]