Direct infusion electrospray ionisation mass spectrometry in the negative ion mode [ESI(_)-MS] was employed to evaluate the authenticity of aged cachaças, a traditional and valuable Brazilian alcoholic beverage prepared from the distillation of brewed sugarcane juice and aged in barrels made of common woods. Counterfeit samples were prepared by adding dyes, sawdust or essences to a freshly-distiled, much less valuable sample (white cachaça) to simulate the 1–2 years long natural ageing in wooden barrels. A simple visual inspection revealed remarkable differences between the ESI(_)-MS of the authentic samples (aged in oak or amburana casks) and the artificially-aged counterfeit samples. A set of diagnostic ions were detectable in the ESI(_)-MS of the authentic samples aged in oak (m/z 197, 241, 301 and 307) and amburana (m/z 271 and 377/379). This fast and direct methodology seems useful as a routine procedure to monitor this highly profitable and common counterfeit practice.