Mezcal is a traditional alcoholic Mexican beverage that is produced from the distillation of fermented agave juices. For centuries, the production of this spirit has preserved its artisanal form of preparation and testing. Of particular interest is the method used to evaluate the alcohol content of mezcal. The maestro mezcalero pours a stream of the distilled liquid into a small vessel to observe the formation of pearls, milimetric bubbles that form at the surface. If the bubbles indeed form and remain stable for some time, then the mezcal is said to be ready for consumption. In this video, we investigate the conditions for which such pearls form. We conduct controlled experiments that emulate the traditional technique, considering water-alcohol mixtures and also artisanal handcraft mezcal. We found that for the correct jet size and speed, pearls form as a result of the impact of drops on the surface. Moreover, the life time of such pearls is strongly correlated with the alcohol content of the liquid. The pearl life time reaches a maximum at some intermediate concentration, which is in accordance with that of mezcal. We discuss that the longer life time is a result of the unexpected increase in viscosity of water-alcohol mixtures. Interestingly, this simple, yet counterintuitive, method is also used to assess the quality of other drinks such as whisky and vodka.
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