Mezcal is a traditional Mexican spirit, obtained from the distillation of fermented agave juices. Its preparation has been conducted for centuries in an artisanal manner. The method used to determine the correct alcohol content is of particular interest: a stream of the liquor is poured into a small vessel to induce surface bubbles. These bubbles, known as pearls by the Mezcal artisans, remain stable for tenths of seconds only if the alcohol content is close to 50%. For higher or lower alcohol content, the bubbles burst rapidly. The long bubble lifetime is the result of surfactant-induced surface tension changes. However, the precise mechanism and its relation to alcohol content remain unexplained. In this investigation, the extended lifetime of pearls was studied both experimentally and numerically. It was found that changes in surface tension, density, viscosity (resulting from mixing ethanol and water), and the presence of surfactants are all relevant to extend the bubble lifetime. The dimensionless bubble lifetime was found to reach its maximum value when the Bond number was close to unity, corresponding to 2 mm Mezcal bubbles. These findings show that the traditional empirical method does work. Beyond this, the understanding of the process provides physical insight to many other natural and industrial problems for which the stability of surface bubbles is of importance, such as bio-foams, froth floatation, and volcanic flows.

梅斯卡尔（Mezcal）是墨西哥传统的烈酒，得自发酵的龙舌兰汁蒸馏而成。它的制备已经以手工方式进行了几个世纪。用于确定正确酒精含量的方法特别受关注：将液体流倒入一个小容器中以引起表面气泡。这些气泡，被梅斯卡尔（Mezcal）工匠称为珍珠，只有在酒精含量接近50％的情况下，才能保持十分之几秒的稳定时间。对于更高或更低的酒精含量，气泡会迅速破裂。气泡寿命长是表面活性剂引起的表面张力变化的结果。但是，确切的机理及其与酒精含量的关系仍无法解释。在这项研究中，通过实验和数值研究了珍珠的延长寿命。发现表面张力的变化，密度，粘度（由乙醇和水混合产生）以及表面活性剂的存在均与延长气泡寿命有关。当键数接近于1时，发现无量纲的气泡寿命达到最大值，相当于2 mm Mezcal气泡。这些发现表明，传统的经验方法确实有效。除此之外，对过程的理解还为许多其他自然和工业问题提供了物理洞察力，对于这些问题，表面气泡的稳定性至关重要，例如生物泡沫，泡沫漂浮和火山流动。对应于2毫米的Mezcal气泡。这些发现表明，传统的经验方法确实有效。除此之外，对过程的理解还为许多其他自然和工业问题提供了物理洞察力，对于这些问题，表面气泡的稳定性至关重要，例如生物泡沫，泡沫漂浮和火山流动。对应于2毫米的Mezcal气泡。这些发现表明，传统的经验方法确实有效。除此之外，对过程的理解还为许多其他自然和工业问题提供了物理洞察力，对于这些问题，表面气泡的稳定性至关重要，例如生物泡沫，泡沫漂浮和火山流动。