Mezcal. In recent years, the oldest spirit in the Americas has been reinvented as a pricy positional good popular among booze connoisseurs and the mixologists who use it as a cocktail ingredient. Unlike most high-end distillates, most small-batch mezcal is typically produced by and for subsistence farming communities, often under challenging conditions. As Granville Greene spends time with maestros mezcaleros, who distill their drinks using local agaves and production techniques honed...