Mexico carefully guards the name and legacy of its national spirit. Any liquor bearing the label “tequila” must be produced in Mexico, from blue agave (Agave tequilana azul) of the Weber Blue variety grown in Jalisco, or tequila of specially designated regions of Nayarit, Guanajuato, Michoacán and Tamaulipas. Distilleries are also carefully regulated, and assigned a NOM (Norma Oficial Mexicana) number. Much of the mass-produced tequila found in American liquor stores comes from fairly young agave plants, harvested when the sap is tart and acidic.