Tequila is undoubtedly the most well recognized Mexican liquor outside of Mexico and is a staple of Mexican restaurants throughout the United States. However, many are unaware that it is a subset of a less well-known genre of alcoholic beverage: Mezcal.
Tequila, as an agave based spirit, falls under the classification of Mezcal, in the same way that bourbon is a type of whiskey. Mezcal comes from the indigenous language meaning "oven-cooked agave".
Similar to bourbon, there are legal requirements for a Mezcal to be called Tequila. Tequila is specifically made from the Blue Agave plant, and additionally Mexican law states that Tequila can only be made in the Mexican state of Jalisco and few other municipalities around Mexico (much is actually made in or around the town of Tequila in Jalisco, the birthplace of the drink that bears its name). This area is especially suited to growing Blue Agave due to the nutrient rich volcanic soil.
In contrast, Mezcal can be made from around 30 varieties of agave plants, though only a handful are commonly used. Most Mezcal is produced in the state of Oaxaca, although it is made in several other areas of Mexico as well. Due to its lower popularity, Mezcal production has remained largely handcrafted by small-scale manufacturers, unlike Tequila, which has had large commercialization.
The production of both Tequila and Mezcal starts with harvesting agave plants with the right maturity to ensure good carbohydrate content for proper fermentation. This process is still largely a manual process with the farmers (jimadores) passing the skill down through the generations. Using a special knife called a coa, the leaves are removed from the plant to form the agave "pina". These agave pinas are then cooked in an oven, crushed and mashed to extract the liquid, and allowed to ferment. After fermentation, the resulting liquid is distilled twice.
Besides the types of agave and the manufacturing location, Mezcal and Tequila can also vary in cooking method. Tequila is cooked in an above ground oven while Mezcal is traditionally cooked in an in-ground oven over hot stones and then covered in moist agave flavor. This typically results in Mezcal being imparted with a smoky flavor, however owing to the flexibility in the Mezcal classifications, it can also be made in a similar fashion to Tequila, which results in a similar flavor.
After distillation, the resulting spirit can either be bottled immediately or placed in wooden barrels to age. Those aged less than 3 months are called joven (Mezcal) or blanco (Tequila). Those labeled Reposado have been aged up to a year and those labeled Anejo have been after longer than a year.
When shopping for Tequila or Mezcal, its a good idea to look for those labeled as 100% Agave, otherwise they are considered mixto and only required to contain 51% agave and can use sugar and other additives.
Also, feel free to skip the worm. It's a marketing gimmick.
There is an expression used in Oaxaca. "Para todo mal, mezcal, y para todo bien, también." ("For everything bad, mezcal, and for everything good, as well.")