Tequila Production:

The official Mexican standard or NOM defines Tequila as the product of fermentation and distillation of the blue agave juices (mostos) obtained at the distillery from agave cores or piñas grown in the Tequila Region and allows for the addition of up to 49% sugars from sources other than the agave plant. However the NOM defines as Tequila 100% Agave as the one containing sugars exclusively from the blue agave plant and it must be bottled at the distillery. Alcohol content must be between to 35º and 55º Guy Lussac (70 to 110 Proof).
Harvesting the agave plant remains a manual effort, unchanged by modern farming technologies, and stretching back hundreds of years. The agave is planted, tended, and harvested by hand. The men who harvest it, the "jimadores", possess generations of knowledge about the plants and the ways in which they need to be harvested. The jimadores must be able to work swiftly in the tight rows, pull out the hijuelos (Agave offspring) without damaging the mother plant, clear the piñas (Spanish for pineapples), and decide when each plant is ready to be harvested . Too soon and there are not enough sugars, too late and the plant will have used its sugars to grow a quiote (20-40 foot high stem), with seeds on the top that are then scattered by the wind. The piñas, weighing 40 to 70 pounds, are cut away with a special knife called a coa. They are then shredded, their juices pressed out and put into fermentation tanks and vats.
Some tequila companies still use the traditional method (artisanal) in which the piñas are crushed with a Tahona (stone wheel). The musto, (Agave juice, and sometimes the fiber) is then allowed to ferment in either wood or stainless steel vats for several days to convert the sugars into alcohol. Each company keeps its own yeast a closely guarded secret. Juices ferment for 30 to 48 hours then they are distilled twice in traditional copper stills or more modern ones made of stainless steel or in continuous distillation towers. The first distillation produces a low-grade alcohol and the second a fiery colorless liquid that is later blended before being bottled. Alcohol content may be between 70 and 110 Proof. At this moment the liquor is no longer mezcal but tequila.
Some distilleries distill the product again to produce a triple distilled product. From there the Tequila is diluted and bottled as a "silver Tequila", or it is pumped into barrels to begin the aging process.
There is a clear difference in taste between tequila that is made from lowland and highland agave plants. Agave plants that are grown in the highlands often have more fruit flavor due to the growing process. The plants are grown on west-facing slopes, allowing them to receive the most amount of sunlight throughout the day. These plants are taller, wider, and juicier. Agave grown in the lowlands have more earthy flavors, and are typically on the smaller side.
It is a common misconception that some tequilas contain a 'worm' in the bottle. Only certain mezcals, usually from the state of Oaxaca, are ever sold con gusano, and that only began as a marketing gimmick in the 1940s. The worm is actually the larval form of the moth Hypopta agavis that lives on the agave plant. Finding one in the plant during processing indicates an infestation and, correspondingly, a lower quality product. (Note: for more information on how tequila is made, see mezcal.) However this misconception continues, and even with all the effort and marketing to represent tequila as a premium—similar to the way Cognac is viewed in relation to brandy—there are some opportunist producers for the shooters-and-fun market who blur these boundaries.[20]