After the first distillation, an alcohol content of around 25% is reached.  This is called ordinario.  It is very cloudy in appearance, and has a lot of impurities.  During the 2nd distillation, the alcohol content will increase to 40-65%.  

The unwanted elements such as methyl alcohols and aldehydes that are in the heads, as well as the heavier elements in the tails, are discarded.  6-8 hours are need for distillation.

 

While the Spaniards were given credit for bringing distillation to the New World, there have been recent archaeological findings that suggest that distillation had taken place before the Spaniards invaded Mexico.