The juice (and sometimes some of the pulp as well) is placed into large vats, mixed with water and yeast, and allowed to ferment. Depending on the distillery, the yeasts can be commercial brewer’s yeast or cultivated forms of the wild yeasts that grow on and around agave plants. In some cases, the vats are left open to the air, to attract wild yeasts that develop complex flavors in the ferment. In other cases, the vats are closed off, to promote a more efficient fermentation. Closed vats, however, seal out wild yeasts, and many tequila lovers prefer the complex flavors that develop in open vats.
If sugar is added during fermentation, the tequila is a mixto, or a mixture of agave and sugar. I’ll talk more about mixto in a bit.
Over a century ago, piñas were cooked in pits, dug into the ground, over wood fires. The deforestation of Jalisco, however, forced a change, first to coal- or gas-fired ovens, and then to the steam-powered ovens used today. Some distilleries use traditional ovens made of stone or clay; others use stainless-steel ovens.
Piñas are slow-baked at around 140 to 185o F for about 50 to 72 hours. Slow-baking ensures that the starch molecules break down into sugars, but doesn’t allow the sugars to caramelize, which can introduce off notes into the agave flavor. (Some larger distilleries pressure-cook the piñas, at higher temperatures for a shorter period, but aficionados decry this practice, saying it makes for a less flavorful tequila.)
