The Tequila Making Process

05. Fermentation

05

Fermentation: Converting the Sugars in Pressed Agave Juice into Alcohol

A producer has many choices when it comes to elements that contribute flavor during the fermentation process, the main three being: yeast strain, fermentation conditions, and whether or not to include Bagaso.

Yeast Strain

Yeast are microorganisms that convert sugar to alcohol; they occur in the wild but are also propagated commercially. Some alcoholic beverages derive much of their flavor from their main sugar source (tequila from agave, brandy from grapes), while others derive much from their flavor from the process of fermentation (notably rum and whiskey). In all spirits, the strain of yeast used to convert sugars to alcohol is one element that differentiates spirits made from the same raw material.

Fermentation Conditions

Yeast operate and optimize at very specific temperatures and the change of a few degrees can yield wildly different flavors. This is partly due to the fact that yeast are competing with other microorganisms and bacteria for the sugar in the agave juice. Producers may choose to control the temperature of their fermentation vats either naturally, using materials that are natural insulators like pine, or through technology, most frequently jacketed vats. Likewise, they may choose to alter the acidity of their fermentation to both optimize yeasts and select those yeasts over competing fermenting microflora and microfauna.

Including or Removing Bagaso (fibers)

Generally, tahona-milled agave is fermented with some of the bagaso, which contains a lot of fermentable sugars. In these fermentations, bagaso floats to the top and forms a cap on top of the mosto, or juice. This cap limits evaporation, creating an anaerobic environment in which the yeast creates a specific set of flavors. Roller-milled agave is generally fermented without bagaso, as the more efficient milling process does a better job of extracting sugars from the fibers. These fermentations are exposed to the air (aerobic) and tend to experience higher levels of evaporation leading a different set of flavors to develop.

An illustration of a Fermenting Wood Vat

credit: Chloe Harrison-Ach

at patrón: we use small pine fermentation vats.

All fermentation at Patrón takes place in small wooden tanks made from pine wood planks. These have become extremely rare in the tequila industry because they require meticulous cleaning after each use and must be replaced every four years. We believe wood vats provide the best sugar conversion, as they have natural thermal control that protects against temperature extremes in both hot and cold seasons.

at patrón: two fermentation methods = two different products.

Tahona-milled agave mosto, or juice, is fermented together with its bagaso, or fibers. Fermented mosto from this process ends up with a rich baked agave scent and taste, plus pronounced earthy flavors. Roller-milled agave mosto is fermented without the fibers, as the fibers were separated during milling, so its mosto is fermented alone. This produces tequila with citrus fruit and fresh agave characteristics. 

The two fermentations end up tasting significantly different, and remain separated throughout the distillation process. It’s not until after distillation that the two tequilas are blended together.