Fermentation & distillation

The agave juice now goes into fermentation tanks, usually stainless steel, sometimes wood. Yeast, most often a strain of Saccharomyces cerevisiae, converts the sugars into ethanol along with the aroma and flavour compounds that give each tequila its character. The tanks warm up as the yeast works, and fermentation usually takes several days.

Every distillery has its own approach. Some use commercial yeast, others cultivate a house strain or rely on wild yeast from the air; some ferment the juice together with the agave fibres. Yeast, vessel, temperature and time all shape the final flavour. The result is a mosto, a wort with roughly the strength of beer.

A short history

People in Mexico were fermenting agave long before the Spanish arrived; pulque, a milky fermented agave drink, is still made today. What the Spanish brought was distillation. Missing their brandy, and taxed heavily on what the Crown imported, settlers began distilling fermented agave in the 16th century. The result became known as mezcal wine, and the version made around the town of Tequila eventually took the town's name.

Two distillations

The law requires tequila to be distilled at least twice. The first run produces a cloudy, rough spirit called ordinario. The second turns it into clear tequila. A few producers distil a third time, though many connoisseurs feel this strips out too much agave flavour.

Heads, hearts and tails

Not everything that comes out of the still is kept. The first portion, the heads, carries the most volatile compounds, including methanol, which boils at 64.7 °C (148.5 °F), and sharp-smelling aldehydes. The last portion, the tails (colas), is heavy with water and oily compounds. Both are separated off. Only the middle portion, the heart (corazón), becomes tequila. How and where the distiller makes those cuts is one of the most important decisions in shaping the spirit.

Pot stills

Most tequila is made in pot stills (alembics), traditionally copper, ranging from about 100 to 2,000 litres. Smaller stills are slower but are often thought to give a more flavourful spirit, while larger ones produce more, faster. A single run takes four to eight hours.

Column stills

Column stills, also called Coffey stills after their 19th-century inventor Aeneas Coffey, distil continuously and far more efficiently, but they are rare in tequila. The only one I have seen is at Tequileña. Because the rules require two distillations, producers with a column still have typically run the first distillation in a pot still, so that the second distillation in the column can be verified.