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Alcohol Chemistry

#NationalTequilaDay: Types and flavour chemistry of tequila

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Today (July 24) is National Tequila Day. What contributes to the flavour of this Mexican spirit? This graphic takes a look at how tequila is made, the different varieties, and some of the compounds that contribute to its taste.

Tequila is made in Mexico – specifically, in a select number of Mexican states. It was first made in the town of Tequila, in the state of Jalisco. Today, it is produced throughout this state and in the territory of four others.

The blue agave plant is the raw material for the production of tequila. Making tequila involves harvesting the heart of the blue agave, then cooking, mashing or milling to get a juice that is rich in sugars. To be called tequila, the blue agave plant must be the source of 51% of the fermentable sugars.

The juice is fermented with yeast to generate alcohol, then distilled twice to concentrate the alcohol. It is then diluted with water to give an alcohol concentration of between 35% and 55% alcohol by volume.
There are five recognised types of tequila. The first type, blanco (or white) tequila, is the diluted distillate. The second type, joven (or gold) tequila is blanco tequila with a small amount of aged tequila added. In some cases, colour and flavouring is used instead.

The three other types of tequila are all aged in oak barrels or vats, with the length of ageing determining the type. Reposado tequila is aged for at least two months. Añejo is aged for at least a year, and extra añejo is aged for at least three years.

The flavour chemistry of tequila is complex. The different stages of production contribute different chemical compounds, and studies have identified hundreds of different chemicals in various tequilas. Not all of these contribute to flavour, but research has also revealed which compounds make significant contributions.

Some compounds derive from the blue agave plant and emerge unchanged from the production processes. These include terpene compounds such as alpha-terpineol, linalool and citronellol.

The fertilisation and distillation processes form other compounds. Several studies have identified compounds which are key contributors to the flavour and aroma of blanco tequila. These include esters (such as ethyl hexanoate), alcohols (such as 2-phenyl ethanol and isoamyl alcohol), and others (such as beta-damascenone).

These compounds contribute to the flavour and aroma of aged tequilas, too. Barrel-ageing also makes significant additions to the compounds present. The breakdown of lignin in the wood, combined with subsequent reactions, gives a variety of compounds. These include vanillin, eugenol and guaiacol.

Some of these compounds are also found in other aged spirits, for example whisky. Whisky lactones are compounds found in both whisky and tequila due to the barrel-ageing process.

Despite the knowledge we have of the compounds that give tequila its character, chemists still can’t substitute for the real thing. Some studies have tried to reconstitute a tequila simulation from the key compounds identified. So far, they’ve been unsuccessful in capturing the nuances of tequila flavour.

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