How long does tequila stay good after opening?

An unopened bottle of tequila keeps almost indefinitely.

According to the Mexican standard NOM-006-SCFI-2012, tequila is bottled at 35 to 55 percent alcohol. A spirit drink in the European Union must contain at least 15 percent alcohol, so tequila is well above that. At that strength the liquid is not a breeding ground for micro-organisms: no fermentation starts and there is no microbiological spoilage.

The European food information regulation therefore excludes drinks with 10 percent alcohol or more from the mandatory best-before date. A bottle of tequila therefore carries no expiry date, and should not. What can happen to a closed bottle over the years is slow evaporation along the closure.

Oxygen in the headspace slowly changes aroma and flavor, without the tequila spoiling.

As soon as the bottle is open, there is air above the liquid. The oxygen in it reacts with the volatile compounds that the agave and the cask have given. Fresh, sharp notes become flatter and rounder. The more that has left the bottle, the larger the layer of air and the faster that change proceeds.

Every time the bottle is opened, the air above the drink is replaced by fresh air with new oxygen. With a bottle that is still nearly full, that is a thin layer of air. With a last dribble at the bottom, it is almost the entire bottle's volume of air.

An opened bottle stays at its best for months to years, depending on how much is left in it.

As a guideline, the trade literature uses half the bottle. As long as more than half is left, the change is slow. From half empty, twelve months is a reasonable period to finish the rest.

• Bottle of nog vrijwel vol: een tot twee jaar zonder merkbaar verlies.
• Bottle of halfleeg: binnen twaalf maanden opmaken.
• One more finger's width in the bottle: two to three months.

Pouring it into a smaller bottle filled to the brim extends those periods, because there is then hardly any air above the tequila.

Upright, at a stable 13 to 18 degrees and out of the light.

Upright is the rule for spirits, even with a closed bottle. Strong alcohol that is constantly pressed against a cork or a synthetic stopper attacks that closure, after which the seal starts to leak. A screw cap does not have that problem, but there too the cap must be closed firmly after every use.

Trade journals give 13 to 18 degrees as the storage temperature, with as little fluctuation as possible. Drops on the inside of the neck point to too much heat or too much variation, and then the bottle is better moved to a cooler spot.

Sunlight is the fastest way to make a bottle deteriorate. UV light breaks down colour and aroma compounds, and a bottle in the sun warms up, so more evaporates past the closure. A closed cabinet or a window with a UV-blocking coating prevents that.

Blanco shows the change fastest, añejo and extra añejo hold on to their character longer.

The classes are fixed by law. Blanco or silver spends no time or less than two months in wood, reposado at least two months, añejo at least a year and extra añejo at least three years, in casks of at most 600 liters. A blanco therefore relies entirely on light, volatile agave aromas, and those are the first to go from a bottle that has become half empty.

In Bathmen there are 78 tequila products from 31 brands, all from Mexico. Of these, 21 are blanco or silver, 19 reposado, 9 añejo and 1 extra añejo; there are also 20 mezcals and 4 tequila liqueurs. The longer a bottle has spent in wood, the more heavier aroma compounds it contains, and these keep an opened bottle at its best for longer.

The freezer is not a good place for a 100 percent agave tequila.

A mixture with 40 percent alcohol only freezes at around 23 degrees below zero, and at 50 percent at around 32 degrees below zero. A household freezer reaches about 18 degrees below zero, so the bottle does not freeze. What does happen: the liquid becomes syrupy and the aroma barely comes out.

It is precisely in a 100 percent agave tequila that the character lies in that aroma. At room temperature or slightly below, that is where you notice it most. For longer storage the freezer adds nothing, because the change depends mainly on the amount of air in the bottle.

We do not sell alcohol to anyone under the age of 18.