There is a small moment of panic that happens in front of the tequila shelf. Three bottles from the same brand, near-identical labels, wildly different prices, and one word standing between you and a confident purchase: blanco, reposado or añejo. It is National Tequila Day, which feels like the right moment to make that word do its job.

It all comes down to time in oak

Here is the whole secret in one sentence: the categories are defined by how long the tequila has rested in barrel. Everything else, the colour, the softness, the price, follows from that. The agave is the same plant, the distillation much the same. What changes is patience. Understand the ageing and you understand the entire shelf.

Blanco: the agave, undressed

Blanco (or silver) is unaged, bottled within a couple of months of distillation with little or no time in wood. This is the agave with nothing in the way: bright, peppery, faintly citrus, with that green, mineral snap that good tequila has and cheap tequila hides. Because there is no oak to soften the edges, a blanco is where you taste the distillery's true character, which is exactly why it is the bartender's choice for cocktails. Patrón Silver taught a generation that blanco could be premium; Volcán Blanco and Casa Dragones Blanco carry the idea further.

Reposado: rested and rounded

Reposado means rested, and that is precisely what it is: aged between two months and a year in oak. The barrel rounds off the blanco's sharper corners and lends a gentle wash of vanilla, caramel and warm spice, without burying the agave underneath it. This is the crowd-pleasing middle, the tequila that works equally well in a thoughtful cocktail or over a single cube. Don Julio Reposado, with its honeyed eight months in American white oak, is the benchmark here, alongside Fortaleza Reposado and the endlessly gift-able Clase Azul Reposado.

Añejo: aged, amber and sipping territory

Añejo is aged at least a year, and often longer, in barrels no bigger than 600 litres. The result is properly amber, with dried fruit, toffee, oak and a long, warming finish that has far more in common with a good aged rum or a whisky than with the shot glass of memory. This is tequila to sip slowly, neat, at the end of an evening. Patrón Añejo and Casamigos Añejo are easy places to start, but the one that made the world take añejo seriously is Don Julio 1942, all liquid caramel and roasted agave; and if you want to see how far the category can go, the extra añejos aged beyond three years are a different conversation entirely.

The curveballs: joven and cristalino

Two more words worth knowing. Joven is a blend, usually a blanco married with a little aged spirit for roundness without the full oak commitment; Casa Dragones Joven is the luxurious example. Cristalino is the clever trick of the moment: an aged tequila, often añejo, that is charcoal-filtered to strip the colour back out, leaving all the barrel flavour in a crystal-clear liquid. Volcán Cristalino is the easiest way to understand why people have fallen for them. And then there is the assemblage: Volcán XA blends reposado, añejo and extra añejo into a single bottle that refuses to sit in any one box, which is rather the point.

So which should you buy?

Keep it simple. If you are mixing margaritas and palomas, buy a blanco and let the agave do the talking. If you want one bottle that does everything and offends no one, a reposado is the safe, delicious answer. And if you are settling into an armchair with a good glass and no plans, an añejo is the one to pour. Three words, three moods. Happy Tequila Day; you now know exactly what you are reaching for.