If you’re reading this, I assume you have at least a passing familiarity with spirits of various kinds. You may be open minded on what you like to drink, or perhaps you’ve already settled on a favorite. I like to vary my consumption. Variety is, as they say, the spice of life. But even within an individual producer’s range of offerings, you may find some fascinating differences due to one major thing: the oak in which the spirit was aged. It’s always a pleasure to see the surprise on people’s faces when they discover the color of a spirit in the bottle is largely tied to the length of time it spent in oak. But why this range of colors? Let’s find out.

Oak aging goes back to the moment it was decided that a product needed to be kept long enough to be enjoyed, and perhaps even transported. Roman amphorae found in Scandinavia show that wine was transported to the very north of Europe. Clay and oak were both used to transport many different liquids, as a multitude of individual containers weigh much more, in the aggregate, than one large vessel.

Spirits, subject to the laws of thermodynamics, do not mature in the bottle so oak is used instead. They can be aged as little, or as long, as the producers wish. Señor Rio’s portfolio includes Blanco, Reposado, Añejo, and the exquisitely presented Extra Añejo. The Blanco never spends time in oak, but all the rest do to varying lengths of time.

Several things happen as spirits age, including evaporation, oxidation, and the oak itself leaching into the spirit. The difference in oak types, the treatment of the wood before and after a cooper makes the barrel, and the nature of the spirit entering the barrel, all play an important part in determining the flavor of the spirit at the time the producers eventually remove it for blending and bottling.

Why oak? Why not one of the other types common to Mexico like the magnolia or the ficus? Simply put…oak grows everywhere, it’s easy to harvest, and shape into the staves that make up your tequila, rum or whisky barrels. Oak also provides flavors that other woods are incapable of.

The most obvious thing that oak does is provide color. When you compare Señor Rio Blanco, Reposado, and Añejo expressions, you’ll see that one looks like water while the other two get progressively darker. The color comes exclusively from the oak and the reason for this is the toast. This refers to the Cooper (barrel maker) exposing the inside of the finished barrel to a flame. Typically, this is a metal drum filled with a fire over which the barrel is rolled to allow the flame and heat to sear the wood. The heavier the toasting of the oak, the more surface particulates that enter during the aging process resulting in a darker color.