Legs: What do they mean?

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Capn Jimbo
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Legs: What do they mean?

Post by Capn Jimbo »

Legs, Leggy, Legacy, Legitimate?

Yup, we all do it. Raise our glasses, peer at the rum within, move it around to catch the light and study it carefully. And what do we learn? Less than we think.

Or possibly more.

Here's why. First, let's consider what legs are. The Artic Wolf actually believes they represent the "oil" in the rum that somehow appears as a matter of barrel aging. He also believes that observing two different patterns in a rum implies that it is a blend of older and younger rums (as if they never merged). Except there are no such things or effects. Perhaps a little history is in order...

In 1855 James Thompson (no relation) published a paper named "On Certain Curious Motions Observable at the Surfaces of Wine and Other Alcoholic Liquors". For a second there I thought he was talking about my ex-wife's sexual activities. Thompson correctly posed that what we now call "legs" or "tears" are the result of capillary motion and surface tension.

What's in a pure rum is of less consequence than its surface tension.

We now know that this phenomena is due to both surface tension and the alcoholic content of the rum. When you pour and swirl the alcohol evaporates first, leaving rivulets of higher water content rum to run down the side of the glass in either thin or thick, fast or slow legs depending on the surface tension. In essence the legs express the conflicting forces between more watery or more alcoholic regions of the rum (as the alcohol evaporates). It may also leave "beads" of different sizes at the top (which we call a "pearl necklace".

More alcohol and/or more surface tension = thicker, slower legs.

Another gentleman named Carlo Marangoni performed similar studies of what he called the "Marangoni Convection" which referred to this surface tension convection (movement). He was even able to observe that whisky in a flat dish displayed moving hexagonal "columns" as the alcohol evaporated.

Ever see those? Better pour another dram.

Back to business. In a pure spirit thinner legs usually indicate a younger rum, while an aged rum displays thicker, slower legs. This is due to the increased interaction of the wood and rum to produce ever longer molecules of flavor elements, which result in higher surface tension and thicker, slower legs. Except for one thing:

Distillers cheat.

It is not unusual to add sugar, glycerol and other substances for the purposes of sweetening, flavoring and smoothing a younger rum. These also increase the surface tension - like a bottle of pancake syrup - and lead to misleading, artificial legs.

Shameful, really.

When tasting rums you may often hear me exclaim to discover "scary slow legs" on a rum. When I also detect what I consider unexpected sweetness I know I've been had and will tell you so in the review.

Legs in wine or whisky are much more meaningful as these spirits are much less likely to have been "tweaked". And one other note: although swirling will release aroma it also piles up rum nearer the rim - leading to a false and irreproduceable legs.

The correct way to observe legs is to gently tip the glass toward you, then just as gently back upright and observe. This is entirely reproduceable with different rums and is a fair comparision.

Cheers!
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