Checking out the long legs of liquid gold

Artwork © Lauren Delora Sears

Today’s song couldn’t really be anything other than Whiskey in the Jar by The Dubliners but it highlights the different spellings of whiskey (in the song) and whisky (in this post). The Irish spell it with an ‘e’ to differentiate it from Scotch whisky which is produced in Scotland under a myriad of rules and regulations. Needless to say, I felt compelled to stay true to my Scottish roots by referring to whisky.

And it seems that, if you’re Scottish, you are highly likely to have whisky flowing through your veins. In fact, it appears so common to love the tipple that I sometimes feel I’m the only exception!

The alluring, and seductive, liquid gold takes pride of place at tables in pubs and living rooms across the country – and the world. Sensory exploration of its nuances in character can keep whisky buffs entertained until the wee hours. I have seen that first hand. Like most things, people have personal preferences and whiskies are usually classified according to geography and flavour characteristics. Yet, even though I don’t like it at all, I have come to be able to recognise basic divisions according to how it looks and its aroma.

In actual fact, we use our senses of sight, smell, touch and taste, to evaluate whisky. And usually in that order.

Whisky is essentially a mix of flavoured water and alcohol. One of the first things a whisky drinker does, after checking the colour, is to swirl it in the glass and observe the formation of whisky ‘tears’ or ‘legs’.

Whisky legs. Photo credit: tienvijftien

Whisky legs. Photo credit: tienvijftien

Legs are drips, that flow downwards from a ring of clear liquid on the inside of the glass, above the surface of the whisky. They’re also known to form in wine. The length of the legs gives an indication of  alcohol content and they are created by the difference in surface tension between the two liquids.

Surface tension is caused by the tendency for molecules at the surface of a liquid to stick together (cohere) strongly. These cohesive forces are shared between all the molecules but, because there are no molecules above them, the ones at the surface bond with those alongside even more strongly. This is especially true for water molecules.

The increased bonding forms a line of resistance just like a row of people with linked arms. Just as you would huddle tighter in that row to prevent anyone breaking through, the surface of the water contracts. That is what is responsible for the spherical shape of water droplets. That extra resistance on the surface is also what allows water striders to walk on water without breaking through and sinking.

So, as the whisky in the glass is swirled, a thin film of the mixture is pushed up the side of the glass. Water and alcohol are both evaporated from the surface of the glass but alcohol is evaporated faster. This reduces the alcohol concentration of the film and a greater proportion of water is left on the glass.

Since water has a higher surface tension than the alcohol, and the bulk of the mixture, more whisky is hauled up the side of the glass, creating an upwards flow. The water at the top of the film beads, at first, then starts to flow downwards back into the whisky as gravity takes over. The higher the alcohol content of the whisky, the more easily and further the water can pull the mixture – hence longer legs. This phenomenon is called the Gibbs-Marangoni effect after Italian physicist Carlo Marangoni and American physicist Josiah Willard Gibbs who both worked it in the middle to late 19th century.

The alcohol content also affects the texture or feel in the mouth. If it is high, it can dry the mouth and be considered fresh. Whisky with lower alcohol content covers the mouth with a smooth, viscous coating. Although I must admit, I think I’ll leave that bit to someone else!

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