Some Science about Gin and Tonic

The Science of G&T.

An article looking at the science behind why a good G&T is so awesome.

Photo by Jez Timms on Unsplash.

One of the best things to happen to the UK over the last 10 years has been the revival of the love affair that us Brits have with the humble Gin and Tonic.


You would be hard-pressed to go into any pub in the UK today and not be able to have a choice between what Gins you are served.


There has also been a significant shift in the quality of Tonics on offer, riding the crest of this Gin revolution.


So all is good in the Gin garden?


Well, not quite.


Not only is it still possible, but it is often certain in many pubs you will be served a poor G&T, due mainly to ignorance.


So what makes a bad G&T if the quality of Gins and Tonics has improved over the years?


Well, picture the scene and see if it seems familiar;


You order a Hendrick’s from the bar.

The bar staff grab a tall glass and add a nice double Gin to the bottom.

They reach into the fridge, pull out a bottle or can of Tonic, open it and add the contents to the glass.

Next they drop in a slice of lemon or lime and with a final flourish, they scoop in a couple of ice cubes from a bucket on the bar.

Voila, a poor G&T.

Time for some science....

But why?


To answer that, let’s cut through the pretentiousness and snobbery and delve into what makes a good G&T and why!


Most of our taste comes from our olfactory senses, in that we smell it. We have far more taste receptors in our nose than on our tongue.


Gin molecules and Tonic molecules have a similar makeup, that means they are likely to attract and when they join they form a different molecule shape, known as an aggregate molecule.


This is good for us, as the combined molecule creates a flavour that is actually different from the sum of its parts, or as the professor of Chemistry at American University, Matthew Hartings, put it;


this is why a Gin and Tonic doesn’t taste exactly like Gin plus Tonic”;


it is because it’s now a new flavour, not just a Gin flavour and a Tonic flavour. This is also a reason why people who don’t like the taste of Gin often like the taste of a good Gin and Tonic!

IT's all about the molecules

But we digress;


Molecules from the botanicals in the Gin escape from the liquid and interact with our flavour receptors in our nose.


These molecules fit into protein receptors which trigger signals that tell your brain what it smells and tastes like.


So in our example above, does the choice of glass matter?


Simply, yes.


The use of a highball glass only gives the drink a small surface area for molecules that break free of the surface, to reach your nose.


Small surface area means less molecules to smell. What is needed is a balloon type glass with a wide open top which can release more of the molecules at once from the surface, intensifying the smell and taste!


Now part of this smelling process is governed by the bubbles in your drink.

As they burst on the surface, they propel more of the botanical molecules nose-ward!


It stands to reason then, that the longer the bubbles are present in your drink, the more they can release molecules that can reach your nose; it is therefore desirable to have the bubbles hang around as long as possible.


The Tonic contains dissolved carbon dioxide, which is added under pressure during the bottling/canning process.


Like most things, the warmer it is, the more energy that is present. If the gas molecules have enough energy, they will leave the solution quite easily (hence why cola goes flat quickly on a warm day).


If we lower the temperature, the molecules have less energy, and therefore remain in suspension longer.


The best way to do that is to keep the drink as cold as possible.

The order matters

If you add the ice to the glass first, as the Gin is poured over it, almost every molecule of Gin will come into contact with the ice as it cascades over the cubes.


The laws of thermodynamics dictate heat moves from a warm body to a cold body, so each molecule of Gin will lose heat (and get colder) and the ice will gain the heat.


As all the Gin has been in contact with the ice, it cools through conduction.


By doing it this way round, the Gin will be chilled almost instantly.


Adding the ice at the end will not chill the drink enough before the ice has melted, as it uses convection to lower the drink temperature due to the ice only being in contact with a small amount of liquid.


So, now you have a balloon glass with a wide top, filled with ice and Gin over the top.


Next, in goes the Tonic.


For most drinks, the Tonic should be added in about a 2/3 tonic to 1/3 gin ratio, but this can be altered to taste.


Is it important?


Well yes, as we discussed earlier, it is the combination of Gin molecules with Tonic molecules which form aggregate molecules that dictate the taste.


Too much of one, or not enough of the other will affect this balance and you miss out on the real flavour you are trying to enjoy.


As the advertising slogan of a particular Tonic brand states, most of your drink is Tonic, so why have a rubbish one (or words to that effect).


So choose a good tonic if one is available.


Finally the garnish. It is not just added to be pretentious, but it should complement the particular botanicals present in your Gin.


Again, it comes down to chemistry and the combining of similar molecules.


Hendrick’s is brilliant with a slice of cucumber, but in the main, not with lemon or lime.


Good bar staff should have a selection of garnishing ingredients including orange, cucumber, thyme and seasonal berries.


Poor ones will just drop a wilted bit of lemon in regardless.

And there you go, a basic guide on what to look for in a good Gin and Tonic, but also a reason why.


Now, I think you deserve a drink after reading this lot.



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