Have you ever poured yourself a dram, added some ice, and noticed your whisky go cloudy? Or taken a bottle from the back of a cold cupboard and spotted the same?

It might be something you have never seen. But if you do have any whisky that is non chill filtered, you could add some ice and just see what happens!

A few people who have purchased Coppersmith – which is non chill filtered – have noticed their whisky go cloudy and have been in touch to find out if something is wrong.

The simple answer is: “No, it’s cloudy but fine!”

It’s just caused by some wonderful aromatic compounds call esters (and also fatty acids) which are a natural part of your dram. These compounds have large molecules which, at lower temperatures, can separate out of solution to make your whisky appear cloudy.

A lot of distillers chill filter their whisky prior to bottling – by cooling the spirit to four degrees and passing it through fine mesh sieves – to remove these naturally-occurring compounds. This ensures that consumers are always guaranteed a crystal-clear measure.

But to my mind this occasional cloudiness signifies that what you have in your glass is as close as possible to the spirit that came out of the original cask.

To get rid of the cloudiness, just let your whisky come up to room temperature and the clouds will disappear.

That’s the short answer!

The long answer – if you’d like to find out more – is a wee bit more complex!

Pour yourself a dram, add some ice (if you like!) and read on….

The science of whisky

With whisky, many stories and mythologies abound. All of these stories and mythologies conspire to create a great mystique around whisky – which is great if it encourages people to appreciate and explore the great whiskies of Scotland, but not so good if it will put someone off.

Chill filtering is a topic that divides whisky drinkers. I know plenty of people who will dismiss whisky that has been chill filtered as an inferior product. I’d like to explore the use of chill filtering in the industry and what it means. Is it inferior and what does chill filtering do anyway?

So, let’s start by explaining the science. As we all know, Scotch whisky is not just alcohol and water. It is a very complex mixture of a huge number of organic compounds – including natural fatty acids, esters and proteins.

Where do these compounds come from?

Well, they are introduced at each step of the process, and the exact combination depends on the type of malted barley (and grain) used to make the whisky, the type of yeast, as well as fermentation time and the distillation process. It also depends on the casks used to mature the whisky.

These compounds produced during mashing, fermentation, distillation and maturation all end up giving the whisky its distinctive nose and flavours.

That is what makes each whisky unique!

For example, one of the areas of great interest is the wood used in maturation. The oak imparts different types of aldehydes to the whisky, and one of the best known is vanillin, which gives the vanilla note to the nose. Other aldehydes can give the familiar almond and grassy notes.

One of the other major contributors to the nose of a particular whisky are compounds known as esters. These occur when alcohol and a natural acid react together. These esters are bigger heavier molecules and are really important in the contribution of a fruity nose to the whisky.

Bananas, vinegar and pear drops!

Each ester’s name comes from the alcohol and the acid that produced it.

So for example one of the simplest esters is ethyl acetate which comes from ethyl alcohol (the primary alcohol in whisky) and ascetic acid (a natural acid found in the fermentation process, also known as common or garden vinegar!)

As an ester, ethyl acetate is what gives a whisky that pleasant pear-like nose.

If you have ever tried a pear drop, its distinctive flavour comes from the esters isoamyl acetate (banana) and ethyl acetate (pear).

Other esters formed with increasingly complex natural acids and with other types of alcohol create increasingly complex aromas in the whisky and so we get raspberry, peach, pineapple and so on.

The interesting thing is that esters are formed during each of the processes in whisky making – during fermentation, during distillation and during maturation.

So if you want a fruity nose to the whisky, many distilleries will go for a longer fermentation time – the esters are formed and we get that great banana and pineapple nose.

Another common ester is ethyl formate (an ester of ethanol and formic acid) which has the characteristic smell of rum and can also be picked up in the nose as raspberries.

There is a very interesting graphic here showing the variety of aromas based on the alcohol and natural acid used in the formation of the ester. With thanks to James Kennedy.

To filter or not to filter?

The downside of larger esters (and the fatty acids also found in whisky) is that they are more complex molecules and as a result they are more difficult to dissolve.

If we have a whisky with a high alcohol level (around 48% ABV) all of the complex esters and fatty acids will almost always stay in solution and the whisky remains clear.

But if the whisky gets cold or the concentration of alcohol is lower (and many whiskies are bottled at around 40% ABV), the esters begin to separate out of solution and you can see them as wispy clouds in the whisky bottle.

You can create this effect at home by adding some water and ice to your favourite non-chill filtered whisky – after a few minutes the whisky will become cloudy.

Many customers do not appreciate looking at a cloudy whisky, so many distilleries chill filter their spirits to remove the esters.

To do this, they chill their whisky to lower than four degrees centigrade and once chilled, pass the whisky through a series of tightly knit metallic meshes or paper filters under pressure to separate out the fatty acids and cloudy esters.

This means that a customer who adds water or ice will enjoy a whisky without the cloudiness.

As an alternative, many distilleries bottle their whisky at 48% alcohol and above. This ensures that the higher concentration of alcohol will (in most circumstances) keep the esters dissolved and the whisky clear.

However, if you cool the bottle down – even at 48% the whisky may become cloudy. This is what has happened with a few bottles of Coppersmith (which is 48% ABV). Simply warming it up again and giving the bottle a good shake will restore the whisky to a non-cloudy state.

Does it matter?

Well although many distilleries insist that chill filtering has little or no impact on nose or flavour, I would tend to disagree. If you remove any element from whisky – particularly those compounds that contribute so much to a dram’s nose – then surely it will affect the final product.

That needs to be balanced against the aesthetic of seeing a cloudy whisky. However, comparing a chill filtered product against a non-chill filtered product is impossible; no distillery that I know of releases both a chill and non-chill filtered version of the same product.

As always with whisky, there is no right or wrong.

If you enjoy the non chill filtered whisky – great, continue enjoying it. If your favourite dram is a chill filtered dram – enjoy it too!

But remember: whisky is a journey, never be afraid to explore.

By Max McFarlane, Master Whisky Maker, the Ardgowan Distillery