CHILL FILTRATION

THE WHISKY PURIST'S NIGHTMARE

Chill filtration has applications in several beverage categories and in many industrial processes. When it comes to whisky, chill filtration involves chilling matured whisky to between -10⁰C and +4⁰C Celsius, then filtering by adsorption (not absorption), which is the adhesion of dissolved particles to a surface. In the case of whisky, these particles are things like fatty acids and proteins.

The whisky is chilled, as this helps to precipitate (clump together) the particles so that they can be easily filtered from the liquid. Not every distillery chill filters in the same way, and in the winter months, some distilleries even chill filter at the high end of the range (3⁰C to 4⁰C), without actually chilling the whisky first. Temperatures around zero are typical, with the higher temperatures being less effective in removing all the fatty acids and proteins than lower temperatures.

Why Do Distilleries Chill Filter?

Not all distilleries chill filter their whiskies and many that do, still have non-chill filtered releases in their range. Regardless on your views of chill filtration, it is fair to say that there is a passionate and growing demand for non-chill filtered whiskies. So if most distilleries spend money to chill filter most of their whiskies when a growing group of people are demanding that they don’t, there must be some advantages to chill filtration to the distillery, as indeed there are.

In essence, whisky is a mixture of ethanol, water and just a little bit of other stuff that contributes to the colour, aroma, mouth-feel and flavour. That ‘other stuff’ includes a host of different chemicals including esters, ketones, congeners, aldehydes, phenols, tannins, furfurals and many more. A typical commercial whisky is approximately 40% alcohol (principally ethanol), 59% water and 1% other stuff. But here’s the rub. Everything organic contains something called lipids, which are also known as fatty acids or fats. Some of the lipid content of the barley used to make whisky persists all the way through gristing, steeping, fermentation, distillation and maturation, and is found in the resulting whisky. They certainly aren’t a problem in terms of health or calories, and their contribution to flavour and aroma is part of that argument I don’t want to get into, except to say, plenty of people love to drink whiskies with the lipids left in.

When whisky is above 46% alcohol at room temperature, there is no issue with lipids. But if you add enough water, if you chill the whisky or if you do both of these by adding ice to your whisky, something significant happens; the whisky goes cloudy. This does not mean the whisky has gone bad or doesn’t taste as good, it just means that it loses the classic bright golden shine that is associated with whisky. People who aren’t familiar with this phenomenon could be excused for thinking they have an inferior or flawed whisky if it goes cloudy when they add ice. In short, lipids are removed through chill filtration for almost purely aesthetic reasons. Whether chill filtering noticeably changes the flavour or mouthfeel is a subject of much debate. You can easily do some cloud formation experiments yourself with a bottle of non-chill filtered whisky, preferably with an alcohol percentage between 46 and 50% ABV.

Experiment 1: Pour some of the whisky into a glass and add twice as much pure water. You should see the whisky go cloudy fairly quickly.

Experiment 2: Put the bottle of whisky in your freezer. After a few hours of cooling, you will see that the entire bottle of whisky has gone cloudy, even without dilution. Leave the bottle at room temperature and the cloudy haze will slowly disappear, with no negative effects.

Experiment 3: While your whisky is still cloudy from the freezer in Experiment 2, pour some of it through a coffee filter paper to replicate the chill filtration process, and then seal it in a smaller bottle to prevent oxidation. Once the bottle and the chill filtered sample have both returned to room temperature, you can do your own taste comparison.

It’s worth noting that just as each whisky has different levels of esters, aldehydes or phenols, they can also have different levels of lipids, and some will exhibit this behavior more strongly than others. For an incredibly stark example of the same principle, try the same experiments with some Greek Ouzo, which goes from clear to opaque white. Absinthe also gives a very strong result.

So Why Does it go Cloudy?

The appearance and disappearance of cloudiness in whisky comes down to the properties of lipids, the properties of the water-ethanol mix, temperature, and something called micelles. 

Diagram 1 - Representation of a Lipid

Fig.1

The lipids in whisky are basically fats, and like most fats they have a hydrophilic (water loving) ‘head’ characterised by an electrically charged -OH group, and a hydrophobic (water hating) ‘tail’ characterised by one or more long carbon chains (see Diagram 1). It is the dominance of these long hydrophobic carbon chains that prevent oil (oil being fat that is liquid at room temperature) from mixing with water. Ethanol, on the other hand is a slightly stranger character. It also has a hydrophilic -OH group at one end and a carbon chain at the other, but the carbon chain is very short. The charged -OH group is therefore able to dominate the short carbon chain, allowing it to mix easily with water. In contrast, alcohols with longer carbon chains than ethanol, like hexanol, do not mix readily with water.

Fortuitously, the short carbon chain of ethanol is still sufficiently friendly with the long carbon chains of lipids to allow them to mix together as well. So, in a mixture of water, ethanol and lipids, ethanol ensures that everything is hunky dory. But if the ethanol drops sufficiently, there will no longer be enough of it to keep the oil and water mixed and they will separate. This starts to happen when the ethanol drops below the magic number of 46% ABV at room temperature. At lower temperatures, the party mood is dampened, and the oil and water will separate even with higher concentrations of ethanol. This is what happens when distilleries chill filter, and it is also what happened in the freezer experiment above.

As the lipids and the water stop mixing, the lipids form something called micelles. A micelle is basically a spherical clump of lipid molecules, where the hydrophobic carbon chain ‘tails’ all point in to the centre, away from the water, while the hydrophilic ‘heads’ all point outwards  towards the surrounding water (see Diagram 2). 

Fig.2

Though these clumps of lipid molecules are still tiny, when there are millions of them scattering  light in the same glass, the result is a cloudy suspension of solid particles in a liquid, known as a colloid. Incidentally, the cell walls in a human body are constructed in an almost identical way. 

Animal cell walls have an outer layer of lipid molecules, with the hydrophilic heads pointing outwards, and a reversed inner layer, with hydrophilic heads pointing into the cell. The hydrophobic tails of the molecules in each layer point to each other between the layers. Quite bizarrely, non-chill filtered whisky and cell biology have much in common. Maybe that’s why whisky makes me feel so good!!

Does This Always Happen?

Some whisky lovers believe that if a whisky is bottled at say 43%, it MUST be chill filtered. Others will even go so far as to say that chill filtered whisky is an inferior product, not worth drinking. I disagree on both counts but I will only address the former, the latter being somewhat more subjective.

All non-chill filtered whisky has some level of lipids, and lipids will always contribute to cloudiness when the ethanol content is low enough. However, as mentioned above, not all whiskies have the same lipid levels, and cloudiness does not appear en-mass when whisky first drops just below 46%. The length of the hydrophobic carbon tail (or tails) varies between different lipids, and it is the length of this carbon tail that determines their solubility in ethanol. Longer carbon tails make lipids less soluble, and these lipids form micelles just below 46% ethanol. Others need the ethanol concentration to drop further.

Experiment 4: Take a non-chill filtered whisky and add just a little bit of water at a time, allowing time for the micelles to form between each addition. You will see that gradually more water brings out gradually more cloudiness, until you reach a maximum.

The magical 46% is not a switch that flicks cloudiness on and off; it simply marks one end of the micelle forming range as each lipid has its own critical micelle concentration. There are a number of non-chill filtered whiskies bottled at 43%. This is low enough for micelle formation to begin, but sometimes for it to be less than obvious. Nonetheless, putting one of these whiskies side by side with a chill filtered whisky of similar colour often reveals that the 43% non-chill filtered whisky is not as bright and shiny, a fact that may not be obvious when it is observed alone. Alcohol strength alone is usually not sufficient to determine whether a whisky is, or is not, chill filtered. 

For those who wish to delve deeper into Chill Filtration and whether it affects people or not, check out this experiment:

Spontaneous Cloud Formation

That’s not the end of the story for cloudiness in whisky, as there is another notable effect that can occur as the result of another property of ethanol. A person who grows up in a very hot but dry city like Bikaner who moves to Mumbai will notice a strange new phenomenon in non-chill filtered whiskies – spontaneous cloudiness.

What’s the explanation? The first was oxidation in the glass, but cloudiness did not seem to coincide with the appearance of notes associated with oxidation, nor could I identify any specific oxidation reactions that would induce cloudiness in whisky. Higher evaporation of ethanol than water in accordance with Raoult’s Law on vapour pressure* was another suggestion, but some very careful measurements indicated that evaporation of ethanol could not have been sufficient to drop the ABV below 46% in the time elapsed. In fact, the volume had marginally increased! Those anomalous measurements and that this phenomenon is prevalent in Mumbai but not Bikaner, led to another hypothesis.

While Bikaner and Mumbai are both known for hot weather, the former is famed for a very dry heat while the latter is renowned for intense humidity. Could the whisky be somehow taking atmospheric water vapour from Mumbai’s humid air? Further investigation revealed another relevant property of ethanol. Due to its molecular structure, particularly that –OH group discussed earlier, ethanol exhibits a force known as ‘hydrogen bonding’. This means that ethanol is hygroscopic, which in turn means that it readily absorbs water vapour from air. BINGO! While ethanol certainly evaporates from a glass faster than water, providing a contribution to the curious observation of spontaneous cloudiness, the whisky simultaneously pulls water molecules in from the atmosphere, and it does so more quickly in humid Mumbai than dry Bikaner. 

With falling ethanol content and rising water content, a cask-strength, non-chill filtered dram in Mumbai can quickly drop below 46% ABV and become cloudy, without a detectable loss of volume. No doubt this would eventually happen in Bikaner as well; I just never left it in the glass long enough!

YET ANOTHER DISTILLERY IN SCOTLAND

 THE EDEN MILL STORY

The Eden Mill story started with a mission to revive the lost art of distilling and brewing in St Andrews.  As Scotland's first single-site distillery and brewery, Eden Mill spirit is created by distillers in copper pot-stills and exhibits a wide range of flavours from botanicals sourced from the local area, as well as from around the world. As creators of whisky, craft gin and beers, the team of distillers have the opportunity to marry the best practices from all these disciplines. The team is challenged with applying modern techniques and understanding to time honoured traditional methods. An appreciation of the intricacies of barrel ageing and quality wood is one benefit enjoyed from this special status.

THE ST ANDREWS LINK

St Andrews is the renowned home of golf, and the arts of brewing and distilling were once integral to the town. Based on the site of a historic distillery on the banks of the River Eden, Eden Mill were the first to make spirits in the region for 150 years. In 1810 the Eden Estuary was offering its crystal clear waters to the legendary Haig brothers, helping them distil and lay down some of St Andrews' finest whiskies. Before them, this same site hosted the Seggie Brewery, known for their strong connections with local farmers and agricultural workers

In 2012, Eden Mill resurrected this fine tradition with its own take on Scottish craft brewing and distilling. Eden Mill was Scotland's first single site brewery and distillery –benefitting from the best of local water sources, regionally grown barley and a dynamic, international team with some of the best education and experience the world can offer. Their distillers are at the forefront of experimental wood ageing and distillation methods to bring out more of the outstanding flavours found in their products.

SUSTAINABILITY

Sustainability is at the heart of everything done in the aim to build Scotland’s first carbon neutral distillery by 2022, 29 years ahead of the UK’s carbon neutral target. The state of the art distillery will be located within the University of St. Andrews’ Eden Campus; power and heat for the stills will be supplied by the University’s biomass plant and solar panels on the distillery’s roof. Building the new distillery aligns with their want to decrease our carbon footprint as much as possible, and they are always striving to create new, innovative and unique ways to improve the sustainability of products and packaging.

EDEN MILL WHISKIES

The Eden Mill story encompasses the uncompromising approach in making their whisky. With the history of distilling on site, the heritage and reputation of St Andrews and the industry experience of the founder, they are on a mission to create the ultimate small batch Single malt whisky ranges for discerning drinkers to enjoy.

In 2018 Eden Mill released the first Single Malt whisky to be distilled in St Andrews in over 150 years. The First Bottling was sold at auction and broke the world record for a first release, at £7,100.

The distillers immerse themselves in Eden Mill’s hands-on process: No computers or vast production tanks – just a personalised approach of creation, tinkering and experimenting. They touch, taste and smell their products every day to make sure everything reflects the Eden Mill ethos.

Most ingredients and botanicals are sourced ethically and locally from the verdant fields and wild coasts of Scotland and the recipes are designed to excite the palate and tantalise the imagination. With every sip a new layer of complexity is revealed and the true craft nature of their approach can be enjoyed.

The Eden Mill story encompasses the uncompromising approach taken in making whisky. Inspired by the pioneering spirit of the Haig family and many other greats who have carved their name on the town's illustrious history, Paul Miller and a team of three began alcohol production from the old derelict site in 2012.

There is a realisation, now more than ever that the value of good whisky is no longer just about its age. Re-determining value and quality is opening up a whole new world of adventure for  enthusiastic, increasingly knowledgeable and discerning whisky loving friends.

They initially launched the new make spirit which was followed by 1-year old expressions; Their 2-year old expressions followed and these were the prelude to the launch of their maiden Single Malt whisky in 2018. They also released a series of four blended whiskies, Art Of The Blend, which are now sold out.

Single Malt - Hip Flask Series: In April 2018, their Hip Flask Series was launched in a progressive and pioneering range of single cask expressions of Eden Mill single malt scotch whisky. To date, 17 different expressions have been released.

SINGLE MALT ANNUAL RELEASES

2018 also saw the release of their very own single malt whisky for the first time. For the 2020 release single malt, they have produced a limited run of 800 bottles of single malt scotch whisky. This edition of their single malt showcases the evolution of their casks and spirits, bringing out light vanilla and toasted cinnamon from bourbon barrels, combined with the rich fruit and subtle spice from their distinctive range of sherry casks, leading to a creamy biscuity finish.

The 2020 Release is the fourth single malt whisky by Eden Mill in three years, since the unveiling of the first bottling in 2017. From the moment they realised their site in St Andrews was founded on the same site as the Haig Family, they knew the whisky world is where Eden Mill belonged. 2022 will be a huge year with a new distillery a work-in-in progress, where whisky is at the forefront of their future plans.

2021 SINGLE MALT WHISKY HAMPER

Eden Mill unveiled a limited number of ultra-premium 2021 Single Malt Hampers in celebration of St. Andrews Day 2021.

This Luxury Hamper Includes:

-One of 800 bottles of the 2021 Single Malt Whisky

-A luxury tasting pack that includes 2 x previous releases of Eden Mill whisky alongside first access to 2 x miniatures of exclusive unreleased Eden Mill Single Malt.

-Bespoke Eden Mill whisky glass.

2021 Release Single Malt is crafted using a perfect marriage of first-fill bourbon casks and ex-oloroso sherry casks, incorporating spirit distilled using pale malted barley. The result is a beautifully rich dram that carries notes of caramelised pears and fruit crumble with undertones of hazelnut praline and a long-lasting peppery finish.

The tasting pack within this luxury hamper includes Eden Mill 2018 and 2019 Releases of Single Malt as well as 2 x miniatures of unreleased Single Malt, giving you first access to sample these exclusive liquids before they are released.