What is chill-filtration?
Ever wanted to know what the heck everyone is talking about when say a whisky has been 'chill-filtered'? This guide will fill you in.
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What is chill-filtration? How much impact does it have on your dram? Why is it such an emotive issue for whisky fans? There’s a lot to filter through in this often clouded issue, but we’ll aim to clear thing up in our guide to chill-filtration.
Why is whisky filtered?
Whisky is filtered for a number of reasons, usually to remove visual or textual imperfections. There are many types of filtration employed in whisky production. You can even have a go at home yourself and put some whisky through a coffee filter or even a Britta filter if you so wish. You rascals.
Coarse filtration, which entails passing the spirit through a filter to catch any char or toast from the barrel that became detached, is standard practice. Some distillers will let gravity do its thing, placing the spirit in an inert vessel where the fragments will sink to the bottom and form sediment.
There's also charcoal or carbon filtration. You've probably heard vodka producers boast about creating a smoother spirit by filtering it several times through charcoal and whisky makers can employ the same method. The carbon is efficient and absorbs harsher components, but a powerful variant like activated charcoal can also strip away the spirit's colour, so it's rarely used for whisky.
In Tennessee whiskey making, the Lincoln County Process is employed and this is a form of carbon filtration. The method entails placing sugar maple charcoal in mellowing vats or tanks, large vessels with pipes that conduct the freshly distilled spirit positioned above. The spirit then drips from these pipes to spread evenly across the entire surface of the charcoal filter. The belief is this helps remove any impurities and mellows the spirit.
What is chill-filtration?
Chill-filtration, as you might have guessed, is a method of filtering whisky by chilling the spirit. Within whisky there are a number of congeners, protein chains, fatty acids, esters oils, and fats. If you bring the whisky to temperatures between -10 and 4°C and then pass it through a very fine filter, certain types of these compounds (we don’t want to get too chemical here, so we’ll just group them as fats and oils) come out of solution and form into clumps that can’t pass through. The exact size of the particles removed will vary depending on the distillery’s filtration process and the size of the filter’s pores. This is measured in microns, with a pore size of 5 microns (0.0005mm, for reference) common.
Almost all whisky goes through some kind of filtration
Why is whisky chill-filtered?
Chill-filtration is used to remove visual imperfections. Say you enjoy your whisky with ice or water. Well, if the whisky isn’t chill-filtered, then there’s potential for a haze effect to occur. The cloudy appearance won’t affect the quality or flavour of the whisky, but it doesn’t look appetising. It’s a presentation issue for whisky makers who want to remove any notion that the spirit is faulty or compromised, particularly for bottles made on a large scale where subtle differences in appearance will be noticed more.
This happens because the composition of the oils and fats we mentioned earlier changes on a molecular level when exposed to new temperatures and/or dilution. The esters within the compounds undergo flocculation, or floc, a fancy Dan scientist way of saying they clump together and that presents as a cloudiness in the spirit. This process is also referred to as louching.
Chill-filtration enables producers to be sure of the liquid’s clarity and bright appearance when it’s poured into the glass. The process is only necessary if the bottling strength of a whisky is below 46% ABV. This is due to the presence of long-chain ethyl esters (sometimes referred to as fatty acid esters) which occur naturally in whisky and are insoluble in alcohol less than 46% ABV. Once the whisky drops below that ABV these esters gradually drop out of solution and create a haze in the bottle.
Without chill-filtration, this whisky could turn hazy. But is it worth it if flavour is compromised?
Is there a problem with chill-filtration?
There is a belief that in filtering the whisky, you’re not simply altering presentation, but flavour. Fat is flavour, after all. The oils, fats, and esters that are being removed can not only contribute to flavour, but also texture. Bruichladdich has a long post on its website about why it doesn't chill-filter any of its whisky, reasoning that it would “rather have a haze in the glass than to lose the flavour and texture created all those years ago during fermentation and ameliorated over years of maturation”.
But there’s a larger issue at play here, one ultimately concerned with whisky’s quest for authenticity. Concepts like provenance, terroir and sustainability are all the rage now. And in an age where the average whisky drinker/fan/enthusiast has more access to knowledge than ever, transparency is everything. No more hoodwinking the consumer.
This has led to the establishment of the idea there are pillars of whisky production that guarantee quality. Whisky should have no colouring or additives, the bottling strength shouldn’t just be 40% ABV because it’s the minimum required, and there’s no chill-filtration. Whiskies that tick these boxes are appreciated by purists.
Michter's Distillery employs a unique chill-filtration system
Valid concerns?
These are valid points of contention. But the conversation is also too often simplified into a binary good/bad discussion. This narrows the understanding of a process that is full of options. This could be the temperature to which whisky is chilled, the structure of the filter and how it much it removes, or even how fast the whisky is pushed through the filter.
There are expert whisky makers who maintain that a light touch can remove the haze without stripping out flavour from the whisky. Brian Kinsman of William Grant & Sons fame explained to me that he undergoes regular analysis of pre and post-filter samples on a sensory level to ensure the filtration is working efficiently and preserving all of the flavour. He says that the main flavour compounds will remain in solution at lower strengths if the set up allows. That means establishing the correct flow rate, pressure drop, and surface area which means only long chain esters that have formed a haze will be removed and everything else will flow freely through the filter.
There’s nuance within the process. At Michter’s, for example, a customised chill filtration process is employed for each whisky. There’s no typical carbon filtration or one-size-fits-all approach common at many distilleries. In Michter’s system, multiple plates can be removed and added, filtering to select for flavour, with micron filters selecting which fats go into the whiskey. It’s not a commercial, cynical approach to chill filtration, it’s a flavour-led approach that can be adjusted based on what the whisky makers believe is best suited to each individual whiskey.
It’s also worth considering our own place in this discussion. If we were better as an industry in educating people about why the haze occurs and not to be concerned about it, then maybe we wouldn't even bother with chill-filtration. If you do see some cloudiness then don’t panic, basically. It’s like olive oil, sometimes it goes cloudy but the label explains why this happens and nobody seems to mind.
Even if you buy whisky above 46% ABV, adding a drop of water to the whisky will dilute it and can create the conditions for floc to occur. So the labels of many non chill-filtered whiskies often contain notes explaining the potential of this happening. We’re obviously comfortable giving consumer advice on a label so it doesn’t seem like a stretch to inform, not filter. But the expense, time scale and lack of guaranteed results involved sadly mean many will see this as an idealistic solution.
Should I care about chill-filtration?
So, chill-filtration is unlikely to go anywhere and doesn’t have to impact your whisky enjoyment. There’s plenty of great whisky that is chill-filtered, and plenty of underwhelming whisky that isn’t. Maybe one day a whisky distillery could organise a blind tasting so we can see if we can tell the difference between a sample of whisky before and after chill-filtration. Do you reckon you’d pass? Be honest now…
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