2. Chill Filtration
The second of our organoleptics series following on from The Colour of Whisky is a timely focus on Chill Filtration in whisky.
What is Chill Filtration?
From our own Whistionary definition: Chill filtering is a method in whisky making for removing residue. In chill filtering, whisky is cooled to between -10° and 4° Celsius (often roughly 0°) and passed through a fine adsorption filter. This is done mostly for cosmetic reasons – to remove cloudiness, rather than to improve taste or consistency. Chill filtering prevents the whisky from becoming hazy when in the bottle, when served, when chilled, or when water or ice is added, as well as precluding sedimentation from occurring in the bottles. Chill filtering works by reducing the temperature sufficiently that some fatty acids, proteins and esters (created during the distillation process) precipitate out so that they are caught on the filter.
Why is whisky Chill Filtered?
As mentioned above non-chill filtered whisky can be subject to turning cloudy when chilled, this haze or technically flocullation occurs when colloidal particles come out of suspension. Basically whisky contains certain compounds such as larger alkyl esters and ethyl esters of long-chain fatty acids (i.e. fats or oils) that are soluble in mixtures of solvents (such as ethanol and water) at certain temperatures and relative concentrations (ABV). Flocculation generally doesn’t occur above 46% ABV, hence stronger ABV whiskies do not require chill-filtration. Whisky below 46% ABV may be subject to flocullation should the temperature drop.
The anecdotal story told at many distillery visits concerns the major export of Scotch whisky to the US. Apparently ships laden with Scotch whisky were locked into US ports by a severe ‘Cold wave’. This is a rare climatological event that sees temperatures plummet across North America. Particularly bad cold wave events can lead to the sea turning to ice and thus freezing ships in port. The result was a whole batch of Scotch exports being refused and returned as faulty due to their cloudy appearance – only to return to Scotland crystal clear as this flocullation is reversible upon raising the temperature – adding to the idiom ‘Scotch Mist’ referring to something that is hard to find or doesn’t exist!
The process of chill-filtering whisky is presumed to be a rather recent or modern addition to the process. The original adoption of Chill filtering in whisky production was first recorded in 1933 by The Distillers Company Ltd. who pioneered it. It appears that it was only much later adopted more widespread by the rest of the whisky industry in the 1970’s. The history of refrigeration stems back to the start of the 1800’s but it wasn’t until the middle of that century that gas compression refrigerants (using ammonia), suitable for industrial application are patented. This date of 1933 is also remarkably close to one of the lowest recorded temperatures of −52 °F (−46.7 °C) recorded during the partial freeze of New York Harbour on February 9th 1934 and also the 1936 North American cold wave. So perhaps there is some merit in the anecdotal story and chill-filtration of exported Scotch whisky commenced to prevent delivery of cloudy Scotch to the US? On a related note previous cold waves that froze the Hudson River in the 1860’s, and earlier, spurred the building of the Brooklyn Bridge.
How does chill filtration impact whisky?
The million-dollar question here is does the removal of these compounds affect the flavour and organoleptic presentation (e.g. mouthfeel) of the whisky? There are many within the industry who suggest it must. Chilling whisky and filtering out these larger compounds must impact in some way and indeed some producers have stopped this process and raised their whisky ABV accordingly to circumvent its absence in their production process. Indeed Ian McMillan, master blender at Burns Stewart, persuaded the company to drop chill filtration in 2010 and raise the standard ABV to 46.3% across their range of single malts including Bunnahabhain, Deanston, Tobermory and Ledaig. In a similar vein Bruichladdich and Arran (Lochranza) distilleries also refuse to chill filter their products. You can read more about Bruichladdich’s advocacy against chill filtration here: https://www.bruichladdich.com/faq/bruichladdichs-guide-chill-filtration/
In the past the presence of clouding in distilled spirits such as whisky would have been linked to impurities such as poor distillation and the possible threat of poisonous methanol contamination or oxidation of the whisky – both of which would have a negative impact upon consumers. Today with production methods rigorously controlled we are much less prone to approach a cloudy whisky with the same caution! The debate will continue to rage around the flavour-altering ability of chill filtration. Personally I could not tell you if a whisky was chill filtered or not from blind tasting, however I would love to try the same whisky pre- and post-chill filtration all in the name of science of course.
Is chill filtration here to stay?
Well it seems a hearty Yes! is the answer to this question. Not least in your average entry-level bottle of blended Scotch Whisky at 40% but also in well-regarded single malts too. Here in lies the current consternation revolving around Brown-Forman’s operations at the Benriach, Glendronach and Glenglassaugh distilleries acquired in 2016. A recent social media storm erupted over the removal of the statement Non Chill Filtered from the packaging of Glendronach’s core bottlings from around October 2020. A spokesperson for Benriach and The GlenDronach said:
“We have removed ‘Non Chill Filtered’ from our packaging to provide the flexibility in our processes to optimise consistently exceptional quality, clarity and stability. Our much-loved whiskies continue to be crafted to the highest standards, and the update marks no change to the taste of our award-winning Single Malts. All of our Single Malts continue to be of natural cask-imparted colour and maintain the same ABV, expertly selected and married by our Master Blender Dr. Rachel Barrie.
“Non Chill Filtration has already been removed from Benriach’s packaging following its redesign last year. The update is now being introduced for selected expressions of The GlenDronach and Glenglassaugh.”
Whilst I have been fan of all three distilleries particularly under their new stewardship I was not invited to sample the new Benriach range. So, like most, I completely missed this change to their core range packaging. I don’t remember much fuss raised when the Benriach range relaunched? What this doesn’t mean is that Benriach or Glendronach will automatically be chill-filtered or that this process is occurring in anticipation of dropping their ABV to under 46%. Others have already pointed out the expense in redesigning packaging is such that any and all changes would occur at once and not incrementally.
What this does suggest however is that chill-filtered expression will be being produced by these distilleries and perhaps an increase in diversity of core range expressions available, and based on this change most likely at the more affordable/entry level. Another possible consequence could be adoption of chill filtering within their standard range thus giving us the chance (as mentioned above) to compare readily available whisky in both non- and chill-filtered variants as long as older stocks are available?
Regardless of the implications I personally would rather reserve my judgement until I have had the opportunity to sample these whiskies myself.
Finally are technical advancements blurring the lines between chill and non-chill filtration?
On researching this piece I discovered this article detailing advancement in chill filtration techniques / haze removal https://www.pall.com/en/food-beverage/blog/what-is-chill-haze-how-do-you-remove-it.html#. Advances in filter design and material could potentially allow filtration of whisky to occur without the cost of pre-chilling. Although one tour guide once joked with me they don’t need to pre-chill their whisky before filtering! If they do it early enough in the morning as Scotland rarely exceeds 4° C before lunchtime!