Chill Filtering

Chill filtration has been another one of those tricky topics in which the reality was somewhat distorted by marketing and preconception. In the past, whiskies were chill filtered to improve clarity and consistency; generally considered a good thing. Today however, many labels make the point of including the words ‘non-chill filtered’ in their description, as though they offer a whisky with more integrity and of a higher quality. If this were the case, though, why has this filtration process been an industry standard for so long?

Lack of clarity

You can understand the process by simply finding a bottle of whisky with these very words on the label and subjecting a dram to an ice cube or two (or just put the whole bottle in the fridge for a while). You’ll notice that once chilled the whisky becomes somewhat cloudy and opaque, and perhaps of even greater interest will return to its previous clarity and colour upon warming up again. Herein lies the perceived problem.

Imagine ordering a whole case of whisky from a distributor, only for it to arrive one cold morning with a significant haze completely unlike the last bottles you received - this could give anyone pause, and indeed has led to many a concerned enquiry. Similarly, customers might overlook the slightly cloudy bottle sitting on the shelf for fear it has in some way become spoiled or 'gone off'.

The process of chill filtration was developed to prevent such a scenario. It’s a pretty straightforward case of carefully reducing the whiskies temperature in order to trigger the formation of this haze in a controlled manner, then running it through a fine filter to screen out the culprits before bottling. The drop in temperature brings about the precipitation of long-chain fatty acids and complex esters, in a process known as flocculation (brewing enthusiasts will recognise the term, as it is the same means in which yeast conveniently coheres in the latter stages of fermentation, making for easy removal). By instigating this phenomenon under artificial conditions and filtering out these compounds, distillers ensure that this haze will not form in their customers' warehouses or glasses, reducing the chances of their product being rejected.

Aesthetics subject to taste

Of course, one could argue (quite rightly) that there is nothing inherently wrong with a bit of haze in a whisky, as it is simply caused by naturally present components responding to changing temperature. This being the case, is it really necessary to remove them when they may well be contributing to the pleasing character of the whisky? Do we lose something more than a bit of cloudiness by screening them out? Particularly in recent years proponents for leaving the whisky in its natural state, haze and all, have argued it is not so much the ‘flavour’ of the whisky being impacted as it is the ‘mouthfeel’, or texture.

It is worth noting that this reversible flocculation is dependent not only on temperature but also the strength of the whisky; at higher strengths, usually anything above 46%abv, these various complex chemical chains are less likely to come out of solution in the first place. This means that a whisky bottled at its natural cask strength, say 56%abv is unlikely to be concerned with chill haze at all. That is of course until someone adds a few drops of water or their ice begins melt, in which case cloudiness is predicted once again. Still, this is one reason we’ve seen an increasing number of whiskies bottled at or above the benchmark of 46.8%abv.

It may well be that much of this has become marketing bluster; certainly I have yet to meet anyone who can consistently identify the difference between chill filtered whiskies and those that remain as they were found in the cask. For some time yet we’ll no doubt continue to see a bit of both. Just know that a bit of haziness in your glass is nothing to be concerned about, it just means you’re just getting the full authentic experience.