Distillery Diaries - Filtration

Posted on November 17, 2017

Filtration is probably the least discussed element of the multi-step process that is whiskymaking; the extent of the debate currently seems to be whether a whisky should be chill filtered or not. Chill filtration is a clever process in which the mature whisky is chilled down to -2'c or thereabouts. This causes some compounds to come out of solution - become chunkier essentially - so when the chilled whisky is then passed through a filter, these newly chunky compounds are caught and removed. The filtered whisky no longer contains compounds that form a haze, so it will remain bright and crystal clear in the bottle even when cold. This is purely an aesthetic consideration - the industry reckons that if a customer saw a hazy bottle of whisky on the shelf they would presume it was faulty. Chill filtration has been used in whisky production for decades and the majority of whiskies on sale today have been through this process.

However, some producers have stopped doing it, arguing that these potential-haze-forming compounds were actually responsible for flavour and body in the whisky, so removing them leaves a thinner, less characterful whisky. They faced the same concern though - that a customer won’t buy a hazy whisky. In order to avoid this they bottled the whisky at 46% abv or higher; the long-chain esters and haze-forming compounds do not come out of solution easily at this strength.

But proclaiming 'non-chill filtered' on a whisky’s label only tells part of the story.

Now, you will always need to do some filtering. You most definitely would not want to drink the fragments of charred wood that come out of the cask when you disgorge it. So at the most basic level, you're going to be draining the cask through a fine mesh that will catch these bits of char.

You also need to remove any fine dust or bits that might have got into the disgorging vat, so you pass the whisky through a filter before it lands in the bottle. It's here, however, that the little-discussed subtleties of filtration are built in.

We knew we definitely didn't want to do chill-filtration, but the filtration technology company explained that we needn't worry, even without chill filtering there were industry-standard filters we could use that would ensure a beautifully bright and ‘polished’ whisky. This seemed a bit weird – he was talking about removing esters (flavour compounds) to make the whisky look prettier, whilst still proudly being able to state ‘non-chill filtered’ on the label. Fully acknowledging that we're very new to this business and happy to take expert advice, we handed over samples of our not-quite-whisky to be put through various filter levels.

We were tasting our young single malt spirit at 20 months as a control sample, and then 3 samples at increasingly fine levels of filtration, down to 3-micron, all at 46% abv. We also tasted each of those samples diluted down to about 20% abv to amplify any differences in flavour or texture. So that was 8 nigh-on identical samples. An almost impossible task, especially for people new to professional nosing, like us. In tasting samples like this it's more a matter of gut instinct; at a push you can say you prefer one to another. So you whittle them down; I prefer sample 3 to sample 7. And on, and on. Eventually you admit defeat - write down a list of numbers starting with your favourite (don't know why it is, it just is) ending with your least favourite (likewise). Miraculously, all three of us had the same favourite and the same least favourite. Maybe we're not so bad at this tasting lark after all.

The surprising bit - we all chose the 50-micron, 'course filtered' sample as our favourite. The nice man from the filtration company is looking quite flustered at this point. Apparently, everyone goes down to at least 3 microns, it’s industry standard practice. But we reassure him - all the single malt spirit we sell in the shop has only been through one of these coarse filters and we've never had any complaints about it looking hazy or about fine sediment collecting at the bottom of the bottle.

So it's decided (to his disbelief) that we'll just do the same basic filtering that we've done so far. If people start complaining that there's unsightly sediment in our bottles then we will reassess. We never wanted to chill-filter because we don't believe in putting aesthetic considerations over flavour and mouthfeel. So that same philosophy should apply here too - we're just going to produce the best tasting whisky we can. And that's a big part of what we're doing at the distillery with all our products - we're making traditional products certainly – but when you drill down to the tiny details along the way, we're not too bothered about doing things ‘because that's how everyone else has always done it’. If we can find a way that makes it taste better - be that different yeast strains, higher botanical loads or coarser filtering - that's what we're going to do. We hope you enjoy the results.


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