Don’t fear the filter

Filtration is one of the things which I never understood before I got to see it happen a few days a week. As I didn’t understand it, I say it as a bad thing, something only the big breweries did as part of their flavour-reduction mission, but I was wrong.

This is the filtering process I know (there might be other ways of doing it): unfiltered beer from the tank mixes with kieselguhr, a diatomaceous earth (which Wikipedia explains better than I can). The kieselguhr catches the yeast still left in the beer, clumps it together and this then gets left behind on a gentle plate filter (you can choose how fine or coarse you want the plates to be) which the beer passes through. So it goes in cloudy and comes out clear and the process is there just to remove the haze. But it’s about the flavour and that’s important.

Filtration inevitably removes flavour as it passes through the filter, but what is left behind is just yeast so what you find is that the flavour changes, the body changes and your perception of the beer changes. I can give the three examples I know: a lager, pale ale and wheat beer.

First, the one that’s unfiltered: wheat beer. It’s all about the yeast in the beer and you can taste and feel it when you drink: it’s got a fullness to it, a fatness, a juicy roundness. The yeast is there to give texture, flavour and aroma – it’s very different when it’s not cloudy and it becomes drier and crisper, lacking the creaminess that you want from wheat beer. The beer is tastiest cloudy.

Lager is the best way of showing filtered beer: unfiltered it has a rich fullness to it, a rounded flavour profile, a softness; filtered it becomes dry, crisp and sharp. Lager should have a snappy finish to it and so filtration is key to get that refreshing quality (though I do totally adore unfiltered lager, it’s just a different drink to the filtered stuff). It’s similar with pale ale: you want the hops to be bold but in unfiltered beer you’ve got other stuff softening the bitterness and wrapping it in the roundness of yeast. By filtering you take the roundness and make it sharper. It’s like a sentence which ends with a dash or one which ends with an exclamation mark.

Then there’s fining. Have you ever seen a pint of isinglass – the dried swim bladders of fish – before they go into a cask? The first time I saw it I almost posted back my CAMRA card. I’m okay with knowing that there’s something in my beer which makes it clear, but it looks like a pint of body fluid and makes me think of a story my mate Matt often tells: he was on a big night out and one of the group was sick into his pint glass. A bit later he was back drinking from the same pint: “It’s ok,” he said, “it’s sunk to the bottom.”

Drinkers don’t want opaque beers. Every beer is different: some styles are better filtered, others are better unfiltered, some work best with isinglass pulling the yeast to one side (though only in cask beer). Sometimes I want my lager to be unfiltered but it’s doing a different job to if it’s the crisp and refreshing filtered version; the flavour changes, the body is different, the beers are different, but both are good.

Filtering isn’t beer’s F-word. 


UPDATE: In trying to talk about the good side of filtering, I left out a whole paragraph about the bad side of filtering, because not all of it is gentle and not all of it is done as described above (the DE filtration described is the only one I have experience of). See comments below for more where I stopped. As for the 'triple filtered' Stella Artois, I suggest they need a new filter that does the job once.