I recently saw a neon sign in a store window that read Cold-Filtered MGD. It got me thinking about cold -filtration and what it means. First of all, as far as I know all filtered beer is cold-filtered. I've never heard of anyone filtering a beer while it's warm and there is a reason for that, which I'll address after we examine why beer is filtered.
Beer is filtered to produce a more stable and bright (very clear) final product. The filter removes small particles such as yeast and proteins that can make beer appear hazy. Why we filter beer cold has to do with two compounds found in finished beer, proteins and phenols. These proteins and phenols will bind together in a protein-tannin complex when cooled to temperatures near freezing. This complex is heavy enough to precipitate out of beer on its own if left undisturbed long enough. But, in order to move beer more quickly from the cellar to the tap, these protein-tannin complexes can be filtered out. If beer were filtered warm these complexes are not formed and the two constituents separately can pass through the filter, only to bind together again when the beer is chilled, causing haze. When beer is cold-filtered the complexes are intact and have a large enough particle size to be trapped in the filter medium.
So while it is true that cold-filtration is a quality enhancing procedure, using it as a marketable attribute would be akin to running as ad campaign stating, "Our beer is brewed with water." Which would be true of course, but all beers are brewed that way.
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