Google using a brita filter.

There was a story a couple years ago about some college kids using one
to purify cheap vodka.

I believe the end result after three passes was that you couldn't tell
the difference between cheap stuff and expensive.

John Public wrote:
> I use rum/vodka to fortify wine and make liqueurs, and I noticed
> something strange when I shook a bottle of plain white rum. (The same
> thing happened with vodka.) When I shook the bottle, the liquid's
> appearance changed in three quick stages:
>
> - cloudy all over (first 1-2 seconds)
> - started to clear, but a thin layer (< oz.) of white foamy/starchy
> substance surfaced (3-7 seconds)
> - everything cleared back to normal (8-10 seconds)
>
> I'm aware that cheap alcohol is usually not filtered as much as
> top-shelf brands, so I'm suspecting the shaking caused a temporary
> "centrifugal effect" that, for a short time, surfaced many of the
> impurities. If I poured out the little oz. or so of the foamy liquid,
> would the remaining liquor be cleaner?