The background: I brewed up 10 gallons of an all-malt lawnmower beer (OG=42, FG=10, IBU=17) to serve at a recent picnic from the keg. I didn't want to have the yeast sediment stirred up (like last year) so I decided to filter.
This is the filtering setup I used, http://webpages.charter.net/patriot-bre ... Filter.JPG
I purchased it from More Beer. It comes with a 1 micron filter. I also picked up a 3 micron. From the data, these spun poly filters are 85% effective at a given rating. An absolute filter would be essentially 100% effective at a given rating. I decided to use the 1 micron filter.
It was simple to use. Sanitize the filter housing (not the filter), the lines, insert the filter, purge the receiving keg and filter of air, and filter. I applied 3-5 psi. Both kegs of aged, flat beer took a total of 20 minutes to filter. After use, clean the housing and discard the filter. The filters can handle 200 gallons, but they don't recommend reusing them. I could see the stream of sediment going into the filter, but none was leaving the filter. Since the proof's in the pudding, here's what a typical keg looks like with no filtration
http://webpages.charter.net/patriot-bre ... %20Keg.jpg
and here's what the picnic batch looked like after filtration
http://webpages.charter.net/patriot-bre ... %20Keg.jpg
(Please note: these are not from the same batch! I don't have a picture of the pre-filtered picnic batch, so I used another keg I had)
It's important to know you should really only filter flat beer. Force carbonate it after filtering. Why? Well, I also decided to filter 2.5 gal of my carbonated pale ale. Once the beer hit the filter, the CO2 started outgassing--bubbles everywhere. I had to increase the drive pressure slightly. By the time I got done filtering it, which took almost as long as the two kegs of flat beer, foam came out of the vent relief. That's right...2.5 gals of beer AND 2.5 gals of foam. Good thing it wasn't a full keg to start with.
Ok, I know. You want to know about stripping. Everyone hears filtering strips the beer, and I suspect alot of people don't filter because of stripping fears. Well it does strip to a certain degree, once you start getting below 1 micron. The texts I've read from the late Dr. Fix and on brewing lagers, suggest a 3 micron (absolute) polish filtration--which reduces yeast biomass to the point where it's invisible to the naked eye-- doesn't affect body, color, or bitterness/aroma. So you get the benefits of filtering and the benefits of having yeast remain in contact with the beer. Even at 1 micron (absolute) there's a very minor drop in these figures. The stripping really takes off below 0.5 micron. I rationalized that my 1 micron (85% effective) filter should perform similar to a 3 micron (absolute) filter.
To be honest, I did before and after taste samples and I couldn't detect a difference other than clarity. I even took before and after hydrometer readings--they had the same readings. I also measured the pale ale which had an OG=65 and FG=16. The filtered version still had an FG=16. I also couldn't detect any difference in color, even by placing the hydrometer jar samples in front of a white background.
And the beer tasted great--at least that's what everyone said
. A side benefit of filtering under CO2 is that you'll be able to scrub any green-beer volatile aromas (sulfur, etc.) out during the transfer. Also, don't prematurely filter--you'll want the bulk yeast during aging to be there to properly condition your nectar. Then filter, force carb, and serve!As for me, I plan on doing more filtering. Hope this helps, let me know if you got any more questions.
v/r
Bill
