I’m considering purchasing some kind of filter system for my beer. What type of filter should I use, and how is filtering best done?
Often you can achieve mature, clear beer without filtering if you have the time available to let natural processes work. However, in a commercial environment, brewers frequently filter the beer to reduce the time needed for their beer to clear so they can get it to market more quickly, as time is money. They also want to remove the yeast from the beer before bottling to avoid shelf-stability issues.
At a homebrew level, filtering is best done between two kegs. Most homebrewing filters are inline filters you set in the transfer line between the two kegs. The beer is forced using CO2 pressure from the source keg through the filter and into a clean destination keg. You can filter a 5-gallon (19 l) keg in as little as 10 to 15 minutes, which is a quick way to get your beer cleared.
There are several different types of filters available. I recommend staying away from simple water filters because many are not really sized or designed to handle beer yeast and sediment. Ceramic and carbon water filters can also alter the flavor of your beer. Most homebrewing filters are single-use paper filters designed with either a canister or plate layout. Of the two, I prefer the plate-style filters because they offer a wide surface area and are less prone to clogging. Although the paper filters are generally single use, you can filter multiple batches on the same day with one set of filters if you plan ahead.
Perhaps as important as the filter layout is the filter size. To remove all yeast and sediment from the beer, you generally need to go down to 1 micron in size. However a 1-micron filter is also prone to rapid clogging. To solve this problem, the best idea is to use a two-stage filter with a coarse 3- to 5-micron filter at the first stage and a finer 1-micron filter at the second stage.
Before using a filter, you want to sanitize it—along with the hoses— properly and run some clean plain water through it to flush it. This is also useful because some units are prone to leaks, and you want to resolve any leaks before filtering your beer. I also recommend filtering your beer cold if possible. Chill haze in beer is the result of small molecules that bind at lower temperature, so cold filtering your beer will remove more of this haze.
Filtering is not for everyone. As I said at the beginning, you can accomplish the same results in most cases by simply giving your beer additional time, but when you don’t have the time and want your beer cleared quickly, filtering is a good option.