Practical Guide to Filtration

One of the first differences beginning brewers may notice between their creations and commercial beer is clarity — or a lack thereof. I can remember when I’d sometimes run across a slightly cloudy beer and be completely convinced it was spoiled. Of course this was long before I started brewing beer or knew much about it. The haze I’d find in the occasional commercial beer could have been normal or due to contamination; I wouldn’t have known the difference.

Now, with the widespread availability of ale on tap, it’s common all across the country to find beer that is served less than crystal clear. At a local brewpub (home of what I feel is the best IPA on this earth) the opaque hefe-weizen is one of its most popular beers. In fact extremely clear or “brilliant” beer is almost a sure sign of filtration and often cause for some negative comments among beer drinkers I know.

Still, there’s a huge difference between the appearance of a commercial, stripped lager and that hazy homebrew that refuses to clear on its own. Many brewers would prefer something just a little cleaner looking and would prefer not to wait for months for the last particles to settle out on their own. It’s especially satisfying to serve a glass of your own beer that has the color, head, aroma, and clarity of a fine commercially brewed product.

Like every other aspect of amateur brewing, the popularity of the craft has opened up a market niche for filtering equipment — a niche that many enterprising manufacturers and suppliers have been only too happy to fill. If you’ve thought filtering might be something you’d like to try, there is plenty of filtering equipment available from which to choose. But before getting into equipment, let’s talk about haze.

Types of Beer Haze

Any particles of material that stay suspended in the beer and make it less clear than desired can be called haze. There are two broad types of beer haze: haze due to living things (biological), and haze due to everything else (non-biological). Most brewers would probably want to distinguish between biological haze due to bacterial or wild-yeast contamination and that due to brewer’s yeast.

Filtration is not the answer to bacterial contamination in beer. The proper fix is better brewing practices. Generally, contaminations will show up with a number of other symptoms —haze will be the least of your problems. For the all-grain brewer one such tell-tale symptom is the fermentation that never seems to end. An incredible acidity and a gravity that hits 1.000 and continues to drop are sure signs of a long lost batch. Cloudiness isn’t an issue.

Likewise, filtration is not really the solution for removing extraordinary amounts of brewer’s yeast. With good aeration of the freshly pitched wort, a fermentation allowed to complete, and careful handling of your beer during racking, enough yeast should settle out of the beer to leave it only very slightly hazy. Some yeasts, such as the British ale yeasts from Wyeast Laboratories for example, settle out quickly and very completely, leaving exceptionally clear ale even without fining agents.

That brings us to non-biological hazes. This group is further divided into two major categories: chill haze and permanent haze. If clear, finished beer reveals a haze when chilled to near 32° F but appears clear when allowed to warm to room temperature, the beer is said to have a chill haze. If the uncontaminated beer is hazy at all temperatures, it’s said to have permanent haze.

The bulk of these hazes are caused by proteins and tannins. Hazes are formed as proteins and tannins join and get large enough to become visible. It’s also possible for amateur brewers to experience starch haze due to incomplete mashing of all-grain recipes or due to the use of more adjuncts than can be converted during the mash.

Filters and Filtering

The concept of filtering is a purely mechanical one and very simple: build a screen with holes in it too small to allow the passage of the particles you don’t want in the final product. Then build this screen large enough that as the holes are blocked by particles, enough passageways remain to allow the flow of the liquid you’re trying to filter.

Filtering billions of microscopic particles from beer with filters small enough to be practical requires pressure. The beer has to be forced through the filter material under enough pressure to ensure that as the passageways are plugged, new passageways are found. Therefore, any practical filtration of beer requires the use of pressure to drive the beer through the filter material. The only practical solution for amateur brewers is a complete CO2 kegging system. The bottom line is this: If you want filtered beer, you’ll need to invest in a kegging system.

Filters all share some basic design features. Beer enters an inlet, is forced to pass through some sort of filter material, and exits an outlet. The filter material may be an integral part of the filter housing or may be a removable cartridge. Filters commonly sold for household drinking water use are exactly the same used for filtering beer. Polypropylene is the most common filter material, available in three styles: wound, spun, and pleated.

Filters are most often rated by the average size of the particles they will filter, with the size given in microns. Filters intended to keep out rust particles for household water systems may be rated “nominal 20 microns” for example, while those intended to filter out bacteria may be rated “nominal 0.4 microns.”

A pleated filter is basically a sheet of very finely spun plastic that is folded, or pleated, much like an auto air cleaner. The pleating increases the surface area of the filter (more passageways) while keeping the overall size of the filter to a minimum. The liquid to be filtered is forced from the outside of the pleated cylinder to the center, then out through the filter housing outlet.

A wound filter looks like nothing fancier than a spool of white cord. The plastic fibers are first made into a heavy cord about two millimeters in diameter, then the cord is wound onto a perforated plastic, cylindrical spool. The liquid to be filtered is forced to pass from the outside of the winding to the inside, through the perforated cylindrical spool, then out through the filter housing ( Figure 1). Wound filters are usually available only in a 20-micron rating and are useless for filtering anything but trub from your beer.

Spun filters look a little like stiff foam packing material and are usually available with a five-micron rating. The cartridges have the same overall dimensions of the pleated and wound filters, and load the same way into the filter housing.

An important aspect of these filters is their rated efficiency. The efficiency rating of a filter reflects the percentage of passed particles smaller than the filter’s micron rating. For example for a 0.5 micron pleated filter rated 99.8 percent efficient (a $35 to $50 filter cartridge), only 0.2 percent of the particles it allows to pass through will be larger than 0.5 microns.

Although the spun filters available at plumbing or building materials stores are rated “nominal five microns,” usually they don’t have efficiency ratings shown.

Ceramic materials are also used for household filtration systems, particularly those that are intended to remove bacteria. These filters are too fine for beer filtration use because they remove particles so small that color and flavor are degraded. Such extremes of filtration are used in the commercial megabreweries, since neither substantial color nor overwhelming flavor are desired properties of the super-light lagers.

If you want to experiment with the variety of filter cartridges available, then choose a filter system that supports replaceable filter cartridges. After looking around at the products available, you’ll discover that many cartridges work in several popular canisters. By choosing a system that’s well supported by a local store or other supplier, you can decide for yourself if a 0.5 micron filter affects taste or if a one-micron filter leaves your beer clear enough.

Filters suitable for beer are available from many sources, including your favorite homebrew supply shop, many mail-order shops, and even the local home improvement or plumbing shop. Most of the filters sold for homebrewers are in fact just “under-sink” or “whole-home” filter canisters with replaceable cartridges. These systems are built to be plumbed into your household plumbing with standard pipe fittings and can be easily set up with hose barb fittings for both inlets and outlets. Three filters are shown in Figure 2 (page 40). Two have re-usable, replaceable cartridges, while the third is a low-cost unit with a non-replaceable filter that can be re-used.

An advantage of selecting a filter from your homebrew supply shop or a homebrew mail-order house is that it will come with all the fittings you need to connect the filter to your CO2 and keg system, and the supplier will sell a filter that is appropriate for beer filtration. On the other hand if you decide to do it yourself down at the building materials store, find out which cartridges are routinely available.

Preparing the Filter Assembly

As always, everything that comes into contact with the beer should be sanitized, and you always want to avoid aeration. With a CO2 kegging setup, it’s fairly easy to meet both requirements. These procedures apply to the canister-type filters available at plumbing shops, hardware stores, and at all the nationwide home improvement chains.

First, filter housing caps generally have inlets and outlets threaded for standard 3/8-inch threaded pipe (3/8-inch NPT), and often come with plastic adapters for 1/4-inch copper water supply lines for under-sink use and for filtering icemaker water supplies. A convenient way to set up these filters is to buy brass adapters with male 3/8-inch NPT on one side and male 1/4-inch copper flare on the other. The 1/4-inch male flare fitting is the same as that found on the quick-disconnect fittings used in home kegging systems. Using two pieces of 3/16-inch vinyl tubing (the kind used for kegging systems) with all ends fitted with 1/4-inch swivel nuts, you’ll have a very flexible setup. Figure 3 shows the parts and order of assembly. Use 1/2-inch white Teflon plumber’s tape wrapped tightly two to three turns over the threads on the adapters.

Now it’s time to assemble the filter and hoses and conduct a pressure test using CO2 pressure. First, connect a 1/4-inch swivel nut to the pressure tubing attached to your gas regulator using either a hose clamp or a crimp-on clamp. Then, with the filter cartridge removed, fill the lower filter housing with water and thread the cap into the housing, ensuring that the rubber washer or o-ring seal is in place and lightly lubricated with Keg-Lube or similar non-petroleum lubricant. By filling the housing with water, you can safely pressure test the assembly — if a failure occurs, parts won’t be launched like missiles by a huge increase in gas volume.

Keeping the filter upright, connect the CO2 tank gas line to one of the 1/4-inch male flare fittings on the filter housing cap (it doesn’t matter which one), and connect the 3/16-inch vinyl hose to the other filter cap flare fittings. Cap the end of this hose with either a picnic faucet or a quick-disconnect fitting. Tighten all joints lightly with a wrench.

Keeping the filter upright, immerse the entire assembly and all joints in a large bucket of water. Make sure the regulator screw is backed out of the regulator (it should jiggle slightly if it isn’t applying pressure to the regulator), then open up the CO2 tank. Proceed slowly and cautiously when pressurizing. Begin applying pressure to the system by threading in the regulator screw, starting at 5 psi, then 10 psi, and finally 15 to 30 psi. During this process, tighten joints moderately to stop bubbles. If you have a lot of leakage at the adapter fittings, you may have to pull the fittings and redo them with more wraps of Teflon, then reassemble and try it again.

Prior to using a new filter cartridge, assemble it in the housing and flush it with water for 10 to 15 minutes or per the manufacturer’s instructions. You can do this in the kitchen by using the same setup used for a chiller coil. With a garden hose adapter threaded into the spout on the kitchen sink, connect a three-foot length of washing machine water-supply hose. The hose is modified by cutting one end off. That end fits snugly over the 1/4-inch male flare fitting on the filter housing cap; it’s held on securely with a hose clamp. Make sure to connect the flush water source to the in side of the filter assembly.  Backflush when you’ve finished filtering the same way but with the hose connected to the out side of the filter.

After testing, you have a setup that can be used to filter beer and, with an appropriate shut-off valve and activated charcoal cartridge, one that can normally function as an under-sink or icemaker filter too. With a little imagination you can now see how funds from the household maintenance budget can be diverted, or rather “leveraged,” for other purposes.

Closed-System Filtration

The goal is to transfer unfiltered beer from one keg, through the filter, and into the final dispense keg without aeration or contamination. This is the kind of beer-handling challenge that makes home kegging systems such a joy.

If you haven’t already done it, sanitize a Cornelius keg as you normally would, transfer the beer from your fermenter into this keg, then purge with CO2 and seal the keg. Sanitize a second Cornelius canister, and purge and seal it as well. Finally, sanitize the filter assembly and the two transfer hoses used to connect the filter to the two Cornelius kegs. This can be done easily by filling the housing with sanitizer, installing the filter cartridge, and assembling the filter and hoses. After an appropriate soak time drain the filter assembly out through the hoses, then connect all equipment. The airlock tube can be your picnic faucet tubing with the faucet held open with a rubber band. Put this tube into the airlock first, then attach the quick-disconnect to the dispense keg.

After all equipment is connected, begin applying pressure slowly to the system while monitoring for leaks. Minor leaks are just an inconvenience; you can tighten things up as the transfer proceeds. Hold the filter housing upside down. As the source keg empties gas will flow into the assembly, forcing the remaining beer through the filter. When the transfer is complete, remove the quick-disconnect at the airlock side of the system first, then the quick-disconnect at the inlet to the dispense tank.

Finally, remove the gas-in disconnect at the source keg and attach it to the gas-in side of the dispense tank. Pressurize the dispense tank as you normally would and start chilling.

Procedures are basically the same for non-cartridge filters. You can also add adapter fittings to this filter as suggested for the cartridge units. That way, the hoses you’ve terminated with swivel nuts can be used elsewhere when the filter is not in use.

Filter Care

Filter manufacturers make all sorts of claims about filter lifetimes and the amount of beer that can be filtered with a single cartridge. It’s almost impossible to predict these numbers, since there’s no way of knowing how much junk is in the beer being filtered or how the filters are being cleaned between uses. A used filter allowed to dry out completely can become useless quickly depending on your water supply and other factors such as mold growth.

One way to extend the useful lifetime of a filter is to backflush it after use. A backflush of warm water and completely dissolved TSP, followed by a complete cold-water rinse, can help tremendously. But you won’t get out all of the particles embedded in the filter material. In time you may find you have to use extremely high pressure to get any reasonable beer flow. At that point it’s time to get a new cartridge.

The Choice Is Yours

If you already own a kegging setup or are planning to get one, filtration is a convenient process that will only make your equipment investment more versatile and slightly more expensive. Still, you’ll have to be the one to decide if the extra clarity is worth the effort and investment. One thing is certain: Because of the variety of equipment offered by hardware stores, mail-order companies, and homebrew supply shops, setting up a filtration system is easier than ever.

Issue: August 1997