Sterile Filtration, a form of filtration fine enough to remove spoilage organisms. For beer, “sterile filtration” is understood to reduce yeast and beer spoilage organisms to extremely low levels, such that the packaged product will last for its intended shelf life, which may vary by brand, region, or market. Sterile filtration does not promise the complete absence of microorganisms and generally describes the reduction of organisms without the heat treatment of beer as used in tunnel or flash pasteurization. It can also be referred to as “cold sterilization” or “draught filtered.” A typical laboratory quality assurance value for sterile beer would be less than 1 cell per 100 ml of beer.

Sterile filtration can be accomplished in different ways. It can take place in successive depth filtrations using kieselguhr filters, with depth filtration via a single pass on a sheet filter, or with absolute filtration on a cartridge filter. Normally, any pore rating on a filter with 0.45 μm or less will yield sterile beer.

Proponents of sterile filtration claim that it avoids any negative flavor changes that may come from pasteurization, but the process will have higher costs because of the increased equipment and operating costs. Other brewers, including those brewing more flavorful beers, believe that sterile filtration can remove body, aroma, and color from beer and therefore approach such technologies cautiously. Regardless, sterile filtration cannot be seen as a replacement to poor brewing practices upstream and it only works as the very last step in a well-run brewing process with care toward proper cleanliness and proper maintenance.