The types of filter elements available for use in the Handtmann "Multi Micro System" multiple sheet filter (described in Brauwelt, 20 May 1993, 133(20), 863-872) are listed and their application to the removal of microorganisms from beer is discussed. Trials have shown that even beers artificially contaminated with spoilage bacteria at cell concentrations of over 250 million cells/ml can be rendered virtually sterile using appropriate filter elements. As the filter unit is small (having a liquid contents volume of only 3 hl for a throughput capacity of 200 hl/hour) and is purged with carbon dioxide before and after use, there is little or no need for filtration liquor to precede the beer into the filter or to wash the last of it out. Air is also effectively excluded, reducing oxygen uptake below the detection limit, so that beer quality is not significantly affected. One possible source of problems affecting filter performance is the leakage of kieselguhr, PVPP, etc., from filters upstream of the "Multi Micro System", which can cause irreversible clogging, but is unlikely if the primary filters are well maintained. Depending on the concentrations of microorganisms and other particles remaining in the beer after primary filtration, the "Multi Micro System" may need to be backflushed with warm water and sterilized with hot water after every filtration run or as infrequently as only once a week. If the filter sheets become clogged with organic material (microorganisms, proteins, beta glucan, etc.) they can be regenerated by backflushing with 1% caustic solution. Because the whole filtration surface of the filter matrix is under a constant pressure, variations in flowrate or liquid pressure have little effect on performance, and it is possible to interrupt and restart the filtration process at any time without any risk of letting microorganisms pass through. This enables the filter to be installed directly upstream from the filling machine of a packaging line, without any need for a buffer tank. Larger versions of the filter incorporate hydraulic lifting units to facilitate the rapid and safe removal and replacement of the filter elements.
Keywords : beer filter sheet performance sterile filtration