Membrane filtration maintains beer freshness and microbial stability
Membrane filtration technology is taking an increasingly large share of today’s beer production applications. Compared to traditional diatomaceous earth filtration, cross-flow filtration is now well established and the trend towards “sterile” membrane filtration of beer is changing, although it still has some way to go.
There have been perceived challenges to the microbial stability of membrane-filtered beer compared to heat treatment techniques such as pasteurization and instant sterilization. In the brewing industry, no one likes heat-treated beer, but safety requires that it be treated. More recently, the historical notion that “sterile” filtration of beer using cartridge membranes was expensive and unsafe has been proven wrong.
Membrane filtration technology is evolving very rapidly and is superior to pasteurization in many areas. Over the years, high-end brands in China, Japan, Korea, the U.S. and Europe have moved away from heat treatment and have adopted membrane filtration to maintain microbial stability. Unpasteurized beer has created awareness of the freshness and natural quality of beer, which is in line with consumer trends and has a competitive advantage in the market.
To drive this trend, Pall Food & Beverage has developed a new CFS Neo filtration technology, which has been successfully applied by more than 250 companies worldwide.
1. Basic Knowledge
Brewers use the term “sterile” in a pragmatic way to denote a product that is microbiologically stable, rather than one that is completely devoid of any microorganisms. The term applies whether brewers use heat treatment or membrane filtration techniques to maintain the microbial stability of their beer.
The International Codex Alimentarius Commission (WHO/FAO) CAC/RCP 40-1993 defines “commercially sterile” low-acid foods as having no microorganisms capable of growing in the beer during its production, distribution and storage under normal, non-refrigerated conditions. Therefore, the purpose of aseptic filtration is to remove spoilage bacteria that may cause product quality deterioration at later stages of distribution. The term “aseptic” in this document refers to “commercial aseptic”.
2. Cluster Filtration Systems
In the 1980s, the first installations for final membrane filtration of beer were based on a large multiple cylinder filter jacket, coupled to an existing CIP system and installed downstream of a diatomaceous earth and plate filter. In the last decade, along with the growing interest in sterile filtration of beer, the design has gradually changed and the filtration system design is now better suited to the specific application and process. The first cluster filtration system was introduced to the brewing industry in 1993 and overcame the disadvantages of large multiple cylinder jacket installations by installing multiple cartridges in a single unit, see Figure 1.
With cluster filtration technology, the filter cartridges used for beer filtration are arranged in a numbered arrangement, with each of the seven filter cartridges forming a bundle that operates together during beer filtration and completely separated during cleaning, regeneration and integrity testing.
The original cluster filter design was based on a large vessel that held all of the filter cartridges, divided into bundles, each carrying 7 x 40″ cartridges, with each bundle of cartridges opened and closed by a separate valve, see Figure 2.
The CFS Neo design further optimizes cluster filtration technology by replacing large vessels with small cluster housings, each housing a 7 x 40″ cartridge with cluster filters arranged in parallel, each controlled by an independent discharge valve, see Figure 3. The modular design reduces water and detergent consumption and reduces beer losses compared to standard multi-cylinder and large cluster vessel designs. The modular design allows for great flexibility in production capacity, allowing for 50 to 600 hl/h of beer.
The new CFS Neo filtration system includes: filter modules with jackets, each holding 7 x 40″ cartridges; a coupling module for beer entry and exit and CIP entry and exit; a membrane cleaning module (CIP) with all associated components for rinsing, cleaning and regeneration systems, independent of the periphery and parallel to pipe cleaning; and an integrity testing unit. Control Panel. Batch or continuous operation is possible.
3. Pasteurizer Replacement Cartridge PARE
To round out the design of the new CFS Neo system, Pohl has developed a special product for Pasteurizer Replacement Elements for Beer (PARE), consisting of a series of pre-filters and hydrophilic membrane filters that are combined with the CFS Neo system, see Figure 4.
The sterile filter cartridges are suitable for repeated hot water sterilization and on-site steam sterilization cycles to extend their useful life in the CFS Neo system. They are also suitable for the removal of microorganisms unique to beer. The support and drainage materials are optimized for greater mechanical strength. Repeated hot water, chemical and steam sterilization applications increase beer filtration capacity and reduce brewers’ operating costs.
4. Microbiological Safety
The company’s PARE cartridges for beer filtration have microbiological requirements for the main beer spoilage bacteria and yeasts, describing the microbiological performance of the filter in operation. This requirement is usually a periodic evaluation of microorganisms that have grown in the specific growth medium of the beer under specific conditions. The filter pore size itself is indicative of microbial removal, but is not guided by any internationally accepted standards or codes and therefore is not a true evaluation representing a safe level of performance.
A comparison of the microbial effectiveness of membrane filtration and heat treatment in general is favorable in support of cold filtration of beer, see Figure 5. Under normal pasteurization (15-25 PU), the microbial effectiveness of membrane filtration is 103-104 log higher compared to heat treatment of beer, both for instant sterilization and tunnel sterilization of beer.
An important advantage is that membrane filtration removes cells and spores, whereas heat treatment merely inactivates the cells. This leaves dead cells in the beer, limiting the effectiveness of DNA-based analyses such as PCR analysis.
5. Integrity Testing
Integrity testing is used to test and document the filter’s ability to remove microorganisms in practice, and such integrity testing must meet the following criteria.
(1) Fast, simple and repeatable procedures with clear criteria and documentable test results.
(2) The specific parameters used to characterize the filter material and filter element in use.
(3) Non-destructive testing that does not affect the filter material and can be repeated, usually after each cleaning and disinfection.
(4) Challenges associated with live bacteria – represents the ability of the filter to remove microorganisms from the filtration process.
The sensitivity of an integrity test measurement is a direct function of the surface area of the membrane being tested. As the number of filter cartridges tested increases, once the limit of discrimination is reached, the integrity test itself becomes less accurate and can no longer provide a direct relationship between the test value and the actual microorganisms trapped in the filter. This problem of discrimination can lead to erroneous delivery of results that could potentially cause microorganisms to accidentally penetrate through the filter and into the packaged beer. This problem can be eliminated using CFS filtration techniques, where up to 7 cartridges can be tested simultaneously.
If the integrity test results are negative, the CFS Neo system automatically separates the special cartridges and applies the remaining cartridges throughout the process. As a result, in the event of a cartridge failure, beer production can continue. Approximately 25% of the installed cartridges can be shut down without any impact on filter safety or performance. During the next production shutdown, the identified cartridge jackets are opened, the malfunctioning cartridges are identified and replaced.
6. Pre-Treatment Of Beer
The upstream clarification process is important for “sterile” filtration and affects the economics of the sterile filtration process. Cross-flow membrane systems usually provide sufficient pre-clarification so that no further elaborate filtration steps are required. Pohl’s Profi technology demonstrates that sterile filter cartridges can achieve good pre-clarification results even at maximum service life. Diatomaceous earth filters in combination with plate filters also provide good pre-filtration for membrane filters, however, diatomaceous earth filtration affects the service life of the membranes and causes gelatinous or granular turbidity. Therefore, it is recommended to apply depth filtration upstream of membrane filtration. For the safe and reliable separation of particles and colloids in beer, the CFS Neo system also comes with an integrated pre-filter (upgrade). the PARE cartridge filter family includes two pre-filters that primarily handle high colloidal loads and high particulate loads from diatomaceous earth filtration.
7. Cleaning Of Membranes
The rinsing and cleaning procedures and frequency determine the economy. The frequency of washing is directly related to the beer filtration output and the pressure differential. After a certain amount of filtration, hot water rinsing is necessary, even if the differential pressure does not increase significantly. The specific quantity of filtered product depends on the pre-clarification and filtering capacity of the beer. Lager allows a longer life cycle than stouts and draught beers. The main factors influencing the filtration capacity are the various glucan fractions, protein content, iodine value and turbidity.
In the chemical cleaning process, a standard lye solution of 0.5 to 1% and a temperature of 65°C are most common. If the water hardness is high, fouling may be a problem, and in this particular case, the concentration and temperature of the alkaline detergent can be increased appropriately.
Cartridge life can be significantly extended through the use of enzyme regeneration. Commonly used and effective are cellulose-based enzymes, which hydrolyze the (1,4)-β-D-glucosidic bonds in cellulose and other β-D-glucans and stimulate β-glucanase activity. In a few cases, other enzymes may be selected, depending on the blockage. This needs to be evaluated on a case-by-case basis, in close cooperation with the filter membrane supplier.
Application of enzyme regeneration, combined with alkaline cleaning and flushing, as required by the recommended procedure, can extend the life of the cartridge filter and reduce filtration costs, see Figure 6.
8. Specifications Of The Membrane
The correct membrane size has a significant impact on filter cartridge life. The installed filter area is an exponential function of the filter’s filtration output. Doubling the filter area can result in a fourfold increase in cartridge life. The ideal beer filtration process strikes a balance between maximizing beer filtration throughput at low flow rates and maximizing regeneration capacity at high cleaning rates during beer filtration.
Ideal filtration conditions are low and moderate flow rates (0.5 to 1 hl/10″*h) during beer filtration and high intensity flow rates (3 to 8 hl/10″*h) during rinsing and cleaning.
Membrane sizes that are too small for beer filtration (>1.5 hl/10″*h modules) have a direct impact on the life of the filter cartridge and, therefore, on the total cost of ownership. The savings in capital expenditure are quickly offset by higher operating costs over the life of the system. Insufficient flow during flushing and cleaning can lead to partial membrane fouling, which again affects filter throughput and operating costs.
Individual filter jackets have always sought a compromise between these two requirements, so cluster filtration technology has been developed to meet both criteria.
9. Installation
The main advantage of cold aseptic filtration is that the filter is installed directly upstream of the filling line, without a buffer tank. The membrane with a stable substrate maintains its separation characteristics at different flow rates and pressure differentials, including start/stop conditions. During the filtration process, the CFS Neo thus acts like a pipeline. It provides maximum microbiological safety, minimum beer loss and real flexibility during beer brand changes and start/stop operations.
The elimination of the buffer tank upstream of the filling equipment avoids critical recontamination points, minimizing beer loss during production start-ups and brand changes, and reducing CO2 consumption costs.
10. Running Costs
Due to the use of a single cluster jacket design, water, detergent, enzyme consumption and large vessels compared to the cluster filter system, 25 to 30%; compared to the standard multi-cylindrical jacket design, reduced by 45%. The increased flow rate in the rinse process shortens the cleaning time from 20 to 30 min for each multi-cylindrical jacket to 30 to 60 seconds for a single cluster shell.
Compared to the heat treatment unit, the water and energy savings are significant. Instant sterilization consumes up to 75% of the water and up to 80% of the energy in terms of heat and electricity. The tunnel pasteurizer consumes more compared to the CFS Neo filtration system. With the introduction of enzymatic regeneration technology, the filtration membrane life cycle has increased by a factor of 3 to 5, significantly reducing filtration costs from 0.5 to 0.9 USD/hl to 0.1 to 0.3 USD/hl.
The system is fully automated and operated by the infuser operator, so labor costs and membrane replacement costs are negligible.
Taking all financial aspects into account, the overall cost is significantly lower than tunnel pasteurization and in most cases lower than instant pasteurization.
11. Taste And Quality
By eliminating the exposure of beer to high temperatures, maintaining a low flow rate during the beer filtration process, and adopting a minimal oxygen uptake design, the CFS Neo system did not have any negative impact on beer freshness or taste stability. Compared to the endogenous antioxidant vigor EAP, which is an indicator of oxidative flavor stability of beer, cold-filtered beer showed better EAP than direct pasteurization of beer. With cold-filtered beer, there was little change in taste over a long period of time after bottling, whereas heat treatment of pasteurized beer negatively affected the freshness of the beer.
12. Conclusion
With its newly developed technology for aseptic filtration of beer, CFS Neo sets new standards for brewers replacing heat treatment of the final product upstream of the filling line. In addition to greater microbiological safety, in terms of economics it is now equal to or better than filtration using cold aseptic membranes, and also optimizes cleaning. This has a positive impact on the consistency of beer taste and also increases consumer acceptance, giving brewers the opportunity to enhance their brand positioning, improve shelf life, generate economic benefits and ultimately achieve higher customer satisfaction.
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