Brewing Series: The Final Filtration Step

The final beer filtration step is a crucial process in brewing that aims to remove any remaining solids, yeast, and other unwanted particles from the beer before it is packaged for distribution and consumption. Removing some of the components such as the yeast is not always a positive! Beer flavour is more stable when suspended yeast remains in the beer because it promotes strongly reducing conditions. It is one of the benefits of cask conditioning and encouraging live yeast in the bottle. You often find in brewing that the total removal of yeast is left to the last minute of the processing. It is also worth considering that centrifugation is now a rival to filtration as a process.

Filtration is usually conducted over a number of steps so as to achieve an orderly and managed removal of particulates. This part of the process is essential for achieving clarity and stability in the beer, as well as ensuring that it meets quality standards.

Maturation and Clarification

Before filtration, the beer typically undergoes a maturation and clarification process. This involves allowing the beer to rest in tanks, allowing any remaining yeast or solids to settle to the bottom.

Successful filtration usually requires chilling of the beer. As the temperature is lowered, some cold trub and chill haze develops. Filtration is designed to remove this material as well as yeast cells. It is key that the temperature of the beer does not rise otherwise the haze disappears. Beer processed this way is maintained at -2 to -1ºC (28 to 30 ºF). The turbidity of the beer leaving this filter must be less than 0.5 ºEBC.

The First Step In Final Filtration

It is common to see beer clarified using bag filters or centrifuges. In high volume operations where production volume is high or the hop content of the beer is substantial, then a separation process that removes just the coarse hop and yeast particles is needed. Hopping is an important step in generating beers such as IPA. Dry hopping improves the aromatic profile of the beer which is why extra hops are added to the bag filter. When depth filter cartridges or sheets are used, or when a stacked disc cartridge is called for instead of using bag filters or centrifuges, its often the situation that high levels of direct exposure to hops means these types of filter are blocked. In most cases, it is preferred that a coarse filtration is needed.

The next (second) filtration step is a clarification performed in one or two steps depending on the level of filtration needed. More steps mean a finer beer with a smoother mouth feel. The number of steps also reduces the colour content as well. Clarifying filtration has a critical role in the appearance of the final product. The degree of foaming produced by the beer also affects clarification.

The third step is trap filtration and fine filtration which we have discussed elsewhere. A variety of filtration steps can be employed here – sheets, stacked disc cartridges and filter cartridges and often with different filter media types.

If a brewer is only producing about 500 litres or 130 gallons of beer per week then a stacked disc cartridge or depth filter cartridge is used. It depends on the practices and philosophy of the brewer however and how they wish to present the beer in its final form. Sheet filters are more flexible than filter cartridges whereas stacked disc cartridges and depth filter cartridges provide a greater advantage as part of an enclosed system. Each of the three methods offers similar levels of control.

Cartridge replacement is relatively short – about 1/2 hour in terms of replacement and checking at maximum. Sheets can take longer dependent on well the system is set up and pressurised.

The final (fourth) filtration step is before bottling or kegging to ensure optimal quality and perhaps one that dictates the appearance of the beer. It all depends on the brewer as to how this is performed and with what level of control. The most common types of filter used are 5 – to 20 micron depth filter cartridges and stacked disc cartridges which are typical of craft brewing. Home brewers may well focus on the turbidity of the beer but for large-scale breweries ensuring that the beer contains as little yeast as possible is important.

Filtration Media

Filtration is often carried out using specialized filter media such as diatomaceous earth (DE), perlite, or membrane filters. Diatomaceous earth, a natural sedimentary rock, is commonly used. These materials act as a sieve, trapping particles and allowing only the liquid to pass through.

The filtration media must not remove any colour, flavour, bitterness compounds and foaming potential.

The type of filter medium used is important. We can choose the following:

• Pure cellulose filter sheets absorb less hop oil without the addition of mineral components and generally cause fewer aromatic changes. They are usually the medium of choice for craft beer brewers at every filtration step.
• Standard filters, which are available as depth filter sheets or stacked disc cartridges, may also be used, though they are very specific to the brewing process being adhered to.
• Back-flushable pure cellulose filter sheets boast a longer service life, due in large part to their cleanability, which allows the stacked disc cartridges to be used more frequently.

Filtration System

Filtration systems can vary, but they generally involve passing the beer through a series of filters that become progressively finer. Some breweries use plate and frame filters, others use cartridge filters, and modern breweries may utilize membrane filtration systems.

Pre-Coat or Filter Aid Addition

In some cases, a pre-coat of filter aid like diatomaceous earth is applied to the filter medium before beer filtration. This can enhance the efficiency of particle removal.

Pressure and Flow Control

The beer is often pumped through the filtration system under controlled pressure and flow rates. This helps maintain the effectiveness of the filtration and ensures that the beer is filtered uniformly.

Particle Removal

The filters trap particles such as yeast cells, proteins, and other solids. The size of the filter media determines the particles that are removed. Finer filters can remove smaller particles but may require more pressure and maintenance.

Quality Checks

Throughout the whole filtration process, brewers typically monitor the beer for clarity i.e. turbidity and quality. Samples are taken at various points throughout the brewing process to check for any unwanted particles or off-flavors. The most critical is right at the end – is it the beer or cider you thought it should be?

Packaging Following Final Filtration

Once the beer has been successfully filtered and meets quality standards, it is ready for packaging. It can be transferred to kegs, bottles, or cans, depending on the brewery’s preferred packaging method.

Filter Maintenance

Filtration is one of those steps which can be extremely damaging to the overall efficiency of the brewing plant. Separation of sediment or ‘tank bottoms’ from the maturing beer either by, or before filtration is important to success. Disposal of the sedimented material is an issue in waste management.

The head brewer is responsible for the overall management of the brewing process including the final filtration step however a brewing technician will perform much of the manual work. As we often refer to it is their philosophy of brewing which dictates the process and level of clarification needed.

One thing that brewers in the craft beer world decide upon, stabilization is important but only the producers of session beers decide upon using pasteurisation to stabilise beer. Not using pasteurization means the aroma profile is protected and not altered. Also craft beers are consumed relatively quickly so shelf-life extension is not a major requirement.

Many breweries use old equipment which they could have had for 50 years or more and a number of it being second-hand. In many cases replacement parts are not available, the companies that manufacture the various systems have disappeared or been bought out. There is always the possibility that parts which are needed can be cannabilised from other equipment or are still available in a supplier’s inventory. It is not unheard of for breweries to buy equipment off the internet such as Ebay. Some modern suppliers will try to help by supplying equipment or even designing replacement parts to meet the needs of customers needing such pieces of equipment.

All the filters need to be part of a planned routine maintenance rather than one that is reactive simply because it could cost a brewery production. It may be policy to replace all the consumables for filtration every 3 months with inspections conducted every month to 6 weeks to check for fouling, or to see any part of the housing is damaged. Spares for the most susceptible parts need to be kept on hand. All filtration media need to be checked for foul odours and the presence of foreign bodies especially insects.

The larger breweries have in place systems for planned maintenance and there are many different models available to satisfy management initiatives.

Safety Considerations In Filtration Especially To Replace Pasteurisation

Ensuring the safety of final filtration as a replacement for pasteurization in beer involves a combination of testing, monitoring, and adherence to specific protocols. The primary goal is to eliminate or control any potential microbial contamination while preserving the desired flavor, aroma, and quality characteristics of the beer. Below are key steps and considerations for proving and confirming the safety of final filtration in beer production:-

Microbiological Testing

• Conduct regular microbiological testing of both the raw materials and the final product. This includes testing for bacteria, yeast, and mold. It is crucial to establish baseline microbial levels in the raw materials and monitor for any changes throughout the brewing process.
• Implement a robust quality control program to detect and identify any potential microbial contaminants. This may involve using a variety of testing methods, such as plating, PCR (Polymerase Chain Reaction), and other rapid detection techniques.

Validation Studies

• Perform validation studies on the final filtration process. This includes determining the efficiency of the filtration system in removing microorganisms, especially heat-resistant ones. Validation studies often involve challenging the system with known concentrations of microorganisms to ensure effective removal.

Particle Analysis

• Conduct particle analysis to ensure that the filtration process effectively removes undesirable particles and contaminants. This can be done through microscopic examination or automated particle counting methods.

Monitoring and Record-Keeping

Implement a comprehensive monitoring system to continuously track critical parameters during the brewing process. This includes monitoring temperatures, pressures, flow rates, and other relevant variables.

Maintain detailed records of the filtration process, including equipment specifications, operating conditions, and any deviations from standard procedures. These records can be essential for traceability and troubleshooting.

Integrity Testing

• Perform integrity testing on the filtration system to ensure that the filter membranes are intact and functioning as intended. Common methods include bubble point testing, pressure decay testing, and diffusion testing.

Cleaning and Sanitization

• Develop and implement thorough cleaning and sanitization protocols for all equipment involved in the filtration process. Proper cleaning is essential to prevent the buildup of biofilms or other contaminants that could compromise the integrity of the final filtration.

Sensory Evaluation

• Conduct regular sensory evaluations to ensure that the beer maintains its desired flavor, aroma, and appearance after final filtration. Sensory panels can help detect any off-flavors or other quality issues that may arise during the process.

Regulatory Compliance

• Ensure compliance with local and international regulations and standards for food safety and beverage production. Regulatory bodies often provide guidelines for microbial control in beverages, and adherence to these standards is crucial for confirming the safety of final filtration.

Process Optimization

Continuously optimize the filtration process based on data and feedback from quality control measures. This may involve adjusting filtration parameters, upgrading equipment, or implementing new technologies to enhance microbial control.

Training and Documentation

• Provide comprehensive training to personnel involved in the filtration process to ensure proper execution of procedures. Documentation of training, standard operating procedures (SOPs), and best practices is essential for maintaining consistency and reliability in the production process.

The final beer filtration step is crucial for producing a visually appealing and stable product. It not only contributes to the beer’s appearance but also helps extend its shelf life by removing elements that could contribute to off-flavors or haze over time.