Lesson 8 - Clarification – Filtration

Let us summarise the essential features of a filtration system:

• A filter! There are numerous types available. You must base your choice on the level of automation required, the filter capacity, and your support services. The options include:

    Filter aid (normally KG) filters

• • Plate and frame

• • Horizontal leaf

• • Vertical leaf

• • Candle

    Cartridge filters

• • Lenticular (depth)

• • Candle form (depth)

• • Candle form (membrane)

    Other types

• • Cross-flow filtration

• • • Sheet

• Additional filters for specific operations. Such as:

  • Regenerable polyvinylpolypyrrolidone (PVPP) stabilisation filter – to reduce the risk of product haze formation and to improve shelf-life stability (as discussed in the Process Aids and Additions lesson).

  • Trap filter – to capture any DE or PVPP that may have leaked from the filter/s.

  • Sterile filters – to capture micro-organisms and thus avoid biological contamination in the bright beer tank (BBT) or final product tank (FPT).

• Beer quality adjustment. Post-filtration, a brewer needs to use processes to correct quality parameters, such as dilution if brewing at high gravity, carbonation, and other post fermentation ingredient additions (as described in the Process Aids and Additions lesson).

• Process aid dosing. Using process aids requires a process aid dosing plant, along with the filter. This doses the required amount of filter material (e.g. DE and silica gel) to ensure optimum clarity on the filter outlet.

• Throughput. We must aim to obtain maximum throughput per filter run by optimising filter powder dose rates to gain a balance between throughput and lowest possible haze value.

• Capacity. The filter must be sized appropriately to meet the demands of the brewery, especially during peak production periods.

• Ancillary equipment and process control. The process must facilitate transfer from maturation to BBT/FPT through process equipment without microbiological contamination or oxygen ingress. The essential components of the system include plant for dosing in ingredients (e.g. post-fermentation bitterness, hop oil, colour addition), process aid dosing plant, transfer pumps, valves, temperature control (via beer chillers), turbidity meters, CO₂ supply, compressed air supply, and all associated automation controls (if automated).

• Cleaning and sanitation. The filter must be designed to allow effective cleaning to remove organic soiling and sanitation, which in turn removes and prevents any microbial activity.

• Buffer tanks. Breweries may choose to use pre- and post-buffer tanks in the filtration process. These intermediary vessels help to protect against pressure shocks in the system as vessel and pipework valves are opened and closed and pumps are started and stopped. Buffer tanks also help to provide a steady flow of beer to the filter in case of any start/stop upstream. Pressure shocks can damage the filter bed integrity (particularly if using a DE filter) and force the filtration run to stop. In the case of DE filters, the filter bed would have to be removed and the whole process of filter preparation would need to be started all over again. In the case of any other filter, it may cause bleed through of yeast, bacteria, haze material, or may physically damage the filter material, necessitating filter medium replacement.

We can also use a pre-buffer tank to collect the first and last portions of a maturation vessel. This is the first and last 1-2% of the total volume of the maturation tank, which may be high in suspended solid particles. By collecting this volume in the tank, it can then be dosed back into the bulk beer stream in a controlled manner (5-10%) to reduce the solid loading onto the filter. This might otherwise ‘blind’ or block the filter, reducing the filter run length. Recovering the beer also helps to reduce beer losses.

Alongside these features, quality and best practice must be maintained. We can do this by ensuring that the beer transferred is of the right age (has matured long enough) and that the temperature of the beer going to the filter is maintained at maturation temperatures. Also, we must use the correct type and amount of process aids (if applicable) to aid yeast, protein, and polyphenol adsorption. This will in turn achieve optimum clarification.