In the first or 'roughing out stage', most breweries use kieselguhr as the filtration medium, supported by Carlson W2N support sheets. The purpose of this filtration stage is to remove visible turbid matter. The role of the filter sheet is to capture the kieselguhr filter medium and help establish the build up of the filter cake within the filter.
In most breweries it is impractical to add kieselguhr powder in bulk to the beer prior to filtration. Consequently this is usually achieved with automatic dosing equipment, which injects metered quantities of kieselguhr in slurry form into the beer flow line.
The dose rate will vary according to the condition of the beer and ranges from 35 to 200 grammes per hectolitre. The typical beer flow rate through the filter is commonly 3.5 hectolitres per square metre per hour.
Specially designed for this type of application, W2N sheets offer a number of benefits to the brewer:
Provision of high wet strength and durability due to manufacture from natural fibres incorporating carefully chosen food grade wet strength resins within the cellulose matrix.
Even control of pore size distribution of the sheet to ensure even build up of the filter cake on the sheet. This ensures that filter capacity is maximised and that there is minimum risk of bleed through of even the finest of fines, whilst minimising the pressure drop through the filter.
Very tolerant of pressure transients during the filtration cycle because the formulation used in their manufacture, coupled with the manufacturing process, produces an extremely durable yet flexible sheet.