Chapter 15

Beer Filtration

Direct-End and Cross-Flow Filtration

Filtration can either be classified as direct-end or crossflow filtration. Direct-end (sometimes called perpendicular flow) filtration is applied when all the fluid to be filtered is driven, due to a supply pressure, in a direction perpendicular to a filtering surface; few applications are done by gravity feed. Direct-end filtration falls into two main categories, depth filtration and surface filtration. Contaminants are captured within the filtration media or build up on the surface, causing the differential pressure across the filter to rise as it blocks over the duration of the filtration process. Cross-flow filtration is a filtration configuration in which the feed fluid to be filtered is continuously recirculated tangentially to a filtration membrane surface.

Direct-End Filtration

Direct end, also known as direct flow filtration, removes material by the capture of material both in the depth and on the surface of the filter. Particulates are primarily removed by the direct interception mechanism, that is, the particles are too big to go through the passages. Thus, the media should be designed to capture and retain as much material as possible. At the same time, dissolved substances are removed by adsorption.

Depth Filtration

Depth filters are not absolute filters because they do not have a precisely defined pore size or structure. They remove particles that are larger than the aperture or pore size of the filter by mechanical retention of the particles, by adsorption, or by an electric charge that can attract and trap smaller particles, generally within or inside the filtration medium.

Surface Filtration

Surface filters are generally absolute filters with precisely defined maximum pore sizes and these include 0.65 µm and 0.45 µm or sterile filtration. They remove particles like a sieve, with larger particles retained on the surface of the filter, which gradually blocks the flow.

Cross-Flow Filtration

Unlike direct-end filtration where the beer impacts the membrane perpendicularly, cross-flow filtration (tangential) relies on the product flowing across the surface of the membrane tangentially. Cross-flow filtration works by introducing feed beer under pressure across the membrane surface, instead of directly onto the filter.

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