Wine Filtration
Direct-End versus 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
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 ?m and 0.45 ?m or sterile filtration. They remove particles like a sieve, with larger particles retained on the surface of the filter, which gradually blocks the flow. Absolute filtration is useful for sterile filtration at the bottling line and to guarantee removal of microorganisms.
Cross-Flow Filtration
Unlike direct-end filtration where the wine 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 wine under pressure across the membrane surface, instead of directly onto the filter. During filtration, any material smaller than the cross-flow membrane pore passes through the membrane, while larger suspended particulates remain in the retentate stream.
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