Filters

Filter include...

- Sieves of all kinds, e.g. metal sieves, slotted sieves or parallel arrangement of wedge wire in candle filters

Metal or cloth tissue
- The metallic tissues are easier to clean & sterilize
- But modern textile cloths e.g. polypropylene are not use for beer filtration because they can not be sterilized so well

Filter sheets
- Made of cellulose, cotton, kieselguhr, perlite, glass fibres or other materials (asbestos, is no longer used on health safety grounds)
- Filter sheets are now very widely used & are available for very different filtration cut off limits down to sterile filtration
- Particles smaller than the cut off limit may pass through the filter
- The lower the cut off limit the sharper the filtration

Loosely packed beds
- For example small pebble filters for water filtration & layers of powdery filter aids used as “precoats” on filter sheets

Porous bodies
- Such as sintered metal or metal frits as used for atomizing air & to an increasing

Membrane
- These are made of polyurethane, polyacrylate, polyamide, polyethylene, polycarbonate, cellulose acetate & other substances
- The membranes are very thin (0.02 to 1 mm) & therefore applied on large – pored support layers, because they would otherwise tear
- They are manufactured by impregnation, spraying or deposition
- The pores themselves are made;
- By incorporating salts which are later dissolved out again to form pores
- By etching

- Because of the different manufacturing materials used, nowadays membranes with any desired pore size can be made & they can correspondingly filter out materials of any chosen molecular size
- Because these filters contain very fine pores, one speaks of;
- Microfilters when the range is concerned 10-1 to 10-2 mm
- Ultrafilters or nanofilters when the range is concerned 10-3 to 10-4 mm
- Ceramic material with very fine channels are often used for microfiltration