Filtration is a separation process, through which yeast cells and other turbid substances still exist in beer are separated from beer. Otherwise, these substances will precipitate from the beer at a later stage, leading to beer turbidity.
The purpose of filtration is to keep the beer in good condition. At least, the appearance of beer should not change during the “minimum storage period”, so as to ensure the perfect appearance of the beer.
1. Filtration method
During filtration, the turbid liquid (not filtrated) is separated from the intercepted solid substance by the filter medium. The power of separation is based on the pressure difference between the inlet and outlet of the filter.
The pressure at the inlet is always higher than that at the outlet. The greater the pressure difference, the greater the resistance of the filter, which affects the filtration process. Especially at the end of filtration, the pressure difference rises rapidly.
The separation effect can be divided into the following types：
①Screen surface or surface effect 1: particles can not pass through the pores of the filter medium and are trapped on the surface of the thickening filter layer. The filtering accuracy is higher and higher, but the flow is smaller and smaller.
②Depth effect 2: porous materials retain particles in liquid due to their large surface area and deep and tortuous path. Due to the mechanical effect, the particles with a certain size are intercepted, so the holes are constantly blocked, leading to the gradual decline of the efficiency of the filter.
③Fine particles are adsorbed and retained. This kind of adsorptive stone is caused by the different charge of filter materials and particles.
④Screening effect and adsorption effect appear simultaneously in most cases.
3. Filter material
Filter materials are divided into the following categories:
①Different types of sieves: for example, metal sieves, wedge wire false bottom or wedge wire filter installed parallel to candle filters.
②Metal or textile woven fabric: the cleaning and sterilization effect of metal woven fabric is better, and textile woven fabric is also ideal. For example, polypropylene woven fabric has almost the same performance as metal woven fabric in many aspects, but it is not easy to sterilize, so it is rare in beer filtration.
③Filter board: filter board can be made of fiber, cotton, diatomite, perlite, glass fiber, and other materials.
④Loose materials: for example, sand filters are used for water filtration, and filter agents are used to forming filter layers.
⑤Porous materials: sintered metal, for example, for wort oxygenation.
⑥All kinds of membrane: now more and more use membrane filtration. There are many materials for making films, such as polyurethane, polypropylene, polyamide, polyethylene, polycarbonate, cellulose acetate, and other materials.
4. Filter media
They are filter media, such as diatomite, or perlite. Because of its special shape and structure, it can be used for filtering. Filter media cannot be used without filter materials. The most common is the wedge wire filter element for the diatomite filter.
The following substances are often used as filter media in breweries:
①Diatomite for beer filtration
②Wort filter for perlite