Shelf life of beer in terms of filtration

Primary beer filtration 

Primary beer filtration is a process during which bulk yeast is removed from the fermented beer. On entry,

the typical turbidity of such beer is 60-120 EBC and the number of yeast cells some 10 mil/ml. Sedimentation

on its own cannot produce the clarity of the beer required for the subsequent production stages.

Primary filtration also helps remove components contributing to the formation of a veil or turbidity in the

form of a cluster of proteins and polyphenols and hop resin. The most commonly used filter in primary

filtration is the diatomite filter, which has a nominal selectivity of 0.5 - 30 micrometres. Cross flow filters

(selectivity up to 0.65 micrometres) have been gaining more ground recently, but they are usually combined

with centrifugal separation which eliminates a large amount of the yeasts in beer.

Trap beer filtration

Trap particle filtration removes residual filtration material from the filtrate. In most cases this applies to

diatomite and cellulose. All types of diatomite filters have a certain amount of diatomite escaping into

the filtrate and this must be removed prior to expedition of the beer, otherwise fine filtration must follow.

There is a number of trap filtration materials. The most commonly used are filtration cartridges made of

materials such as glass and polymers, filtration plates made of cellulose, and also special cartridges made

of steel and other inorganic materials. The typically applied selectivity of trap filters is 5 - 10 micrometres

(>ß 1000).

Secondary filtration – final microfiltration of beer

End microfiltration is the last filtration step before bottling. In breweries employing a three stage filtration

system (trap, fine and final filtration), fine filtration filters also serve as prefilters protecting the final

membranes. The purpose of final filtration – also referred to as cold microbiological stabilisation – is to

remove all the yeasts and common beer-spoiling bacteria from the beer. That is why filtration membranes

with selectivity from 0.45 do 0.65 micrometres are used for beer, ensuring a reduction of microorganisms,

but not sterility of the product.