BE1011287A3 - BEER FILTER. - Google Patents

Abstract

The invention relates to a beer filter comprising a filter medium based on metal fibers. The filter medium is a multilayer, sintered, cold isostatically pressed metal fiber fleece, preferably based on stainless steel fibers with an equivalent diameter, which is comprised between 2 and 30 µm. The porosity of the filter medium is included between 30 and 60%.

Description

BEER FILTER

The invention relates to a filter medium for filtering beer.

Usually the beer is filtered in the final stage of production to remove the suspended particles, such as, among other things, entrained yeast cells. Also, the liquid that remains in the fermentation and maturation tanks after pumping over the intended consumption beer, the so-called tank bottom, is also essential beer, which indeed contains a large amount of suspended particles (typically 5% and more). Filtration of these tank bottoms provides a certain amount of beer for the time being.

Preliminary filtration is often carried out using an auxiliary filter medium such as Kieselgur or diatomaceous earth. The final filtration then removes the entrained auxiliary filter medium and the entrained yeast cells.

In what follows, the term "beer" refers on the one hand to the intended drinking beer in which a normal amount of solid particles is suspended (typically 0.1%), but on the other hand also to the tank bottoms and similar beer-type liquids in which a much larger amount of solid particles is suspended.

Various requirements are imposed on a beer filter medium. In the first place, the medium must yield a filtrate that meets various quality requirements such as purity (complete fermentation retention), turbidity, cold turbidity, bitterness, and other specific quality requirements that are imposed on drinking beer. In addition, the filter medium must have significant mechanical and thermal resistance. After all, it must be able to withstand the high flows and pressures, but also high temperatures, which can be achieved, for example, when sterilizing the devices with steam at more than 120 ° C.

It is also very important that the filter media can be regenerated. The conventional filter media mentioned above are often, if not always, intended for single use. However, the replacement of a filter medium is labor-intensive and has not yet been fully automatic. The frequency of replacement of the medium thus has a direct influence on the process or operating costs of the beer production.

Different types of filter media are conventionally used for beer filtration.

European patent EP 0208450 describes the use of ceramic filter membranes in the single or multi-stage filtration of the beer.

The use of a heat-sintered filter medium comprising metal fibers and optionally also metal powder is also known from European patent EP 0457611. Furthermore, cellulose filter media or candle filters based on (synthetic) resins are also frequently used.

Numerous problems are associated with the use of these conventional filter media. For example, these media are not or only very difficult to regenerate, they have only a limited mechanical strength and service life, and they deliver a filtrate (consumer product) that does not always meet the required quality requirements.

In addition, the frequently used Kieselgur as an auxiliary filter medium is presumably carcinogenic, difficult to handle, abrasive, expensive, and therefore to be avoided as much as possible.

The object of the invention is thus to provide a beer filter medium that guarantees complete glass retention, yields a filtrate that meets all the required quality requirements, and is easily regenerable. In addition, it is an object of the invention to provide a filter element that has a high mechanical and thermal resistance, as well as a long service life.

The invention meets these preconditions by providing a beer filter comprising a metal fiber-based filter medium, the filter medium being a multi-layered, sintered, cold isostatically pressed metal fiber web.

The principle of cold isostatic pressing is known and has been described in the European patent EP 0329863 of the applicant. It is a method for homogeneously compacting a sintered metal fiber fleece, in which the pressing pressure is transferred to the fleece via a flexible medium. The same pressure is applied to each point on the surface of the web. The pressure transmission medium can be a gas, a liquid, a flexible membrane, or any felt-like material.

Cold isostatic pressing results in a product with homogeneous permeability over the entire surface.

An isostatically pressed material is characterized by a rough surface along the side on which the pressure was applied.

The beer filter medium according to the invention is obtained by cold isostatic pressing of a sintered or non-multi-layered metal fiber fleece.

The metal fiber fleece, preferably based on stainless steel fibers (type 316L or for example AISI 300 or 400 series materials, FeCralloy®, AlloyHR, Aluchrome®, ...) with an equivalent diameter between 2 and 30 µm, and a weight which is understood to be between 300 and 1500 g / m2, is cold-pressed isostatically at at least 2000 bar (2,108 Pa).

The equivalent diameter of a fiber is the diameter of a fictitious round fiber with the same transverse cross-section as that of the real fiber under consideration.

The absolute filter fineness of the material thus obtained is less than 1.2 µm. The dust retention capacity and tool life are more than 20% higher than those of the conventional cellulose filters. The porosity of the isostatically pressed filter medium is comprised between 30 and 60%. The air permeability of the medium is at least 1 L / dm2 / min at a pressure drop of 200 Pa over the medium.

The suitability of the proposed filter medium will be further demonstrated on the basis of a concrete embodiment and corresponding test results.

Example

The example is based on a multilayer metal fiber fleece based on bundled drawn stainless steel fibers of the steel type AISI 316L. Likewise, one could start from fibers obtained by shearing the head edge of a wound film, as described in patent EP 0319959.

Taken according to the filter direction, the following metal fiber fleeces are stacked: 6.5 / 75 - 4/300 - 2/450 - 6.5 / 75. The notation x / y refers here to a metal fiber fleece based on metal fibers with an equivalent diameter of x µm, and with a weight of y g / m2.

The multilayer metal fiber fleece is then heat sintered, and then cold isostatically pressed at 2500 bar (2.5.10® Pa) by a method described in applicant's patent EP 0329863.

In the present example, the isostatic pressing was done by applying the pressure of the pressing medium along one side of the sintered web. The Product therefore has one rough and one smooth surface. It is used as filter medium with the raw side as the outflow side.

The filter medium thus obtained has a porosity of 48.7% and an air permeability of 1 L / dm2 / min at a pressure drop of 200 Pa over the medium. The medium has a filter fineness of 1 µm, which guarantees complete fermentation retention.

The strength of the filter medium according to the invention ensures a smooth regeneration by back flushing, even at elevated pressure. The cleaning of the medium turned out to be even smoother by applying pressure pulses (approx. 2 bar) of limited amounts of water or filtered beer. Several dozen regenerations could be performed.

The filter medium of the invention can be used in cylindrical candle filters, disc filters or other filter embodiments.

The results of the beer filtration tests will be discussed below. The beer filter according to the invention will be compared with a conventional, frequently used sterile cellulose filter Strati Dépurai K10.

Even after dozens of regenerations, the turbidity of the filtrate remains between 0 and 0.15 EBC, thus within the generally accepted standard.

This is a very important advantage over the conventional cellulose filters. When rewinding over a cellulose medium, cracks are repeatedly observed which make regeneration completely impossible.

Filtration under constant pressure and with incompressible filter cake is described mathematically by Ruth's equation:

with and where t: time (s), V: filtrate volume per unit filter area (m3 / m2), ε. the porosity of the filter cake (m3 pore volume / m3 filter cake), h: volume fraction of particles in the suspension (m3 particles / m3 suspension), μ: viscosity of the fluid (Ns / m2), dp: particle parameter (m), Δρ: pressure drop (Pa), and Rm: measure of the mechanical flow resistance of the filter carrier and the filter itself (1 / m).

Kt can thus be regarded as an indicator for clogging the filter. A higher Kt value also implies lowering the total filtration capacity.

Since μ and Δρ are almost constant, K2 can be regarded as a measure of the mechanical flow resistance of the filter material.

Experimentally, tN can be plotted as a function of V. Kt was determined from the direction coefficient of the line, from the intersection with the ordinate K2. For example, the following results were obtained:

This shows that the filter medium according to the invention clogs much more slowly than the conventional cellulose filter media. The mechanical flow resistance of the filter medium according to the invention is also considerably lower than that of the conventional cellulose filter media. This again illustrates some of the advantages of the beer filters according to the invention.

Furthermore, the beer filter medium according to the invention was tested for yeast breakdown. To measure the yeast breakdown, the filtrate was passed through a Sartorius filter (0.45 μιτι) which was then incubated on wort agar. Before filtration, the entire setup was sterilized in an autoclave (20 minutes at 121 eC). The first 100 ml filtrate was passed over a first Sartorius filter, and the next liter of filtrate on a second. The petri plates were then placed at 25 ° C

incubated. The number of yeast colonies was then counted. Only after filtration from a pressure drop of more than 2 bar (2,105 Pa), a slight yeast breakdown was observed on the second petri plate. Conventional filters already show yeast breakdown (total overgrowth of the petri plate with yeast colonies) after filtration at a pressure drop of 0.5 bar (5,104 Pa) over the medium.

Tests to evaluate the foam retention on the beer after filtration over the filter medium of the invention resulted in positive results. The stability, color and bitter value of the beer were also positively evaluated after filtration.

In an alternative embodiment for the beer filter, it is further possible to start from a metal fiber web which is provided with a hydrophobic coating before or after the isostatic pressing in order to prevent the adsorption of bitter substances to the medium, which can lead to a better bittering value of the filtered beer. For example, a DYLYN® coating can be applied along the inflow side of the filter medium. The application of such a coating is described in applicant's European patent application EP 97201867.5.

The filter medium according to the invention thus results in a filtrate that meets all the quality requirements imposed on the beer.

Claims (6)

Beer filter comprising a filter medium based on metal fibers, characterized in that the filter medium is a multi-layered or sintered, cold isostatically pressed metal fiber fleece. Beer filter according to claim 1, wherein the metal fiber fleece consists of stainless steel fibers with an equivalent diameter, which is comprised between 2 and 30 µm. Beer filter according to claim 1, wherein the weight of the metal fiber fleece is comprised between 300 and 1500 g / m2. Beer filter according to claim 1, wherein the sintered metal fiber fleece is cold-isostatically pressed at at least 2,101 2 Pa. Beer filter according to claim 1, wherein the absolute filter fineness of the filter medium is less than 1.2 µm. Beer filter according to claim 1, wherein the porosity of the filter medium is comprised between 30 and 60%. Beer filter according to claim 1, wherein the permeability of the 2 filter medium is more than 1 L / dm2 / min at a pressure drop of 200 Pa over the filter medium.