Brewing unit with three-dimensional brewing filter and fully automatic coffee machine with such a brewing unit

Abstract

A brewing unit (10) for brewing a beverage from ground food powder, in particular a brewing unit (10) of a fully automatic coffee machine, comprising a filter (1) for retaining a filter cake of the food powder, a filter plane (2) of the filter (1), and through-holes in the filter plane (2), is further developed by a plurality of filter planes of the filter (1). The invention also relates to a fully automatic coffee machine equipped therewith.

Description

The invention relates to a brewing unit for brewing a beverage from ground food powder, in particular a brewing unit of a fully automatic coffee machine, having a filter for retaining a filter cake or sister or puck of the food powder in a brewing chamber of the brewing unit, having a filter plane of the filter and having perforations or through holes in the filter plane. Depending on the type of filter and the filter material, the through-holes can be circular or shaped in some other way. The invention also relates to a fully automatic coffee machine equipped therewith.DE 1 579 376 A1 describes and claims a metal screen for use in preparing food and food products. The filter is electroplated or etching, has funnel-like perforations in the direction of passage to avoid plugging, and is coated with a noble metal to protect the flavor.The object of the invention is to reduce the clogging of a filter of a brewing unit.This object is achieved in the brewing unit mentioned at the beginning according to the invention by a filter having a plurality of filter planes of the filter which are arranged one behind the other in the flow direction of the filter and at a certain distance from one another.In contrast to a screen, which by definition separates solids from each other, a filter serves to collect solids from a gas or liquid stream. The filter of the brewing unit according to the invention offers according to the invention a plurality of filter levels. In the case of perforated metal sheets as a filter, the filter is composed of a plurality of perforated metal sheets which are arranged at a certain distance from one another. Each perforated plate represents a filter plane. This applies to wire nets which can likewise each represent a filter plane.The effectiveness of the filter is therefore not limited only to its top or viewing surface in its length and width direction, i.e. in its usual plane of extension as the sole filter plane. Its plurality of filter planes expand its effective filter area into the third dimension, namely into the thickness of the filter in the flow direction. With the same plane of extension, its filter surface is thus considerably enlarged. It is also characteristic of the three-dimensional filter according to the invention that it not only offers a conventional flow possibility orthogonal to its plane of extension, but also in principle in its plane of extension and thus orthogonal to the direction of flow and in all directions therebetween. This is because, due to the distance between the filter planes, the three-dimensional filter also enables a transverse flow between the filter planes transversely to the direction of flow through the filter. The distance between the filter planes therefore preferably moves in a dimensional range which is comparable to the dimensions or to the diameter(s) of the through-holes of the filter.The invention thus differs from providing an only two-dimensional filter in the form of a perforated sheet or a wire mesh in the brewing unit, whereby only one filter plane is available which can therefore clog more quickly. This is because, during brewing in the fully automatic coffee maker, very fine particles of the coffee powder, i.e. particles with a size of less than 100 μm, migrate within the compressed triester in the direction of the filter. The finest particles can build up before the filter and form a barrier for the subsequent fluid. This can lead to an undesired pressure increase in the fully automatic coffee maker. On the other hand, a high fine content in coffee powder is desirable for taste reasons, especially in the preparation of espresso. This is because the finer the powder, the greater the surface area of the particles which can be wetted by the preparation water. The larger the surface area of the particles, the more coffee flavors can be released in a short time.In order to avoid an undesired pressure increase, grinding units of fully automatic coffee machines are often adjusted in such a way that the fine fraction is below the critical limit of, for example, 50%. Since both the processed bean types and the component tolerances can lead to considerable variations in the fine fraction, the distance of the fine fraction set on average from the limit fine fraction should be relatively high. For this reason, grinding mills are currently often set relatively roughly. However, the brewing efficiency of the fully automatic coffee maker thus falls. The lower brewing efficiency results in a comparatively high consumption of beans.Rather, the invention follows the principle of significantly enlarging the filter surface of the brewing unit with largely identical component dimensions, in particular of the brewing chamber, in that the filter according to the invention provides not only a filter surface which is effective in its plane of extension, but also in its depth. It thus offers not only the conventional, one-dimensional and rectilinear flow direction orthogonal to the filter plane. The filter according to the invention now permits a quasi three-dimensional flow possibility, according to which a flow through the three-dimensional filter is also possible with directional components in the filter plane and on curved, even buckling and at least longer paths.Experiments have shown that with the three-dimensional filter design in the fully automatic coffee maker coffee powder with a fine fraction of up to 70% can be processed. Up to 70% of the particles can thus have a smaller particle size in the coffee powder than 355 μm. The coffee concentration can be increased with such powders to up to over 7%-compared to a currently maximally achievable coffee concentration of about 6%. Because the filter according to the invention permits powders with higher fines, cost-intensive adjustments and measurements of the grinding mills in production can be dispensed with. In addition, in the automatic coffee maker with the filter according to the invention, a larger spectrum of the beans available on the market can be processed reliably.Because of the possibility of processing coffee powder with a higher proportion of very fine fractions without problems, the same extraction rate as in current fully automatic coffee machines can be achieved with a significantly lower use of coffee beans. The savings to be achieved thereby can lie in a range of up to 20%, whereby in particular the customer-side costs for operating a fully automatic coffee machine equipped according to the invention also decrease. The saving of coffee beans per preparation cycle also enables a smaller device size of the fully automatic coffee machine, because it is no longer necessary to process as much coffee powder for the same preparation result. The dimensions of both the brewing chamber and the triester container can therefore be smaller. In addition to the more compact design of the fully automatic coffee machine, a longer service life of its grinding mechanism is also to be expected, because it has to grind less coffee powder per preparation cycle.The filter is provided according to the invention for retaining the filter cake and is arranged in particular accordingly. For this purpose, it is arranged in particular downstream of the filter cake in the brewing unit.In principle, the filter of the brewing unit according to the invention can consist of several conventional perforated plates or wire nets arranged one above the other and at a certain distance from one another. The filtering effect of each plane can be increased by the fact that the through-holes of different filter planes are not aligned with one another. According to an advantageous embodiment of the invention, the through-holes of the different filter planes can therefore be arranged offset with respect to one another in a flow direction of the filter. The offset of the through holes helps form a cross-flow and turbulence of the fluid within the filter, thereby reducing the accumulation and settling of particles in the filter.According to a further advantageous embodiment of the invention, the filter can comprise a multi-layer and close-mesh network. It can be designed, for example, as a close-mesh three-dimensional mesh, woven fabric or knitted fabric made of relatively thin threads. It can thus offer a high pressure resistance, which is of importance in particular when pressing the trimester. Very fine particles which now migrate in the direction of the filter during brewing can no longer build up to the same extent as in known filters owing to the three-dimensional filter geometry. The thin threads, which surround the mesh of the net as through-holes, lead to a ratio of openings or through-holes to closed areas that is changed relative to a perforated plate. On the closed areas which are now smaller in area, namely on the filaments which are regularly round in cross section, the particles can settle less well. The three-dimensional structure of the filter and the transverse flows which are therefore possible also lead to turbulences in the fluid which prevent the particles from accumulating and building up in the filter and even before it.The braid, fabric or knitted fabric can be substantially homogeneously braided, woven or knitted and thus have a structure distributed equally in each direction at openings of the same or different size. According to a further advantageous embodiment of the invention, the filter can have different diameters of the through-holes or mesh widths in different filter planes. Different diameters can thus be assigned to different filter planes insofar as the diameters of one filter plane cannot occur or occur much less frequently in another filter plane. In a simple case, for example, the outer filter planes of the filter can be assigned a smaller diameter of the through-holes than a middle filter plane, whereby the filter cannot be used around accidentally in reverse. Not only does an individual diameter have to be assigned to an individual filter plane, but several different diameters can be present there. In this respect, different distributions of diameters of the through-holes in different filter planes can be provided. By selecting and distributing the diameters of the through-holes within the three-dimensional filter, the properties thereof can thus be controlled in a targeted manner.The material for forming the filter can be selected largely arbitrarily as long as it is heat-resistant and the filter can be formed so as to be pressure-resistant. According to a further advantageous embodiment of the invention, the filter can consist at least partially of metal, preferably partially or entirely of stainless steel. Both pressure- and heat-resistant structures can be produced from metal, which in addition are relatively easy to clean and which are foodstuff-safe.According to an alternative embodiment of the invention, the filter can consist at least partially of plastic. The filter can be formed wholly or partly as a foam of plastic, which can preferably be elastic. Its production should therefore be less expensive. In addition, this makes it possible to utilize a self-cleaning effect of the filter, which is produced by being compressed during each preparation cycle and subsequently relaxed again. During this movement, the pores of the elastic foam are compressed and relaxed. As a result, the "mesh width" of the filter changes, which additionally counteracts deposition of particles. During the flushing of the brewing chamber, adhering particles can then be successfully flushed out beforehand. Depending on the design requirements, the filter can also be formed partly from metal and partly from plastic.The object mentioned at the beginning is also achieved in an above-mentioned fully automatic coffee machine according to the invention by the brewing unit described above with the filter for eluting a portion of a food powder. Reference may be made to the above-mentioned advantages during the production and operation of the fully automatic coffee maker according to the invention. The filter is arranged to retain the filter cake. According to a first embodiment, the filter according to the invention can be arranged instead of the conventional flat metal filter or instead of the perforated plate known per se.According to an advantageous embodiment of the invention, the fully automatic coffee machine can be equipped with a conventional flat metal screen with the bores for retaining a filter cake of ground food powder and additionally comprise only the filter of a brewing unit according to the invention ("additional filter"). The additional filter can then be arranged directly upstream of the known metal filter and thus downstream of the triester or puck in the flow direction of the brewing unit. The additional filter requires a certain space within the brewing chamber which cannot be used by coffee powder. However, this loss of space or coffee is at least compensated for by the efficiency of the brewing process as a result of the additional filter. Conventional fully automatic coffee machines can consequently also be retrofitted by the additional filter.According to a further advantageous embodiment of the invention, the additional filter can be arranged both upstream and downstream of the trimester, puck or portion of the food powder. The downstream filter may be arranged in addition or alternatively to the conventional metal filter and may operate in the manner described. The upper filter in the direction of flow can assume a water-distributing function instead of a pure filter function. It thus avoids the so-called "channeling", in which the preparation water does not flow uniformly through the compressed ground coffee or the puck, but rather flows more strongly at some points and other points therefore elute less frequently, if at all.The principle of the invention is explained in greater detail below by way of example with reference to a drawing. The single drawing shows, in a greatly simplified manner, a section of a wall 11 of a cylindrical brewing chamber of a brewing unit 10, in which filter 1 according to the invention is arranged. According to the cylindrical brewing chamber, the filter 1 has a circular periphery U. The filter 1 is made entirely of a three-dimensional wire mesh, which is constituted by a metal thread weave of a thin metal thread. It has a thickness D of only approximately 2 mm, so that it requires little additional space even as a retrofit object in an existing fully automatic coffee machine.In the use according to the invention, the filter 1 contacts a coffee triester portion with its upper side 2 which can be seen in the figure. As a retrofit object, i.e. as a single filter 1 without brewing unit 10, it rests with its underside 3 facing away from the figure on a conventional perforated plate as a filter of a brewing chamber. The upper side 2 forms a first filter plane which, owing to the three-dimensional structure of the filter 1, follows further filter planes in the flow direction, which are not separately recognizable in the figure.The upper side 2 of the filter 1 is not perfectly geometrically planar because of its three-dimensional weave. This applies to the further filter planes which together form the three-dimensional filter 1. For this reason, they can also be referred to as filter layers.When the coffee tester elutes, preparation water or eluate flows through the brewing unit 10 and thus the filter 1 in a flow direction R as the main direction. The filter 1 supports the particles of the coffee tar against the flow direction R. Nevertheless, rearrangements and migration movements, in particular of very fine particles, occur. This is because the filter 1 divides the eluate flow coming from the triester into many partial flows which do not run exclusively in the direction of flow, but as oblique flows also at an angle thereto and even orthogonally to the direction of flow, that is to say transversely thereto as transverse flows.Particles are partially deposited on the upper side 2 of the filter 1. However, because they do not find sufficient supporting surfaces there because of the thin threads of the wire mesh, they can no longer form a fluidic blockage, as in conventional filters. Now, on the other hand, they pass into the filter 1 and partially flow through it. They can hardly accumulate even within the filter 1, because these impede turbulences in the filter fabric through which flow takes place due to the oblique and transverse flows.The filter 1 offers a significantly larger wettable surface because of its plurality of filter layers. In principle, more particularly very fine particles can be supported on this. However, they are now distributed over a substantially larger area and more finely. As a result, they can no longer form a fluidic barrier which would lead to an undesired pressure increase in the fully automatic coffee maker. The filter 1 thereby enables the processing of coffee powders with a significantly higher fine fraction than previously. The filter 1 thereby not only opens up further types of beans for the successful and process-safe processing in a fully automatic coffee machine, but also leads to a lower consumption of coffee beans with at the same time a stronger aroma.Since the brewing unit described above is an embodiment, it can be modified in a conventional manner by the person skilled in the art to a wide extent without departing from the scope of the invention. In particular, the specific type of production of the filter by weaving, knitting, etc., or the specific configuration of the circumference of the filter can also take place in a different form than in the one described here, in particular if it requires technical requirements or a different cross-sectional shape of the brewing chamber of the brewing unit. The filter itself can likewise be designed in another shape or from another material, if this is necessary for space reasons or design reasons. Furthermore, the use of the indefinite article "a" or "an" does not exclude that the features in question can also be present multiple or multiple times.List of reference characters1 Filter 2 Upper side 3 Lower side 10 Brewing unit 11 Wall of a brewing chamber D Thickness R Flow direction U CircumferenceReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 1 579 376 A1

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Claims

Brewing unit (10) for brewing a beverage from ground food powder, in particular brewing unit (10) of a fully automatic coffee machine, having a filter (1) for retaining a filter cake of the food powder, having a filter plane (2) of the filter (1) and having through holes in the filter plane (2), characterized bya plurality of filter planes of the filter (1).Brewing unit (10) according to claim 1, characterised in that the through-holes of different filter planes are arranged offset to one another in the flow direction (R) of the filter (1).Brewing unit (10) according to claim 1 or 2, characterized in that the filter (1) comprises a multi-layer and tight mesh net.Brewing unit (10) according to one of claims 1 to 3, characterised in that different filter planes of the filter (1) have different diameters of the through-holes.Brewing unit (10) according to one of claims 1 to 4, characterised in that the filter (1) is at least partially made of metal.Brewing unit (10) according to one of claims 1 to 4, characterised in that the filter consists at least partially of plastic.Fully automatic coffee machine, in particular for household purposes, characterised bya brewing unit (10) for eluting a portion of a food powder according to one of the above claims.Fully automatic coffee maker according to the above claim 7, comprising a brewing unit with a conventional flat metal screen with bores for retaining a filter cake of ground food powder, characterised bya filter of a brewing unit according to any one of claims 1 to 6 as an additional filter immediately upstream of the metal screen.Fully automatic coffee machine according to one of claims 7 or 8, characterised bya filter of a brewing unit according to one of claims 1 to 6 as an additional filter (1) in the brewing unit both upstream and downstream of the portion of the food powder.

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