Brewing unit having a three-dimensional brewing filter, and fully automatic coffee machine having 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, having a filter (1) for retaining a filter cake of the food powder, having a filter plane (2) forming part of the filter (1) and having through-holes in the filter plane (2), is developed by the filter (1) comprising a plurality of filter planes. The invention also relates to a fully automatic coffee machine equipped therewith.

Description

[0001] Brewing unit with three-dimensional brewing filter and fully automatic coffee machine with such a brewing unit

[0002] 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, comprising a filter for retaining a filter cake or grounds or puck of the food powder in a brewing chamber of the brewing unit, a filter plane of the filter, and perforations or through-holes in the filter plane. Depending on the filter type and filter material, the through-holes can be circular or otherwise shaped. The invention also relates to a fully automatic coffee machine equipped with such a filter.

[0003] DE 1 579 376 A1 describes and claims a metal sieve or metal filter for use in the preparation of food and beverages. The filter is manufactured by electroplating or etching, has perforations that widen in a funnel-like manner in the direction of flow to prevent clogging, and is coated with a precious metal to protect the aroma.

[0004] The object of the invention is to reduce the clogging of a filter of a brewing unit.

[0005] This object is achieved according to the invention in the brewing unit mentioned at the outset by a filter with a plurality of filter levels 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.

[0006] In contrast to a sieve, which by definition separates solids from one another, a filter serves to capture solids from a gas or liquid stream. The filter of the brewing unit according to the invention offers a plurality of filter levels. In the case of perforated plates as a filter, the filter consists of a plurality of perforated plates arranged at a certain distance from one another. Each perforated plate represents a filter level. A similar situation applies to wire mesh, which can also each represent a filter level.

[0007] The effectiveness of the filter is therefore not limited to its top or visible surface in its length and width directions, i.e. in its usual plane of extension as the only filter plane. Its multiple filter planes extend its effective filter surface 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 therefore considerably increased. Another characteristic of the three-dimensional filter according to the invention is that it not only offers a conventional flow possibility orthogonal to its plane of extension, but basically also in its plane of extension and thus orthogonal to the flow direction as well as in all directions in between. Because of the distance between the filter planes, the three-dimensional filter also enables cross-flow between the filter planes transverse to the flow direction of the filter.The distance between the filter planes is therefore preferably within a dimensional range that is comparable to the dimensions or diameter(s) of the through-holes of the filter.

[0008] The invention therefore moves away from providing a purely two-dimensional filter in the form of a perforated sheet or a wire mesh in the brewing unit, which would mean that only one filter level is available and can therefore become clogged more quickly. This is because during brewing in a fully automatic coffee machine, the finest particles of the coffee powder, i.e. particles with a size of less than 100 pm, migrate within the pressed grounds towards the filter. The finest particles can build up in front of the filter and form a barrier for the subsequent fluid. This can lead to an undesirable increase in pressure in the fully automatic coffee machine. On the other hand, a high proportion of fines in the coffee powder is desirable for taste reasons, especially when preparing espresso. This is because the finer the powder, the larger the surface area of ​​the particles that can be wetted by the preparation water.The larger the surface area of ​​the particles, the more coffee aromas can be released in a short time.

[0009] To avoid an unwanted increase in pressure, grinders in fully automatic coffee machines are often set so that the fine fraction is below the critical limit of, for example, 50%. Since both the types of beans processed and component tolerances can lead to considerable fluctuations in the fine fraction, the difference between the average fine fraction and the limiting fine fraction should be relatively high. For this reason, grinders are currently often set relatively coarsely. This, however, reduces the brewing efficiency of the fully automatic coffee machine. The lower brewing efficiency results in a comparatively high bean consumption. Rather, the invention pursues the principle of significantly increasing the filter surface of the brewing unit while maintaining largely the same component dimensions, particularly of the brewing chamber, by ensuring that the filter according to the invention provides an effective filter surface not only in its extension plane but also in its depth.It thus offers not only the conventional, one-dimensional, and straight flow direction orthogonal to the filter plane. The filter according to the invention now allows a quasi-three-dimensional flow possibility, whereby flow through the three-dimensional filter is also possible with directional components in the filter plane and on curved, even bending, and in any case longer paths.

[0010] Tests have shown that the three-dimensional filter design in fully automatic coffee machines allows coffee powder with a fines fraction of up to 70% to be processed. This means that up to 70% of the particles in the coffee powder can have a particle size smaller than 355 pm. The coffee concentration can be increased to over 7% with such powders – compared to the currently maximum achievable coffee concentration of approximately 6%. Because the filter according to the invention allows powder with higher fines fractions, cost-intensive adjustments and measurements of the grinders in production can be eliminated. Furthermore, a wider range of commercially available beans can be reliably processed in fully automatic coffee machines with the filter according to the invention.

[0011] Because coffee powder with a higher proportion of fines can be processed smoothly, the same extraction rate as with current fully automatic coffee machines can be achieved with significantly fewer coffee beans. The resulting savings can be as much as 20%, which in particular also reduces the customer's costs for operating a fully automatic coffee machine equipped with the invention. The savings in coffee beans per preparation cycle also allow for a smaller fully automatic coffee machine because not as much coffee powder needs to be processed to achieve the same preparation result. The dimensions of both the brewing chamber and the grounds container can therefore be smaller. In addition to the more compact design of the fully automatic coffee machine, a longer service life of its grinder can be expected because it has to grind less coffee powder per preparation cycle.According to the invention, the filter is intended to retain the filter cake and is arranged accordingly. For this purpose, it is arranged downstream of the filter cake in the brewing unit.

[0012] In principle, the filter of the brewing unit according to the invention can consist of several conventional perforated sheets or wire meshes arranged one above the other and at a certain distance from each other. The filtering effect of each level can be increased by not aligning the through holes of different filter levels. According to an advantageous embodiment of the invention, the through holes of the different filter levels can therefore be offset from one another in the direction of flow through the filter. The offset of the through holes supports the formation of crossflow and turbulence of the fluid within the filter and thus reduces the accumulation and settling of particles in the filter.

[0013] According to a further advantageous embodiment of the invention, the filter can comprise a multi-layer, close-meshed net. It can, for example, be designed as a close-meshed, three-dimensional braid, woven fabric, or knitted fabric made of relatively thin threads. This allows it to offer high pressure resistance, which is particularly important when pressing the pomace. Thanks to the three-dimensional filter geometry, very fine particles that migrate towards the filter during brewing can no longer build up to the same extent as with known filters. The thin threads that surround the mesh of the net as through holes lead to a different ratio of openings or through holes to closed areas compared to a perforated sheet. The particles are less able to settle on the now smaller closed areas, namely on the threads with a regular, round cross-section.The three-dimensional structure of the filter and the resulting possible cross-flows also lead to turbulence in the fluid, which prevents the particles from accumulating and building up in the filter and even in front of it.

[0014] The mesh, woven, or knitted fabric can be largely homogeneously braided, woven, or knitted and thus have a structure of openings of the same or different sizes that is evenly distributed in every direction. According to a further advantageous embodiment of the invention, the filter can have different diameters of the through holes or mesh sizes in different filter levels. Different filter levels can therefore be assigned different diameters in that the diameters of one filter level may not occur or may occur much less frequently in another filter level. In a simple case, for example, the outer filter levels of the filter can be assigned a smaller diameter of the through holes than a middle filter level, which prevents the filter from being accidentally inserted upside down.A single filter plane doesn't necessarily have to be assigned a single diameter; rather, several different diameters can be present. Thus, different distributions of through-hole diameters can be provided in different filter planes. By selecting and distributing the through-hole diameters within the three-dimensional filter, its properties can be specifically controlled.

[0015] The material used to construct the filter can be chosen largely arbitrarily, as long as it is heat-resistant and the filter can be made pressure-resistant. According to a further advantageous embodiment of the invention, the filter can be made at least partially of metal, preferably partially or entirely of stainless steel. Metal can be used to create both pressure- and heat-resistant structures that are also relatively easy to clean and food-safe.

[0016] According to an alternative embodiment of the invention, the filter can be made at least partially of plastic. The filter can be made entirely or partially of plastic foam, which can preferably be elastic. This should make its production more cost-effective. In addition, the filter's self-cleaning effect can be utilized, which occurs when it is compressed and then relaxed again during each preparation cycle. During this movement, the pores of the elastic foam are compressed and relaxed. This changes the "mesh size" of the filter, which further counteracts the accumulation of particles. When rinsing the brewing chamber, previously adhering particles can then be successfully rinsed out. Depending on design requirements, the filter can also be made partly of metal and partly of plastic.

[0017] The aforementioned object is also achieved according to the invention in a fully automatic coffee machine mentioned above by the previously described brewing unit with the filter for eluted portion of a food powder. Reference is made to the above-mentioned advantages in the manufacture and operation of the fully automatic coffee machine 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 sheet known per se.

[0018] According to an advantageous embodiment of the invention, the fully automatic coffee machine can be equipped with a conventional flat metal sieve with holes 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 in the flow direction of the brewing unit directly upstream of the known metal filter and thus downstream of the grounds or "puck". Although the additional filter requires a certain amount of space within the brewing chamber that cannot be used for ground coffee, this loss of space or coffee is at least compensated for by the brewing efficiency resulting from the additional filter. Consequently, even conventional fully automatic coffee machines can be retrofitted with the additional filter.

[0019] According to a further advantageous embodiment of the invention, the additional filter can be arranged both upstream and downstream of the grounds, the puck, or the portion of food powder. The lower filter in the flow direction can be arranged in addition to or alternatively to the conventional metal filter and function as described. The upper filter in the flow direction can perform a water distribution function instead of a pure filtering function. This avoids so-called "channeling," in which the preparation water does not flow evenly through the pressed ground coffee or the puck, but flows more strongly in some places and elutes less frequently or not at all in other places.

[0020] The principle of the invention is explained in more detail below using a drawing as an example. The single drawing shows, in a highly simplified form, a section of a wall 11 of a cylindrical brewing chamber of a brewing unit 10, in which the filter 1 according to the invention is arranged. Corresponding to the cylindrical brewing chamber, the filter 1 has a circular circumference U. The filter 1 consists entirely of a three-dimensional wire mesh resulting from a metal thread weave of a thin metal thread. It has a thickness D of only around 2 mm, so that even as a retrofit object in an existing fully automatic coffee machine it requires hardly any additional space. When used according to the invention, the filter 1 contacts a portion of coffee grounds with its upper side 2 (shown in the figure). As a retrofit object, i.e. as the sole filter 1 without a 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 level, which, due to the three-dimensional structure of the filter 1, is followed in the flow direction by further filter levels that are not separately visible in the figure.

[0021] Even the top surface 2 of filter 1 is not geometrically completely flat due to its three-dimensional weave. The same applies to the other filter layers that together form the three-dimensional filter 1. Therefore, they can also be referred to as filter layers.

[0022] During elution of the coffee grounds, preparation water or eluate flows through the brewing unit 10 and thus through the filter 1 in a flow direction R as the main direction. In doing so, the filter 1 supports the coffee grounds particles opposite to the flow direction R. Nevertheless, rearrangements and migration movements occur, particularly of the finest particles. This is because the filter 1 divides the eluate flow coming from the grounds into many substreams that do not run exclusively in the flow direction, but as oblique flows, also at an angle to it, and even orthogonal to the flow direction, i.e., transverse to it as cross flows.

[0023] Some particles settle on the top surface 2 of filter 1. However, because they lack sufficient support there due to the thin threads of the wire mesh, they can no longer form a fluid blockage, as is the case with conventional filters. Now, however, they enter filter 1 and partially flow through it. Even within filter 1, they are barely able to accumulate because turbulence in the filter mesh caused by oblique and cross flows impedes this.

[0024] Filter 1 offers a significantly larger wettable surface due to its multiple filter layers. While this allows for more particles, especially the finest ones, to adhere to it, they are now distributed over a much larger area and more finely. As a result, they can no longer form a fluid barrier, which would lead to an undesirable increase in pressure in the fully automatic coffee machine. Filter 1 thus enables the processing of coffee powders with a significantly higher fines content than previously possible. Filter 1 not only opens up additional bean varieties for successful and reliable processing in a fully automatic coffee machine, but also leads to lower coffee bean consumption while simultaneously achieving a stronger aroma.

[0025] Since the brewing unit described above is an exemplary embodiment, it can be modified to a wide extent by those skilled in the art without departing from the scope of the invention. In particular, the specific method of manufacturing the filter by weaving, knitting, etc. or the specific design of the circumference of the filter can be different from that described here, particularly if technical requirements or a different cross-sectional shape of the brewing chamber of the brewing unit require it. Likewise, the filter itself can be designed in a different shape or from a different material if this is necessary for reasons of space or design. Furthermore, the use of the indefinite articles “a” or “an” does not exclude the possibility that the features in question can be present multiple times or multiple times.

[0026] List of reference symbols

[0027] 1 filter

[0028] 2 Top 3 Bottom

[0029] 10 brewing units

[0030] 11 Wall of a brewing chamber

[0031] D Thickness R Flow direction

[0032] U circumference

Claims

PATENT CLAIMS 1. Brewing unit (10) for brewing a beverage from ground food powder, in particular a brewing unit (10) of a fully automatic coffee machine, with a filter (1) for retaining a filter cake of the food powder, with a filter level (2) of the filter (1) and with through holes in the filter level (2), characterized by a plurality of filter levels of the filter (1).

2. Brewing unit (10) according to claim 1, characterized in that the through holes of different filter levels are arranged offset from one another in the flow direction (R) of the filter (1).

3. Brewing unit (10) according to claim 1 or 2, characterized in that the filter (1) comprises a multi-layer and close-meshed net.

4. Brewing unit (10) according to one of claims 1 to 3, characterized in that different filter levels of the filter (1) have different diameters of the through holes.

5. Brewing unit (10) according to one of claims 1 to 4, characterized in that the filter (1) consists at least partially of metal.

6. Brewing unit (10) according to one of claims 1 to 4, characterized in that the filter consists at least partially of plastic.

7. Fully automatic coffee machine, in particular for household purposes, characterized by a brewing unit (10) for eluted a portion of a food powder according to one of the above claims.

8. A fully automatic coffee machine according to claim 7 above, having a brewing unit with a conventional flat metal sieve with holes for retaining a filter cake of ground food powder, characterized by a filter of a brewing unit according to one of claims 1 to 6 as an additional filter immediately upstream of the metal sieve.

9. Fully automatic coffee machine according to one of claims 7 or 8, characterized by a 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 food powder.

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