Abstract:
The invention is directed to a filtering device, a filter element therefor and a method of manufacturing the filter element ( 28 ) from filter paper. The filter element ( 28 ) has a receiving cavity ( 76 ) to be filled with extractable materials such as coffee grounds or tea leaves. Following contact with hot water, the extractable materials deliver extractive substances to the water, resulting in a brewed beverage that is drained from the filter element ( 28 ). During this process, the filter element ( 28 ) is held by the filter support ( 1 ) by way of a supporting member which includes a rim ( 39 ) formed on the filter element ( 28 ) and having a bearing surface ( 40 ), and a supporting surface ( 24 ) formed on the filter support ( 1 ). The rim ( 39 ) of the filter element ( 28 ) is reinforced mechanically by providing the filter paper with exposed pleats ( 42, 51, 52 ) which cooperate with corresponding elevations ( 115 ) and recesses ( 79 ) formed on the supporting surface ( 24 ) of the filter support ( 1 ). Such a filtering device of the present invention enables its manipulation and manufacture to be significantly facilitated. At the same time, improved brewing results are obtained. The operations of inserting such a filter element ( 28 ) in a filter housing ( 16 ) and filling it with coffee grounds, for example, are also improved. It is possible to manufacture a plurality of filter elements ( 28 ) in a single operation. At the same time, the filter elements are stackable in a minimum of space. The filter element is held in the filtering device without any additional fastening.

Description:
This is a continuation of PCT application serial no. PCT/EP98/00864, filed Feb. 16, 1998, which claims priority from European application serial number 97104260.1, filed Mar. 13, 1997, (pending). 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a filtering device for making brewed beverages. Furthermore, a second invention relates to the filter element insertable into the filtering device referred to above. Finally, a third invention relates to the method necessary for manufacturing the filter element. 
     From U.S. Pat. No. 3,089,405 there is already known a filtering device for a coffee maker serving to prepare brewed beverages. The filtering device is comprised of a ring-like portion of a water pipe, briefly referred to as ring pipe, on the outside of which a filter sack is freely suspended. The filter sack is adapted to be filled with coffee grounds, and hot water can be introduced through the filter sack&#39;s mouth for the purpose of filtration. The hot water entering through the open end of the annular water pipe, upon taking up extractive substances from the extractable material (process of extraction), is drained freely along the outer wall of the filter sack to be received in a container placed underneath. 
     For installation, the filter sack is secured to the filter support using holding means. For this purpose, an elastic band or an elastic string is drawn into the filter sack&#39;s upper end, which band or string, together with the mouth of the filter sack, is pulled from outside around the ring pipe configured as the filter support. After the widened mouth of the filter sack above the ring pipe is released, the elastic string will be shirred in such a way that the diameter of the filter sack above the ring pipe becomes smaller than the section around the ring pipe. In this manner, the filter sack is secured to the ring pipe and hence prevented from falling down during the brewing cycle. 
     Aside from the relatively complicated procedure of securing the filter sack upon the ring pipe—requiring the mouth of the filter sack to be opened by pulling the elastic string apart until the sack can be fitted over the outer surface of the ring pipe from below—, a highly elaborate process is involved to draw an elastic band or an elastic string into the upper end portion of the filter sack to make sure that the elastic string secures the filter element on the filter support. 
     Such securing of a filter sack to a filter support of a beverage brewing apparatus is an elaborate and complicated procedure depending ultimately on the operator&#39;s skills in opening the mouth of the filter element, fitting it over the ring pipe, and subsequently aligning the filter element on the filter support to make sure that the longitudinal axis of the filter element extends essentially perpendicularly; in the event of an improper installation, the paper filter sack tends to be askew, to tear and/or even detach itself from the filter support, entailing the risk of an operator scalding himself or herself. 
     The need to use an elastic string or rubber band fitted to the filter element as an extra addition and the elaborate assembly of this rubber band to the filter sack is far from comfortable and adds to the unit price of the filter sack, which makes itself felt clearly in particular in cases where coffee is brewed several times a day. Such mounting of a filter sack is in all likelihood only suitable for use where the sack itself is made of a stable filter material. 
     Furthermore, from EP-A-0 741 988 a filtering device is known in which the filter element is assembled from two shell-shaped paper strips to form a single piece. In the area of its mouth the filter element has a free rim which is folded over such as to form a pocket. The pocket opens in downward direction, extending essentially in the direction of the wall of the receiving area. The filter support comprises a substantially round section of a circle bent from wire and having bent thereon a wire-shaped holder and a stud member at the opposite ends. The semicircular sections of the holder serve to hold the filtering device, while the diametrically opposite supporting sections serve to support the filtering device on the rim of a vessel. 
     If in this filtering device the ring member is not accurately at the deepest point of the pocket, that is, at the location where the rim is folded towards the filter body, it cannot happen that the rim opens upwardly causing the filter element to fall down due to its weight increase as the water slowly penetrates the coffee grounds, the receiving cavity and in consequence also the rim of the filter element during the brewing cycle, because the filter layers and the rims are made of a composite fabric of heat-sealable fibers or similar woven fabrics, these elements being even connected by heat sealing this composite fabric or by similar means. The costs for such a filter element made of a composite fabric are however, considerable, particularly when this filter element is intended for use as a disposable filter involving high quantities. When used as reusable filter the same cost considerations apply as mentioned in the foregoing. 
     From DE-40 38 023 A1 a method of manufacturing a two- or multi-shell container from paperboard or a similar material is known as described in the prior-art portion of patent claim  31 . In this method, the paper, also referred to as the blank, is drawn from the edge side of the die half in addition to being drawn from the blank side while further material is fed. In this process, stock present between the two die halves is available to compensate for the forming of the paper in the die cavity, without the material being subjected to excessive strain. In this method, therefore, a receptacle is formed by feeding in stock. 
     From U.S. Pat. No. 5,171,457, in particular from FIG. 6, a rimmed coffee filter container cup is known into which an equally rimmed coffee filter is insertable in accordance with FIG.  7 . In this arrangement, the rim of the coffee filter takes support upon the rim of the coffee filter container cup. The cylindrical wall of the cup-shaped coffee filter has exposed ruffles shaped in a zigzag configuration and oriented outwardly. The exposed ruffles continue in the rim extending at approximately right angles to the cylindrical wall by being apparently pressed together in the rim. 
     Finally, from FR-A-2 691 059 a filter cartridge made of filter paper is known whose mouth is provided with a rim extending away from the filter cartridge at approximately right angles thereto. The mouth of the filter cartridge is closed with a filter paper lid extending over the rim. The rim ensures a perfect position of the filter cartridge in the interior of a metal filter of a coffee maker. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the first invention to provide a filtering device of the type initially referred to, with which very good brewing results are obtained at a short brewing time and at low manufacturing cost and which affords particular ease of handling. It is an object of the second invention to configure the filter element utilized for the filtering device in a particularly simple and manageable fashion, ensuring a stable mounting in the filter support without the need for additional components while being of a particularly straightforward and economical construction. Finally it is an object of the third invention to provide a method of manufacturing this filter element of the invention, which method enables also a thin filter element to be manufactured with ease, at low cost and in high quantities without subjecting the material to excessive stresses, strains and loads. 
     The object of the first invention is achieved as follows. By providing the rim with the exposed pleats, the filter element manufactured from conventional filter paper is stiffened in an axial direction, enabling its large bearing surface to bear against the supporting surface formed on the filter support. By virtue of the stiffened rim, the operation of inserting the filter element into the filter support is facilitated until subsequently the rim of the filter element bears against the supporting surface of the filter support. The awkward procedure of unfolding the filter element by hand is not necessary for insertion of the filter element into the filter support because the filter element already possesses its final shape necessary for the brewing operation. By reason of the stiffened rim, the filter element maintains its shape when suspended in the filter support also when the filter paper is imbibed with water. In this configuration, both the exposed pleats and the rim itself contribute to the stiffening of the filter paper, obviating the requirement of having to provide external stiffening means. As filter paper conventional filter paper qualities for electrically powered or other beverage making units for domestic use may be employed. 
     The term exposed pleats as used herein means that not a single section of the pleats&#39; surfaces is concealed in the direction of the longitudinal axis of the filter element, that is, in the direction in which the individual filter elements are separated from each other, meaning that when looking down on the imaginary longitudinal axis of the filter element, practically the entire surface of the filter element has to be visible, similar to a flat filter element in which however the surfaces are visible not in shortened form because of the absence of a slanting configuration, but which is precisely the case with the three-dimensional configuration of the ring member and the wall of the receiving area. 
     According to the present invention, the formation of exposed pleats results in a particularly large bearing surface in the rim area of the filter element, with the effect that a particularly large load-bearing surface is obtained in the rim area of the filter element in order to thus distribute the relatively high forces bearing on the filter paper as a result of the wet coffee cake to a large paper surface of the filter element. The occurring tensile stresses—which are essentially the only stresses occurring with the filter paper wet—are thereby maintained at a level below the tensile stresses permissible for the filter paper employed. This makes it possible to use particularly thin filter paper with good perviousness to extractive substances, producing the advantageous effects of both a low price of the filter element of the invention and an excellent quality of the beverage, particularly coffee. It will be understood, of course, that it is not necessary for the elevations and recesses formed on the supporting surface of the filter support to correspond exactly to the number of elevations and recesses of the filter element, a lower number being likewise possible. In cases where fewer recesses and elevations are formed on the circumference of the filter support, it must only be ensured that these be spaced on the periphery such as to still register with the elevations and recesses of the filter element. 
     With the first invention a particularly simple filtering device is provided in which the filter element, owing to its handling convenience, is readily insertable into the filter support until it is suspended freely in the filter support, its rim then bearing with the filter element&#39;s full weight, inclusive of the weight of the coffee grounds, against the supporting surface of the filter support. No additional parts are needed to serve as holding means for the filter element. Such a freely suspended filter element manufactured solely from filter paper, in combination with the filter support of the present invention, produces particularly good extraction results on brewing, because it enables the hot water to be drained almost freely along the outer surface of the filter element. This also results in a comparatively speedy passage of the hot water through the material being extracted, in particular coffee grounds, preventing bitter principles and other undesirable flavors from being extracted from the coffee grounds and dissolved in the hot water. The result is a particularly aromatic and tasty coffee beverage. Because the hot water passes through the coffee grounds relatively speedily and uniformly to enter a container provided beneath the filtering device, the liquid cools hardly noticeably between the moments of entering and leaving the filtering device, so that the brewed beverage has an optimum temperature also after the extraction cycle without the provision of external heating. 
     Apart from facilitating its manufacture, greater handling convenience of the filter element can be obtained because the rim forms the end of the mouth of the filter element. While it is entirely conceivable to arrange the rim, by pleating, in the mid-area of the filter element if the dimensions of the filter support were such as not to permit it otherwise, this solution however would then require the area of the filter element projecting upwardly beyond the rim to be configured such as to maintain its shape also under wet conditions. 
     Because the area of the filter element bounding the receiving cavity is likewise provided with pleats engaging in mating elevations and recesses formed on the filter support, this area, too, carries a certain share of the supporting function, supporting the filter element also in this particular area. At the same time, the function of locating the filter element centrally is additionally improved through this area. By reason of the increased surface of the area bounding the receiving cavity, which is obtained by the pleats provided here additionally, the load-carrying capability of the filter element is enhanced also in this area so that the filter element, even when wet, holds the equally wet coffee cake on the filter support without the risk of the filter element slipping off of the filter support or, still worse, tearing because of excessive load on the filter paper material. 
     It should be noted in this connection that in the filter element of the present invention the diameter in the transition from the area bounding the receiving cavity to the rim should always be somewhat greater than the opening surrounded by the supporting surface of the filter support, in order to ensure that the rim of the filter element can rest against the supporting surface with its entire bearing surface. As the filter element is inserted into the filter support, the area of the filter element&#39;s receiving cavity bounding the supporting surface of the filter support should be resiliently urged radially inwardly until the bearing surface on the rim of the filter element rests flush against the supporting surface. As a result the filter element resides always snugly within the filter support, while at the same time being located centrally by the filter support. Accordingly, the area bounding the receiving cavity should always be urged resiliently against the filter support in its transition area, thereby further improving the support of the filter element in the filter support itself as well as the handling convenience during insertion of the filter element. The snug seat of the filter element in the filter support enables an operator to have better control of the individual manipulations, avoiding damage to the filter element. As soon as the filter element then becomes wet in the brewing cycle, these tensile stresses disappear, yet with the consequence that the filter element continues to cling to the filter support. 
     In lieu of the transition area formed by a substantially wider surface area, it is also possible to use a basket which is open downwardly in the direction of flow, or a basket may adjoin the transition area. In this arrangement, for example, the basket may be injection-molded onto the filter support as an integrally formed piece, or alternatively the basket may be inserted into the filter support as a separate part in a subsequent operation. The basket is comprised of individual braces to minimize the areas of contact with the outer surface of the filter element in order to thus enable a nearly unrestrained discharge of the brewed beverage. The basket serves as an ancillary holding means for the filter element in addition to the supporting surface, while on the other hand locating the filter element in the filter support centrally. 
     Other features are provided to enable the brewed beverage to be drained along the outer surface of the filter element practically freely. In this arrangement, the braces are disposed above the filter element substantially at a level where they practically present no impediment whatsoever to the passage of the brewed beverage through the filter element. 
     In a further configuration of the present invention, the supporting surface of the filter support and the bearing surface of the filter element are configured in such fashion that during the brewing cycle a water layer penetrates between the filter element and the filter support, provoking in this area an adhesive effect which in turn further contributes to additionally securing the filter element onto the filter housing. Hence these additional securing means do not take effect until after the filter element is imbibed with liquid, that is, after the coffee cake has become particularly heavy due to the take-up of water. The effect of adhesion which then sets in makes it even possible for the bearing surface of the filter element to be reduced without the water-imbibed and hence relatively heavy filter element, inclusive of the wet coffee cake, slipping out of the filter support. Because the filter paper utilized for the filtration of extractable materials has fine pores, being thus of a microporous structure, liquid creeps particularly well along the still dry wall of the filter element into the transition area and onwards into the rim due to the capillary action occurring when the coffee grounds held in the receiving cavity of the filter element become wet. 
     With this additional support provision on the filter element, it is possible to employ extremely thin filter papers without these papers slipping out of the filter support. It is precisely when filter paper becomes wet, hence losing its flexural rigidity nearly completely, that the effect of adhesion produces an additional holding force refraining the filter element from losing its original shape in addition to causing the filter element to be still held securely in the filter support. To obtain maximum possible adhesive forces, it is advantageous for the bearing surfaces of the filter element on the filter support to be particularly large. This is accomplished by the exposed pleats on the one hand and by the relatively large diameter of the filter element on the other hand. 
     In a filter element in which water is prevented from entering the rim area, which may be accomplished, for example, by providing on the filter element a waterproofing layer such as plastic or similar liquids entering the filter paper, the stiffness of the filter element is nevertheless ensured although the effect of adhesion cannot occur in the then dry rim area, because the pleats operate to provide for sufficient reinforcement or stiffness of the rim and, where applicable, of the transition area as well. It is thus for the first time that a suspended filter element manufactured from filter paper is provided in simple manner, which takes support within the filter support securely without additional supporting means. In consequence, handling advantages and a better brew result. 
     In another embodiment, seating engagement of the filter element with the filter support is improved in that the angle between the supporting surface of the filter support and the vertical axis of the filtering device is smaller than or equal to 90°. In this configuration, the filter element virtually hooks onto the outwardly slanting and downwardly extending supporting surface of the filter support, the force exerted on the filter paper being at its maximum in particular in the corner at the junction of the bearing surface with the transition area of the filter element. 
     Although the above-described holding approaches for the filter element (rim, transition area, basket, radial bias of the filter element in the transition area and adhesion) are perfectly sufficient, the added possibility exists to select a retaining device which, acting against the rim of the filter element, urges the bearing surface of the filter element against the supporting surface on the filter support. In this arrangement it is sufficient for the retaining device to rest lightly, by its own weight, on the outer surface of the rim of the filter element on the side facing away from the bearing surface. In addition to the adhesive effect, the retaining device exerts a bearing force on the rim of the filter element. The retaining device may be fabricated from plastic or some other material affording ease of manufacture. Alternatively, it may also be part of a ring arrangement adapted to swing upwards on the filter support, which ring arrangement is urged against the rim&#39;s upper supporting surface upon insertion of the filter element. 
     In yet another embodiment, a free hanging filter element is provided having its outside encompassed by a relatively spaced shell-shaped filter housing structure in a thermally insulating fashion. Preferably, this filter housing structure may be of a transparent plastic material to enable an operator to watch the brewing and draining cycles of the filter element from outside to be thus able to detect the end of the filtering cycle. An ellipsoid has proven to be particularly advantageous for the contour of the filter element because this shape enables the hot water entering the filter element to be distributed uniformly radially outwardly from the center. As a result, hot water penetrates the coffee grounds with maximum possible uniformity throughout, so that optimal utilization of the coffee grounds is accomplished also where only small quantities are involved. As an ellipsoid a substantially hemispherical outer surface has proven to be useful whose draining area covers a larger radius than the remaining area and whose transition area proximate to the rim follows the generating surface of a truncated cone. While the draining area on the filter element with the less pronounced radius has the effect of reducing the draining period, the frusto-conical transition area on the filter element enables a better engagement surface to be obtained on the conformably shaped area of the filter support while on the other hand facilitating the forming of the filter element and the filter support in this particular area when this area extends above the center of a hemisphere. 
     In still another embodiment, the filter support is composed of two or more parts. Such a solution is appropriate when the supporting surface for the filter element is part of an intermediate member fabricated from single braces, which member takes support upon the filter support proper. As a result, both the intermediate member and the filter support afford greater ease of manufacture because of greater simplicity of the forming dies, and these parts can be cleaned by hand more easily and effectively because they are separable from each other. In this embodiment, the bearing surface of the filter element is able to bear against the supporting surface of an intermediate member which in turn bears against the filter support. Alternatively, the intermediate member may also be first hooked or clipped or otherwise secured to the transition area of the filter element. In any case, in this arrangement the intermediate member combines with the filter support to form the filter support proper for the filter element. However, if required by injection molding considerations, manufacturing the filter support from more than two parts and assembling it to form a “complete filter assembly” may be contemplated as well. 
     In still yet another embodiment, in combination with the filtering device of the present invention, a beverage making apparatus suitable for domestic use is provided. In this apparatus, the water held in a water reservoir of the beverage maker is supplied to a water through-flow heater where it is heated and directed preferably through a riser to the mouth of the filter element where it flows onto the surface of the coffee grounds or the tea leaves, distributing itself uniformly in the receiving cavity. Upon extraction, the beverage is drained through the lower discharge point of the filter element directly or through the housing of the filter support into a container placed underneath. However, it is also entirely conceivable to place the filtering device onto a container and perform the filtering by hand. 
     In another aspect, the invention relates to the filter element itself which is fabricated from filter paper and has a mouth and a receiving cavity to be filled with extractable materials such as coffee grounds or tea leaves. The filter element has a rim extending in a direction away from the receiving cavity, which rim is reinforced by exposed pleats. By means of its rim, the filter element is readily seatable on a conformably shaped rim, bearing against it. The exposed pleats of the present invention not only stiffen the rim area but also increase its resistance to tearing and its flexural stiffness because of reinforcement of the material. Such a filter element affords ease of handling and is sufficiently elastic when inserted into a filter support conformed to the shape of the filter element. Handling convenience is ensured because the filter element has its final shape already prior to insertion. Such filter elements are stackable in nests requiring a minimum of household storage space. In this manner, it is also possible to produce several filter elements in a single operation, using several filter papers in superposed arrangement. 
     The exposed pleats may be formed either in only the rim or only the transition area, or ultimately on both parts. In the use of the exposed pleats, a particularly flexible filter element results which invariably returns to its initial position even when subjected to major deformations from outside. In this embodiment, a highly elastic and yet dimensionally stable filter element in dry condition is obtained which, by reason of the exposed pleats, is radially compressible in diameter. During the brewing cycle the filter element takes support in the filter support securely although it undergoes a stability variation as it changes from dry to wet. 
     In another embodiment, the area bounding the receiving cavity is also pleated. In this arrangement also this area is reinforced by overlapping paper in addition to the rim in order for the stability of the filter element to be increased in this particular area. 
     If the pleats extend in the longitudinal direction of the filter element in accordance with the features maximum tensile strength is achieved in the transition area and on the rim of the filter element. In this arrangement the pleats are maintained nearly unchanged. The most favorable pleat arrangement is obtained when the pleats extend radially outwardly, beginning at some distance from the draining area on the circumferential surface of the filter element. In this arrangement, the depth of the pleats increases radially outwardly, reaching its maximum in the rim area. The increase in pleat depth may proceed continuously or in steps. 
     In order to be able to better reduce the tensile forces occurring on the filter element in the area of the receiving cavity, which forces are due to the weight of the wet coffee grounds and the wet filter paper as well, the features make provision for a sharp corner or sharp edge in the range from 0.2 mm to 1 mm at the junction of the rim with the transition area of the filter element. It is thereby ensured that the bearing surface rests on the supporting surface, bearing against it uniformly. According to the filter element is integrally made of filter paper with a gsm substance of 20 to 60 g/m 2 , preferably 35 g/m 2 . The use of thinner filter paper material is hardly possible because then the load on the filter paper when filled to maximum capacity becomes too high during brewing, entailing the high risk of tears occurring in the filter paper. 
     With the features the shape of the area of the filter element bounding the receiving cavity is determined. Such an ellipsoidal shape has proven to be optimal for filtering coffee, because the hot water penetrates nearly uniformly all areas of the coffee grounds. However, because of the increased discharge rate, it is therefore necessary for the supply of hot water to be suitably adapted. 
     According to another aspect of the invention it is possible to continue those pleats that extend from the transition area bounding the receiving area towards the rim and farther over the corner into the rim of the filter element, yet then in reverse form. Hence, when looking down onto the filter element, it will be seen that a pleat having its sides facing each other extends from the transition area to the corner, whilst it extends from the corner to the rim as a pleat having its sides facing away from each other, that is, on the rim a trough pleat turns into a crest pleat. In this arrangement, it is irrelevant whether the pleats are of an undulating or zigzag configuration. The corner invariably follows a zigzag or undulating course common to both the trough and the crest pleats. 
     In order to adapt the loadable area of cross-section of the filter element to the weight increasing in the direction of the rim, the paper cross-section increases in the direction of the rim, preferably at a substantially constant rate. This is accomplished in that the number of pleats on the circumference of the filter element increases in the direction of the rim. This increase in load-carrying ability towards the rim can be further assisted by the increasing the depth of the pleats in the direction of the rim of the filter element. It is only in this way that the filter element can be based on a flat round blank of paper. 
     In still another embodiment, a tab serves to facilitate the removal of a filter element from the stack. 
     In accordance with another aspect of the invention, a method of manufacturing a formed part to be shaped from paper is provided, in which the formed part is a filter element made of thin filter paper and having a mouth and a receiving cavity to be filled with extractable materials such as coffee grounds or tea leaves. The filter element has a rim which extends in a direction away from the receiving cavity and is reinforced by pleats. This filter element is formed by pleating the filter paper as it is inserted into the die cavity, so that the filter material is not subjected to excessive strain. Accordingly, the shape of the filter element is such that the resulting excess material is distributed in spatial areas constituted by pleats. With this method it is possible to integrally form a filter element made from thin filter paper. Such a method enables a filter element to be formed to any desired shape. This method is particularly suitable for use on filter elements in which an ellipsoidal outer contour is adjoined radially outwardly by an annular rim. For the manufacture of filter elements, this is an extremely simple, economical and time-consuming method. 
     Sill other features are provided to impart a particularly stable final shape to the rim of the filter element. The reinforced rim adds to the dimensional stability of the filter element itself, improving its handling convenience. However, it is also possible to reinforce the entire filter element or further parts thereof in this manner. 
     With the two-piece configuration of the blankholder, the outer ring holds the filter paper in place as it is drawn into the die half. In this process, the inner ring may contribute to the holding function as well. With the use of two independently operating blankholders acting on the filter paper with different forces, better control of the filter paper feed operation is possible. Thus the application pressure of the inner blankholder against the filter paper during feeding can be lower than the application pressure of the outer blankholder in order to prevent the requisite forming forces on the filter paper at the junction of the rim with the transition area from becoming excessive during feeding, which could easily cause tearing of the filter paper. Control of the application forces can be effected by raising or lowering the blankholders. However, as soon as the filter element forming operation is completed, the inner blankholder contributes to applying counter-pressure against the filter element, whilst the outer blankholder is not required to assume a function for processing the filter paper. The blankholder parts may also be formed of a single blankholder which then assumes all the functions. 
     Other features are provided in order to prevent the filter paper from slipping out of location within the die, so that a filter element as concentric as possible results from the forming operation. 
     According to still other features, the locating means include a movable retainer adapted to travel in and out of the die half. 
     According to further features, the locating means may be produced by forces of suction or pressure. However, other locating means as, for example, projections or recesses to be provided on the filter element and engaging in centering devices on the die assembly may also be contemplated. 
     In a further embodiment, the surfaces of the die parts are configured in such fashion as to ultimately bring the filter element into the desired final form. The surfaces of the dies extend such that during the process of manufacturing a filter element pleats are produced which are free from undercuts, hence extending as exposed pleats. This enables the placement of several layers of filter paper into the die in order to thus manufacture a major number of filter elements in a single operation. How many layers of filter paper can be inserted depends on the thickness of the paper and on the forming die. 
     Advantageously, ten to twenty circular filter paper blanks for manufacturing filter elements in a single pressing operation have proven to be suitable. In this process, the punch half presses all the round blanks into the die half simultaneously. 
     Other features the invention enable the flank areas of the crest and trough pleats of the filter element to be drawn by the filter element forming die in order to prevent the flank areas from resting against the forming die walls during pressing. Unwanted additional pleating within the desired pleats is thereby avoided during pressing, which is the prerequisite to enable the removal of the individual filter elements from the filter stack. 
     In yet another embodiment, the formation of pleats is predetermined, and hence in particular facilitated, by the prior operation of producing pressed edges in the filter paper blank. 
     It will be appreciated that it is also possible to produce the filter element first without rim and subsequently forming the rim using a plurality of movable punch halves which are distributed on the circumference and fold the rim radially outwardly, pressing it into shape. 
     In still yet another embodiment, the smooth structure of die half, punch half and blankholder enables filter elements with closed pleats to be obtained, in which event however the filter elements have to be produced one by one. In this process the pleats occur by their own accord, being hence pressed into overlapping pleats subsequently. Because the pleats are closed, this method enables the production of only a single filter element at a time. The closed pleats are subsequently intensified by pressing die half, punch half and blankholder firmly against each other, as a result of which the filter element is pressed between these parts. This enables a particularly stable and yet elastic filter element to be obtained. 
     Several embodiments of the present invention will be explained in more detail in the following with reference to the accompanying drawing. In the drawing, 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a first embodiment of a filter housing, with filter element and retainer inserted therein and the pleats of the filter element closed; 
     FIG. 2 is a perspective view of the filter element inserted in the filter housing of FIG. 1; 
     FIG. 3 is a longitudinal sectional view of the filter element of FIG. 2; 
     FIG. 4 is a partial cross-sectional view of the filter paper substantially perpendicular to the rim, taken along the line IV—IV of FIG. 3, but on an enlarged scale; 
     FIG. 5 is a partial cross-sectional view of the filter element in its transition area, taken along the line V—V of FIG. 3, but on an enlarged scale; 
     FIG. 6 is a perspective view of a second embodiment of a support ring of a filter support and a filter element inserted therein having its pleats pressed in relative opposition (not shown), the illustration differing from FIG. 1 in that adjoining the filter support in downward direction is an open basket and that the supporting surface extends horizontally; 
     FIG. 7 is a perspective view of the support ring of FIG. 6, but shown without filter element; 
     FIG. 8 is a perspective view of a second embodiment of a filter element having exposed pleats in both the rim and the transition areas; 
     FIG. 9 is a top plan view of the filter element of FIG. 8; 
     FIG. 10 is a longitudinal sectional view taken along the line VIII—VIII of FIG. 9; 
     FIG. 11 is a longitudinal sectional view of a second embodiment of a filter support, with support ring and with the filter element suspended therein and provided with exposed pleats as in the embodiment of FIG. 8; 
     FIG. 12 is a perspective side view of a domestic coffee maker, with the filter support shown in FIG. 11 in longitudinal section in closed position, but on a reduced scale; and 
     FIGS. 13 to  17  show individual process steps for the manufacture of the filter element of the present invention in a die assembly provided for this purpose, including die half, punch half, blankholder, filter element and locating means. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1,  11  and  12  show a filter support  1  which according to FIG. 12 is insertable into a housing  2  of a coffee maker  3  for domestic use and is carried by the housing. According to FIG. 12, a brewing head  4  fixedly connected to the housing  2  by means of an arm  5  is provided above the filter support. Adjoining the arm  5  laterally is a water reservoir  6  which sits on a base  7  of the housing  2 . The transition from the base  7  to the water reservoir  6  is indicated by the horizontally extending parting line  8 . Extending from the base  7  in forward direction is a plate-shaped rest  9  having at its front a rocker switch or a slide control  10  connected to an electric switching device mounted inside the rest  9  but not shown here in greater detail. The rest  9  has its upper side bounded by a warming plate  11  on which a vessel  12 , preferably a glass carafe, is sat. The upper side of the glass carafe  12  terminates with a lid  13  fitted onto the glass carafe  12 . A handle  14  is affixed to the outer circumference of the glass carafe  12 , preferably by adhesive bonding. 
     Formed in the rest  9  beneath the warming plate  11  of FIG. 12 is an electric through-flow heater, not shown in more detail, whose inlet pipe is connected to the water reservoir  6  through a conduit not illustrated in greater detail. The outlet of the through-flow heater is connected to the brewing head  4  through a riser, not shown in more detail, which also extends within the arm  5 . The water reservoir  6  is closable with a lid  15 . 
     According to FIGS. 1,  11  and  12 , the filter support  1  is comprised of a filter housing  16  preferably injection molded from a plastic material and of a substantially hemispherical or ellipsoidal cross section. Provided in the lower area and extending concentrically with the filter housing  16  is a tubular skirt  17  terminating with its end surface  18  a small distance from the top of the lid  13  according to FIG.  12 . At the deepest point of the ellipsoidal filter housing  16  of FIGS. 1 and 11 is a central discharge orifice  19  which according to FIG. 1 is preferably provided with an annular collar  20  for improved discharge of the brewed beverages. The skirt  17  serves to improve the thermal insulation of the brew as it exits the discharge orifice  19 . According to FIG. 12, the brewing head  4  closes the mouth  21  of the filter support  1  completely in order to avoid heat losses during the brewing cycle. 
     According to FIGS. 1 and 11, a support ring  23  rests on the rim  22  of the filter housing  16 , the ring combining with the filter housing  16  to form the filter support  1  proper. The support ring  23  may also be integrally formed with the filter housing  16 . For better cleaning results, it is however advisable to configure the filter housing  16  and the support ring  23  in two parts. A further embodiment of a support ring  23  is illustrated in FIGS. 6 and 7. 
     According to FIGS. 1,  6 ,  7  and  11 , the support ring  23  itself or the ring member  36  of the support ring  23  has a supporting surface  24  which in FIGS. 6,  7  and  11  extends substantially horizontally and radially outwardly, while in FIG. 1 it is of a substantially outwardly sloping configuration, that is, it extends conically downwardly. At its inner edge the supporting surface  24  forms a relatively sharp edge  25  (with a very small radius at most) continuing downwardly in a transition area  26 . The edge  25  is of a ring-shaped configuration as is the supporting surface  24 . The wall of the transition area  26  is conformed to the outer envelope  29  of the outer wall  27  of the filter element  28  as shown in FIGS. 1 to  6 , while the wall of the transition area  26  of the support ring  23  of FIG. 11 is conformed to the shape of the transition area  30  of the outer wall  27  of the filter element  28  (FIGS. 8 to  11 ) against which it bears likewise practically with its entire surface. The transition areas  26 ,  30  of FIGS. 1,  2 ,  3  and  7  have a smooth structure—apart from the paper&#39;s roughness—, while the transition areas  26 ,  30  of FIGS. 11,  8 ,  9  and  10  are of a zigzag-shaped configuration. 
     In FIG. 11 the support ring  23  is an integrally formed part whose lower transition area  26  is adjoined by a downwardly open basket  33 , as becomes apparent from FIGS. 6 and 7. The basket  33  comprises relatively spaced downwardly extending braces  34  which all terminate in a horizontally extending ring  35  through the opening  78  of which the filter element  28  passes in downward direction (FIG. 11) so that the filter element  28  sits in the filter support  1  in substantially suspended fashion. The braces  34  essentially match the envelope  29  of the filter element  28 , that is, in the area of the braces  34  and the ring  35  the filter element  28  of FIG. 11 is partly supported in both a radial and a vertical direction. The major share of the supporting function is, however, carried by the rim  39 . The basket  33  provides for additional lateral securing of the filter element in the filter support  1 . 
     While the support ring  23  of FIG. 11 is integrally formed, it is formed of two parts in FIG. 1, comprising an ellipsoidal portion  32  and an upwardly adjoining ring member  36 . The portion  32  and the ring member  36  may be joined together at  61  by adhesive bonding, welding, threading, snap-fitting or similar fastening means. The ellipsoidal portion  32  of FIG. 1 is formed by a wall enclosure  37  extending at a distance to the filter housing  16 . With the double-walled construction of the filter support  1 , a particularly thermally protected filter support unit  1  is obtained. According to FIGS. 1 and 11, the support ring  23  enables this unit to be withdrawn from the coffee maker  3  without removing the filter support  1 , however, in FIG. 1 the closed ellipsoidal portion  32  provides for better protection of the filter element  28  than it does in the open configuration of FIG.  11 . In FIG. 1 the ring member  36  bears against the filter support  1  through the rim  22 . 
     In FIGS. 1,  6  and  11  the filter element  28  made of thin filter paper is inserted into the mouth  21  of the support ring  23  of the filter support  1 , which filter element essentially follows the contour of an ellipsoid and has its free end adjoined by a rim  39  extending radially outwardly and advantageously formed by an annular collar. It will be understood that the rim  39  may also be composed of individual sections. The bearing surface  40  formed on the underside of the rim  39  of the filter element  28  is practically in perfect registry with the supporting surface  24  of the filter support  1  unless the filter element  28  has minor deformations due to its relatively large flexibility. These deformations may however be eliminated using manual pressure against the bottom  62  once the filter element  28  is inserted. The ring-shaped rim  39  of the filter element  28 —conforming to the contour at the junction of the supporting surface  24  with the transition area  26  of the filter support  1 —has a relatively sharp corner  41  in order to improve the transmission of the weight load of the filter element  28  to the rim  39  and thus achieve a stable position of the filter element  28  in the filter support  1  also in wet condition. 
     According to FIGS. 1 to  6 , the filter element  28  is comprised of overlapping pleats  42  which, as shown clearly in particular in FIGS. 1 and 2, extend parallel to the longitudinal direction of the center line  43 , that is, radially towards the lowermost point  63  lying on the center line  43  of the filter element  28 , of the outer wall  27  of the filter element  28 . In the cross-sectional views of FIGS. 4 and 5, the pleats  42  extend in a substantially Z-shaped configuration, with the upper side  64  and the underside  65  (FIG.  4 ), and the outer side  66  and the inner side  67  (FIG. 5) extending substantially in the circumferential direction U in superposed (FIG. 4) and, respectively, juxtaposed (FIG. 5) arrangement, so that an area of overlap  116  results. In FIGS. 4 and 5, the pleats  42  are not perfectly closed, so that a very narrow gap remains which, however, in the extreme case when the pleats are very firmly pressed on, may even be closed in dry condition. 
     As becomes apparent from FIGS. 2 and 3, the filter element  28  extends frusto-conically in the transition area  30 , whilst continuing in a substantially hemispherical configuration from the parting line  44  downwards. The angle  45  of the truncated cone in the transition area  30  amounts to about 15° at a diameter D of about 115 mm in the mouth area. The angle  45  may also be smaller than 15 °. However, it invariably needs to be greater than 0° in order to obtain a bevel which is necessary to enable the filter element  28  to be withdrawn from the forming die. The same applies when the filter element is removed from a stack. The height H of the filter element  28  is 75 mm, approximately. As becomes apparent from FIG. 3, the rim  39  extends outwardly, sloping at the same time downwardly while enclosing an angle  46  of about 5°. Corresponding dimensions in these areas apply equally to the lowermost areas  80  of the supporting surface  24  of the V-shaped grooves  79  on the filter support  1  according to FIGS. 1,  6 ,  7 ,  11  and  12 , and to the filter elements  28  of FIGS. 1,  2 ,  6 ,  8 ,  9 ,  10  and  11  as well. To make sure that the filter element  28  rests at all times snugly against the transition area  26 , the diameter D is preferably selected so as to be some millimeters wider. On insertion into the filter support  1 , the filter element  28  is thus always compressed under radial bias and hence prevented from slipping through. 
     According to FIG. 1 a retaining device  38  is placed down onto the mouth  21  of the filter support  1 , resting with its own weight on the upper side of the rim  39  for holding the filter element  28  in place and locating itself centrally by means of the inner edge  66  of the filter element  28 . To enable the filter element  28  to be removed from, and inserted into, the filter support  1 , it is however also possible to provide for pivotal movement of the retaining device  38  using suitable pivot elements (not shown) such as hinges, and for securing the filter element  28  the retaining device can be urged against the supporting surface  24  of the filter support  1  or ring member  36  using suitable fastening elements such as clips, snap-fit connectors, etc. To avoid heat losses, the retaining device  38  is provided with a cover  49  having a central opening  50  for the inflow of hot water. The retaining device  38  operates to hold the filter element  28  clamped between it and the support ring  23  or the filter support  1 . 
     According to FIG. 1 a wall  47  projects from the left area of the filter support  1 , which wall serves to mount the filter support  1  in the coffee maker  3  of FIG.  12 . The wall  47  merges into an ellipsoidal shape on the circumference of the filter support  1  and continues to be ellipsoidal in FIG. 1 on the right hand side of the filter support  1  of FIG.  1 . 
     In FIGS. 8 to  11  a filter element  28  is shown which, in contrast to the filter element  28  of FIGS. 1 to  6 , has exposed pleats  48  in upward direction (rim  39 ) and in radially outward direction (transition area  30 ). Exposed pleats as used herein means that the pleats have no undercuts—in contrast to the overlapping pleats  42  as in FIGS.  4  and  5 —, that is, when looking down into the receiving cavity  76  of the filter element  28  as shown in FIG. 9, the visible surface of the filter paper can be seen without undercuts looking from above. 
     According to FIGS. 8 to  11 , the exposed pleats  48  are formed by trough pleats  51  and crest pleats  52 . As appears from FIG. 9, the trough and crest pleats  51 ,  52  are oriented in the direction of the lowermost point  63 . Each two adjacent crest pleats  52  combine with a trough pleat  51  to form an exposed pleat  48  which in cross section in the direction of the center line  43  widens in V-shape from its beginning in upward direction (FIG. 10) and has the side walls  53 ,  54  as its boundaries. Trough pleats  51  are understood to mean those pleats which when looking down into the receiving cavity  76  are recognizable as recesses or notches  71 . When viewing these notches  71  of FIGS. 8 and 10 from below or from outside and from below, this notch  71  presents itself reversed, that is, as a crest pleat  52  in the form of a gable roof like elevation  72 . By analogy, the same applies to the gable roof like elevations  72 . Hence it always depends on the position from which a person views the filter element  28 , looking either into the inside of the receiving cavity  76  or at the outer wall  27  from outside. Accordingly, when a trough pleat  51  or a crest pleat  52  is mentioned in connection with the subject matter of this application, invariably those pleats are meant that present themselves to the viewer when looking at the interior of the receiving cavity  76 . 
     As becomes apparent from FIGS. 8 and 10, the crest pleats  52  start from points  69  as a line splitting into two pleats at points  81 . This is so because the displacement of paper material diminishes towards the lowermost point  63 , that is, in this area the pleats  51  merge with the outer wall  27  of the ellipsoidal portion  32 . The crest pleat  52  on rim  39  turns into a trough pleat  51  at point  69 , extending as such down to point  81 . 
     As appears from FIGS. 8 and 9, the pleats  48  formed on the rim  39  are all of like geometry, that is, all the outer peaks  67  of the trough pleats  51  lie on a common horizontal plane when the peaks  67  are connected with each other. Because the trough pleats  51  have a downward inclination with an angle  55  of about 2° from outside to inside, they are at a horizontal level when imaginary concentric rings are laid about the center line  43 , striking the rim  39 . The angle  55  results from the horizontally extending crest pleat  52  and the geometric configuration of the exposed pleats  48 , provided that circular blanks are selected as filter paper which are then pleated and formed to produce the filter element  28  illustrated in FIGS. 8 to  10 . As becomes apparent from FIG. 9, the outside diameter D 1  of the rim  39  of the formed, that is finished, filter element amounts to about 130 mm, the hemispherical cavity (ellipsoidal portion  32 ) bounded by the envelope  29  then having a diameter D 5  of about 105 mm. The envelope  29  is defined as an imaginary surface area which results when a very thin membrane is stretched over the crest pleats  52  and over the lowermost point  63 . 
     According to FIGS. 8 and 10, a transition area  30  extending upwardly from the parting line  44  adjoins the hemispherical area of the outer wall  27  of the filter element  28 . In this embodiment, both the trough pleats  51  and the crest pleats  52  extend from the parting line  44  in upward direction at an angle  45  of about 8° slightly conically outwardly, which is however not clearly recognizable in the drawing. This bevel  68  serves to aid in the removal of the filter element  28  from the die following the forming operation. 
     According to FIGS. 8 to  10 , long and short pleats  56  and  57 , respectively, are arranged on the filter element  28 , which pleats are spaced uniformly apart on the circumference and are all oriented towards the lowermost point  63 . Between each two long pleats  56  there are two short pleats  57 . In FIG. 9 the pointed ends  58  of the long pleats  56  lie on a common diameter D 3  of about 57 mm. Equally, the pointed ends  59  of the short pleats  57  lie on a common diameter D 4  of about 87 mm. 
     As becomes apparent from FIGS. 8 and 10, a trough pleat  51  formed in the rim  39  changes into a crest pleat  52  at the sharp corner  41  towards the transition area  30 , extending from this point downwards to the diameters D 3  (long pleat  56 ) and D 4  (short pleat  57 ) of the ellipsoidal portion  32 . The transition from a trough pleat  51  to a crest pleat  52  is represented by point  60 , while the transition from a crest pleat  52  to a trough pleat  51  is represented by point  69 . The points  60  lie on a diameter D of about 110 mm, while the points  69  lie on a diameter D 2  of 120 mm. Serving as a handle for the filter element  28 , a tab  117  projects outwardly from the rim  39  to facilitate the removal of a filter element  28  from the stack. 
     To be able to provide an ellipsoidal portion  32  with a radially outwardly extending rim  39  without any additional means and without the formation of overlapping pleats, it is absolutely necessary according to the present invention to make provision for a reversal of an inwardly pointing crest pleat  52 , that extends from the transition area  30 , into a trough pleat  51  at point  60 , meaning that a notch (trough)  71  changes into a roof-shaped elevation  72  at the transition line  70 . It is only in this manner that exposed pleats  48  can be represented on a hollow spherical filter element  28  with rim  39 , the pleats continuing from a concave outer wall  27  in a radially outwardly extending rim  39 . 
     In order to be able to better displace the paper material which, for forming the filter element  28 , is a round filter paper blank (not shown) of a diameter of about 225 mm without complicating manufacture, two short pleats  57  are formed between each two long pleats  56 . It would be conceivable, of course, to use pleats of equal length throughout instead of the two short pleats  57 , but then a different flank angle  73  would have to be selected in order to achieve the same paper displacement as with the formation of two pleats  59 . The flank angle  73  in a short or long pleat  57 ,  56  is about 67.5°, but this angle results automatically with the number of pleats spaced uniformly on the circumference of the filter element  28  at given diameters D 1  and D 2 , as does the pleat angle  74  on the rim  39 . 
     According to FIG. 10, the short and long pleats  57 ,  56  do not increase linearly in depth  74  and width  75 . Linearly increasing pleats are known in the art from cup-shaped filter elements in which the side wall rising from the circular bottom forms a truncated cone. When it is desired to obtain an ellipsoidal or hemispherical shape of the filter element  28  as is the case in the present invention, the pleats  48  are required to fold away the filter material such that, when developed, a plane results, while when formed to filter shape, an ellipsoidal or hemispherical form is obtained. 
     According to FIGS. 1,  11  and  12 , the mode of operation of the filter unit of the present invention which is comprised of a filter element  28  inserted into a filter support  1  is as follows: 
     From a stack of filter elements  28  or filter bags—a stack being understood to mean several nesting filter elements  28  which are however not illustrated in the drawing—a single filter element  28  is removed and inserted into the filter support  1 . According to FIG. 12, this operation is preceded by the filter support  1  being pulled forwardly out of the housing  2  of the coffee maker  3  or swung open to the side to have free access to the mouth  21  of the support ring  23  or the filter support  1  from above. Then the filter element  28  is inserted through the mouth  21  into the support ring  23  or the filter support  1  until its rim  39  rests snugly against the supporting surface  24 . In this process, the outer wall  27  of the filter element  28  is elastically compressed radially inwardly by the transition area  26  of the support ring  23 , causing the trough pleats  51  to rest with a small bias against the transition area  26  of the filter support  1  or the support ring  23 , thus preventing the filter element  28  from virtually falling through the mouth  21  on insertion, until it finally has its rim  39  in engagement with the supporting surface  24 . The radial constriction on the filter element  28  is taken up particularly elastically by the V-shaped trough and crest pleats  51 ,  52  extending upwardly and radially outwardly, enabling the filter element  28  to be inserted into the filter support  1  with great ease and little effort. 
     If the rim  39  of the filter element  28  is yet short of its uniform engagement with the supporting surface  24  on insertion into the filter support  1 , an operator may use his or her hand to press down on the bottom  62  in the area of the lowermost point  63  to properly locate the filter element  28  centrally in the filter support  1  and cause the rim  39  to rest snugly on the supporting surface  24 ; this is in particular so because the surface of the supporting surface  24  and the surface of the transition area  30  have the same contour as the filter element  28  in the area of the contacting surfaces. As the filter element  28  of FIGS. 8 to  11  is inserted, the filter element  28  turns until the trough pleats  51  engage within the registering grooves  79  and elevations  115  on the support ring  23  and are centrally located in position. 
     The elastic action of the filter element  28  of FIG. 2 is however not as good as in the filter element  28  of FIGS. 9 to  11  because of the presence of overlapping pleats rather than exposed pleats  48  on the filter element. The stiffness is however greater. According to FIG. 1, upon insertion of the filter element  28  the ring member  36  is subsequently placed down onto the rim  39  of the filter element to urge the rim  39  of the filter element relatively firmly against the supporting surface  24  of the ring member  36 . 
     Preferably then, ground coffee (not shown) is filled in. Subsequently, the filter support  1  is moved into the closed position shown in FIG. 12 in which the brewing head  4  closes the mouth  21  from above and the conduit (not shown) from the through-flow heater is positioned above the mouth  21  of the filter element  28 . When hot water is poured over the coffee grounds by hand or, according to FIG. 12, when the through-flow heater (not shown) is activated by means of the switch  10  causing hot water to enter the mouth  21  via the arm  5  and the brewing head  4 , this hot water will penetrate the coffee grounds, extracting extractable substances from the material being extracted. By reason of the nearly equal distance between the center M (designating roughly the area which results when water enters and a mean liquid level is present with the coffee grounds filled in to medium up to full capacity on the one hand, and on the other hand the area of the filter element  28  from which the radial distance to the wall of the filter element  28  is approximately equal) and the outer wall  27  of the filter element  28 , the beverage thus brewed is drained freely and uniformly along the outer wall  27  without encountering any appreciable impediment by parts of the filter support  1 . 
     Due to capillary action, humidity travels also up to the rim  39  of the filter element  28 , forming a liquid layer between the bearing surface  40  and the supporting surface  24 . This thin liquid layer contributes to ensure that the filter paper of the filter element  28 , which meanwhile has become very limp, is retained on the supporting surface  24  with its rim  39  and particularly also in the transition area  26 , which effect enhances the supporting function. Although the filter element, once wetted, loses its stiffness nearly completely, its hemispherical shape is nevertheless substantially maintained, and the filter element  28  does not collapse radially which in FIGS. 1 and 11 would entail sinking of the filter element  28  down into the receiving cavity  77  of the filter housing  16 . 
     According to the embodiment of FIG. 11, the braces  34  of the basket  33  provide for an additional improvement of the position of the filter element  28  in the filter support  1 . In this embodiment, the braces  34  serve to hold the filter element  28  radially, in addition to securing the filter element against falling out of the opening  78  of the ring member  36  due to its own weight. Supporting the filter element  28  solely through its rim  39  is however entirely sufficient. 
     As becomes apparent from FIG. 11, it should be mentioned further that both the transition area  26  of the support ring  23  and the supporting surface  24  are configured such as to match the outer contour of the filter element  28 , being accordingly provided with V-shaped grooves  79  and elevations  115  engaged by the trough pleats  51  of the filter element. The side walls  53 ,  54  engage the wall surfaces of the grooves  79  and elevations  115 , on which side walls  53 ,  54  they are held due to the effect of adhesion. 
     According to FIGS. 1 and 11, the brewed beverage is drained along the outer wall  27  of the filter element  28  nearly uniformly after the extractable substances are extracted evenly from all areas of the material being extracted. As soon as the brewed beverage has reached the lowermost point  63  of the filter element  28 , it leaves the filter element  28  and flows into the receiving cavity  77  from where it exits the filter support  1  through the orifice  19 , entering a glass carafe  12  placed underneath. Once the extraction cycle is completed and the extract is discharged from the filter element  28 , the brewing cycle is completed. The ellipsoidal shape of the filter element  28  also obviates prolonged dripping so that dripping stops as early as after about four drops. 
     Then the filter support  1  of FIGS. 1 and 11 can be removed again from the housing  2 , and the filter element  28  together with the coffee cake (not shown) can be discarded by turning the filter support  1  upside down. However it is also conceivable to remove only the support ring  23  with the filter element  28  sitting therein by means of a handhold formed on the support ring  23  but not shown in the drawing, and to remove the filter element  28  by turning it upside down (FIG.  11 ). According to FIG. 1 this first requires the retaining device  38  to be swung open or otherwise removed from the ring member  36  or the filter support  1 . 
     With the filter element  28  of the present invention which is fabricated from very thin filter paper, preferably of a thickness of only 0.1 mm, a filter paper shape is provided which, for the first time, continues to be quite stable also in wet condition, the filter element  28  being held in the filter support  1  without elaborate holding means. The stable filter paper shape makes handling a simple matter and allows excellent brewing results due to its ellipsoidal form. With this filter element  28  particularly, the brewed beverage can be drained along the outer surface nearly without any hindrance, which reduces the period of time during which the hot water is held in the filter element  28 , thus preventing undesirable flavors or aromatics from being introduced, in addition to preventing the brewed beverage from cooling too rapidly. 
     FIGS. 13 to  17  illustrate the individual process steps for manufacturing one or several filter elements  28  (FIGS. 1 to  11 ) by means of a die assembly  92 . In this process, the die assembly  92  comprises a punch half  82 , a die half  83 , a blankholder  84  and a retainer  89  serving as locating means. The die half  83  has an ellipsoidal cavity  97  whose inner wall is either smooth or has V-shaped notches  96 . Where the inner wall  98  is smooth, a filter element  28  according to FIGS. 1 to  6  is obtained, whilst in the case of an inner wall  98  having V-shaped notches  96 , a filter element  28  of the type illustrated in FIGS. 8 to  11  is produced. Obviously then, the surface of the punch half  82  has to be smooth (filter element  28  of FIGS. 1 to  6 ) or it has to be provided with V-shaped elevations  95  (filter element  28  of FIGS. 8 to  11 ) suitable for engagement in the mating V-shaped notches  96  in the die half  83 . 
     According to FIGS. 13 to  17 , a bore  100  is formed in the center of the die half  83 , through which bore the retainer  89  configured as locating means extends. According to FIGS. 15 and 16, the inner surface  101  on the retainer  89  combines with the inner wall  98  of the die half  83  to form an enclosed ellipsoidal cavity  97  which is present, for example, when the filter element  28  is formed to its final shape or when the die half  83 , together with the retainer  89 , is on its upward travel or has completed its upward travel (FIG.  16 ). Equally, the inner surface  101  of the retainer  89  is either smooth or provided with V-shaped notches  96  registering with the elevations  95  on the punch half  82 . The die half  83  is displaceable relative to the retainer  89  in the longitudinal direction of the central axis  102 . The retainer  89  is vertically displaceable relative to the die half  83  equally in the direction of the central axis  102 . In addition, both the retainer  89  and the die half  83  are movable up and down simultaneously. According to FIG. 13, the end of the inner wall  98  has an adjoining annular surface  103  which is likewise provided with the V-shaped notches  96  which extend normal to the central axis  102 . 
     According to FIGS. 13 to  17 , the punch half  82  is arranged vertically beneath the die half  83  and the retainer  89 , which punch half is essentially comprised of an ellipsoidal hemisphere  104  extending centrally to the central axis  102 . V-shaped elevations  95  are formed on the surface of the ellipsoidal hemisphere  104 , said elevations extending such as to fill the space in the filter element&#39;s  28  notches  71  of FIGS. 8 to  10  on the one side, or the notches  96  in the die half  83  on the other side, when the punch half  82  and the die half  83  are in the closed position. Adjoining the lower end of the punch half  82  in radially outward direction is an annular shoulder  105  serving as a pressure device against the blankholder  84 . 
     It should be noted in this connection that the die assembly  92  of FIGS. 13 to  17  is illustrated without the associated actuating and guiding devices and control elements for greater clarity of illustration of the forming operation proper. 
     The mode of operation of the die assembly  92  of the present invention is as follows: 
     FIG. 13 shows the die assembly  92  in open position, that is, die half  83  and retainer  89  are in spaced relationship to and above the punch half  82 , producing a clearance space  106  between the punch half  82  and the die half  83  with its retainer  89 , which space enables a gripper, not shown, to load a round paper blank  93  or a stack  112  including several round paper blanks  93  from the side, placing it onto the upper side of the outer ring  87  of the blankholder  84 . In the embodiment shown, the thickness d is intended to designate several round paper blanks  93  in superposed position. 
     As becomes apparent from the Figures, the outer ring  87  of the blankholder  84  has at its radially outer end an upwardly extending hollow cylindrical wall  107  which locates itself centrally on the outer wall  108  of the die half  83  when the outer ring  87  is urged against the die half  83 . As appears from FIGS. 13 to  15 , the underside  109  of the bottommost round blank  93  rests against the upper side  110  of the outer ring  87 , while the upper side  111  of the inner ring  86  extends slightly beneath the upper side  110  of the outer ring  87 , that is, a small clearance space  85  is formed between the inner ring  86  and the underside  109  of the last round paper blank  93 . As this clearance space  85  may be vanishingly small, it is only intended to indicate that the inner ring  86  will not present an impediment to the filter paper stack  112  as the filter paper  90  is loaded into the die. 
     In the next step of the process, the die half  83  and the retainer  89  approach the punch half  82  and the blankholder  84 , it being irrelevant whether only the die half  83  with the retainer  89  moves, or only the punch half  82 , or whether there is relative movement of all parts in concert. The die half  88  travels against the outer ring  87  of the blankholder  84  until the V-shaped elevations  95  on the outer ring  87  engage slightly within the V-shaped notches  96  on the die half  83 . As this occurs, the outer regions of the round paper blanks  93  are pre-formed into slightly V-shaped notches  71  and roof-shaped elevations  72 . Subsequently, the retainer  89  travels against the surface of the filter paper stack  112 , biasing the underside  109  of the bottommost round paper blank  93 , and hence the entire filter paper stack  112 , against the surface  99  of the punch half  82 . In this manner, the round paper blanks  93  are located and centered relative to the die assembly  92  as becomes apparent from FIG.  14 . 
     Then either the die half  83  with the blankholder  84  travels against the punch half  82 , or the punch half  82  enters into the ellipsoidal cavity  97  of the die half  83 . While in the first variant the retainer  89  remains stationary during this travel and the die half  83  with its bore  100  of FIG. 14 slides along the outer surface  113  of the retainer  89 , in the second variant the outer surface  113  slides along the bore  100  of the die half  83 . Accordingly, as the punch half  82  enters the ellipsoidal cavity  97 , the filter paper stack  112  engages the surface  99  of the punch half  82 , in which process the area of the filter paper stack  112  that is slightly urged against the annular surface  103  of the die half  83  by the outer ring  87  slides radially inwardly, causing the die half  83  and the blankholder  84  to produce in the filter element  28  the trough pleats  51  and the crest pleats  52  according to FIGS. 8 to  10 . As this occurs, the force exerted by the outer ring  87  on the filter paper stack  112  is of a magnitude just sufficient to maintain the stack adequately tensioned for the formation of the pleats  51 ,  52 , while at the same time the radially outer edge of the filter paper stack  112  slides away inwardly out of the clearance space  85 . 
     In the final step of the process, the inner ring  86  rests only slightly against the underside  109  of the filter paper stack  112 . The deeper the punch half  82  travels into the cavity  97  of the die half  83 , the more the filter paper stack  112  is deflected in the corner area  114  of the die half  83  and pressed into the V-shaped notches  96 . According to the present invention, therefore, the filter paper stack  112  is virtually drawn over the corner area  114 , while at the same time the die half  83  and the blankholder  84  operate to form the trough pleats  51  and the crest pleats  52  of FIGS. 8 to  10 . This process continues until the position illustrated in FIG. 15 is reached in which the punch half  82  has completed its travel into the cavity  97 . During the time the V-shaped elevations  95  are in engagement with the V-shaped notches  96 , the filter paper stack  112  is pressed into its final shape, which also includes the inner region which does not slide over the corner area  114 . 
     Then the punch half  82  is pressed firmly against the die half  83  and the retainer  89  so that the filter paper stack  112  is formed to its final shape according to FIGS. 8 to  10 . During this pressing operation only the trough and crest pleats  51  and  52 , respectively, are pressed, excluding however the side walls  53 ,  54  of FIG.  10 . This is accomplished by suitably designing the notches  96  and elevations  95  in the die assembly  92 . At the same time, the inner ring  86  is urged against the rim  39  of the filter paper stack  112 , causing the clearance space  85  to be eliminated and the rims  39  of the filter paper stack  112  to be pressed against each other firmly to obtain a stable form of many filter elements  28  in the filter paper stack  112 . After a predetermined dwell period the forming operation is completed. 
     According to FIG. 16, the die half  83  with retainer  89  then commences its upward travel out of the punch half  82 , while yet the inner ring  86  continues to press firmly against the rim  39 . Then the blankholder  84  moves away from the die half  83 , so that the filter paper stack  112  is held in the die half  83  only due to its radial bias which acts against the inner wall  98  of the die half  83 . In the event of the biasing force being inadequate, entailing the risk for the filter paper stack  112  to fall out of the cavity, provision may be made for a suction device (not shown) on the retainer  89  to cause the filter paper stack  112  to be maintained in firm engagement with the retainer  89 . 
     In the embodiment of the die assembly  92  of FIG. 17, the filter paper stack is intended to be held by a vacuum device not shown) provided in the retainer  89 . To hold the filter paper stack  112  against the retainer  89 , it can also be considered that provision is made for a platen device (not shown), which engages within the receiving cavity  76  while at the same time urging the bottom  62  against the inner surface  101  of the retainer  89 . In a subsequent step, the retainer  89  can be made to travel into the die half  83  (FIG. 17) to enable the finished filter paper stack  112  to be withdrawn from the die assembly  92  and place it into a package conformably shaped to receive the filter paper stack  112 . This then terminates the very simple process of manufacturing one or several filter elements  28 .