Foam generating device for producing liquid foam, as well as foam dispensing device and beverage dispensing device

Abstract

The device for generating liquid foam from a liquid, in particular a milk-containing or at least milky liquid, comprises a frothing unit 300 with a frothing chamber 350 having a liquid inlet 310 and a frothing outlet 320 that are spatially separated from each other. A rotor body 330 arranged for rotation about a rotation axis X is provided in the frothing chamber. The rotor body 330 leaves a gap 360 around its entire periphery relative to chamber walls 351, 352 of the frothing chamber. The liquid inlet 310 and the frothing outlet 320 are connected via the gap. In the axial direction from the liquid inlet 310 to the frothing outlet 320, the rotor body has an externally decreasing active section, in particular tapering. The chamber walls 351, 352 and the rotor body 330 have opposing, at least substantially parallel, active surfaces, at least one of which is undulating at least at the location of the gap 360. Such a foam generating device is particularly suitable for foam dispensing devices and / or beverage dispensing devices.

Description

[Technical field]

[0001] The present invention relates to a device for generating liquid froth from a liquid, in particular from a milk-containing or at least milky liquid. The device comprises a frothing unit having a frothing chamber with a liquid inlet and a froth outlet, which are spatially separated from each other. The frothing chamber is provided with a rotor body for rotation about a rotation axis, which rotor body leaves a clear gap to the chamber wall of the chamber all around, the liquid inlet and the froth outlet being connected via the gap. It should be noted here that, unless otherwise expressly stated or implicitly clear, when the application merely refers to one wall, it should also be understood to mean an assembly of several walls connected together. The present invention further relates to a foam dispensing device and a beverage dispensing device to which such a foam generating device is applied. It should be noted here that when the application refers to the generation of foam, it is also understood to mean the stabilization and / or modification of a foam already partially generated from a liquid and supplied at the liquid inlet as a fluid. [Background technology]

[0002] A foam generating device of the type described in the introduction can in particular be used for the so-called frothing of milk, at least of a milk (protein)-containing liquid, for addition to a coffee product. There are different techniques for generating milk foam from milk. For example, known techniques are those in which steam is introduced into the milk under pressure, for example in a turbulent manner, thereby generating the final milk foam directly, as is done manually by traditional artisan coffee baristas. It is also known to generate milk foam in a mainly mechanical manner, by mechanically introducing air with stirring elements such as whisks or rotors. In fact, such milk foam generated by frothing milk has been found to be particularly firm and stable.

[0003] A foam generating device for producing milk into liquid milk foam in such a mechanical way is known, for example, from WO 2016 / 151422 in the name of the Italian company Rancilio Group SPA. The device known therefrom comprises a frothing unit with a frothing chamber. The frothing chamber comprises a liquid inlet for any heated liquid, such as heated milk, and downstream of which an outlet through which the generated foam can escape. A rotor, which is set to rotate around the central axis of the frothing chamber by a motor provided for this purpose, is arranged in the frothing chamber between the inlet and the outlet. Here, the conical rotor body carried by the rotor is spaced at a constant narrow gap from the wall of the frothing chamber which is correspondingly formed.

[0004] This gap is the only flow path available for the liquid from the liquid inlet to the liquid outlet. The liquid is therefore forced into this flow path, and air is entrapped within it. This leads to a laminar flow behavior of the liquid in a gap between two parallel surfaces rotating relative to each other, also called Taylor-Couette flow. In the narrow gap, the liquid is exposed to viscous induced resistance (drag). At low rotational speeds (i.e. rotational numbers), this flow is stable. However, when the rotational speed is increased beyond a threshold value, the liquid flow becomes unstable and increasingly turbulent, leading to the formation and entrapment of gas bubbles. Finally, these gas bubbles appear as liquid foam that can be removed at the outlet.

[0005] A milk foam considered to be of good quality means that it is firm, aerated and stable and maintains its volume for a longer period. The foam here preferably consists of fine bubbles rather than large bubbles. The foaming power of the device is judged from the increase in foam volume relative to the amount of starting liquid. The device is further preferably relatively insensitive to the nature and temperature of the starting liquid used. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Patent Application Publication No. 2016 / 151422 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the invention is in particular to provide a foam generating device capable of generating such a stable aerated milk foam. [Means for solving the problem]

[0008] To achieve the above mentioned object, a foam generating device of the type described in the preamble has the characteristic according to the invention that in the axial direction from the liquid inlet to the foam outlet, the rotor body has an external decreasing active section, in particular tapering, and the chamber wall and the rotor body have opposing at least substantially parallel active surfaces, at least one of which is accidented, at least at the gap location. What is important in this respect is that the rotor body according to the invention tapers towards the outlet. The associated reduction in rotation speed is believed to stabilize the foam before it is dispensed at the outlet.

[0009] The undulations provided on one or both active main surfaces provide additional agitation of the foamed liquid, which is ultimately manifested in terms of foam generation in the form of an increased output. A particular embodiment here has the feature according to the invention that the active surface of the outer wall tapers at least substantially gradually, in particular conically, in the axial direction, and the gap from the liquid inlet to the foam outlet has an at least substantially fixed (i.e. constant) gap width over at least a part of its length.

[0010] With regard to the gap width of the gap formed between the active surface of the rotor body and the chamber wall of the chamber, a balance between flow resistance on the one hand and effective foam generation of the liquid on the other hand is a particular objective. Indeed, it has been found that an optimal balance, particularly for hot foam, is achieved in a further particular embodiment of the foam generating device according to the invention, which is characterized in that the gap width is less than about 1 mm, in particular between 0.1 and 0.6 mm, more particularly between 0.3 and 0.6 mm.

[0011] According to the invention, at least one of the two active main surfaces is undulating, which may include more or less random undulations as well as any more or less regular pattern of unevenness, in particular in the form of protrusions, recesses or a combination of protrusions and recesses.

[0012] In a first preferred embodiment, the foam generating device has the feature according to the invention that the irregularities are at least substantially congruent with one another and are arranged in a regular pattern. The surface in particular comprises a pattern of holes, more particularly round holes, also referred to here as depressions, ridges, grooves or ribs. The density and the individual shapes and dimensions can here be varied to further optimize the intended foam quality.

[0013] Another particular embodiment of the foam generating device according to the invention is characterized in that the asperities are elongated and that their longitudinal direction extends at a fixed angle to a transverse plane passing through the axis of rotation of the rotor body. The further embodiment has here the feature that successive asperities are always oriented against the direction of rotation of the rotor body. Such surfaces of elongated recesses (holes) and / or protrusions (ridges) convey the liquid alternately along the longitudinal direction thereby defined therebetween and along the radial direction imposed by the rotation. Such agitation of the liquid leads to the formation of finely distributed air bubbles from the liquid, in particular animal or plant-based milk, and gradually to a mass of foam with tightly aerated bubbles.

[0014] For the purpose of axial transport of the liquid to the foam outlet, another particular embodiment of the device is characterized in that the successive irregularities are here mutually offset in the axial direction, in particular arranged at least substantially along one helical line of a plurality of imaginary mutually parallel helical lines, the successive irregularities thus conveying the liquid along a helix to the outlet, whereby a particular pumping action is obtained, which improves the distribution of the foam at the outlet.

[0015] This is further improved by another particular embodiment of the device, characterized in that at least one contoured active surface has a pattern of recesses that respectively taper towards the foam outlet. The narrowing of the recesses here leads to a smaller closed volume from which the liquid is thus forced out. This self-draining action further improves the axial liquid transport of the liquid and / or foam produced therefrom towards the outlet.

[0016] In a second preferred embodiment, the foam generating device according to the invention is characterized in that one of the active surfaces comprises a number of ribs each extending helically along one of a number of imaginary mutually parallel helical lines, more particularly the helical lines defining a pitch oriented in the direction of rotation of the rotor body. When the rotor rotates, such a pattern of helical ribs leads to corresponding turbulence in the liquid, and air bubbles are formed and trapped therein in a particularly effective manner. In addition, such a number of helices provides a particularly powerful forward propulsion of the liquid / foam mixture to the foam outlet, which improves liquid transport and foam evacuation.

[0017] Comparative studies have shown that, among several configurations compared with one another, the preferred embodiment of the device is always characterized in that the rotor body has at least one contoured surface. If the rotor body is now in a removable form, its possible cleaning, replacement and / or maintenance is further facilitated.

[0018] The device is suitable for generating both cold and hot foam, the liquid being preheated or heated in the latter case in the chamber. For such latter purpose, a first particular embodiment of the foam generating device has the feature according to the invention that the foaming chamber has a steam inlet near the liquid inlet for admitting hot steam therein, and a second particular embodiment is characterized in that a heating device is provided upstream of the liquid inlet for heating the liquid. Another particular embodiment of the foam generating device has the feature according to the invention that the heating device has a steam generator for generating hot steam and introducing it into the liquid.

[0019] Very good results have been obtained with a preferred embodiment of the device according to the invention, characterized in that, for generating a cold or at least unheated foam, both the outer wall of the rotor body and the chamber wall of the foaming chamber have an undulating surface. For generating both a cold or at least unheated and a hot or at least heated foam, it is preferred to use here a further preferred embodiment of the foam generating device according to the invention, characterized in that the outer wall of the active surface of the rotor body has one of a regular pattern of recesses and a plurality of helical ribs with a pitch in the direction of rotation, and the chamber wall has an active surface with a regular pattern of recesses.

[0020] The invention also relates to a foam dispensing device comprising a foam generating device according to the invention as described above. According to the invention, such foam dispensing device has, in addition to such a foam generating device, a housing comprising a liquid reservoir for holding a liquid, in particular a milk-containing or at least milky liquid, pump means with a liquid conduit for conveying the liquid from the liquid reservoir to an inlet of the frothing unit coupled to the liquid inlet of the frothing chamber, switchable heating means in heat exchange contact upstream of the liquid inlet with the liquid in the liquid conduit for optionally heating the liquid, and a foam outlet coupled to the foam outlet of the frothing chamber capable of receiving foam generated from the liquid.

[0021] The invention now provides an automatic device for producing a liquid foam from a starting liquid, in particular from a plant-based or animal milk. In particular for extending the shelf life of the animal milk product, a preferred embodiment of the foam dispensing device here has the feature according to the invention that cooling means are provided in heat exchange contact with the liquid reservoir.

[0022] For application with hot beverages it is preferred to utilize a similar hot foam in order to at least to a lesser extent affect the temperature of the hot beverage.To this end, a particular embodiment of the foam dispensing device has the features according to the invention of a device in which the heating means comprises a mixing device downstream of the pump means, the mixing device comprising a mixing chamber, the mixing chamber comprising a first inlet to which the liquid conduit is coupled, a second inlet to which the steam conduit is coupled and an outlet coupled to the inlet of the foaming unit.

[0023] The present invention also relates to a beverage dispensing machine equipped with a foam generating device according to the invention as described above. According to the present invention, such beverage dispensing machine comprises such a foam generating device and a decoction device for preparing a hot beverage from water and grounds, in particular from boiling water and ground coffee, a liquid reservoir is provided for holding a liquid for frothing, in particular a milk-containing or at least milky liquid, the liquid reservoir is connected by a liquid conduit to a liquid inlet of a foam generating device foam frothing chamber, the decoction device has a water inlet to which a water conduit is connected for supplying a quantity of water, the decoction device has a product outlet through which a water-containing mixture or extract of grounds leaks out during operation, the foam outlet of the foam generating device foam frothing chamber is connected to a foam dispenser, the product outflow of the decoction device is connected to a product dispenser in the vicinity of the foam dispenser, the foam generating device and the decoction device are connected to a shared water supply, the housing comprises control means, the control means being capable and arranged to run and control the decoction device and to control the water and grounds supply to the decoction device for running and controlling the foam generating device.

[0024] This includes in particular what are usually called coffee machines, in which the liquid reservoir is intended and configured to keep cold animal or plant-based milk or at least a milky liquid suitable for producing milk foam, and the powder comprises coffee grounds. The milk foam thereby produced in combination with a coffee extract is particularly suitable for the preparation of coffee milk foam variations such as cappuccino and latte. A particular embodiment of the beverage dispensing device here is characterized in that cooling means are provided in heat exchange contact with the liquid reservoir. Cooling here extends the shelf life of the milk product.

[0025] The invention is further explained hereinafter with reference to exemplary embodiments and the accompanying drawings. [Brief description of the drawings]

[0026] [Figure 1] 1 shows an exemplary embodiment of a beverage dispensing device in combination with a foam dispensing device according to the present invention; [Figure 2A] 1 illustrates an exemplary embodiment of a foam dispensing device according to the present invention; [Figure 2B] 1 illustrates an exemplary embodiment of a beverage dispensing device according to the present invention; [Figure 3A] FIG. 2 is an exploded view of a foaming unit as applied to the foam generating device of each of the devices of FIGS. 1, 2A and 2B. [Figure 3B] FIG. 3B is a cross-sectional view of the whipping unit of FIG. 3A. [Figure 4] FIG. 4 is a perspective view of a steam injector for application in the frothing unit of FIGS. 3A and 3B. [Figure 5A] FIG. 2 is a perspective view of a first embodiment of a foaming chamber of a foam generating device according to the invention; [Figure 5B] FIG. 2 is a perspective view of a second embodiment of a foaming chamber of a foam generating device according to the invention; [Figure 6A] 5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 6B]5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 6C] 5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 6D] 5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 6E] 5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 6F] 5A and 5B show different embodiments of the rotor body as can be applied in the foaming chamber of FIGS. [Figure 7] FIG. 2 is an electro-mechanical operational diagram of the device of FIG. 1. [Figure 8] FIG. 2C is an electro-mechanical operational diagram of the device of FIG. 2B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] It should be noted here that the figures are merely schematic and are not necessarily drawn to scale. Some dimensions in particular may be exaggerated to a greater or lesser extent for the sake of clarity. Corresponding parts are designated in the figures by the same reference numbers.

[0028] 1 shows the arrangement of a device 100 for preparing hot beverages adjacent or at least close to a device 200 for generating a liquid foam that can be used in combination with the beverage. It includes in particular a somewhat traditional coffee / espresso machine 100 with one or more bean reservoirs 102 for coffee beans, which open onto a grinding unit (not shown) in a housing 104 of the machine. Moreover, not shown, but as will be well understood by those skilled in the art, the housing further provides space for a hot water appliance such as a boiler or heat block, a control unit and a pump by which hot water is conveyed at great pressure to the brewing group.

[0029] The brewing group here comprises an brewing chamber in which ground coffee powder is received from the grinding unit and compressed under great pressure with a single dose of hot water to extract a coffee extract therefrom. This extract can be received in a double dispenser 106. This can be an espresso coffee of the desired strength, or another coffee product such as a lungo or americano, depending on the user's preferences, which can be entered via a user interface 110 provided for this purpose. The housing also houses a steam generator and a steam dispenser 112 capable of removing hot steam. A set of further dispensers 113 for dispensing hot and cold water is also provided.

[0030] The brewing group may optionally be fed with ground coffee powder received directly from the reservoir or inlet, in which case a bean grinder may optionally be dispensed with in the device. A soluble product such as freeze-dried coffee may also be used, in which case the brewing device would have nothing more than a mixing chamber in which the product is mixed with a dose of hot water and dissolved therein.

[0031] A stand-alone device 200 capable of producing milk foam from cold milk in combination with the coffee product obtained from the coffee machine 100, for example to prepare a cappuccino or a latte, is arranged close to the coffee machine. The device has for this purpose a cooled milk reservoir 202 with a suitable animal or plant-based milk product. By means of a pump provided for this purpose in the housing 204 of the frothing device 200, the milk is conveyed from the reservoir 202 to the liquid inlet of the frothing unit, further shown in Figures 3A and 3B.

[0032] Upstream of the liquid inlet, the liquid passes through a steam or air injector 400 (see FIG. 4) and, for this purpose, is received in a milk conduit. This has an inlet connection 410 and an outlet connection 420 in line with the milk conduit, as well as a set of inlets 430 for steam and an outlet 440 for atmospheric air. To prevent the air / steam / liquid mixture from escaping from the injector 400, non-return valves are provided in or near the otherwise open inlets 430, 440.

[0033] The steam inlet 430 can be supplied by an own steam generator in the housing 204 of the frothing device 200. However, it is also possible to obtain hot steam from the coffee machine 100 via a steam conduit 150 provided for this purpose and a corresponding connection provided between the two devices 100, 200. Conversely, the steam generator of the frothing device 200 can also serve the coffee machine 100 via a steam conduit 150 provided for this purpose. The injector 400 supplies the frothing unit 300, from which liquid milk foam is generated by the frothing unit, the air / milk or steam / milk mixture being conveyed to the main device 100 via a conduit 250 provided for this purpose and can be removed in the second dispenser 206. The operation of the frothing unit is explained in more detail below.

[0034] The frothing device according to the invention can also be applied in a stand-alone manner. Figure 2A shows an example of this. In the stand-alone embodiment, the conduits 150, 250 are absent or at least not connected and the device 200 itself comprises a foam dispenser 206, but the device is mainly identical to the device 200 arranged close to the device 100 for preparing hot beverages in Figure 1. On the upstream side, the foam dispenser 206 is coupled to the outlet of a milk frothing unit received in the device 200.

[0035] Instead of taking the form of two separate devices, the assembly of Fig. 1 can also be integrated into a single device as shown in Fig. 2B. In this case, the device, besides the function of preparing a coffee product as described above, also has the function of optionally preparing milk foam. Besides the bean reservoir or reservoirs 102, a cooled milk reservoir 202 is provided in the device for this purpose, and the device also has a dispenser 206 for milk foam in the double coffee dispenser 106.

[0036] As further shown in the development view of Fig. 3A and in the cross-sectional view of Fig. 3B, the milk frothing unit 300 comprises a frothing chamber 350 with a liquid inlet 310 and a foam outlet 320. The inlet part of the liquid inlet 310 is here coupled to the outlet 420 of the steam injector 400 and the foam outlet 320 is coupled to the foam dispenser 206 of the device. The rotor body 330 is rotatable in the frothing chamber 350 about an axially guided rotation axis X driven by an electric motor 340 whose output drive shaft 345 projects into the rotor body 330. The output drive shaft 345 here projects through an opening in a cover 370 closing the frothing chamber 350, a bearing and a liquid barrier both being provided in the opening. The rotor body 330 is also bearing mounted and fixed at its distal outer end. The frothing chamber 350 has a press-fit base bearing 355 for this purpose. The electric motor 340 is encased in a motor housing 380, which is then connected to the frame 390 of the apparatus.

[0037] As shown particularly clearly in FIG. 3B, the liquid inlet 310 and the foam outlet 320 are connected to each other by a narrow gap 360 between the rotor body 330 and the chamber wall of the frothing chamber 350. Optionally, the heated milk admitted via the liquid inlet 310 may only reach the foam outlet via the gap 360. The rapidly rotating rotor body here agitates the liquid, which mixes with air and forms bubbles therein. The milk foam thus produced leaves the frothing chamber via the foam outlet. It is important here, within the scope of the invention, that the cross section of the rotor body 330, and likewise the cross section of the frothing chamber 350, decreases in the axial direction. This (here) tapering of the rotor body results in a smaller peripheral speed for a given rotational speed, which makes the produced foam more stable. The rotational speed of the rotor body is typically in the order of magnitude of 2000-5000 revolutions per minute, the diameter of the rotor body going from wide to narrow in the axial direction over the length of the passage 360.

[0038] It is also important within the scope of the present invention that at least one of the outer surface of the rotor body and the surface of the chamber wall is not flat but has undulations at the location of the path 360. This can take various forms. In the example of Figs. 3A and 3B, the surface of the rotor body is provided with a plurality of substantially congruent depressions 331 arranged on its periphery in a continuous row (see also Fig. 6A). The depressions 331 of the axially continuous row are here offset from one another so as to be at least substantially on one imaginary helical line of a plurality of mutually parallel helical lines. As shown in Fig. 3A, each of the depressions 331 tapers towards the outlet 320, i.e. in the downstream direction. This progressively smaller volume of the depressions 331 causes the liquid to be progressively pushed out from them. This makes the depressions 331 self-draining.

[0039] As shown in Figure 5A, a frothing chamber 350 can be used with a perfectly flat smooth inner wall 351 at least at the rotor body 330, but this inner wall can also be provided with irregularities 352, as shown in Figure 5B. With these irregularities, use is made of a chamber wall preferably made of recesses 352 with regard to proper cleaning of the system, which must remove any possible milk residues. In the case of such an uneven chamber wall 350, a smooth rotor body 330 with a smooth peripheral wall 336 can be used if necessary, for example as shown in Figure 6B.

[0040] Figures 6C-6F show another non-limiting example of a rotor body 330 as can be implemented within the scope of the present invention. Figures 6C and 6D now include elongated recesses 332 and protrusions 333, respectively, arranged in a regular pattern. The associated asperities 332, 333 are now oriented with their main axis along one imaginary helix of a number of mutually parallel helices that can be imagined on the surface of the rotor body. The pitch of said helix is ​​guided against the direction of rotation R of the rotor body 330 and thus also against the orientation of the associated asperities.

[0041] Another alternative embodiment of a rotor body 330 is shown in Figures 6E and 6F, in which the surface of the rotor body 330 is contoured in that a set of parallel ribs 334, 335 or grooves extend thereon. These ribs / grooves 334, 335 now rotate along the direction of rotation R of the rotor body 330, i.e. run along one imaginary helical line of a plurality of parallel helical lines with a pitch guided in this direction of rotation.

[0042] The gap 360 between the rotor body 330 and the chamber wall typically has a width of less than 1 millimeter. For producing cold milk foam, it has been found that the particular width is not crucial here. Excellent foam yields can be obtained in the entire area below a gap width of 1 millimeter. In some cases, the stability of the foam decreases significantly starting with a gap width above about 0.6 millimeters. It is therefore preferable to use a gap width below the 0.6 millimeter dimension. In this case, it has been found that the foam does not collapse or is less likely to collapse, even after 5 minutes.

[0043] It has been found that in order to produce hot foam, gap widths below 0.8 mm, in particular between 0.3 and 0.6 mm, are in any case preferred. Within such overall range, the foaming device produces an acceptable foam yield in terms of increased capacity, and at gap widths between 0.3 and 0.6 mm, the foam maintains its shape for a sufficient period of time. It has always been found that both foam yield and stability increase with decreasing gap width. On the other hand, the flow resistance of the device also increases with decreasing gap width, and the yield per unit time also decreases. In addition, good flow-through is also important when the device is being flushed to clean components. For the purposes of said yield, flow-through, and especially tolerance, gap widths above about 0.1 mm are therefore preferably maintained. In the exemplary embodiment provided here, a gap width of about 0.3 to 0.6 mm is used as a preferred compromise.

[0044] Figures 7 and 8 show diagrammatically a brief technical operational diagram of the devices of figures 1 and 2 respectively. Figure 7 here shows a standalone foam dispensing device 200 adjacent or at least close to a beverage dispensing device 100 as shown in figure 1. The beverage dispensing device 100 has a steam generator 70 with a water supply 71 for its own steam dispenser 112 (see also figure 1). Via a steam conduit 150 provided for this purpose between the two devices 100, 200, this steam generator 70 is also utilized in the foam dispensing device 200, here coupled to the steam inlet 430 of the steam injector 400. The foam dispensing device 200 can optionally also be applied in a standalone manner, in which case such or a similar steam provision 70 is placed within the foam dispensing device 200 itself.

[0045] The foam dispensing device 200 has one or more reservoirs 73, 74 in which the liquid to be frothed can be held. This example includes two milk containers for animal or plant-based milk, the two reservoirs being arranged so that they hold twice the amount of the same liquid together or can contain different milk products, for example animal milk and plant-based soy milk or almond milk, respectively. The selection between the two products can be made by a three-way valve 76 applied for this purpose in the downstream liquid conduit. A reservoir 77 for holding a cleaning liquid is additionally coupled to the three-way valve, allowing to flush the device from the reservoir with the cleaning liquid held therein periodically or on demand. In order to extend the shelf life of the milk products in the first two reservoirs 73, 74 mentioned above, it is realized with a thermally insulated casing and with forced, preferably thermostatically controlled cooling.

[0046] The reservoirs 73, 74, 77 are coupled to a pump 75, whereby, depending on the position of a three-way valve 76, liquid is drawn therefrom and pumped under pressure to the inlet 410 of a steam injector 400 arranged in the milk conduit 160. In the steam injector, a milk / steam mixture is formed, where the liquid is heated under the influence of hot steam, typically to a temperature between 55°C and 65°C. This mixture leaves the steam injector at its outlet 420. A set of non-return valves 78, 79 prevents this mixture from being able to enter the steam conduit 150 or the air conduit 180. Here too there is the possibility upstream of air being blown into the mixture downstream thereof, using an air pump 72, provided for this purpose, drawing air from the surrounding area. The steam / air mixture thus formed is conveyed to the inlet 310 of the frothing unit 300, where the mixture is generated by stirring, as described above, into a stiff and aerated milk foam, which can be removed at the foam outlet 320.

[0047] The generated foam can be conveyed via a foam conduit 170 between the two devices to a foam dispenser 206 arranged in the vicinity of the coffee dispenser 106 of the coffee machine 100 so as to receive the coffee with milk foam product thereunder. Alternatively, the foam dispenser 206 can also be provided in the foam dispensing device 200, as shown in FIG. 1. In this case, the user must move a cup or mug from one device to the other to receive both products. For operation, control and monitoring of the foam dispensing device, a processor-controlled control unit 80 is provided in the device 200, which is also operatively coupled to at least the steam generator 70 in the coffee machine 100 when making its use, similar to the situation shown. The control unit 80 is further operatively coupled in particular to two pumps 72, 75, a three-way valve 76 and a frothing unit 300, each as shown in dashed lines in the figure.

[0048] Instead of two separate devices, a fully integrated application can also be used, as shown in figure 1, in particular where the infusion device for preparing the hot beverage and the foam generating device are both housed in a collective housing. Such a device is shown in figure 2, and figure 8 provides a possible operating diagram with some components particularly relevant therein. In this case, a separate steam injector 400 is not applied, but steam and air are directly admitted into the frothing chamber via an inlet of the frothing chamber or a shared inlet 450 provided for this purpose, although the components corresponding to those of the device in figure 7 have the same reference numbers and substantially the same operation. In this case, the operation and monitoring of the foam generating device is also controlled by a processor-controlled control unit 90 provided for this purpose and coupled to or forming part of a control unit 91 of the coffee preparation part of the device, which will not be discussed further here but is assumed to be well known. The milk foam generated leaves the frothing chamber via a foam conduit 170.

[0049] Although the invention has been described above with reference to only a single exemplary embodiment, it is clear that the invention is not limited thereto, on the contrary, many variations and embodiments are possible within the scope of the invention to those skilled in the art.

Claims

1. A device for producing liquid foam from a liquid, in particular from a milk-containing or at least milky liquid, comprising a frothing unit with a frothing chamber, said frothing chamber having a liquid inlet and a foam outlet spaced apart from each other, in which a rotor body is provided for rotation about an axis of rotation, said rotor body being clearly spaced all around its periphery from a chamber wall of said frothing chamber, and said liquid inlet and said foam outlet being connected via said gap, The liquid inlet and the foam outlet are both offset from the axis of rotation, the rotor body has an outer cross-section that decreases in an axial direction from the liquid inlet to the foam outlet; the chamber wall and the rotor body having cooperating opposing surfaces that are at least substantially parallel; and An apparatus according to claim 1, wherein the surface of at least one of said cooperating surfaces is contoured at least at the location of said gap.

2. 2. A foam generating device according to claim 1, characterized in that the cooperating surfaces of the outer wall taper at least substantially gradually, in particular conically, in the axial direction and that the gap from the liquid inlet to the foam outlet has an at least substantially constant gap width over at least a part of its length.

3. 3. A foam generating device according to claim 1 or 2, characterized in that the gap width is less than about 1 mm, in particular between 0.1 and 0.6 mm, more in particular between 0.3 and 0.6 mm.

4. 4. The foam generating device according to claim 1, 2 or 3, characterized in that the at least one contoured surface has projections and recesses.

5. 5. The foam generating device of claim 4, wherein the irregularities are substantially coincident and arranged in a regular pattern.

6. 6. A foam generating device according to claim 4 or 5, characterized in that the irregularities are elongated and their longitudinal direction extends at a constant angle with respect to a transverse plane passing through the rotation axis of the rotor body.

7. A foam generating device as described in claim 6, characterized in that, when viewed in the axial direction from the liquid inlet side, continuous irregularities are aligned in a spiral shape wound in the opposite direction to the rotational direction of the rotor body.

8. 8. A foam generating device according to claim 1, characterized in that the at least one cooperating contoured surface has a pattern of a plurality of recesses each tapering towards the foam outlet.

9. 9. A foam generating device according to one or more of claims 4 to 8, characterized in that the successive projections and recesses are offset from one another in the axial direction, in particular at least substantially along one of a number of imaginary mutually parallel helical lines.

10. 4. A foam generating device as claimed in claim 1, 2 or 3, characterized in that one of the cooperating surfaces has a plurality of ribs each extending helically along one of a plurality of imaginary mutually parallel helical lines.

11. 11. Foam generating device according to claim 9 or 10, characterized in that the helical lines define a pitch oriented in the direction of rotation of the rotor body.

12. 12. Foam generating device according to one or more of the preceding claims, characterized in that the rotor body at least has at least one said surface that is contoured.

13. 13. Foam generating device according to one or more of the preceding claims, characterized in that both the outer wall of the rotor body and the chamber wall of the frothing chamber have an undulating surface.

14. 14. The foam generating device of claim 13, wherein the outer wall of the cooperating surface of the rotor body has one of a regular pattern of recesses and a plurality of helical ribs at a predetermined pitch in the direction of rotation, and the chamber wall has a cooperating surface with a regular pattern of recesses.

15. 15. Foam generating device according to one or more of the preceding claims, characterised in that a motor is provided for rotating the rotor body about the axis of rotation.

16. 16. A foam generating device according to one or more of the preceding claims, characterized in that the foaming chamber has a steam inlet near the liquid inlet for admitting hot steam therein.

17. 17. Foam generating device according to one or more of the preceding claims, characterized in that a heating device is provided upstream of the liquid inlet for heating the liquid.

18. 18. The foam generating device of claim 17, wherein the heating device comprises a steam generator for generating hot steam and introducing it into the liquid.

19. A foam generating device according to one or more of claims 1 to 18; a liquid reservoir for holding said liquid, in particular a milk-containing or at least milky liquid; pump means comprising a liquid conduit for conveying said liquid from said liquid reservoir to an inlet of said foaming unit coupled to said liquid inlet of said foaming chamber; switchable heating means in heat exchange contact with the liquid in the liquid conduit upstream of the liquid inlet for optionally heating the liquid; a foam outlet coupled to the foam outlet of the foaming chamber capable of receiving foam generated from the liquid; A foam dispensing device having a housing comprising:

20. 20. Foam dispensing device according to claim 19, characterized in that cooling means are provided in heat exchange contact with the liquid reservoir.

21. 21. A foam dispensing device according to claim 19 or 20, characterized in that the heating means comprises a mixing device downstream of the pump means, the mixing device comprising a mixing chamber, the mixing chamber comprising a first inlet to which the liquid conduit is connected, a second inlet to which a vapour conduit is connected and an outlet connected to the inlet of the frothing unit.

22. 19. A beverage dispensing machine comprising a foam generating device according to one or more of the claims 1 to 18 and an infusion device for preparing a hot beverage from water and powder, in particular from boiling water and ground coffee, a liquid reservoir is provided for holding a liquid for frothing, in particular a milk-containing or at least milky liquid, said liquid reservoir being connected by a liquid conduit to the liquid inlet of the frothing chamber of the foam generating device, said brewing device having a water inlet to which a water conduit is coupled for supplying a quantity of water; the brewing device has a product outlet through which the aqueous mixture or extract of the powder escapes during operation; the foam outlet of the foaming chamber of the foam generating device is coupled to a foam dispenser; the product outlet of the brewing device is coupled to a product dispenser adjacent to the foam dispenser; The foam generating device and the brewing device are connected to a shared water supply; A beverage dispensing device, wherein the housing has a control means capable of and configured to control water and powder supply to the brewing device to run and control the brewing device and to run and control the foam generating device.

23. 23. A beverage dispensing system as claimed in claim 22, characterised in that cooling means is provided in heat exchange contact with the liquid reservoir.

24. 18. Foam generating device according to any one of the preceding claims, characterized in that the outer cross-section of the rotor body tapers in the axial direction from the liquid inlet to the foam outlet.

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