Patent Publication Number: US-2022218014-A1

Title: Froth generating device for producing a liquid froth as well as a froth dispensing device and a beverage dispensing device

Description:
The present invention relates to a device for producing a liquid froth from a liquid, particularly a milk-containing or at least milky liquid, comprising a frothing unit with a frothing chamber which is provided with a liquid inlet and a froth outlet which are spatially separated from each other, wherein in the frothing chamber a rotor body is provided for rotation about a rotation axis, wherein the rotor body leaves a gap to a chamber wall of the chamber clear all around, and wherein the liquid inlet and the froth outlet are connected via the gap. It is noted here that, unless expressly stated otherwise or implicitly apparent, where reference is simply made to a wall in the present application, this must also be understood to mean an assembly of connected walls. The invention moreover relates to a froth dispensing device and to a beverage dispensing device in which such a froth producing device is applied. It is noted here that where reference is made in the present application to producing froth, this is also understood to mean stabilizing and/or modifying froth already partially produced from the liquid and supplied at the liquid inlet as fluid. 
     A froth producing device of the type described in the preamble can particularly be utilized for the so-called frothing of milk, at least a milk (protein)-containing liquid for adding to a coffee product. There are different techniques for producing a milk foam from milk. A known technique is for instance to introduce for instance steam into milk under pressure in turbulent manner and thus directly produce the final milk foam, as is also done manually by traditional, artisan coffee baristas. It is also known to produce milk foam mainly in mechanical manner by mechanically introducing air with an agitating member, such as a whisk or rotor. In practice, such a milk foam produced by whipping milk has been found to be particularly firm and stable. 
     A froth producing device which produces milk into a liquid milk foam in such a mechanical manner is for instance known from international patent application WO 2016/151,422 in the name of the Italian company Rancilio Group S.P.A. The device known therefrom comprises a frothing unit with a frothing chamber. The frothing chamber is provided with a liquid inlet for optionally heated liquid, such as heated milk, and downstream thereof with an outlet from which a produced froth can escape. Situated between the inlet and the outlet, in the frothing chamber, is a rotor which is set into rotation around a central axis of the frothing chamber by a motor provided for this purpose. A conical rotor body carried by the rotor here leaves clear a constant, narrow gap to a wall of the correspondingly formed frothing chamber. 
     This gap is the only flow path available to the liquid from the liquid inlet to the liquid outlet. The liquid is therefore urged into this flow path, and entrains air herein. This results in laminar flow behaviour of the liquid in the gap between two parallel surfaces rotating relative to each other, also referred to as Taylor-Couette flow. In the narrow gap the liquid is subjected to a viscosity-induced resistance (drag). At lower rotational speeds (i.e. numbers of revolutions) this flow is stable. When the rotational speed is however increased beyond the threshold value, the liquid flow becomes unstable and eventually turbulent, and air bubbles are formed and trapped. Finally, these air bubbles are manifested as such as a liquid froth which can be taken away at the outlet. 
     A milk foam deemed to be of good quality is firm, aerated and stable, which means that it maintains its volume for longer. The foam is preferably composed here of fine air bubbles rather than larger bubbles. The frothing power of the device is determined from an increase in volume of the foam relative to the quantity of starting liquid. The device is preferably furthermore relatively insensitive to the nature and temperature of the starting liquid used. 
     The present invention has for its object, among others, to provide a froth producing device whereby such a stable and aerated milk foam can be produced. 
     In order to achieve the stated object a froth producing device of the type described in the preamble has the feature according to the invention that in the axial direction from the liquid inlet to the froth outlet the rotor body has externally a decreasing active section, and particularly gradually narrows, and that the chamber wall and the rotor body comprise at least substantially parallel active surfaces directed toward each other, at least one surface of which is accidented at least at the position of the gap. What is important in this respect is that the rotor body according to the invention narrows toward the outlet. It is suspected that the decrease in rotational speed associated therewith stabilizes the froth before the froth is dispensed at the outlet. 
     The relief which is provided on one or both active main surfaces provides for additional agitation in the frothing liquid, which eventually becomes manifest in an increased yield in respect of froth production. A particular embodiment here has the feature according to the invention that the active surface of the outer wall narrows at least substantially gradually, particularly conically, in axial direction and that the gap from the liquid inlet to the froth outlet has over at least a part of a length thereof an at least substantially fixed gap width. 
     In respect of a 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 an effective froth production of the liquid on the other is a particular aim. In practice it has been found that an optimal balance, particularly for hot froth, is achieved in a further particular embodiment of the froth producing device according to the invention, which is characterized in that the gap width is smaller than about 1 mm, particularly lies between 0.1 and 0.6 mm, and more particularly lies between 0.3 and 0.6 mm. 
     According to the invention, at least one of the two active main surfaces is accidented. This can involve a more or less random relief, but also an optionally more or less regular pattern of irregularities, particularly in the form of elevations, depressions or a combination of elevations and depressions. 
     In a first preferred embodiment the froth producing device has the feature according to the invention that the irregularities are at least substantially mutually congruent and are provided in a regular pattern. The surface in question particularly comprises here a pattern of pits, more particularly round pits, also referred to as dimples, bulges, grooves or ribs. The density and individual shape and size can be varied here for further optimizing the quality of the intended froth. 
     A further particular embodiment of the froth producing device according to the invention is characterized in that the irregularities are elongate, with a longitudinal direction extending at a fixed angle relative to a transverse plane through the rotation axis of the rotor body. A further embodiment thereof has the feature here that successive irregularities are always directed counter to a rotation direction of the rotor body. Such a surface of elongate depressions (pits) and/or elevations (bulges) carries the liquid alternately along the longitudinal direction defined thereby and therebetween along a radial direction imposed by the rotation. This agitation of the liquid results in a finely distributed air bubble formation and, eventually, a firm, aerated and voluminous froth from the liquid, particularly from animal or plant-based milk. 
     With a view to an axial transport of the liquid to the froth outlet a further particular embodiment of the device has the feature here that successive irregularities are mutually offset in axial direction and are particularly provided at least substantially along a helical line of a number of imaginary, mutually parallel helical lines. Successive irregularities thus carry the liquid along a helix to the outlet, whereby a certain pump action is obtained, this enhancing the dispensing of froth at the outlet. 
     This is further enhanced by a further particular embodiment of the device which is characterized in that the at least one accidented active surface comprises a pattern of depressions which each narrow toward the froth outlet. The narrowing of the depressions results here in a smaller enclosed volume, so that the liquid will be forced therefrom. This self-discharging action further enhances the axial liquid transport of the liquid and/or the froth produced therefrom toward the outlet. 
     In a second preferred embodiment the froth producing device according to the invention is characterized in that one of the active surfaces comprises a number of ribs, each running helically along a helical line of a number of imaginary, mutually parallel helical lines, and more particularly in that the helical lines define a pitch which is directed in a rotation direction of the rotor body. When the rotor rotates, such a pattern of helical ribs results in a corresponding turbulence in the liquid, wherein air bubbles are formed and become trapped therein in particularly effective manner. In addition, such a multiple helix provides a particularly powerful forward propulsion of the liquid/froth mixture to the froth outlet, which enhances the liquid transport and the froth discharge. 
     Comparative research research has shown that, among a number of configurations compared to each other therein, a preferred embodiment of the device was always characterized in that the rotor body at least comprises the at least one accidented surface. If the rotor body takes a removable form here, this furthermore simplifies possible cleaning, replacement and/or maintenance thereof. 
     The device is suitable for both producing cold froth and producing hot froth, wherein the liquid is in the latter case preheated or heated in the chamber. With a view to this latter, a first particular embodiment of the froth producing device has the feature according to the invention that the frothing chamber comprises close to the liquid inlet a steam inlet for letting in hot steam, while a second particular embodiment is here characterized in that a heating device is provided upstream of the liquid inlet for the purpose of heating the liquid. A further particular embodiment of the froth producing device here has the feature according to the invention that the heating device comprises a steam generator for generating hot steam and introducing it into the liquid. 
     For the purpose of producing cold or at least unheated froth outstanding results have been achieved with a preferred embodiment of the device according to the invention, characterized in that both the outer wall of the rotor body and the chamber wall of the frothing chamber comprise an accidented surface. For the purpose of producing both cold or at least unheated and hot or at least heated froth use is preferably made here of a further preferred embodiment of the froth producing device of the invention, characterized in that the outer wall of the active surface of the rotor body comprises one of a regular pattern of depressions and a number of helical ribs with a pitch in the rotation direction, wherein the chamber wall comprises an active surface with a regular pattern of depressions. 
     The present invention also relates to a froth dispensing device provided with a froth producing device according to the invention as described above. According to the invention, such a froth dispensing device comprises a housing with, in addition to such a froth producing device,
         a liquid reservoir for holding the liquid, particularly a milk-containing or at least milky liquid;   pump means with a liquid conduit for carrying the liquid from the liquid reservoir to an inlet of the frothing unit, which inlet is coupled to the liquid inlet of the frothing chamber;   switchable heating means upstream of the liquid inlet in heat-exchanging contact with the liquid in the liquid conduit for the purpose of optionally heating the liquid; and   a froth outlet coupled to the froth outlet of the frothing chamber, at which a froth produced from the liquid can be received.       

     The invention provides hereby an autonomous device for producing liquid froth from a starting liquid, particularly from a plant-based or animal milk. With a view to extending the storage life of animal milk products in particular, a preferred embodiment of the froth dispensing device here has the feature according to the invention that cooling means are provided in heat-exchanging contact with the liquid reservoir. 
     For the purpose of application with hot beverages use is preferably made of a likewise hot froth in order to thus influence a temperature of the hot beverage to at least a lesser degree thereby. With a view hereto, a particular embodiment of the froth dispensing device has the feature according to the invention that the heating means comprise a mixing device downstream of the pump means, with a mixing chamber which is provided with a first inlet to which the liquid conduit is coupled, a second inlet to which a steam conduit is coupled and with an outlet which is coupled to the inlet of the frothing unit. 
     The invention also relates to a beverage dispensing device provided with a froth producing device according to the invention as described above. According to the invention, such a beverage dispensing device comprises such a froth producing device and a decoction device for preparing a hot beverage from water and a powder, particularly from hot water and ground coffee,
         wherein a liquid reservoir is provided for the purpose of holding a liquid for frothing, particularly a milk-containing or at least milky liquid, which liquid reservoir is coupled by a liquid conduit to the liquid inlet of the frothing chamber of the froth producing device;   wherein the decoction device comprises a water inlet to which a water conduit is coupled for the purpose of supplying a quantity of water;   wherein the decoction device comprises a product outlet at which a watery mixture or extract of the powder escapes during operation;   wherein the froth outlet of the frothing chamber of the froth producing device is coupled to a froth dispenser;   wherein the product outflow of the decoction device is coupled to a product dispenser in the vicinity of the froth dispenser;   wherein the froth producing device and the decoction device are coupled to a shared water supply; and   wherein the housing comprises control means which are able and configured to control a water and powder supply to the decoction device for the purpose of setting into action and controlling the decoction device and setting into action and controlling the froth producing device.       

     This involves particularly what is usually referred to as a coffee machine, wherein the liquid reservoir is intended and configured to keep animal or plant-based milk or at least a milky liquid, which is suitable for producing milk foam, cooled and wherein the powder comprises coffee bean grounds. The milk foam to be produced thereby in combination with a coffee extract is particularly suitable for preparation of coffee-milk foam variations such as cappuccino and latte. A particular embodiment of the beverage dispensing device is here characterized in that cooling means are provided in heat-exchanging contact with the liquid reservoir. The cooling here increases the storage life of the milk product. 
    
    
     
       The invention will be further elucidated hereinbelow with reference to an exemplary embodiment and an accompanying drawing. In the drawing: 
         FIG. 1  shows an exemplary embodiment of a beverage dispensing device in combination with a froth dispensing device according to the invention; 
         FIG. 2A  shows an exemplary embodiment of a froth dispensing device according to the invention; 
         FIG. 2B  shows an exemplary embodiment of a beverage dispensing device according to the invention; 
         FIG. 3A  shows an exploded view of a frothing unit as applied in the froth producing device of each of the devices of  FIGS. 1, 2A and 2B ; 
         FIG. 3B  shows a cross-section of the frothing unit of  FIG. 3A ; 
         FIG. 4  shows a perspective view of a steam injector for application with the frothing unit of  FIGS. 3A and 3B ; 
         FIG. 5A  shows a perspective view of a first embodiment of a frothing chamber of a froth producing device according to the invention; 
         FIG. 5B  shows a perspective view of a second embodiment of a frothing chamber of a froth producing device according to the invention; 
         FIG. 6A-6F  show different embodiments of a rotor body as can be applied with the frothing chambers of  FIGS. 5A and 5B ; 
         FIG. 7  shows an electromechanical operating diagram of the device of  FIG. 1 ; and 
         FIG. 8  shows an electromechanical operating diagram of the device of  FIG. 2B . 
     
    
    
     It is otherwise noted here that the figures are purely schematic and not always drawn to (the same) scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity. Corresponding parts are designated in the figures with the same reference numeral. 
       FIG. 1  shows a setup of a device  100  for preparing a hot beverage, with adjacently thereof or at least close thereto a device  200  for producing a liquid froth which can be used in combination with that beverage. This involves particularly a more or less traditional coffee/espresso machine  100  with one or more bean reservoirs  102  for coffee beans, which open onto a grinding unit (not further shown) in the housing  104  of the machine. Although not further shown, but deemed sufficiently known to a person with ordinary skill in the art, the housing further provides space for a hot water appliance such as a boiler or thermal block, a control unit and a pump with which hot water is carried to a decoction group under increased pressure. 
     The decoction group comprises here a decoction chamber in which ground coffee powder is received from the grinding unit and is compressed so as to then extract a coffee extract therefrom under increased pressure with a dosed quantity of hot water. This extract is receivable at a double dispenser  106 . This can be espresso coffee of a desired strength or another coffee product, such as lungo or americano, depending on a preference of the user, which he or she can enter via a user interface  110  provided for this purpose. The housing also accommodates a steam generator and a steam dispenser  112  at which hot steam can be taken away. A set of further dispensers  113  for dispensing hot and cold water is also provided. 
     The decoction group can otherwise optionally also be fed with ground coffee powder which was received directly from a reservoir or inlet in question, in which case a bean grinder can optionally be dispensed with in the device. Use can also be made of a soluble product, such as freeze-dried coffee, in which case the decoction device will comprise not much more than a mixing chamber in which the product is mixed with a dosed quantity of hot water and dissolved therein. 
     Placed near the coffee machine is a stand-alone device  200  with which a milk foam can be produced from cold milk for the purpose of preparing for instance cappuccino or latte in combination with the coffee product obtained from coffee machine  100 . The device comprises 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 a housing  204  of frothing device  200  milk is carried from reservoir  202  to a liquid inlet of a frothing unit, which is shown further in  FIGS. 3A and 3B . 
     Upstream of the liquid inlet the liquid runs through a steam or air injector  400 , see  FIG. 4 , which is received in the milk conduit for this purpose. This comprises an ingoing connection  410  and an outgoing connection  420  in line with the milk conduit, in addition to a set of inlets  430  for steam and an outlet  440  for ambient air. In order to prevent an air/steam/liquid mixture from escaping from injector  400  non-return valves are arranged in or close to otherwise open inlets  430 ,  440 . 
     Steam inlets  430  can be fed by an own steam generator in the housing  204  of frothing device  200 . It is however also possible to obtain hot steam from coffee machine  100  via a steam conduit  150  provided for this purpose and corresponding connections which are then provided between the two devices  100 ,  200 . Inversely, the steam generator of frothing device  200  can also serve coffee machine  100  via a steam conduit  150  provided for this purpose. Injector  400  produces an air/milk or steam/milk mixture with which frothing unit  300  is fed and from which a liquid milk foam is produced by a frothing unit, which foam is carried via a conduit  250  provided for this purpose to the main device  100  and can therein be taken away at a second dispenser  206 . The operation of the frothing unit will be described below in more detail. 
     The frothing device according to the invention can also be applied in stand-alone manner.  FIG. 2A  shows an example hereof. The device is largely identical to the device  200  which is placed near device  100  for preparing a hot beverage in  FIG. 1 , albeit that in a stand-alone embodiment the conduits  150 ,  250  are absent or are at least not connected, and device  200  itself is equipped with a froth dispenser  206 . Upstream, froth dispenser  206  is coupled to an outlet of a milk frothing unit which is received in device  200 . 
     Instead of taking the form of two individual devices, the assembly of  FIG. 1  can also be integrated into a single device, as shown in  FIG. 2B . In this case the device comprises besides a functional part for preparing a coffee product, as described above, optionally also a functional part for preparing milk foam. Besides one or more bean reservoirs  102 , a cooled milk reservoir  202  is for this purpose also provided in the device, and the device also comprises a dispenser  206  for milk foam in the double coffee dispenser  106 . 
     As shown further in an exploded view in  FIG. 3A , and in cross-section in  FIG. 3B , milk frothing unit  300  comprises a frothing chamber  350  which is provided with a liquid inlet  310  and a froth outlet  320 . An entrance of liquid inlet  310  is here coupled to the outlet  420  of steam injector  400 , while froth outlet  320  is coupled to the froth dispenser  206  of the device. A rotor body  330  is rotatable inside frothing chamber  350  about an axially directed rotation axis X driven by an electric motor  340 , an output drive shaft  345  of which protrudes into rotor body  330 . Output drive shaft  345  protrudes here through an opening in a cover  370  which closes the frothing chamber  350 , wherein both a bearing and a liquid barrier are provided in the opening. Rotor body  330  is also bearing-mounted and fixated at a distal outer end. Frothing chamber  350  comprises for this purpose a press-fit base bearing  355 . Electric motor  340  is accommodated in a motor housing  380  which is in turn connected to the frame  390  of the device. 
     As is shown particularly clearly in  FIG. 3B , liquid inlet  310  and froth outlet  320  are connected to each other by a narrow gap  360  between rotor body  330  and the chamber wall of frothing chamber  350 . Optionally heated milk which is let in via liquid inlet  310  can only reach the froth outlet via the gap  360 . The rapidly rotating rotor body here agitates the liquid, whereby it mixes with air and air bubbles form therein. The thus produced milk foam exits the frothing chamber via the froth outlet. It is important here within the scope of the present invention that a section of rotor body  330 , and likewise a section of frothing chamber  350 , decreases in axial direction. Due to this (here) gradual narrowing of the rotor body, the peripheral speed decreases at a given number of revolutions, whereby the produced froth will stabilise further. The number of revolutions of the rotor body is typically in the order of magnitude of 2000-5000 revolutions per minute, with a diameter of the rotor body running (narrowing) from wide to narrow in axial direction over a length of the channel  360 . 
     Within the scope of the present invention it is also important that at least one of the outer surface of the rotor body and the surface of the chamber wall is not flat but accidented at the position of channel  360 . This can take various forms. In the example of  FIGS. 3A and 3B  the surface of the rotor body is as such provided with a large number of substantially congruent dimples  331  which are arranged over a periphery thereof in successive rows, see also  FIG. 6A . The dimples  331  of axially successive rows are here offset relative to each other and thereby lie at least substantially on an imaginary helical line of a number of mutually parallel helical lines. As shown in  FIG. 3A , dimples  331  each narrow toward outlet  320 , i.e. in downstream direction. Due to this gradually smaller volume of dimples  331 , the liquid will be gradually forced therefrom. This makes dimples  331  self-discharging. 
     Use can be made of a frothing chamber  350  with a completely flat, smooth inner wall  351 , at least at the position of rotor body  330 , as shown in  FIG. 5A , but this inner wall can also be provided with irregularities  352 , as shown in  FIG. 5B . When it comes to these irregularities use is then in respect of the chamber wall preferably made of depressions  352  with regard to adequate cleaning of the system, wherein this system must be rid of any possible milk residues. In the case of such an accidented chamber wall  350  use can if desired be made of a smooth rotor body  330 , for instance as shown in  FIG. 6B , with a smooth peripheral wall  336 . 
       FIGS. 6C-6F  show non-limitative further examples of rotor body  330  as it can be embodied within the scope of the invention.  FIGS. 6C and 6D  involve here respectively elongate depressions  332  and elevations  333  which are provided in a regular pattern. The relevant irregularities  332 ,  333  are here oriented with their major axis along an imaginary helix of a number of mutually parallel helices which can be imagined over the surface of the rotor body. A pitch of the helix in question is directed opposite to a rotation direction R of rotor body  330  and thereby also an orientation of the relevant irregularities. 
     Further alternative embodiments of rotor body  330  are shown in  FIGS. 6E and 6F , wherein the surface of rotor body  330  is accidented in that a set of parallel ribs  334 ,  335  or grooves extends thereover. These ribs/grooves  334 ,  335  here run along an imaginary helical line of a number of parallel helical lines with a pitch that rotates along with the rotation direction R of rotor body  330 , i.e. is directed in this rotation direction. 
     The gap  360  between rotor body  330  and the chamber wall typically has a width of less than a millimetre. For the purpose of producing cold milk foam the specific width has been found not to be very critical here. A good froth yield can be obtained in the whole area below a gap width of 1 millimetre. In some cases the stability of the froth does decrease significantly starting at a gap width above about 0.6 millimetres. Use is therefore preferably made of a gap width below this size of 0.6 millimetres. In that case the froth is found not to have collapsed, or hardly so, even after 5 minutes. 
     For producing hot froth a gap width of below 0.8 millimetres, particularly between 0.3 and 0.6 millimetres, has been found preferable in any case. Within this whole range the frothing device produces an acceptable froth yield in terms of volume increase, wherein with a gap width of between 0.3 and 0.6 millimetres the froth also retains its form for a sufficient period of time. Both froth yield and stability are always found to increase as the gap width decreases. On the other hand, a (through)flow resistance of the device will likewise increase as the gap width decreases, and the yield per unit of time will hereby also decrease. In addition, a good throughflow is also important when the device is subjected to being flushed for the purpose of cleaning the components. With a view to said yield, throughflow and, above all, tolerance a gap width above 0.1 millimetre is therefore preferably maintained. In the exemplary embodiments provided here use is made of a gap width of about 0.3 to 0.6 millimetres as preference and happy medium. 
       FIGS. 7 and 8  shows schematically a concise technical operating diagram of the device of respectively  FIGS. 1 and 2 .  FIG. 7  represents here a stand-alone froth dispensing device  200  adjacently of or at least near a beverage dispensing device  100  as shown in  FIG. 1 . Beverage dispensing device  100  comprises a steam generator  70  with a water supply  71  for the purpose of own steam dispenser  112 , see also  FIG. 1 . Via a steam conduit  150  provided for this purpose between the two devices  100 ,  200  this steam generator  70  is also utilized for the froth dispensing device  200  and is here coupled to a steam inlet  430  of a steam injector  400 . Froth dispensing device  200  can optionally also be applied in stand-alone manner, in which case such a or a similar steam provision  70  will be accommodated in the froth dispensing device  200  itself. 
     Froth dispensing device  200  comprises one or more reservoirs  73 ,  74  in which a liquid for frothing can be held. This example involves two milk containers for animal or plant-based milk, wherein the two reservoirs can be deployed to be able to hold a double quantity of the same liquid together or each individually contain a different milk product, for instance respectively animal cow&#39;s milk and plant-based soy or almond milk. A selection can be made from the two products by means of a three-way valve  76  applied for this purpose in a downstream liquid conduit. A reservoir  77  for holding a cleaning liquid is additionally coupled to the three-way valve, from which reservoir the device can be flushed periodically or on demand with a cleaning liquid held therein. For the purpose of extending the storage life of the milk products in the first two stated reservoirs  73 ,  74  they are embodied with a thermally insulating casing and provided with a forced and preferably thermostatically controlled cooling. 
     Reservoirs  73 ,  74 ,  77  are coupled to a pump  75  whereby, depending on the position of the three-way valve  76 , a liquid is drawn therefrom and is pumped under pressure to an inlet  410  of steam injector  400  which is arranged in milk conduit  160 . In the steam injector a milk/steam mixture is formed and the liquid is heated under the influence of the hot steam to a temperature of typically between 55° C. and 65° C. This mixture exits the steam injector at the outlet  420  thereof. A set of non-return valves  78 ,  79  prevents this mixture from being able to enter steam conduit  150  or air conduit  180 . As is the case here, it is then still possible upstream for air to be blown into the mixture downstream thereof using an air pump  72  which is provided for this purpose and draws in air from the surrounding area. The thus formed steam/air mixture is carried to an inlet  310  of frothing unit  300  wherein the mixture is produced by means of agitation, as described above, into a firm and aerated milk foam which can be taken away at a froth outlet  320 . 
     The produced froth can be carried via a froth conduit  170  between the two devices to a froth dispenser  206  which is placed in the vicinity of a coffee dispenser  106  of coffee machine  100  so as to receive a coffee with milk foam product thereunder. Alternatively, froth dispenser  206  can also be provided in froth dispensing device  200 , as shown in  FIG. 1 . In that case the user has to move a cup or mug from the one device to the other in order to receive both products. For operation, control and monitoring of the froth dispensing device a processor-controlled control unit  80  is provided in device  200 , which unit is also operatively coupled to at least the steam generator  70  in the coffee machine  100  if, as in the shown situation, use is made thereof. Control unit  80  is further operatively coupled to inter aria the two pumps  72 ,  75 , the three-way valve  76  and the frothing unit  300 , as shown with respective broken lines in the figure. 
     Instead of two separate devices, as in  FIG. 1 , use can also be made of a fully integrated application, wherein both a decoction device for preparing a hot beverage and a froth producing device, among other things, are accommodated in a collective housing. Such a device is shown in  FIG. 2 , and  FIG. 8  provides a possible operating diagram therefor with several components specifically involved therein. Components corresponding to those of the device of  FIG. 7  here have the same reference numeral and substantially the same operation, albeit that in this case a separate steam injector  400  is not applied, but steam and air are let directly into the frothing chamber via inlets or a shared inlet  450  of the frothing chamber then provided for this purpose. In this case the operation and monitoring of the froth producing device is also controlled by a processor-controlled control unit  90  which is provided for this purpose and is here coupled to or forms part of the control unit  91  of the coffee preparing part of the device, which is not further discussed here and is assumed sufficiently well known. The produced milk foam exits the frothing chamber via a froth conduit  170 . 
     Although the invention has been further elucidated above with reference to only a single exemplary embodiment, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and embodiments are still possible within the scope of the invention for a person with ordinary skill in the art.