Patent Publication Number: US-2005115419-A1

Title: Automatic device for heating and frothing a liquid, in particular milk

Description:
This application is a divisional application of U.S. patent application Ser. No. 10/312,367, filed Jul. 9, 2003, which is the U.S. National Phase of international application No. PCT/EP01/06966, filed Jun. 19, 201, and claims priority of Italian application No. T02000A000616, filed Jun. 23, 2000. 
    
    
     FIELD OF THE INVENTION  
      The present invention concerns an automatic device for heating and frothing a liquid, in particular milk.  
     BACKGROUND OF THE INVENTION  
      Preferably, the invention is applied in espresso coffee machines for bars, for producing frothy hot milk to be used e. g. in preparing cappuccinos, and the following description will refer to such a preferred application.  
      It is known that, in order to produce milk froth by means of espresso coffee machines, the operator utilises a container into which he pours a certain quantity of milk; then he introduces steam into the milk by a nozzle while stirring the container, so as to create a certain turbulence in the milk and incorporate the ambient air necessary to form the froth.  
      The characteristics and the quantity of the froth produced depend on the modalities of milk stirring and steam introduction, and therefore on the sensitivity and the skill of each operator.  
      Thus, such characteristics, and therefore the characteristics of the cappuccino in which the frothy milk is used, change from one operator to another and may be wholly unsatisfactory for the client, even if the operator judges them optimal.  
      Moreover, with the present technique problems may arise also from the hygienic standpoint, due in particular to the presence of milk crusts on the nozzle tip that are produced by successive frothing operations and that can remain exposed to air for a certain time.  
     SUMMARY OF THE INVENTION  
      A solution of the problems related to the dependency of the product quality on the individual operator is the subject matter of French patent application No. 2,604,077. That application discloses a device in which the steam nozzle is secured to an air feed duct, which has a bottom axial opening for air outlet arranged in front of the steam outlet opening of the nozzle, so that the steam licks the air jet and generates the required turbulence. Such a solution requires, for a proper operation, the presence of a chamber for mixing air and steam before introducing them into the liquid, and this makes the structure rather complex. Moreover, it leaves the problems of hygienic nature unsolved.  
      GB 382 972 discloses an apparatus for making what is known in the culinary art as whipped cream. This apparatus comprises a tank having close to its bottom a block of material porous to air. Between the block and the bottom of the tank a pressure chamber is defined where compressed air is admitted. Whipped cream is produced by forcing air in an ascending direction into the tank through the bottom block which is preferably made of porous stone.  
      EP 0287906 refers to an apparatus for heating and emulsifying liquids, in particular milk, contained in a tank, comprising a tube to be immersed in the liquid in the container, said tube being opened at its upper end for coupling the tube to a source of steam and at its lower end for expelling the steam into the liquid. According to this invention the tube comprises a radial calibrated orifice close to its upper end so as to obtain a level inside the tube equal to the external level.  
      FR 0775618 and FR 0769848 disclose an apparatus for mixing air into a liquid for the purpose of preparing cream through a separating porous plate provided close to the bottom of a tank and defining a chamber for pressurized air between said plate and the bottom of the tank.  
      U.S. Pat. No. 5,335,588 refers to an apparatus for milk frothing comprising a first pipe for admitting steam into the milk through its bottom open end and a second pipe for creating a venturi effect and improving the quantity of air mixed with the milk.  
      DE 29721055U refers to an arrangement for holding a pail on a stove during cooking having a pair of vertical arms which hold the pail firmly in position.  
      The aim of the invention is to provide an automatic heating and frothing device, which allows producing a froth with substantially constant characteristics, is of simple structure and does not give rise to the above mentioned hygienic problems.  
      The characteristics of the invention will become apparent from the appended claims.  
      A device comprising a container for the liquid having a bottom to which there are connected means for introducing pressurised steam into the liquid, according to the non-characterising clause of claim  1 , is disclosed in Utility Model Application No. TO 2000 U 000076.  
      For a better understanding, reference is made to the accompanying drawings, which show a preferred embodiment of the invention, given by way of non limiting example, and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side view of the device according to a first embodiment of the invention;  
       FIGS. 2 and 3  are perspective top and bottom views, respectively, of the milk container of the embodiment shown in  FIG. 1 ;  
       FIG. 4  show the steam and air ducts removed from the container;  
       FIG. 5  is an enlarged view of a detail of  FIG. 4 ;  
       FIG. 6  is a perspective view of the support base for the container shown in  FIG. 3 ;  
       FIG. 7  is a perspective view of a second embodiment of the invention;  
       FIG. 8  is a perspective view similar to  FIG. 7 , showing the container secured to the base;  
       FIG. 9  is a perspective view of the base used in the second embodiment of the invention; and  
       FIG. 10  is a perspective view from the bottom of the container used in the second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As shown in  FIG. 1 , the device essentially comprises a container  1  with a handle  2 , mounted on a base  3 . The base can be connected to the source of pressurised steam provided in a conventional espresso coffee machine (not shown) or it is internally equipped with an own pressurised steam source, independent of the source of the coffee machine. Base  3  further is equipped with an on/off switch  4  and a timer, operated through a control knob  5  and controlling the opening of an electric valve in a duct, internal to base  3  and not shown in the drawing, delivering steam to the container.  
      For sake of simplicity, the drawing shows neither the means for electric power supply of the device, nor the connections, if any, with the espresso coffee machine, nor the water feed/discharge ducts for the internal steam source, if any.  
      Referring to  FIGS. 2 and 3 , a first tube  6 , intended to introduce into the milk the steam supplied through the duct internal to base  3  ( FIG. 1 ), is removably mounted on the bottom of container  1 , inside the container itself. Such a tube  6  is secured to a second tube  7  intended to introduce the air required to produce the froth.  
      Tube  6  is secured onto the internal side of the bottom of container  1  by means of a threaded member  8 , e. g. welded onto the bottom of container  1 , which is engaged by a complementary member  9  arranged on tube  6  near the lower end thereof. Member  8  has an axial through-hole  10  ( FIG. 3 ) intended to receive the end portion of tube  6  and to allow communication between the tube and said duct internal to base  3 . Member  8  outward projects from the bottom of container  1  to allow a tight engagement, through a seal ring  11 , in a cavity  12  (shown in  FIG. 6 ) of the upper surface of base  3 . The steam feed duct internal to base  3  has an outlet  13  opening in correspondence with the bottom of said cavity.  
      Moreover, for securing container  1  to base  3 , the bottom of container  1  is externally equipped with a set of tongues  14  arranged to engage corresponding openings  15  in the upper face of base  3  and to be retained, upon a rotation of container  1  about its axis, by plates  16  separating openings  15 . Openings  15  and plates  16  adjacent thereto are preferably arranged on an annulus concentric with cavity  12 .  
      Turning again to  FIG. 2  and referring also to  FIGS. 4 and 5 , tube  6  includes: a first portion  60  with axis substantially parallel with the axis of container  1 ; an intermediate portion  62 , substantially rectilinear and inclined downwards, connected to the first portion  60  by a bent section  61 ; and an end portion  63 , also with substantially vertical axis, ending near the bottom of container  1 . Preferably, the length of intermediate portion  62  is such that end portion  63  is substantially adjacent with the internal wall of containers. Tip  64  of such end portion  63  is closed, but a radial opening  65  for steam outlet is provided near the tip itself.  
      When pouring the frothy milk, such a shape prevents small quantities of the milk entering tube  6  through opening  65  from flowing out through opening  10  in the container bottom.  
      Air tube  7  is open at both ends and includes two sections  70 ,  71  arranged substantially parallel with the intermediate and end portions  62 , 63 , respectively, of steam tube  6 . The open end of section  70  is to lie above the milk level within the container. End portion  72  of section  71 , as better shown in  FIG. 5 , is tapered or has anyway a reduced cross-sectional size, so as to give rise to an air jet, and it ends with an axial opening  73  arranged in front of opening  65  of tube  6 , so as to partly obstruct opening  65 .  
      The operation of the described device is as follows. Once the container  1  has been filled with the required milk amount (in any case, up to a level below the upper opening of tube  7 ), it is placed on base  3  so that the outward projecting portion of member  8  engages cavity  12  and tongues  14  enter cavities  15 . By rotating container  1 , the engagement of tongues  14  beneath plates  16  is obtained. Thereafter, the desired heating time is set through timer  5 , which opens the electric valve in the duct ending at the bottom of cavity  12 . Thus the steam can pass from the source (inside or outside the base) to tube  6  and flow out through opening  65  thereof. Given the relative position of steam and air outlets  65 , 73 , steam flowing out of opening  65  originates a vacuum, which in turn causes air intake through tube  7 . The steam outflow speed thus creates a turbulence on the milk bottom, making the milk become heated and mix with air supplied through tube  7 . Thus a milk-air-steam mixture is created directly within the milk. When the time set is over, the electric valve is closed thereby stopping steam supply and, after rotating container  1  to release tongues  14 , container  1  can be removed from base  3  to pour the frothy milk.  
      Referring now to FIGS.  7  to  10 , a second embodiment is shown employing different and more robust means for securing container  1  to base  3 . In such Figures, the elements already discussed in connection with FIGS.  1  to  6  are denoted by the same reference numerals. The arrangement of tubes  6 , 7  introducing steam and air into the milk is the same as in the first embodiment.  
      Container  1  has on its external wall a pair of diametrically opposed projections  20  (of which only one can be seen in the drawings), arranged to co-operate with a pair of upright retaining members  21  projecting from the upper surface of base  3 . Retaining members  21  are each made by a bar, with rounded cross-sectional shape, bent to an inverted U shape. Each projection  20  engages, in operating conditions of the device, the underside of a horizontal upper section  21   a  of a respective retaining member  21 , as shown in  FIG. 8 . Horizontal section  21   a  has a central portion slightly curved in a horizontal plane so as to somewhat conform to the curvature of the side wall of containers.  
      A vertical stem  22  projecting from base  3  carries a control panel  23  on which on/off switch  4  and control knob  5  for the timer are mounted. Stem  22  will house the necessary electric wiring for the switch and the knob.  
      As shown in  FIG. 9 , base  3  is also provided, on its upper surface, with a number, e.g. four, of freely rotatable ball supports  24  intended to reduce friction between the bottom of container  1  and base  3  during the container rotation needed to bring projections  20  into engagement with retaining members  21 . Ball supports  24  are mounted in elastomeric members  25 . One of ball supports  24  is also arranged to co-operate with a safety switch (not shown), located within base  3  and intended to cut off power supply during securing and releasing of container  1 .  
      Base  3  has a central projection  26  housing end portion  27  of the steam feed duct located internally of base  3 . Projection  26  is intended to sealingly engage, through a seal ring  28 , a cavity  29  (visible in  FIG. 10 ) provided in fastening member  8 , so as to establish communication between end portion  27  of the steam feed duct and tube  6 .  
      The operation of that second embodiment is quite similar to that of the embodiment shown in FIGS.  1  to  6 . Once container  1  has been filled with milk, it will be put on base  3  between retaining members  21 , so that projections  20  lie externally of such members, as shown in  FIG. 7 . In doing so, projection  26  engages cavity  29  and outlet opening  13  of end portion  27  of the steam supply duct comes into alignment with the inlet of tube  6 . Container  1  is then rotated so as to make projections  20  move into the space defined by the corresponding retaining member  21  and engage the underside of horizontal sections  21   a,  as shown in  FIG. 8 . The cooperation between projections  20  and horizontal sections  21   a  will push downward container  1  against the action of the resilient support members  25  of ball supports  24 . Thus the safety switch is closed. At the end of the heating time, container  1  will be rotated in the opposite direction and, as soon projections  20  are no longer retained by horizontal sections  21   a,  ball supports  24  will push upward the container thereby opening the safety switch and cutting off the power supply. The operations then proceed as already disclosed for the previous embodiment.  
      One can immediately appreciate that the invention allows solving the problems mentioned in the introduction. Actually, on the one side the device is automatic, and hence gives a product of which the quality no longer depends on the skill and/or the sensitivity of the individual operator; on the other side, the portions contacting the milk (in particular, steam and air tubes  6  and  7 ) can be removed from the container and washed immediately after use, thus avoiding possible pollution.  
      It is clear that the above description has been given only by way of non-limiting example and that changes and modifications can be made without departing from the scope of the invention. For instance, the arrangement of switch  4  and control knob  5  shown in  FIG. 7  can be provided also in the embodiment of FIGS.  1  to  6 .  
      Moreover, even if reference has been made to the preparation of milk froth and warm milk in espresso coffee machines, the device can be used to froth and/or heat other liquids, in particularly for preparing infusions.