referring to fig1 to 3 , there is shown a device according to the invention for preparing foam from a milk - based alimentary liquid designated by the general reference numeral 1 . device 1 includes a container 2 for receiving an alimentary liquid , typically milk , from which the foam will be produced . in the example illustrated , container 2 has the form of a generally cylindrical pot with a slightly flared portion provided with a beak ( not shown ). container 2 can be made of any material withstanding temperatures of the order of 200 ° c . for example pyrex glass or similar . other geometrical shapes can of course be envisaged for the container . it will be noted that in this example embodiment , container 2 includes three level markers 2 a , 2 b , and 2 c for determining three filling levels of container 2 . a handle ( not shown ) secured to the container , for example by a metal binding can be envisaged to facilitate handling thereof . the device further includes a frame 4 provided with a support 6 having a surface 6 a of substantially complementary dimensions and shapes to the bottom surface of container 2 for receiving and positioning the latter . for this purpose , the surface of support 6 a is arranged to be slightly set back in relation to the upper surface of support 6 . container 2 is thus removably mounted on support 6 of frame 4 . the surface 6 a of support 6 is in a thermal relationship with an electrical heating element 8 for heating the alimentary liquid contained in container 2 . heating element 8 is , for example , formed of a resistant heating plate or a halogen lamp . in the latter case , it will be noted that the support surface 6 a is formed of a vitroceramic plate underneath which the halogen lamp is arranged . it goes without saying that any other type of electrical heating body can be envisaged . the heating element has sufficient power to quickly heat a quantity of alimentary liquid from 40 ml to 80 ml to a temperature comprised between 60 ° and 85 ° c ., for example with power comprised between 600 and 2300 w . device 1 further includes mechanical stirring means 10 which extend at least partially into container 2 . stirring means 10 are of the rotating type and comprise a rod 10 a provided , at its distal end , with a stirring head 10 b which extends in proximity to the bottom of container 2 . typically , stirring head 10 b includes a ring - shaped helical spring . according to a variant that is not shown , the stirring head can include a plurality of radial and vertical wings . the figures also show that in this example , rod 10 a includes a collar 10 c arranged at approximately mid - length . collar 10 c advantageously enables liquid dripping down from the stirring head to be recovered when the cover is removed from container 2 and rests flat on its upper surface . in this example embodiment , it can be seen that container 2 is associated with a cover 12 which carries stirring means 10 . more specifically , rod 10 a is rotatably mounted via its proximal end in cover 12 . the end of rod 10 a passes through the cover to extend outside the container when the cover closes the latter . this end includes a female coupling part 14 for cooperating with a complementary male coupling part 16 connected to means 18 for driving stirring means 10 . advantageously , coupling with the driving means is achieved via friction for example of the cone on cone type . drive means 18 are typically made in the form of an electrical motor with two directions of rotation capable of rotating within ranges of speed from 500 to 10000 rpm . these drive means 18 are mounted in a mobile cover 20 connected to frame 4 and extending above container 2 . cover 20 is mounted so as to be mobile on frame 4 so that it can pivot between a first position ( fig2 ) in which drive means 18 are coupled to stirring means 10 and a second position ( fig3 ) in which said drive means are uncoupled from stirring means 10 and in which container 2 can be removed from device 1 . it will be noted in this regard that the cover is associated with locking means 22 provided for holding cover 20 respectively in the first and second positions . locking means 22 have here the shape of an articulated hook 22 a secured to cover 20 cooperating with a pin 22 b secured to frame 4 . hook 22 a can be actuated for locking and / or unlocking via a toggle mechanism 23 , one lever 23 a of which is connected to hook 22 a and the other lever 23 b of which is connected to a control member accessible from the outside of cover 4 , lever 23 b resting on pin 23 c secured to the cover . device 2 further includes control means 24 disposed in frame 4 and arranged for managing the control of heating body 8 and drive means 18 . more specifically , the control means are arranged for heating a quantity of liquid to bring it in proximity to a desired temperature level while stirring said quantity of liquid at a first speed during a first phase and for stirring said quantity of liquid at a second speed higher than the first speed during a second phase . since the heating and stirring conditions of the alimentary liquid depend upon the quantity of alimentary liquid contained in container 2 , control means 24 comprise a microcontroller connected to motor 18 and to the heating element , and suitably programmed for controlling one or more foam producing cycles as a function of the quantity of liquid to be foamed . control of these cycles is started by actuating control keys 26 a , 26 b , 26 c , each of the keys corresponding to control by the microprocessor of a foam production cycle for a determined quantity of liquid . in the example shown , the control keys are three in number and correspond respectively to switching on a foam producing cycle for the three levels of liquid defined by the level markings 2 a , 2 b and 2 c of container 2 . these control keys 26 a , 26 b , 26 c therefore form selection means for adapting the quantity of heating energy supplied during the first phase of the foam producing cycle and the duration of the second phase , as a function of the quantity of liquid in container 2 . the heating energy can easily be adapted either by adjusting the power and / or the heating time . typically , the two speed levels can be obtained by acting directly upon the electrical motor control by varying the frequency of the control signal sent by the microcontroller . according to a variant one could also envisage varying the speed mechanically by varying a gear ratio disposed between the motor output and the stirring means . the electrical elements of device 1 are powered via a supply plug 28 secured to the frame and intended to be connected to the mains supply via a conventional supply lead . the method according to the invention for preparing foam from a determined alimentary liquid , in this case milk , will now be described using device 1 according to the invention and illustrated in fig1 and 2 . first of all a quantity of milk , corresponding to one of the three levels marked by marking lines 2 a , 2 b and 2 c , is poured into container 2 . container 2 is then closed by means of cover 12 carrying stirring means 10 . container 2 is then placed on support surface 6 a , cover 20 of device 1 having previously been placed in the open position ( fig2 ). cover 20 is then tipped ( fig1 ). this causes male coupling part 16 connected to the drive means to friction fit into female coupling part 14 secured to stirring means 10 and emerging from cover 12 of container 2 . once in this configuration , control key 26 a , 26 b or 26 c , corresponding to the level of liquid contained in container 2 , can be actuated . such actuation switches on the foam preparing cycle corresponding to the level of liquid selected , this cycle being controlled by control means 24 . during a first phase of the preparation cycle , control means 24 respectively switch on heating element 8 and motor 18 to supply the quantity of calorific energy necessary to bring the quantity of liquid selected to a desired temperature level and to mechanically stir the quantity of liquid at a first stirring speed , lower than the foam creating speed . typically , the desired temperature for facilitating formation of milk foam is of the order of 60 to 70 ° c . and the first stirring speed is comprised between 500 and 1500 rpm and is preferably of the order of 800 rpm . stirring at a relatively low speed homogenises the temperature of the milk in the container preventing layers of different temperatures from forming and in particular , the lowest layer from burning and sticking to the bottom of the container , while activating the desired temperature increase . as soon as the quantity of heat energy corresponding to the quantity of liquid selected has reached the desired value , the microcontroller adjusts the command of heating element 8 so as to keep the quantity of alimentary liquid at the desired temperature level and triggers entry into a second phase during which the foam will be produced . for this purpose , the microcontroller sends a signal to motor 18 to drive the latter at a second stirring speed suitable for forming foam . this speed is typically comprised between 3000 and 10000 rpm and preferably of the order of 5000 rpm . the duration of this second phase which is controlled by the microcontroller varies in accordance with the quantity of liquid selected . typically , for a quantity of liquid from 40 to 80 ml , the duration of this second phase is of the order of 5 to 15 seconds , which enables a foam phase to be prepared of the order of 30 % to 60 % foam with respect to the liquid phase . preferably , the microcontroller is programmed , during this second preparation phase , to drive stirring in a discontinuous manner , or in other words to regularly interrupt and restart stirring during this phase in order to optimise foam formation . typically the interruption frequency is of the order of 0 . 3 to 0 . 5 hz . preferably , the microcontroller can be programmed such that stirring member 10 changes its direction of rotation after each interruption during this second phase . once the second phase has finished , the microcontroller commands the automatic stopping of device 1 . then cover 20 has only to be unlocked , tipped into its opening position and container 2 containing the foam can be removed . the invention is of course not limited to the embodiment described hereinbefore and it will be understood that various alterations and / or improvements evident to those skilled in the art could be made without departing from the scope of the invention defined by the annexed claims . in particular , in order to limit the centrifugation effect during stirring , stirring means 10 could also be moved from top to bottom and / or in a transverse plane to bring the foam back into contact with the stirring means . second stirring means could also be used , which depending upon the geometry of the container , could be disposed at the same level as the first means or at different levels . it should also be noted that the heating could be interrupted during the second foam preparing phase . likewise , passage from a first stirring speed to a second stirring speed in the method according to the invention can occur gradually without departing from the scope of the invention . according to an alternative embodiment , the microcontroller can be associated with means for detecting the temperature ( not shown ) of the alimentary liquid in order to command motor means 18 in accordance with at least two speed levels as a function of the temperature level detected . the temperature detection means typically comprise a thermal switch associated with the heating element and which enables the latter to be switched on as soon as a predetermined desired temperature has been reached . in this case the temperature of the liquid is measured indirectly . one could also envisage arranging a temperature sensor in the container , for example secured to the stirring means in order to obtain a direct liquid temperature measurement . according to this variant , the temperature detection means regularly send signal representative of the temperature to the microcontroller during the first phase . as soon as the temperature has reached the desired value , the microcontroller commands the control of the heating element 8 so as to keep the alimentary liquid at the desired temperature and triggers entry into the second phase during which the foam will be produced , the microcontroller then sending a signal to motor 18 to drive the latter at a second stirring speed suitable for forming foam . it should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art . such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages . it is therefore intended that such changes and modifications be covered by the appended claims .
the invention concerns a method for preparing foam from a milk - based alimentary liquid , including the successive steps of : a ) spacing a quantity of alimentary liquid in a container associated with stirring members ; b ) heating said quantity of alimentary liquid to bring it in proximity to a first desired temperature level while mechanically stirring it at a first stirring speed , lower than the foam creating speed , and c ) stirring said quantity of liquid at a second stirring speed , sufficient to make said liquid foam .