MILK FOAMING DEVICE AND METHOD FOR PRODUCING MILK FOAM

Abstract

A milk foaming device for improving the quality of a milk foam (13) which is produced. The milk foaming device (1) has a mixing chamber (3) in which air (6) and milk (7) can be foamed by a steam flow (9) to provide the milk foam (13). For this purpose the respective flow rates of an air stream (15) and of a milk stream (8), each of which flows into the mixing chamber (3), are set by the air (6) and the milk (7) always flowing together into the mixing chamber (3) through an adjustable, variable opening cross-section (10) which acts as a flow rate reducer for the air stream (15) and the milk stream (8).

Claims

1. A milk-frothing device (1), comprising: a steam nozzle (2); a mixing chamber (3) adjoining the steam nozzle (2) for producing milk froth (13) from steam (5), milk (7) and air (6); a variable opening cross section (10) configured for adjusting a milk flow (8) passing into the mixing chamber (3); wherein the air (6) is guided as an air flow (15) through the variable opening cross section (10) into the mixing chamber (3); a milk supply (12) and an air supply (11) configured such that the air (6) simultaneously with the milk (7) pass through the variable opening cross section (10) as a milk and air flow (14); and a regulating body (22) configured to permit a reliable cleaning of lower portions of the milk supply (12) by the milk supply (12) being completely closeable with the regulating body (22) with which, in addition, the variable opening cross section is also adjustable, and when the milk supply (12) is completely closed, the air supply (1) can still have a flow passing therethrough.

2. The milk-frothing device (1) as claimed in claim 1, wherein at least one of (a) the air flow (15) and the milk flow (8) form the milk and air flow (14), (b) in a region of the variable opening cross section (10), the air flow (15) at least partially delimits the milk flow (8), or (c) the milk supply (12) is closeable such that the milk supply (12) between a milk store and the variable opening cross section (10) is interrupted.

3. The milk-frothing device (1) as claimed in claim 1, wherein the variable opening cross section (10) is dimensioned such that an adjustment of the variable opening cross section (10) adjusts both the milk flow (8) and the air flow (15).

4. The milk-frothing device (1) as claimed in claim 1, wherein the variable opening cross section (10) is mounted upstream of an admixing opening (4) for air (6) and milk (7) that opens into the mixing chamber (3).

5. The milk-frothing device (1) as claimed in claim 4, further comprising an intake chamber (17) mounted upstream of the mixing chamber (3), and the milk and air flow (14) is also guided upstream of the admixing opening (4) through the intake chamber (17).

6. The milk-frothing device (1) as claimed in claim 1, wherein the steam nozzle (2) is shaped such that a steam flow (9) is generatable, causing a negative pressure based on a Venturi effect, such a manner that the milk and air flow (14) is deliverable into the mixing chamber (3) by the negative pressure.

7. The milk-frothing device (1) as claimed in claim 1, further comprising an additional throughflow reducer (18) for limiting the air flow (15).

8. The milk-frothing device (1) as claimed in claim 1, wherein the opening cross section (10) is variable at least in a stepwise manner such that a throughflow of the milk and air flow (14) through the variable opening cross section (10) is adjustable at least in a stepwise.

9. The milk-frothing device (1) as claimed in claim 1, wherein the opening cross section (10) is variable by rotation of the regulating body (22) about a regulating axis (23).

10. The milk-frothing device (1) as claimed in claim 1, further comprising an air switching-off device, and the air flow is switchable on and off by the air switching-off device, such that both milk froth and hot milk are deliverable from the milk-frothing device (1).

11. A method for producing milk froth (13) using a milk-frothing device (1) and for cleaning lower portions of a milk supply (12) of the milk-frothing device (1), the method comprising: frothing air (6) and milk (7) in a mixing chamber (3) using a steam flow (9) to form the milk froth (13), adjusting a milk flow (8) passing into the mixing chamber (3) using a variable opening cross section (10), allowing the air (6) to flow through the variable opening cross section (10) into the mixing chamber (3), the air (6) forming an air flow (15) which flows simultaneously with the milk flow (8) as a milk and air flow (14) through the variable opening cross section (10), closing the milk supply (12) with a regulating body (22) with which the variable opening cross section (10) is adjustable, an air supply (11) of the milk-frothing device (1) continuing to feed air to the opening cross section (10) while the milk supply (12) is interrupted, and when the milk supply (12) is completely closed, directing a flushing water flow through the air supply (11).

12. The method as claimed in claim 11, further comprising adjusting or regulating the milk and air flow (14) by adjustment of the variable opening cross section (10).

13. The method as claimed in claim 12, wherein, by adjustment of the variable opening cross section (10), adjusting both the air flow (15) and the milk flow (8) at least one of simultaneously or synchronously.

14. The method as claimed in claim 11, further comprising increasing a temperature of the milk froth (13) by the milk and air flow (14) being reduced by reducing the opening cross section (10).

15. The method as claimed in claim 11, further comprising varying the opening cross section (10) by rotation of the regulating body (22) about a regulating axis (23) by which a depth, which determines the opening cross section (10), of a surface channel (24) on the regulating body (22) is varied.

16. The milk-frothing device (1) as claimed in claim 7, wherein the additional throughflow reducer (18) comprises a pinhole aperture (19), and the device further comprises a lip seal (20) for preventing a flowback of milk through the pinhole aperture.

17. The milk-frothing device (1) as claimed in claim 9, wherein the variable opening cross section (10) comprises a surface channel (24) on an outer circumferential side and of variable depth, on the regulating body (22), and the air (6) is guided to the variable opening cross section (10) by an air surface channel (25) which is formed on the regulating body (22) and opens into the surface channel (24).

18. The method of claim 13, further comprising dispensing with an additional active regulation of the air flow (15), and wherein air (6) and milk (7) always flow together through the variable opening cross section (10).

19. The method of claim 14, wherein the steam flow (9) is kept constant or is increased, and/or

20. The method of claim 14, further comprising reducing both the air flow (15) and the milk flow (8) by reducing the opening cross section (10).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0100] In the drawings:

[0101] FIG. 1 shows a perspective view of a milk-frothing device according to the invention,

[0102] FIG. 2 shows a perspective view of a longitudinal section of the milk-frothing device from FIG. 1,

[0103] FIG. 3 shows a top view of the longitudinal section according to FIG. 2,

[0104] FIG. 4 shows a side view of the milk-frothing device from FIG. 1,

[0105] FIG. 5 shows a view from above of the milk-frothing device from FIG. 1,

[0106] FIG. 6 shows a perspective detailed view of a partial vertical section through the milk-frothing device of FIG. 1 along the section line shown in FIG. 5,

[0107] FIG. 7 shows a top view from above of a horizontal section through the regulating body in the position according to FIG. 6,

[0108] FIG. 8 shows the detailed view from FIG. 6 after rotation of the regulating body of the milk-frothing device by 90° in the clockwise direction,

[0109] FIG. 9 shows a top view from above of a horizontal section through the regulating body in the position according to FIG. 8, in analogy to FIG. 7,

[0110] FIG. 10 shows a perspective detailed view of the regulating body of the milk-frothing device from FIG. 1 in the 0° position shown in FIG. 1 and FIG. 6,

[0111] FIG. 11 shows a detailed sectional view of a mixing chamber of the milk-frothing device of FIG. 1, and

[0112] FIG. 12 shows a detailed view of the regulating body of the milk-frothing device from FIG. 1, wherein said regulating body precisely closes the milk supply (12).

DETAILED DESCRIPTION

[0113] FIG. 1 shows a milk-frothing device according to the invention, denoted as a whole by 1, which is provided for use on a fully automatic coffee machine with which various coffee beverages can be provided.

[0114] As can readily be seen in FIGS. 2 and 3, the milk-frothing device 1 has a steam nozzle 2 with which a steam flow 9 can be produced which exits from a steam outlet opening 16 and flows into a mixing chamber 3 mounted downstream of the steam nozzle 2. For this purpose, a steam supply connection 32 is also provided, from which steam 5 passes into the steam nozzle 2.

[0115] With the aid of the steam flow 9, both milk 7 and air 6 can be delivered into the mixing chamber 3 using the Venturi effect, in order to froth the milk 7 and the air 6 there to form a stable milk froth 13. In order to configure the milk-frothing device 1 in a structurally simple manner, an additional pump has been omitted here, and therefore the milk 7 and the air 6 are delivered as a milk and air flow 14 into the mixing chamber 3 exclusively because of the negative pressure generated by the steam nozzle 2.

[0116] In order to froth the milk 7, an impact body 31 is provided in the mixing chamber 3, at which impact body turbulent swirling of the milk 7 and of the air 6 occurs, such that fine-pored milk froth 13 arises which then flows out of a milk-froth outlet opening 28 of the discharge module 29, which is shown in FIGS. 2 and 3.

[0117] The milk 7 is supplied here to the milk-frothing device 1 via a milk supply connection 26 and an adjoining milk supply 12, which can be seen in FIG. 1, and therefore a milk flow 8 (cf. FIG. 6) is guided into the mixing chamber 3. Furthermore, a corresponding air supply 11 is also provided, with which an air flow 15 is guided into the mixing chamber 3, wherein the air flow 15 is obtained from the ambient air, as can be seen with reference to FIGS. 2 and 3.

[0118] The milk-frothing device 1 furthermore has a regulating body 22 which is mounted rotatably about a regulating axis 23. A variable opening cross section 10 which reduces or adjusts a throughflow rate of the milk flow 8 is adjustable with the regulating body 22. As will be explained more precisely, a flow rate of the milk flow 8 can be precisely and continuously adjusted here by a rotation of the regulating body 22.

[0119] Since the steam nozzle 2 substantially produces a constant steam flow 9, the temperature of the emerging milk froth 13 can be adjusted with the aid of the regulating body 22. This is because, as soon as the flow rate of the milk flow 8 is reduced while the flow rate of the steam flow 9 remains substantially constant, the temperature of the milk froth 13 correspondingly increases. This means that particularly high temperatures of the milk froth 13 are achieved precisely when the flow rate of the milk flow 8 is at the lowest.

[0120] In order now in such a situation to prevent the milk flow 8 from breaking off and only air 6 from flowing into the mixing chamber 3, according to the invention the air flow 15 is guided through the variable opening cross section 10 into the mixing chamber 3.

[0121] As the detailed view of the regulating body 22 according to FIG. 10 shows, the regulating body 22 has, for this purpose, a first surface channel 24 for guiding the milk 7 or the milk flow 8 and an air surface channel 25 for guiding the air 6 or the air flow 15. Said two surface channels 24, 25 are each formed on the outer circumferential side in a circumferential outer surface or in an outer contour 36 of the regulating body 22. The circumferential outer surface/outer contour 36 of the regulating body 22 is formed cylindrically here in order to permit a rotation of the regulating body 22, as the detailed view of FIG. 10 shows.

[0122] It is apparent with reference to the detailed views according to FIGS. 6 and 8 that the regulating body 22 is mounted in a sealing manner in a regulating body receptacle 34 formed so as to correspond to the regulating body 22. An inner surface of the regulating body receptacle 34 with the respective surface channel 24, 25 defines a respective throughflow cross section which at the same time determines a flow rate of the milk flow 8 or of the air flow 15.

[0123] As the detailed view of FIG. 10 shows, a channel depth of the surface channel 24 is configured so as to be variable in the circumferential direction. The respective channel depth of the surface channel 24 together with the regulating body receptacle 34 determines the variable opening cross section 10 through which both the air flow 15 and the milk flow 8 are guided, as can be seen with reference to the dashed and dotted lines in the detailed view of FIG. 10. For this purpose, the air surface channel 25 opens into the surface channel 24, and therefore, at the opening point 37 shown in FIG. 10, the air supply 11 and the milk supply 12 are precisely brought together, specifically still upstream of the variable opening cross section 10. In other words, the air 6 or the air flow 15 is thus guided with the aid of the air surface channel 25 to the opening point 37 and from there to the variable opening cross section 10.

[0124] In other words, the cross-sectional surface of the opening cross section 10 is therefore varied as soon as the regulating body 22 is rotated. This variation takes place continuously, and therefore the opening cross section 10 can be varied continuously by rotation of the regulating body 22. Consequently, a flow rate of the milk and air flow 14 through the variable opening cross section 10 can thereby be varied continuously.

[0125] In the 0° position of the regulating body 22 that is shown in FIGS. 6 and 7, the variable opening cross section 10 is determined here precisely by a through opening 35 which opens into a chamber 30 in the interior of the regulating body 22 (cf. FIG. 7 together with FIG. 3). In this position of the regulating body 22, both the air flow 15 and the milk flow 8 thus flow through the inflow opening 33, which acts as the variable opening cross section 10, into the chamber 30 and from there as a milk and air flow 14 through an inflow opening 33 into an intake chamber 17 and from there through an admixing opening 4 into the mixing chamber 3 (cf. FIGS. 6 and 8).

[0126] By contrast, in the 90° position of the regulating body 22 that is shown in FIGS. 8 and 9, both the air flow 15 and the milk flow 8 flow in the surface channel 24 initially along the circumference of the regulating body 22, then through the variable opening cross section 10, illustrated as a hatched area in FIG. 10, and only then through the through opening 35 into the chamber 30 in order to pass from there into the intake chamber 17 and finally into the mixing chamber 3. In this situation, it is therefore precisely the cross-sectional area, which is illustrated as a hatched area in FIG. 10, which is the determining feature for the throughflow of the milk and air flow 14, and it therefore acts as the variable opening cross section 10 within the context of the invention.

[0127] In both situations (FIG. 6/FIG. 8), the air 6 together and simultaneously with the milk 7 passes through the variable opening cross section 10 as a milk and air flow 14, wherein the air flow 15 mentioned at the beginning and the milk flow 8 mentioned at the beginning form the milk and air flow 14.

[0128] As is easily conceivable with reference to the detailed view of FIG. 10, the two fluids, i.e. the milk 7 and the air 6, flow next to each other through the variable opening cross section 10 and in the process form a common fluidic boundary surface via which the two fluids interact with each other. This has the result that, in the region of the variable opening cross section 10, the air flow 15 at least partially delimits the milk flow 8. The remaining delimitation is provided here by the walls of the surface channel 24 and by the inner surface of the regulating body receptacle 34.

[0129] In this connection, the variable opening cross section 10 that is determined by the variable channel depth of the surface channel 24 is dimensioned precisely in such a manner that an adjustment of the variable opening cross section 10 adjusts both the milk flow 8 and the air flow 15 simultaneously and in particular in parallel by rotation of the regulating body 22. This means that, in the event that the variable opening cross section 10 is reduced from the 0° position shown in FIG. 6 into the 90° position shown in FIG. 8 by a rotation of the regulating body 22, both a flow rate of the milk flow 8 and at the same time a flow rate of the air flow 15 is reduced. Therefore, the air flow 15 is thus automatically throttled as soon as the milk flow 8 is reduced, for example in order to achieve a high temperature of the emerging milk froth 13.

[0130] Owing to the fluidic coupling between the milk flow 8 and the air flow 15, said coupling arising by means of the common fluidic boundary surface, it is virtually no longer possible for the milk flow 8 to break off.

[0131] As can be readily seen in particular in the longitudinal sectional view of FIG. 3 (in conjunction with FIG. 3), the variable opening cross section 10 is precisely mounted upstream of the admixing opening 4, through which air 6 and milk 7 pass into the mixing chamber 3, with respect to the flow direction of the milk and air flow 14. Furthermore, it can be seen that the milk and air flow 14 is still guided upstream of the admixing opening 4 through the intake chamber 17, which is mounted upstream of the mixing chamber 3.

[0132] The through opening 35, the chamber 30, the inflow opening 33, the intake chamber 17, and the admixing opening 4 thus form a milk and air feed line 21 which guides the milk and air flow 14 from the variable opening cross section 10 into the mixing chamber 3.

[0133] As can be seen, for example, in FIGS. 2, 3 and 6, the air 6 first of all flows through a throughflow reducer 18 in the form of a pinhole aperture 19 and then through a lip seal 20. While the pinhole aperture 19 reduces a flow rate of the air flow 15, the lip seal serves to prevent a possible backflow of the milk 7 in the direction of the pinhole aperture 19.

[0134] FIG. 12 illustrates a further characteristic feature of the regulating body 22 of the milk-frothing device from FIG. 1. Said regulating body has a closure surface 52, and therefore the milk supply 12 can be completely closed by corresponding rotation of the regulating body 22 into the 135° position illustrated in FIG. 12. In this position of the regulating body 22, that is to say with the milk supply 12 completely closed (wherein the milk supply 12, as can be seen in FIG. 12, is interrupted precisely between the milk store (not shown) and the variable opening cross section 10), a flow can continue to pass through the air supply 11. More specifically, air can continue to flow first of all from the throughflow reducer 18 through the air surface channel 25 (cf. FIG. 10) and then through the surface channel 24 (through which the milk normally also flows) and the variable opening cross section 10 and can thus pass through the through opening 35 into the chamber 30 (cf. in this respect also FIG. 3 and FIG. 10). This also becomes vividly clear if it is imagined rotating the regulating body 22 in FIG. 9 by a further 45° in the clockwise direction (as a result of which the situation of FIG. 11 is reached, in which the milk flow 8 impinges on the closure surface 52 and thus can no longer pass into the chamber 30).

[0135] Since the regulating body 22 in FIG. 12 therefore has now been rotated precisely to such an extent that the milk supply 12 is closed, but the air supply 11 continues to be open, the entire lower portion of the milk supply 12 can now be flushed without there being the risk of flushing water being pushed into the upper portion of the milk supply 12 and as far as into the milk store.

[0136] For this purpose, flushing water can be introduced as a flushing water flow 53, as illustrated in FIG. 12, into the air supply 11, for example on the same path as the air through the throughflow reducer 18 or via a separate feed line. As a result, the flushing water flow 53 can flow through the surface channels 24 and 25, the through opening 35 and finally the chamber 30 in order subsequently to pass through the intake chamber 17 into the mixing chamber 3 and, finally, to emerge through the milk froth outlet opening 28 (cf. FIG. 3). Therefore, at least all of the line portions through which the milk and the air jointly flow during normal operation can be cleaned with flushing water, such that, in addition, only the upper portion of the milk supply 12 as far as the closure surface 52 of the regulating body 22 has to be cleaned by hand, in order to ensure hygiene.

[0137] The above-described flushing can be carried out here fully automatically by a fully automatic coffee machine which is based on such a milk-frothing device 1, wherein the fully automatic coffee machine can control both the active flushing and the closing of the milk supply 12.

[0138] The Figures do not show a further possible refinement of the milk-frothing device 1, in which the air flow 15, which flows into the mixing chamber 3 through the variable opening cross section 10, can be switched on or off by means of an air switching-off device in the form of an electrically activatable blocking valve. If the air switching-off device is activated by the fully automatic coffee machine, no more air 6 can flow into the mixing chamber 3, but milk 7 can continue to flow through the variable opening cross section 10 into the mixing chamber 3. In this case, the milk-frothing device 1 therefore specifically does not deliver any milk froth 13 through the milk-froth outlet opening 28, shown in FIG. 3, of the discharge module 29, but rather delivers milk 7 heated by the steam 5. In such a refinement, both milk froth 13 and hot milk 7 can therefore be output by the milk-frothing device 1.

[0139] In summary, the invention aims to improve the quality of a milk froth 13 which is produced by means of a milk-frothing device 1 which has a mixing chamber 3 in which air 6 and milk 7 can be frothed by means of a steam flow 9 to form the milk froth 13. It is proposed for this purpose that a respective flow rate of an air flow 15 and of a milk flow 8, which each flow into the mixing chamber 3, is adjusted by the fact that the air 6 and the milk 7 always flow together into the mixing chamber 3 through an adjustable, variable opening cross section 10 which acts as a flow rate reducer or as a throttle for the air flow 15 and the milk flow 8. In other words, in the solution according to the invention, a variable opening cross section 10 is therefore provided through which an air flow 15 is guided together with a milk flow 8.

[0140] Considered from a different viewing angle which discloses further innovative aspects of the present invention, FIG. 1 shows a milk-frothing device according to the invention that is denoted overall by 1 and is provided for use on a fully automatic coffee machine with which various coffee beverages can be provided, wherein the milk-frothing device 1 conveys milk for the coffee beverages through the fully automatic coffee machine and finally into a cup.

[0141] As can be seen in FIG. 2, the milk-frothing device 1 has a steam nozzle 2 for producing a steam flow 9, and a mixing chamber 3 which adjoins a steam outlet opening 16 of the steam nozzle 2. The delivered milk 7 is guided here as a milk flow 8 along the flow path, shown in FIG. 11 as a dashed line (and provided with reference signs 8/14) through an admixing opening 4 into the mixing chamber 3. The admixing opening 4 opens here into the mixing chamber 3 and therefore defines the entry point 38.

[0142] As can readily be seen in particular in FIGS. 2 and 11, the entry point 38 is mounted upstream of the steam outlet opening 16, specifically with respect to the direction of the steam flow 9 that is illustrated in the Figures with the aid of a straight arrow running through the steam outlet opening 16. The upstream mounting is dimensioned here in such a manner that the distance (vertical in the Figures) that can be measured in FIG. 2 and even better in FIG. 11 between the entry point 38 and the steam outlet opening 16 is greater than the clear diameter 47 of the steam outlet opening 16, is greater than a clear width 43 of the admixing opening 4 and even is greater than an outer diameter 48 of the steam nozzle 2 at the location of the steam outlet opening 16.

[0143] This ample upstream mounting of the entry point or extension of the steam nozzle 2 (in each case in comparison to previously known devices) achieves the flow guide that is illustrated in FIG. 11 with the aid of the dashed line and in which the milk 7 is fed as a milk flow 8 in the direction of the steam flow 9 (compare the arrow in FIG. 11) to the steam flow 9. As can be seen in FIG. 11, the milk flow 8 already flows here in a region 42 of the mixing chamber 3 that is mounted upstream of the steam outlet opening 16, in the direction of the steam flow 9. This is seen in particular by way of the dashed line in the region 42 where the milk flow 8 flows along an outer surface 39 of the steam nozzle 2.

[0144] It can be seen even more precisely in FIG. 11, but even better in FIG. 2, that the steam nozzle 2 at the same time delimits the admixing opening 4 and thus at the same time defines the entry point 38. This is because said admixing opening 4 is configured annularly and is arranged concentrically with respect to the steam nozzle 2, as is readily seen in the perspective view of FIG. 2 or, for example, in FIGS. 6 and 8.

[0145] The entry point 38 is formed here by a constriction 40 (cf. FIG. 3) which separates an intake chamber 17, which is mounted upstream of the mixing chamber 3 in the flow direction of the milk flow 8, from the mixing chamber 3. The milk flow 8 flows as a milk and air flow 14 into the intake chamber 17. In other words, the milk flow 8 thus contains an air portion, the purpose of which will be explained more precisely further below.

[0146] The intake chamber 17 annularly surrounds the steam nozzle 2 (compare FIGS. 2 and 6) and forms a deflecting surface 46 that is likewise formed annularly. By means of said deflecting surface 46, the milk flow 8 flowing into the intake chamber 17 initially transversely with respect to the steam flow 9 is deflected in such a manner that the milk flow 8 already passes through the admixing opening 4 in the direction of the steam flow 9, which can be readily seen with reference to the dashed line in FIG. 11.

[0147] More precisely, the milk flow 8 already flows in the intake chamber 17 around the steam nozzle 2 and then enters as a casing flow through the annular admixing opening 4 into the mixing chamber 3. Subsequently, the milk flow 8 as a casing flow converges continuously with the steam flow 9 and encases the latter in the form of a casing until it is combined therewith to form a steam and milk flow 49 (cf. FIG. 11).

[0148] More precisely, this combining takes place with the aid of a collecting funnel 44 (cf. FIGS. 6 and 11) which is formed in the mixing chamber 3 and which collects and combines the milk 7 and the steam 5. The collecting funnel 44 is constricted here in the direction of the steam flow 9, with said collecting funnel being oriented precisely centrally with respect to the steam outlet opening 16 (cf. FIG. 11).

[0149] By means of this further constriction 40, the mixing chamber 3 is separated from a downstream atomization chamber 41, wherein at the same time an acceleration portion 45 for accelerating the steam and milk flow 49 is formed by the constriction 40 (cf. FIG. 11). The steam and milk flow 49 thereby flows at high speed into the downstream atomization chamber 41 and impacts there against a centrally arranged impact body 31, as a result of which the steam and milk flow 49 is turbulently swirled and therefore heat is transmitted from the hot steam 5 to the milk 7 to be heated.

[0150] As a result, the previously described device 1 can deliver milk at temperatures of up to 80° C. from the milk outlet opening 28 (cf. FIG. 3) without—despite a very low delivery rate—the milk flow 8 breaking off.

[0151] If milk froth is intended to be produced with the milk-frothing device 1, the milk-frothing device 1 delivers a milk flow 8 containing an air portion into the mixing chamber 3. If said milk and air flow 14 is swirled with the steam 5 in the atomization chamber 41, milk froth is produced.

[0152] In such a case, it is very particularly advantageous if the milk-frothing device 1 has a variable opening cross section 10 which has already been explained previously and through which an air flow 14 can be conducted, preferably simultaneously with the milk flow 8. This is because, as will be explained in more detail, it can thereby be ensured, even at low delivery rates, that the milk flow 8 does not break off because the air flow 14 gains the upper hand.

[0153] In summary, the invention according to a first aspect for a milk-frothing device 1, which delivers milk 7 on the basis of the Venturi effect with the aid of a steam flow 9 output by a steam nozzle 2, proposes coupling an adjustment of a milk supply to an adjustment of an air supply by milk and air being conducted via a common, variable, in particular adjustable, opening cross section 10.

[0154] The invention therefore aims to improve the quality of a milk froth 13 which is produced by means of a milk-frothing device 1 which has a mixing chamber 3 in which air 6 and milk 7 can be frothed by means of a steam flow 9 to form the milk froth 13. For this purpose, it is proposed that a respective flow rate of an air flow 15 and also of a milk flow 8, which each flow into the mixing chamber 3, is adjusted by the fact that the air 6 and the milk 7 always flow together into the mixing chamber 3 through an adjustable, variable opening cross section 10 which acts as a flow rate reducer for the air flow 15 and the milk flow 8.

[0155] According to a second aspect, it is proposed, by means of corresponding orientation of an admixing opening 4 and optionally with the aid of deflecting surfaces 46, to allow a milk flow 8, which is sucked up by a steam flow 9, to flow tangentially onto the steam flow 9 in order thereby to still be able to ensure delivery of the milk flow 8 as far as possible without disturbance, even at very low flow rates of the milk flow 8. For this purpose, before the milk flow 8 enters into contact with the steam flow 9, the milk flow 8 is oriented in the direction of the steam flow 9.

LIST OF REFERENCE SIGNS

[0156] 1 Milk-frothing device [0157] 2 Steam nozzle [0158] 3 Mixing chamber [0159] 4 Admixing opening [0160] 5 Steam [0161] 6 Air [0162] 7 Milk [0163] 8 Milk flow [0164] 9 Steam flow [0165] 10 Variable opening cross section [0166] 11 Air supply [0167] 12 Milk supply [0168] 13 Milk froth [0169] 14 Milk and air flow [0170] 15 Air flow [0171] 16 Steam outlet opening [0172] 17 Intake chamber [0173] 18 Throughflow reducer (for 15) [0174] 19 Pinhole aperture [0175] 20 Lip seal [0176] 21 Milk and air feed line [0177] 22 Regulating body [0178] 23 Regulating axis [0179] 24 Surface channel (for 7/8) [0180] 25 Air surface channel (for 6/15) [0181] 26 Milk supply connection [0182] 27 Milk and air feed line [0183] 28 Milk froth outlet opening [0184] 29 Discharge module [0185] 30 Chamber [0186] 31 Impact body [0187] 32 Steam supply connection [0188] 33 Inflow opening [0189] 34 Regulating body receptacle [0190] 35 Through opening [0191] 36 Outer contour (of 22) [0192] 37 Opening point [0193] 38 Entry point (for 7 into 3) [0194] 39 Outer surface (of 2) [0195] 40 Constriction [0196] 41 Atomization chamber [0197] 42 Region (of 3) [0198] 43 Clear width (of 4) [0199] 44 Collecting funnel [0200] 45 Acceleration portion [0201] 46 Deflecting surface [0202] 47 Clear diameter (of 16) [0203] 48 Outer diameter (of 2) [0204] 49 Steam and milk flow [0205] 50 Milk-frothing device [0206] 51 Direction of the steam flow [0207] 52 Closure surface [0208] 53 Flushing water flow