Apparatus for producing a milk drink or a milk foam drink and a method for heating milk or milk foam

Abstract

The invention relates to a device for producing a milk drink or a foamed milk drink, comprising a pump 1, a milk intake line 2 connected to the pump 1 and connectable to a milk storage tank M, an outlet line 3 connected to the pump 1 and a heating element 4. In order to be able to use the device for simple and rapid heating of both milk and foamed milk without unacceptable load fluctuations of the heating element used for heating the milk or foamed milk occurring and in order to avoid deposits or fouling of milk in the heating element, the heating element 4 comprises at least two series-connected flow heaters 4a, 4b. The invention further relates to a method for heating milk or foamed milk, in which cold milk or cold foamed milk is sucked by the pump 1 from the milk intake line 2 connected to the milk storage tank M, conveyed to the outlet line 3 connected to the pump 1 and heated by the heating element 4, the milk or foamed milk passing successively through the at least two series-connected flow heaters 4a, 4b of the heating element 4.

Description

[Technical field]

[0001] The invention relates to an apparatus for producing milk or a milk foam drink according to the preamble of claim 1 as well as to a method for heating milk or milk foam according to the preamble of claim 24. [Background technology]

[0002] From DE 10 200 03 13 A method for producing milk foam or a hot milk drink and an apparatus for carrying out said method are known, in which milk is sucked from a container by means of a pump and conveyed to an outlet, in which in the case of the production of milk foam, air or another gas can be mixed into the milk in a controllable amount. The milk or the produced milk foam passes through a continuous flow heater during suction in order to heat the milk or the milk foam, and then the heated milk or the heated milk foam is conveyed to the outlet via a throttle point. In this connection, by using a continuous flow heater for heating the milk or the milk foam, cold milk can be taken directly from any container without having to be transferred to a special container for heating. Furthermore, by using a continuous flow heater as a heating element for heating the milk or the milk foam, the heated milk or the heated milk foam can be conveyed directly to the outlet via a throttle point, eliminating the need for expensive and high-maintenance resistance passage elements. Furthermore, the use of a continuous flow heater allows for rapid heating of the milk or milk foam, and a continuous flow heater used as a heating element allows for quick and easy cleaning of the device containing the heating element. The use of a flow heater, which can heat cold milk foam to the desired set temperature, eliminates the need for complex mixing devices that produce hot milk foam by sprinkling hot steam through the milk.

[0003] However, the use of flow heaters in the device as heating elements for heating milk or milk foam also brings about disadvantages. For example, locally very high surface temperatures in the flow heater can lead to local scorching of the milk passing through the flow heater and to deposits of fouling or milk in the instantaneous conduits of the flow heater. Since such deposits or milk deposits can only be removed by using aggressive, especially acidic, cleaning with cleaning solutions prepared from expensive cleaning agents is required periodically to remove the deposits or milk deposits from the flow heater. This aggravates and increases the cleaning costs of the device.

[0004] Furthermore, when using flow heaters in devices in which both cold milk and milk foam are to be heated, problems can arise with fluctuating current levels in the power supply network that supplies the flow heaters, due to the different heating powers required to heat milk or milk foam and the associated load fluctuations of the flow heaters. In order to prevent fluctuations in the operating voltage in the power supply network, the larger demands must meet specific requirements for avoiding flicker (voltage fluctuations in the power supply network) as stipulated in DIN EN 61000-3-3. In particular, the larger loads should not exceed a short-term flicker intensity of 1.0 determined over a 10-minute interval. This cannot be easily guaranteed due to the heating load fluctuations when using a flow heater to heat milk or milk foam. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 1593330 Summary of the Invention [Problem to be solved by the invention]

[0006] Against this background, the invention is based on the problem of providing an apparatus and a method by which both milk and milk foam can be heated simply and quickly without causing unacceptable load fluctuations of the heating elements used for heating the milk or milk foam, as well as the problem of allowing simple cleaning of the heating elements by avoiding deposits and fouling of milk in the heating elements. [Means for solving the problem]

[0007] These problems are solved by a device having the features of claim 1 and by a method having the features of claim 24. Preferred embodiments of the device and the method are to be chosen from the dependent claims, and features defined in the device claims can also be assigned to the method and vice versa.

[0008] According to the invention the problem is solved by an apparatus for producing milk or a foamed milk drink, comprising a pump, a milk suction line connected to the pump, in particular at a pump inlet, which is connectable to a milk storage tank, an outlet line connected to the pump, in particular at a pump outlet, and a heating element, wherein the heating element comprises at least two flow heaters connected in series.

[0009] In the method for heating milk or milk foam according to the present invention, cold milk or cold milk foam is sucked by a pump from a milk suction line connected to a milk storage tank, conveyed to an outlet line connected to the pump and heated by a heating element, and the milk or milk foam passes successively through at least two flow heaters connected in series with the heating element for heating.

[0010] By using (at least) two flow heaters connected in series, the (maximum) temperature in the flow heater generated during the heating cycle can be kept lower compared to the use of a heating element that only includes a single flow heater, for heating milk or milk foam in the flow heater, so that fouling and milk deposits in the heating element can be avoided. When using a single flow heater to heat milk, for example to temperatures of 70°C or more, temperatures of more than 100°C are generated locally during the heating cycle, especially in the center of the flow heater. At these high temperatures, which occur especially on the walls of the flow conduits of the flow heater, local scorching of the passing milk can occur, resulting in milk deposits and fouling. This milk deposits and fouling can accumulate on the walls of the flow conduits of the flow heater, thereby reducing the cross-sectional area of ​​the conduits. Alternatively, this milk deposits and fouling can be discharged as particles together with the heated milk from the flow conduits of the flow heater, which can have a negative effect on the product quality of the heated milk drink, in particular leading to undesirable changes in taste.

[0011] By using a heating element with at least two consecutive flow heaters connected in series, the maximum temperature generated in the flow heater can be reduced, in particular to temperatures below 100°C, which reliably prevents the passing milk from scorching. The device and method according to the invention therefore facilitates the cleaning of the heating element used to heat the milk, since the use of two or more flow heaters connected in series prevents the formation of deposits in the flow conduits of the individual flow heaters. Furthermore, the use of at least two flow heaters connected in series improves the product quality of the milk drink produced from the heated milk or foamed milk, since granular milk particles are not produced when the milk or foamed milk is heated, which may have a negative effect on the taste and consistency of the milk drink.

[0012] Furthermore, by using at least two series-connected flow heaters, the heating power of the individual flow heaters can be kept lower compared to the use of a single flow heater, so that specifications regarding voltage fluctuations in the power system can be met compared to the use of a single flow heater. In particular, the short-term flicker intensity of the heating element of the device according to the invention comprising at least two series-connected flow heaters is kept below 1.0.

[0013] In order to achieve the above-mentioned advantages resulting from the use of at least two flow heaters connected in series, it is preferred that the flow heaters of a heating element are controlled or regulated such that the heating output of each flow heater can be set independently from the heating output of one or more of the other flow heaters of the heating element.

[0014] In a preferred embodiment of the device according to the invention, the heating element is arranged in the outlet line, which ensures low heat losses, since the heated milk or heated milk foam only has to be conveyed a short distance in the outlet line to the outlet in order to distribute the heated milk or heated milk foam after heating into a vessel, such as a cup, placed under the outlet of the device connected to the outlet line. Furthermore, this arrangement makes it possible to heat both the milk and the milk foam produced upstream of the outlet line or in the upstream region of the outlet line by mixing the milk with a gas, in particular compressed air, and / or introduced into the outlet line.

[0015] In a preferred embodiment, the heating element comprises (at least) a first and a second flow heater, each having a housing separate from the other flow heater, an inlet and an outlet. Two flow heaters arranged one after the other in the flow direction in the outlet or milk suction line are connected in fluid communication with each other in a series circuit by a connecting line which is part of the outlet or milk suction line, i.e. for example the outlet of the upstream first flow heater is connected to the inlet of the second flow heater arranged downstream in the flow direction. Correspondingly, further flow heaters can be arranged in a series circuit.

[0016] For the production of milk foam, a gas supply line is preferably provided. This gas supply line is connected to the milk suction line and / or to the outlet line and can be connected to a gas source, in particular a compressed gas source, in order to convey compressed gas (hereinafter also called pressurized gas), in particular compressed air, to the milk suction line and / or to the outlet line. As a result, milk foam can be generated either already in the milk suction line or in the upstream area of ​​the outlet line (upstream of the heating element) and can be fed via the outlet line up to a heating element with at least two flow heaters for heating, which is connected to the outlet line. If the pressurized gas is introduced to the milk in the form of pressure pulses, there is in this case a high variability in terms of the properties of the produced milk foam, since the amplitude, frequency, pulse duration and / or duty cycle of the pressure pulses can be varied, thereby producing milk foams of different properties. The properties of the milk foam can furthermore be influenced by the volumetric flow rates of the pressurized gas and / or of the milk.

[0017] The gas supply line is advantageously connected to the outlet line, so that by supplying compressed gas (pressurized gas) a homogeneous milk foam can be produced in the outlet line, in particular in the upstream region of the outlet line before the heating element, in that the compressed gas supplied to the outlet line via the gas supply line can mix with the milk. The mixing of the milk with the compressed gas takes place downstream of the pumping device. Feeding compressed gas to the outlet line has the advantage that the functioning of the pump, which is arranged upstream of the point of introduction, is not adversely affected by the introduced compressed gas. By introducing compressed gas into the milk at an introduction point located downstream of the pump, in particular slippage or loosening of the pump can be prevented, so that the milk foam can be distributed through the outlet line with a uniform volumetric flow rate. Furthermore, the delivery flow rate of the pump and therefore the delivery speed of the milk can be adjusted independently from the volumetric flow rate or the amount of pressurized gas introduced. As a result, pressurized gas can be supplied with different delivery pressures and therefore different portions, even with different pump delivery flow rates. For this reason different foam properties of the produced milk foam, such as fine-pore or coarse-pore milk foam, can be set with adjustable delivery volumes.

[0018] In order to facilitate cleaning of the device, a cleaning line connected to the milk intake line is preferably provided. This cleaning line can be connected to a cleaning agent reservoir (R), in particular to a water connection, in order to supply the milk intake line with rinsing liquid and / or cleaning agent, in particular water and / or an aqueous cleaning solution. In the device according to the invention, it is usually sufficient to rinse the device, in particular the milk intake line, the pump, the outlet line and the heating element, with water only, since the formation of deposits and milk deposits in the heating element can be avoided. This makes the use of expensive cleaning agents, such as cleaning tablets or cleaning solutions, unnecessary.

[0019] The outlet line is preferably provided with at least one throttle point. This can be formed, for example, by a throttle valve. This ensures a homogeneous mixture of milk with the compressed gas supplied through the gas supply line. An adjustable throttle valve is advantageously arranged in the outlet line. This makes it possible to set a suitable cross-sectional area of ​​the throttle point and thus a specific throttle resistance, whereby a desired flow rate of milk or milk foam output from the outlet line to the outlet of the device connected to the outlet line can be set. The throttle point, for example a throttle valve, is advantageously arranged upstream of the heating element, in particular between the inlet point of the gas supply line and the heating element.

[0020] In order to control the heating power of the heating element and to maintain a predetermined target temperature of the milk to be heated or the milk foam, at least one temperature sensor is advantageously arranged downstream of the heating element in the outlet line for detecting the temperature of the milk to be heated or the milk foam.

[0021] A temperature sensor is preferably arranged downstream of each flow heater of the heating element and assigned to the flow heater preceding it in the direction of flow, the heating output of each flow heater being controlled as a function of the temperature of the milk or milk foam detected by its temperature sensor. In this way, the heating outputs of the individual flow heaters can be controlled independently of one another as a function of the measured values ​​of the temperature sensor assigned to the respective flow heater in order to achieve the set temperature of the milk or milk foam as accurately as possible.

[0022] In order to ensure that the milk does not burn during heating in the flow heaters, a maximum heating power is not exceeded in each flow heater, which is preferably less than 1800 W, in particular between 450 W and 1400 W. The exact flow heater heating power can be adapted to the requirements of the beverage to be produced, in particular the quantity of milk or milk foam. The exact flow heater heating power can be adapted to the requirements of the beverage to be produced, in particular the quantity of milk or milk foam.

[0023] A control device is advantageously provided for controlling the heating power generated by each flow heater, which control device is preferably configured such that the heating powers of the flow heaters can be controlled or adjusted independently of each other.

[0024] The control device is preferably set in such a way that during a heating cycle at least one first flow heater of the heating elements operates with a constant heating power p0, in particular a maximum heating power p1, and at least one second flow heater operates with a time-variable heating power distribution p2(t). In order to prevent scorching of the milk, it is preferred that the maximum heating power p1 at which the first flow heater operates and the maximum amplitude p2 of the time-variable heating power distribution p2(t) at which the second flow heater operates are each smaller than 1400 W, the (maximum) heating power being adaptable to the quantity of milk flowing through.

[0025] The control device is preferably arranged such that the constant heating power p0, p1 of the first flow heater and the time-variable heating power distribution p2(t) of the second flow heater are adjusted during the heating cycle so that the milk or milk foam heated in the heating element is heated in stages to a predefined set temperature. In this way, the predefined set temperature can be reached in a targeted and precise manner, regardless of the composition and thermal properties of the milk or milk foam. This can be further improved if a third flow heater and, if necessary, further flow heaters are connected in series with the first and second flow heaters and controlled accordingly, whereby the flow heater, preferably the front one in the flow direction, operates with a constant heating power and at least one of the following flow heaters operates with a heating power that is variable over time.

[0026] The maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater (or further flow heater) is preferably at most as large as the constant heating power p0, p1 of the first flow heater, so that the milk or milk foam can be heated in stages and the temperature can approach the specified set temperature in a targeted manner.

[0027] When heating milk, it is advantageous to set the constant heating power p1 of the first flow heater preferably more than twice, preferably between 1 and 4 times, in particular 3 times, higher than the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater. Due to the higher heat capacity of milk compared to milk foam, a higher heating power is required when heating cold milk compared to heating cold milk foam (in each case at the same initial temperature and the same set temperature). For this reason, when heating milk, the constant heating power p1 of the first flow heater is selected to be higher than the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater.

[0028] On the other hand, when heating milk foam, the maximum amplitude (p2) of the time-variable heating power distribution p2(t) of the second flow heater is advantageously set to at least approximately correspond to the constant heating power p0 of the first flow heater. The maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater is preferably in the range of ±20% of the constant heating power of the first flow heater. This makes it possible to adapt the energy efficiency of the heating power of the individual flow heaters to the properties of the product to be heated (milk or milk foam).

[0029] When heating milk or milk foam to a low temperature, for example in the range from 20°C to 40°C, the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second continuous flow heater may be smaller than the constant heating power p0 of the first flow heater, in which case it is set to a lower level of heating power p0 which is smaller than the maximum heating power p1.

[0030] The time-variable heating power distribution p2(t) of the second flow heater is preferably pulsed, so that during a heating cycle a time course of the variable heating power distribution p2(t) is obtained which comprises at least one or several successive pulses. For example, pulses comprising square or triangular pulses or sawtooth pulses can be generated by pulsed control of the second flow heater with voltage pulses. The resulting time-variable heating power distribution p2(t) of the second flow heater can then correspond for example to a square wave signal, a triangular signal or a sawtooth signal. The time-variable heating power distribution p2(t) of the second flow heater may also have a periodic time characteristic, in particular a sinusoidal shape.

[0031] It is advantageous to be able to vary the amplitude, the pulse duration and / or the pulse frequency, in particular the product of the pulse frequency and the pulse duration (duty cycle) of the pulses, or the periodic time course during the heating cycle. This represents an increased flexibility and makes it possible to make adjustments, for example to the heating power of one or more flow heaters of the heating element, during the heating cycle in order to maintain the final temperature of the heated milk or milk foam as accurately as possible and to adapt it to a specified set temperature.

[0032] The flow heaters of the heating element are preferably designed as thick-film heaters. This allows a fast reaction time and therefore allows the rapid heating of the quantity of milk or milk foam required for the production of a beverage containing milk or milk foam, which quantity is heated in one heating cycle. In this respect, each flow heater configured as a thick-film heater comprises a housing which is at least thermally decoupled or thermally and locally decoupled from the other or other flow heaters. The flow heaters may be arranged on a common plate or in a common framework, but are preferably thermally decoupled from one another and can be controlled separately, so that each flow heater can be operated with a different heating capacity independently of the other flow heaters. By preferably (thermally) decoupling the housings of the individual flow heaters of the heating element, the heating power of each flow heater can be controlled or regulated independently from the heating power of the other or other flow heaters by the current supplied in each case. This ensures selective and independent control of the individual flow heaters of the heating element as a whole, as well as rapid control and adjustment of the heating output of the individual flow heaters during a heating cycle.

[0033] In a preferred embodiment, each flow heater, which is designed as a thick-film heater, comprises a metallic substrate and a cover plate connected to the substrate. A conduit is formed between the substrate and the cover plate for the passage of milk or milk foam, the substrate and / or the cover plate containing a resistive heater to which an electric current can be applied for conductive heating of the milk or milk foam flowing through the conduit. This allows a compact design of the flow heater with low thermal mass and fast reaction times. A particularly compact and space-saving design is achieved if the conduit of each flow heater has a serpentine or helical shape.

[0034] The invention further comprises a method for heating milk or milk foam, in which cold milk or cold milk foam is sucked by a pump from a milk suction line connected to a milk storage tank, conveyed to an outlet line connected to the pump and heated by a heating element, in which the milk or milk foam passes successively through at least two flow heaters of the heating element connected in series.

[0035] In the process, the heating power of each flow heater is preferably controlled or regulated independently from the heating power of the other or other flow heaters, e.g. by the current supplied to the respective flow heater, in order to obtain a predetermined set temperature of the milk or milk foam.

[0036] In order to control the heating power of the individual flow heaters, it is expedient in the process to assign a temperature sensor to each flow heater, whereby the control of the heating power of each flow heater is carried out as a function of the temperature of the milk or milk foam detected by the temperature sensor.

[0037] In the process, it is preferred that during a heating cycle at least one first flow heater operates with a constant heating power p0, p1 and at least one second flow heater operates with a time-variable heating power distribution p2(t), and it is particularly preferred that the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater is at most as large as the constant heating power p0, p1 of the first flow heater.

[0038] In the case of heating milk, the constant heating power p1 of the first flow heater is preferably selected to be more than twice, preferably between 1 and 4 times, in particular 3 times, greater than the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater. A factor greater than 2 has the advantage of meeting the specifications for avoiding flicker. However, a factor greater than 4 would reduce the degree of adjustment freedom, so that the factor is preferably chosen to be smaller than 4.

[0039] In the case of heating milk foam, the maximum amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater in the process is preferably set so that it corresponds at least approximately to the constant heating power of the first continuous flow heater. In this way, jumps in the power of the second flow heater compared to the first flow heater and therefore flickers can be avoided.

[0040] Thereby, it is particularly preferred that the time-variable heating power distribution p2(t) of the second flow heater is pulsed. The time characteristic of the heating power distribution p2(t) of the second continuous flow heater comprises at least one pulse, preferably several pulses following one another, which pulses may have different shapes, such as a square-wave signal, a triangular signal or a sawtooth signal. The time course of the heating power distribution p2(t) of the second flow heater may also be periodic, for example as a sinusoidal signal. In order to achieve a gradual and targeted approach of the temperature of the milk or milk foam to the predefined set temperature as accurately as possible, it is preferred that during the heating cycle the amplitude of the pulses, the pulse duration and / or the pulse frequency or the duty cycle are varied.

[0041] These and other advantages, as well as preferred features and characteristics of the apparatus and method according to the present invention, will be apparent from the illustrative embodiments which are described in more detail below and which are to be considered in conjunction with the accompanying drawings. [Brief description of the drawings]

[0042] [Figure 1] FIG. 1 is a schematic circuit diagram of an apparatus or process for heating milk or milk foam according to the present invention. [Figure 2A] This is a flow chart for heating milk. [Figure 2B] 1 is a flow chart for heating milk foam. [Figure 3A] FIG. 2 shows the time-dependent heating output of a first flow heater according to the invention during a heating cycle. [Figure 3B] FIG. 13 shows the time-dependent heating output of a second flow heater according to the invention during a heating cycle. [Figure 3C] FIG. 13 illustrates the total heating output of a first flow heater and a second flow heater according to the present invention as a function of time during a heating cycle. [Figure 4] FIG. 1 shows a preferred embodiment of a flow heater for use in an apparatus according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] 1 shows a preferred embodiment of the device according to the invention for heating milk or milk foam. The device comprises a pump 1 with a pump inlet 1a and a pump outlet 1b, a milk suction line 2 connected to the pump at the pump inlet 1a, an outlet line 3 connected to the pump at the pump outlet 1b and a heating element 4 arranged in the outlet line. The milk suction line 2 is connected to a milk storage tank M, which may for example be a container of milk placed in a refrigerator. The outlet line 3 is connected at its downstream end to an outlet, which is not shown here.

[0044] Furthermore, the device comprises a gas supply line 5 opening into the outlet line 3 at an entry point E. The gas supply line 5 is connected to a gas source Q providing compressed gas (pressurized gas). In the illustrated embodiment example, the gas source Q comprises a compressor 21 having an air supply 20 which supplies air, for example by drawing in ambient air. The supplied air is thereby compressed by the compressor 21 to a given pressure. To control the amount of compressed gas introduced per unit time from the gas source Q to the gas supply line 5 (volumetric flow rate of compressed gas), a control valve V3 connected to the environment is connected to the gas supply line 5 via a control line 5'. The amount of compressed gas introduced per unit time from the gas source Q to the gas supply line 5 is thus controlled on the one hand by the given pressure of the compressed gas and on the other hand by the position of the control valve V3. The control of the control valve V3 is preferably performed electrically by pulse width modulation, so that a fine adjustment of the valve position can be controlled and thus the volumetric flow rate of compressed gas conveyed to the gas supply line 5 can be controlled. A check valve 9 is arranged in the gas supply line 5 at its downstream end, in particular just before the entry point E, to prevent liquid from entering the gas supply line 5 .

[0045] For cleaning the device, a cleaning line 6, which is connected to a cleaning agent reservoir R, is connected to the milk suction line 2. The cleaning line 6 comprises a first branch 6' and a second branch 6'', in each of which a shut-off valve V1, V2 is arranged. The two branches 6', 6'' of the cleaning line 6 each open into the milk suction line 2 at mutually distant inlet points E', E'', respectively, and a non-return valve 9 is arranged between the two inlet points E', E''.

[0046] The pump 1 is preferably designed as a gear pump, as shown diagrammatically in Figure 1, and comprises two counter-rotating and meshing gears. The pump 1 draws milk M from a milk storage tank into a pump inlet 1a and conveys the drawn milk to a pump outlet 1b which is connected to an outlet line 3.

[0047] In the outlet line 3, between the inlet point of the gas supply line 5 and the heating element 4, a throttle point formed by a throttle valve 7 is arranged. The throttle valve 7 is preferably adjustable so that a suitable flow cross-sectional area can be set in the outlet line 3.

[0048] In the embodiment shown in Fig. 1, the heating element 4 arranged in the outlet line 3 downstream of the throttle valve 7 comprises two flow heaters 4a, 4b connected in series. Downstream of the first flow heater 4a a first temperature sensor 8a is arranged which is assigned to the first flow heater 4a and downstream of the second flow heater 4b a second temperature sensor 8b is arranged which is assigned to the second flow heater 4b.

[0049] The two flow heaters 4a, 4b are each designed as a thick-film heater. A preferred embodiment of such a thick-film heater is shown in FIG. 4. Each flow heater 4a, 4b designed as a thick-film heater comprises a flat metal substrate 11 and a cover plate 12 connected to the substrate 11 and having an undulating structure on the side facing the substrate 11. The substrate 11 and the cover plate 12 are connected to each other liquid-tight and form a housing 10. Due to the undulating structure of the cover plate 12, a continuous conduit 13 for the passage of a fluid is formed between the substrate 11 and the cover plate 12. In the example shown in FIG. 4, the conduit 13 is formed in a helical shape. On the outside of the flat substrate 11, a thermal insulation layer is arranged in which an electric resistance heater in the form of a heating wire with an electrical connection 17 is arranged. In this case, the heating wire forming the electric resistance heater follows the helical shape of the conduit 13 between the substrate 11 and the cover plate 12. When an electric current is applied to the electrical connection 17, the flow heater and the fluid flowing through the conduit 13 are heated. The conduit 13 has an inlet 15 and an outlet 16 for introducing and discharging the fluid to be heated. The inlet 15 and the outlet 16 are connected to connecting parts, not shown here, to each of which a line for the supply and discharge of the fluid can be connected.

[0050] The two flow heaters 4a, 4b of the heating element 4 are arranged in series connection in the outlet line 3. In this case, the housings 10 of the two flow heaters 4a, 4b are preferably thermally separated from each other by maintaining an insulating distance between the housings 10 of the two flow heaters 4a, 4b. The insulation of the housings 10 of the two flow heaters 4a, 4b can also be realized by means of an insulating layer between the two housings 10, so that the two flow heaters 4a, 4b can also be arranged close to each other in the surrounding housing of the heating element 4 or on a common plate to achieve a compact construction. For the passage of milk or milk foam, the inlet 15 of the first flow heater 4a (as shown in FIG. 1) is connected to the outlet line 3 and the outlet 16 of the first flow heater 4a is connected to the inlet 15 of the second flow heater 4b via the connecting line 3'. The outlet 16 of the second flow heater 4b is connected to the outlet line 3.

[0051] For the production of milk foam in the device of Fig. 1, milk is sucked by pump 1 from a milk storage tank M through milk suction line 2 and conveyed to outlet line 3. At the same time, compressed gas, in particular compressed air, is conveyed at a defined pressure via gas supply line 5 to outlet line 3. Milk and compressed gas mix in outlet line 3 to form a milk-gas mixture, in particular a milk-air mixture. A homogeneous mixture of milk and compressed gas can be achieved by suitable adjustment of the pressure of the compressed gas and of the throttle valve 7.

[0052] With the apparatus of FIG. 1, either milk or foam milk can be heated and can be dispensed, via an outlet of the apparatus (not shown here), into a vessel G such as a cup placed below the outlet. If cold milk from the milk storage tank M is to be heated by the apparatus without being foamed, the gas supply line 5 is closed or the gas source Q is shut off. The cold milk drawn from the milk storage tank M by the pump 1 is conveyed to the outlet line 3 and successively passes through the two flow heaters 4a, 4b of the heating element 4. The two flow heaters 4a, 4b of the heating element 4 can be supplied with current independently of each other to heat the passing milk. By doing so, different heating powers are set for the two flow heaters 4a, 4b.

[0053] FIG. 2A shows an example of a preferred flow diagram when heating cold milk in the apparatus of FIG. 1. The first flow heater 4a can be controlled in two different operating stages. In the first operating stage, the first flow heater 4a can operate at a maximum heating power p1. The maximum heating power is selected to prevent the milk from burning and is, for example, 1400 watts. In the second operating stage, the first flow heater 4a may operate at a lower heating power p0 < p1. The second flow heater 4b following in the direction of the flow through which the milk passes can also be controlled in two operating stages. In the first operating stage, the second flow heater 4b can operate at the same maximum heating power p1 as the first flow heater 4a or at a constant heating power p0 lower than the maximum heating power p1. In the second operating stage, the second flow heater 4b can operate with a time-variable heating power distribution p2(t), and the (maximum) amplitude p2 of the time-variable heating power distribution p2(t) is smaller than the maximum heating power and thus smaller than the heating power p1 in the first operating stage of the first flow heater 4a. When heating the milk, the (maximum) amplitude p2 of the time-variable heating power distribution p2(t) is preferably in the range from 0.1·p1 to 0.5·p1. To avoid flicker, the constant heating power p0 or the maximum amplitude p2 of the second flow heater 4b is preferably less than 600 W, particularly less than 450 W.

[0054] In Fig. 3 the course of the heating power over time in the operating phases of the first flow heater 4a and the second flow heater 4b from the exemplary flow chart of Fig. 2A is shown diagrammatically. Fig. 3A shows the course of the heating power over time of the first flow heater 4a, and Fig. 3B shows the course of the heating power over time of the second flow heater 4b. As can be seen from Fig. 3A, the first flow heater 4a has a heating power p1 or p0 that is constant over time both in the first and in the second operating phase. The heating power p1 in the first operating phase corresponds to a maximum heating power of, for example, 1400 watts, while the second operating phase has a lower but equally constant over time heating power p0 during the heating cycle. A heating cycle, in which a quantity of milk, for example 40 ml, is passed through two flow heaters 4a, 4b and heated to a given set temperature, is defined by a start t1 and an end t2, and the total heating time Δt of the heating cycle is obtained from the difference between times t2 and t1: Δt=t2-t1.

[0055] As can be seen from figure 3B, the second operating phase of the second flow heater 4b has several pulses with different pulse durations and pulse frequencies, which follow each other within a heating cycle. During the heating cycle, it is preferable to vary both the amplitude p2 of the pulses and the pulse duration, and / or the pulse frequency, and in particular the duty cycle resulting from the product of the pulse frequency and the pulse duration.

[0056] Figure 3C shows the total heating power of the heater 4 as a function of time during a heating cycle between start t1 and end t2. The total heating power of the heating element 4 is obtained from the sum of the time-dependent heating powers of the two flow heaters 4a, 4b connected in series as shown in Figure 3C.

[0057] In the case of heating cold milk in the device of FIG. 1, cold milk M is conveyed through the heating device 4 according to the flow diagram of FIG. 2A at an initial temperature which may be, for example, between 0° C. and 20° C., in particular between 4° C. and 10° C. The first flow heater 4a of the heating device 4 operates, for example, with a maximum heating power p1 in a first operating phase, and the second flow heater 4b operates with a heating power p2(t) which is variable over time in a second operating phase. For the corresponding control of the two flow heaters 4a, 4b a control device, not shown here, is provided. This control device is arranged in such a way that the heating powers of the two flow heaters 4a, 4b can be set independently of one another and can be controlled to heat the milk up to a set-point temperature which can be predetermined.

[0058] The flow rate of the milk to be heated can be adjusted to the desired amount of hot milk, for example between 10 and 500 ml / min. The intermediate temperature to which the milk is heated in the first flow heater 4a depends on the power level (p1, p0) at which this flow heater 4a is operated and can be higher than the initial temperature of the cold milk, in particular up to 80°C. The final temperature to which the milk is heated after passing through the second flow heater 4a corresponds to the set temperature and is in particular in the range from 20°C to 80°C.

[0059] To control the heating power of the two flow heaters 4a, 4b, the temperature of the milk passing through is detected by temperature sensors 8a, 8b associated to the two flow heaters 4a, 4b. As shown in FIG. 2A, the temperature of the milk passing through the first flow heater 4a is detected by the first temperature sensor 8a and is preferably between 45° C. and 65° C. The final temperature of the milk heated in the heating device 4 after leaving the second flow heater 4b ranges for example from 65° C. to 75° C. To set a predefined target temperature of the heated milk, for example in the range from 65° C. to 75° C., the control device controls the second flow heater 4b during the heating cycle in such a way that the predefined target temperature is reached as accurately as possible. For this purpose, the distribution of the heating power of the second continuous flow heater 4b can be adjusted during an ongoing heating cycle by varying the amplitude p2, the pulse duration and / or the pulse frequency or the duty cycle of the heating power pulses. In particular, the parameters of the time distribution p2(t) of the heating power of the second flow heater 4b can be adapted to the temperature of the milk detected by the preceding first temperature sensor 8a. Furthermore, the parameters of the time distribution p2(t) of the heating power of the second flow heater 4b can be adjusted to the previous heating cycle depending on the parameters detected in the previous heating cycle, in particular the temperature of the milk detected by the two temperature sensors 8a, 8b.

[0060] The control device can also take other parameters into account for the activation or control of the two flow heaters 4a, 4b, such as the milk inlet temperature, which can be detected if necessary by a further third temperature sensor, which is preferably arranged in the milk suction line 2. Furthermore, in the case of heating milk foam, parameters which take into account the composition of the milk foam and in particular the gas content in the milk foam can be taken into account in the control of the two flow heaters 4a, 4b. These parameters can be detected by further sensors, such as a flow meter and / or a pressure sensor in the gas supply line 5, and are fed to the control device.

[0061] FIG. 2B shows diagrammatically the procedure when heating a milk-gas mixture (milk foam M+G) in the device of FIG. 1. For this, milk foam M+G is produced by mixing cold milk (which may have an initial temperature in the range of, for example, 0° C. to 20° C., in particular 4 to 10° C.) with pressurized gas and passes successively through two flow heaters 4a, 4b of the heating element 4. In contrast to the heating of milk, the first flow heater 4a when heating milk foam operates with a lower heating power p0 in the second operating phase. Despite the lower heating power, due to the lower heat capacity of milk foam compared to liquid milk, the milk foam in the first flow heater 4a is heated at least approximately to a temperature that is in the same range as the temperature of the milk heated in the first flow heater 4a in the flow diagram according to FIG. 2A. The lower heating power p0 of the first flow heater is selected accordingly, so that the passing milk foam is heated to a temperature lying in the preferred range of 45 to 65 ° C in the flow diagram of FIG. 2B. The second flow heater 4b operates with a time-variable heating power distribution p2(t) in a second operating phase during the heating of the milk foam again in the flow diagram of FIG. 2B. Thereby, as in the case of the heating of milk according to the flow diagram of FIG. 2A, here too both the amplitude p2 and the pulse duration and / or the pulse frequency or the duty cycle of the pulses can be adapted and even varied during the ongoing heating cycle. The final temperature of the heated milk foam M+G is as close as possible to a specified set temperature, which is preferably in the range of 65 to 75 ° C. The two flow heaters 4a, 4b are therefore controlled by the control device in such a way that the final temperature of the heated milk foam M+G corresponds as close as possible to a specified set temperature. The (maximum) amplitude p2 of the time-variable heating power distribution p2(t) of the second flow heater 4b preferably corresponds at least approximately to the heating power p0 at which the first flow heater 4a operates. In the case of heating milk foam, the (maximum) amplitude p2 of the time-variable heating power distribution p2(t) preferably lies in the range from 0.8·p0 to 1.2·p0.

[0062] The milk or milk foam temperatures given in the example of FIG. 2 should be understood as merely examples and can be adapted to requirements.

[0063] To clean the device, the milk suction line 2 is disconnected from the milk storage tank M and a cleaning agent, e.g. water, is conveyed to the milk suction line 2 through the cleaning line 6. Thereby, via the two branches 6', 6'' of the cleaning line 6, the liquid cleaning agent can be passed to clean both the upstream area of ​​the milk suction line 2 and the downstream area connected to the pump inlet 1a of the pump 1. The cleaning agent can thus be sucked in by the pump 1 and conveyed to the outlet line 3, and it also flows from the inlets 15 of the two flow heaters 4a, 4b, respectively, through the conduits 13 to the outlets 16, thereby clearing the milk components from the two flow heaters.

[0064] The device and the method according to the invention are not limited to the embodiment shown here in the drawings. For example, the heating element 4 may be arranged in the milk suction line 2 instead of the outlet line 3. The gas supply line 5 may also be connected to the outlet line 3 downstream of the heating element 4. Furthermore, the gas supply line 5 may also be connected to the milk suction line 2 instead of the outlet line 3. It is also possible to introduce pressurized gas into both the outlet line 3 and the milk suction line 2. The heating element 4 may also be arranged in the milk suction line 2 instead of the outlet line 3.

[0065] Furthermore, a mixing vessel may be arranged in the cleaning line 6, in which a cleaning agent, for example in the form of a powder or tablets, is dissolved in water to produce an aqueous cleaning solution. Instead of the pump 1, which is designed as a gear pump, other pumping devices may be used in the device, such as a peristaltic pump. Instead of the gas source Q, which is shown in FIG. 1 and comprises a compressor 21, which compresses air supplied from the environment to a predetermined pressure, another gas source may be used, such as a cartridge containing a compressed gas. In addition to air, another food-grade gas, such as carbon dioxide or nitrogen, may be used as compressed gas.

[0066] Furthermore, the number of flow heaters of the heating element 4 connected in series may be increased. It is also possible that some or all of the flow heaters are each operated with a constant heating power in time during a heating cycle. However, it is also possible that one or more flow heaters of the heating element 4 are operated with a constant heating power in time and a further one or more flow heaters are operated with a variable heating power distribution in time, i.e. a controllable heating power distribution.

Claims

1. 1. An apparatus for producing milk or a foamed milk drink, comprising a pump (1), a milk suction line (2) connected to the pump (1) and connectable to a milk storage tank (M), an outlet line (3) connected to the pump (1), and a heating element (4), characterized in that the heating element (4) comprises at least two flow heaters (4a, 4b) connected in series, the heating power of each flow heater (4a, 4b) being controllable or adjustable independently of the heating power of the other flow heaters (4b, 4a).

2. 2. The device according to claim 1, characterized in that at least one throttle valve (7) is arranged in the outlet line (3) and the heating element (4) is arranged in the outlet line (3) downstream of the throttle valve (7).

3. 3. The apparatus according to claim 1, wherein the heating element (4) comprises at least a first flow heater (4a) and a second flow heater (4b), each flow heater (4a, 4b) having a housing (10) that is thermally decoupled from the other flow heater (4a, 4b), and wherein the housings (10) of the first and second flow heaters (4a, 4b) are thermally and locally decoupled from each other.

4. The device described in claim 1, characterized in that two consecutive flow heaters (4a, 4b) of the heating element (4) are fluidly connected to each other via a connecting line (3') which is part of the milk suction line (2) or the outlet line (3).

5. 5. The device according to claim 1 or 4, characterized in that each flow heater (4a, 4b) is designed as a thick-film heater and comprises a substrate (11) and a cover plate (12) connected to the substrate (11), a conduit (13) is formed between the substrate (11) and the cover plate (12) for the passage of the milk or the milk foam, and the substrate (11) and / or the cover plate (12) contain a resistance heater to which an electric current can be applied via a current connection (17) for conductive heating of the milk or the milk foam flowing through the conduit.

6. 2. The device according to claim 1, characterized in that a temperature sensor (8a, 8b) is arranged downstream of each flow heater (4a, 4b), and the heating power of each flow heater (4a, 4b) is controlled or regulated depending on the temperature of the milk or the milk foam detected by the temperature sensor (8a, 8b).

7. An apparatus as described in claim 1 or 4, characterized in that the control device is configured to control the heating power generated by each flow heater (4a, 4b), and the heating power of the flow heaters (4a, 4b) is independently controllable or adjustable by the control device via the current supplied to the flow heaters.

8. The apparatus described in claim 7, wherein the heating element (4) includes at least a first flow heater (4a) and a second flow heater (4b), and the control device is configured to operate the first flow heater (4a) with a constant heating power (p1, p0) and to operate the second flow heater (4b) with a time-variable heating power distribution (p2(t)).

9. 9. The device according to claim 8, wherein when heating milk, the constant heating power (p1, p0) of the first flow heater (4a) is greater than the maximum amplitude (p2) of the time-variable heating power distribution (p2(t)) of the second flow heater (4b).

10. 9. The device according to claim 8, wherein when heating milk foam, the maximum amplitude (p2) of the time-variable heating power distribution (p2(t)) of the continuous second flow heater (4b) essentially corresponds to the constant heating powers (p1, p0) of the first flow heater (4a).

11. 9. The apparatus of claim 8, wherein the time-variable heating power profile (p2(t)) of the second flow heater (4b) comprises a plurality of pulses.

12. The device of claim 11, wherein at least one of the pulse amplitude, pulse duration, pulse frequency, and duty cycle is variable during a heating cycle.

13. 8. The device according to claim 7, wherein the control device is configured to operate the second flow heater (4b) with a time-variable heating power profile (p2(t)) in order to heat the milk or the milk foam to a predetermined set temperature.

14. 1. A method for heating milk or milk foam, in which cold milk or cold milk foam is sucked by a pump (1) through a milk suction line (2) connected to a milk storage tank (M), conveyed to an outlet line (3) connected to said pump (1) and heated by a heating element (4), characterized in that the milk or milk foam passes successively through at least two flow heaters (4a, 4b) of said heating element (4), the heating power of each flow heater (4b, 4a) being controlled or regulated independently of the heating power of the other flow heaters (4a, 4b).

15. 15. The method according to claim 14, wherein compressed gas is conveyed to the milk suction line (2) and / or the outlet line (3) through a gas supply line (5) connected to the milk suction line (2) and / or the outlet line (3) to produce milk froth.

16. 16. A method according to claim 14 or 15, characterized in that a temperature sensor (8a, 8b) is assigned to each flow heater (4a, 4b), the control or regulation of the heating power of each flow heater (4a, 4b) is carried out as a function of the temperature of the milk or the milk foam detected by the temperature sensor (8a, 8b), and the heating power of each flow heater (4a, 4b) is controlled or regulated by a control device in order to heat the temperature of the milk or the milk foam to a predetermined set temperature.

17. A method according to claim 14 or 15, wherein the heating element (4) comprises at least a first flow heater (4a) and a second flow heater (4b), and during a heating cycle, the first flow heater (4a) operates with a constant heating power (p1, p0) and the second flow heater (4b) operates with a time-variable heating power distribution (p2(t)).

18. 18. The method of claim 17, wherein the time-variable heating power profile (p2(t)) of the second flow heater (4b) comprises a plurality of pulses.

Images