METHOD AND DEVICE FOR PRODUCEING TEMPERED MILK FOAM AND / OR MILK

Description

Technical area

[0001] The present invention relates to a method and a device for producing tempered milk foam and / or milk, in particular for producing optionally cold, warm or hot milk foam or milk. State of the art

[0002] Methods and devices for producing either cold, warm or hot milk and / or milk foam are known, particularly in combination with beverage makers, e.g. coffee machines. Depending on the selected beverage and / or coffee speciality, e.g. cappuccino, latte macchiato, café latte, chocolate or chai, the quantity and also the temperature of the milk and / or milk foam provided varies. To produce milk foam, milk is generally sucked out of a container by means of a pump and mixed with supplied air or gas as it flows to an outlet. The milk / air mixture is then heated to a definable temperature in a heating unit and processed into a foam. For reasons of shelf life and hygiene, milk is stored in a cool place, particularly at temperatures between 3°C and 7°C. The heating element in which the milk or milk foam is stored is connected to a heat exchanger.The way in which the milk foam is tempered and possibly produced can be a continuous flow heater, for which different types are suitable.

[0003] In general, there are various ways to create milk foam. For example, in a foaming unit, air, gas, or even hot steam can be mixed with the milk in such a way that the resulting turbulence causes the milk to froth and form a more or less stable foam. However, frothing can also be achieved through mechanical stirring or by means of a throttling device.

[0004] Known methods and devices often provide different flow paths, often parallel, for the milk and the milk / air mixture or milk foam, depending on the selected temperature. Cold milk is conveyed to the outlet via a first flow path, while warm milk is conveyed via a second flow path, in which, in particular, a continuous heating element is arranged. However, these parallel flow paths not only require a complex piping system and a multitude of switchable components, but also pose a problem with regard to contamination and bacterial growth, as well as cleaning.

[0005] Known systems with only a single milk line require the system to always pass through a heating element, regardless of the temperature required for the milk, milk-air mixture, or milk foam. The disadvantage of such a system is that if cold milk or cold milk foam is to be provided immediately after dispensing hot milk or hot milk foam, the cold milk or cold milk foam is heated by the residual heat of the heating element when passing through a switched-off heating element, even if the system is switched off. Accordingly, it is known to at least partially cool and possibly also clean the switched-off flow-through heating element by flowing in cold milk or rinsing liquid.

[0006] WO 2017 / 155403 discloses an arrangement for producing hot or cold milk foam, which can be provided in relatively short succession. This arrangement provides for a flow-through heating unit to be switchable into an active and an inactive state. The flow-through heating unit is designed as a thick-film heater with a small thermal mass. The thermal behavior of the thick-film heater is precisely defined in order to take into account the thermal inertia immediately after the thick-film heater is switched on or off. In particular, the thermal behavior immediately after switching off is defined, i.e., when the heating unit is switched on after producing warm or hot milk foam, and the unit is switched off immediately afterwards, in order to immediately provide cold or only slightly heated milk foam.The thick-film heating is therefore designed so that a small amount of milk of approximately 40 to 60 ml in a frothed state and at a temperature of less than approximately 7°C is heated to a temperature of below 20°C in a fluid channel of the thick-film heating at a fluid inlet of an enclosed milk line as it flows through the flow-through heating unit that has been inactive for less than 10 seconds. Accordingly, a cold drink cannot actually be provided during the first dispensing, as the temperature should be < 10°C, in particular ≤ 7°C. However, even if a larger amount of milk of 60 to 80 ml is required to produce a beverage, the first dispensing is usually too warm, and a cold drink can only be provided during the second dispensing.Accordingly, switching between a hot drink and a cold drink is often only possible with extensive rinsing with cold milk, which can make the system uneconomical and problematic with regard to the formation of a milk skin.

[0007] From EP 3 610 762 A1 a device for processing milk with an integrated rinsing system is known, comprising a pump, a line system which comprises a milk suction line, an outlet line and a rinsing line, via which the milk suction line and at least partially an air supply line can be supplied with a rinsing liquid, as well as an air flow regulator in the air supply line with a first and a second check valve in order to meter air into the milk suction line and a thick-film heater which is arranged in the outlet line.

[0008] In general, when a flow-through heating unit designed as a thick-film heater is switched on, the heating unit first heats up before, after a certain delay, the desired temperature in the enclosed fluid channel is reached. This temperature is crucial for heating the milk foam flowing in the fluid channel. Even if the thick-film heater has a small thermal mass and a steep heating profile, the milk foam is heated according to a flat heating curve, i.e. the heating and cooling phases are subject to a certain time and / or thermal delay. In the case of an overshooting heating system, local overheating can occur during the heating phase, which is detrimental in many ways to food and the deposits that form in the fluid channel as a result of overheating.

[0009] Flow-through heating units designed as thick-film heaters for producing tempered milk foam are already known. A thick-film heater is generally a layered composite comprising a carrier substrate, e.g. a metal element covered with a dielectric coating, e.g. a glass-ceramic layer, which on the one hand acts as an insulator and on the other hand carries conductor tracks made of an electrically conductive material which generate heat when activated. The heat generated can be transferred to a fluid flowing in a fluid channel formed on the thick-film heater, for example a meandering or spiral-shaped one. In particular, the size, shape and / or electrical properties of the thick-film heater can be adapted to the respective task or location. In addition, temperature sensors and other devices can be integrated. Thick-film heaters are characterized by a steep temperature profile orHeating profile and thus by a very fast and short response behavior, so that a thick-film heater is especially not used in a stand-by mode. Summary of the invention

[0010] In contrast to the known methods and devices, according to the invention the production of cold, warm or hot milk or milk foam is achieved with a simple process sequence and a simple structure of the device, ie without parallel flow paths and complex switching of components, as well as without a delay due to selective switching on or off of a heating unit.

[0011] The solution to the problems arises from the features of the independent claims. Advantageous further developments of the inventions emerge from the dependent claims and the figures.

[0012] The method according to the invention for producing optionally cold, warm or hot milk foam and / or milk comprises the following steps: ▪ Providing at least one container for storing milk to be foamed; ▪ Providing a fluid and a fluid line; ▪ Conveying a predeterminable amount of the milk to be foamed by means of a pump through a line system which comprises a milk suction line between the at least one container and the pump and a single outlet line between the pump and at least one outlet; ▪ Optionally supplying air via an air flow regulator into the milk suction line to produce a milk / air mixture upstream of the pump; ▪ Conveying the milk / air mixture or the milk through a heating element designed as a continuous-flow heater, which is arranged in the outlet line and designed as a thick-film heater; and ▪ Dispensing the milk foam or the milk at the at least one outlet.

[0013] The process is characterized by the fact that the thick-film heater is continuously heated to a predeterminable temperature, and after each dispensing of milk foam or milk, the piping system is at least partially exposed to the fluid. In particular, the system located outside of a cooling area can be exposed to the fluid. Water, especially filtered water, is suitable as the fluid.

[0014] Surprisingly, it has been shown that, in contrast to the known methods for producing either cold, warm, or hot milk foam with only a single flow path downstream of the pump, i.e., a simple piping system, the standby mode of a continuous-flow heater designed as a thick-film heater is highly advantageous. This contrasts with the conventional operating mode of continuous-flow heaters designed as thick-film heaters. These are designed precisely to avoid a sluggish and lengthy response time when switching between active and inactive states, and thus to avoid standby mode. Standby mode means that the thick-film heater is permanently heated to a predeterminable temperature when the device for producing tempered milk foam or milk is in operation.

[0015] The advantage is that in standby mode, i.e. when a switchable heating unit is active, if the temperature continues to rise, the heating phase is significantly shortened and more reliable than when the heating unit is switched off and cooled down. In addition, a time delay when setting the temperature in the fluid channel can be largely avoided. Although the heating phase is shortened even with heating units designed as thick-film heaters with low thermal mass and a very steep heating profile, it still takes a certain amount of time until the flowing fluid is heated to the desired temperature. This is particularly disadvantageous if the milk or milk foam only needs to be heated in small quantities. For example, only small quantities of tempered milk or milk foam are required for certain coffee specialities.Milk foam is required, so that ultimately, due to delayed heating, the required temperature of the small amount of milk or milk foam is not reached. A small cappuccino with approximately 80 ml of milk foam or a so-called cortado with an even smaller amount of milk foam could ultimately be too cold. A slow and prolonged response time of the heating unit used to heat milk and / or milk foam is particularly disadvantageous when heating small amounts of milk foam or milk.

[0016] According to one embodiment of the method, the fluid, preferably water, is discharged from the line system via a multi-way valve only before the milk foam and / or milk is dispensed at the at least one outlet provided for this purpose. Accordingly, the line system, and in particular the heating element designed as a thick-film heater, is exposed to the fluid between two dispensings of milk foam and / or milk. This proves advantageous in many ways, as will be explained below.

[0017] According to the invention, the heating element, designed as a thick-film heater, remains permanently active and is therefore not switched on or off as needed. The thick-film heater is preferably heated to a temperature between 60°C and 70°C. Accordingly, a correspondingly high temperature is also permanently maintained in the fluid channel provided in the thick-film heater.

[0018] If the temperature of the thick-film heater needs to be increased further to produce hot milk foam or hot milk, it only needs to be increased by a relatively small temperature difference. This temperature difference can be, for example, approximately 4°C to 7°C. According to a preferred embodiment, this small temperature difference can be quickly and reliably overcome. Localized overheating, caused by an overshoot in the heating unit's control and thus in the temperature of the thick-film heater, can be avoided by the small temperature difference that needs to be overcome.

[0019] According to the invention, to produce tempered milk foam and / or milk, chilled milk, in particular, at a temperature of 3°C to 7°C can be pumped through the piping system via the milk intake line by means of the pump. To achieve a temperature of approximately 64°C to 68°C for the milk foam and / or milk at a dispensing point or outlet, while also taking into account cooling of the pumped milk foam or milk on the flow path to the dispensing point, the temperature of the heating element should be approximately 70°C to 75°C.

[0020] Previously, systems were known in which a heating element designed as a thick-film heater had to be switched from a deactivated or off state to an activated or on state for tempering the milk foam or milk. The heating element heats up from a low temperature according to a heating profile. During this heating phase, local overheating can occur. This can be observed in conventional heating units: after a sudden change in an input variable, an output variable initially exceeds a setpoint and only then is the desired value of this output variable established. Thus, when a thick-film heater is switched on and heated up, the temperature can briefly rise above the actually set temperature, which can lead to local overheating.This overheating has a negative effect on the milk foam to be tempered or the milk to be heated, especially if it leads to denaturation of the milk proteins and, as a result, deposits.

[0021] According to one embodiment, the supply of fluid, e.g. tap water, to the line system after each dispensing of milk foam and / or milk can, depending on the temperature of the fluid supplied in particular to the milk suction line, cool or heat at least sections of the line system and the components arranged thereon. However, even independently of the temperature of the supplied fluid, the fluid is heated by the heat transferred by the heating element, so that at least sections of the line system, in particular the outlet line and the at least one outlet itself, are also heated. Heated line sections and components arranged thereon prove to be extremely advantageous in order to be able to make the milk foam or the heated milk heated in the heating element available at the at least one outlet without any significant cooling.

[0022] If, on the other hand, cold milk foam or cold milk is requested by a user, for example, the method according to one embodiment of the invention provides that the line system and the heating element designed as a thick-film heater are flushed with fluid, so that the thick-film heater is cooled by the flowing fluid in a period of > 10 s to a temperature preferably corresponding to the cooling temperature in the cooling device, i.e. to ≤ 7°C. In particular, the aim can be to cool to a temperature ≤ 4°C in order to largely compensate for heating during the flow path and the elements arranged thereon. In one embodiment, water is used as the fluid, which can be provided, for example, by a municipal supply network.It's important to note that tap water has different temperatures depending on the environment and the season, which is also referred to as the water inlet temperature. Depending on the season, the temperature of tap water can range between 10°C and 25°C.

[0023] In a preferred embodiment, the fluid, e.g., the tap water supplied via the mains supply, can be cooled by means of a cooling unit. The temperature of the milk cooled and stored in a cooling unit can serve as a guide for a cooling temperature to be set. The cooling of the milk or parts of the device can be designed to also cool the fluid to a temperature of ≤ 7°C. Alternatively, the fluid can be cooled in a separate cooling unit, which can be arranged, for example, on the fluid line. This prevents the first dispensing of a cold beverage from actually having a higher temperature than desired.The cooled fluid can, for example, be cooled by a cooling unit arranged in the supply fluid line, so that the line system can be flushed with cold fluid even if, for example, the fluid in the fluid line itself is already warm at high ambient temperatures. For efficient temperature control of the fluid, the use of a latent heat storage device with a phase change material (PCM) is provided, which is known and applicable in various forms. The phase change material can be used to store heat and cold and to limit temperature peaks. The phase change material has a high storage volume, so that the latent energy stored during a phase change can be used for heat management. PCM technology uses the effect that during a transition, for example from a solid to a liquid phase, the temperature remains constant as long as both states of matter exist simultaneously.The latently stored energy is available again during the reverse process. The PCM, and in particular the melting temperature of the material, can be selected according to the application conditions. For example, aqueous salt solutions are suitable for cooling applications, whereby the phase-change material can be used in closed containers, bound in matrix and / or carrier structures, and / or microencapsulated.

[0024] Thus, the use of PCM technology allows for more extensive cooling of the fluid or tap water. The heating element, designed as a thick-film heater, can therefore not only be cooled to the temperature of tap water, i.e., 10°C to 25°C, but can also be cooled while switched on in such a way that a milk and / or milk foam temperature of ≤ 7°C at the outlet can be reached more quickly. With an appropriate cooling design, temperatures in the range of 4°C to 7°C, in particular ≤ 4°C, can be achieved.

[0025] It is particularly advantageous that the cooling of the stored milk uses PCM technology to also cool the fluid or tap water used for application and rinsing.

[0026] The piping system is flushed with fluid when a valve arrangement arranged in the outlet line, preferably designed as a multi-way valve, is in one position, allowing the fluid to be discharged from the piping system. In another position of the multi-way valve, the fluid can be circulated. The multi-way valve can be switched by means of a control unit, which can control additional components. The control unit can be configured to control the process for producing tempered milk foam and / or milk based on an instruction issued by a user.

[0027] According to the invention, a device for selectively producing cold, warm, and hot milk foam and / or milk according to the inventive method is proposed. The device comprises at least one container in which milk to be foamed is stored, a pump, and a line system comprising a milk intake line via which the at least one container can be connected to the pump, and a single outlet line via which the pump can be connected to at least one outlet. Furthermore, a fluid line is provided via which the line system can be supplied with a fluid.Also included are an air flow regulator, by means of which air can be metered into the milk intake line via an air supply line at an inlet point, a heating element designed as a continuous-flow heater, which is arranged in the outlet line and is designed as a thick-film heater, and a throttle device which can be arranged downstream of the pump in the outlet line. Furthermore, a latent heat accumulator with a phase-change material is provided, which is designed to heat the milk and / or the fluid to a certain temperature.

[0028] To produce milk foam from a milk / air mixture, the throttle device can be arranged in the outlet line downstream of the pump and preferably downstream of the heating element designed as a thick-film heater. The throttle device can be designed as a fixed or adjustable nozzle or orifice and, in particular, comprises an adjustable constriction of the flow cross-sectional area. The throttle device is designed to generate a counterpressure, which advantageously has an effect in the heating element designed as a thick-film heater. The generated counterpressure counteracts the expansion of air bubbles in the milk / air mixture that occurs with increasing temperature. Accordingly, large air bubbles are avoided, which not only reduce the quality and stability of the milk foam but also have a negative effect on heat transfer, since air is a poor heat conductor.

[0029] In one embodiment of the device, the heating element designed as a thick-film heater has an electrical resistor applied to a carrier and a fluid channel in contact with the heating element.

[0030] Advantageously, the device can be arranged at least partially in a cooling device.

[0031] Furthermore, the device can comprise a conductivity sensor configured to determine the conductivity of a medium present in the line system. Based on the conductivity, it is possible to determine which medium is involved, in particular milk, a milk / air mixture, fluid, or air.

[0032] According to one embodiment, a multi-way valve is provided in the outlet line, which can optionally connect the outlet line to a spout for discharging fluid, to a circulation line for circulating fluid through the line system, or to the at least one outlet from which milk foam and / or milk can be drawn. The at least one outlet can be designed as an outlet nozzle. A line section between the multi-way valve and the at least one outlet can be dimensioned such that it has only a small filling volume, for example, approximately 2 to 3 ml.

[0033] In one embodiment of the invention, it is further provided that a first check valve and a second check valve are arranged in the air supply line. Between the first check valve and the second check valve, fluid can be supplied into the air supply line via a first valve R1. Accordingly, the first valve R1, which can be controlled by the control unit, is provided in the fluid line in a flow path to the air supply line. The first check valve and the second check valve can preferably be switched independently of one another.

[0034] The first check valve and the second check valve are preferably designed as direct-closing check valves, which can be arranged in a vertical orientation in the air supply line so that flow can occur from top to bottom. Direct-closing check valves generally comprise a closing element, which can be pressed into its seat by a medium and / or due to gravity. Delays and vibrations during the closing process can be reduced. Accordingly, by means of the vertical orientation of the first check valve and the second check valve in the air supply line, precise metering of the air quantity can be achieved by means of the air quantity regulator, which is also arranged in the air supply line. With this arrangement, the supplied fluid can also be used, if necessary, to flush at least parts of the air supply line, which is advantageous with regard to precise air quantity metering.

[0035] Alternatively or additionally, the fluid can be supplied via the fluid line into the milk intake line in order to largely apply the fluid to or flush the sections of the line system carrying the milk, the milk / air mixture, or the milk foam. A second valve R2, which can be controlled by a control unit, is provided in the fluid line to control the introduction of the fluid into the milk intake line.

[0036] In particular, the fluid is water, which can be supplied via a water pipe. Since, depending on the ambient temperature and season, the water in a water pipe may already have a higher temperature (e.g., in the summer months, water of more than 20°C is initially drawn from the water pipe), one embodiment of the invention can provide a cooling unit by means of which the fluid can be cooled to a low temperature, in particular to a temperature ≤ 7°C.

[0037] With the method and device according to the invention for producing optionally cold, warm, or hot milk foam and / or milk, the heating element designed as a thick-film heater can always be kept in an activated state, at least when a connected beverage processor is also in operation. Since the piping system and the continuous-flow heater designed as a thick-film heater are exposed to the fluid between two milk or milk foam dispensings, the thick-film heater can always be kept in standby mode and at a high temperature, so that only short heating or cooling phases of the thick-film heater need be considered, if necessary. Brief description of the drawings

[0038] An embodiment of the invention is explained in more detail below with reference to a drawing. It shows: Figure 1schematically shows a device according to the invention for producing either cold, warm or hot milk foam and / or milk. Detailed description of a preferred embodiment

[0039] The Figure 1The schematically illustrated embodiment of a device 1 according to the invention is designed to selectively produce cold, warm, or hot milk foam and / or milk. The milk to be foamed, or another liquid to be foamed, is stored in a container 10, which is preferably provided in a cooling system 2. The cooling system 2 can preferably be designed such that the device 1 can be at least partially accommodated therein. Since a large number of types of milk are available today, several storage containers 10 can be provided, each of which can store a specific type of milk. A milk suction line 14, which is included in a line system 12, leads from the at least one container 10 to a suction side of a pump 16, in order to suck milk out of the at least one container 10 when a correspondingly provided shut-off valve 11 opens the flow path.

[0040] In the illustrated embodiment, a conductivity sensor 18 is arranged in the milk suction line 14, which is designed to determine the type of medium conveyed in the milk suction line 14 by measuring a conductivity, ie whether it is milk, fluid or water, rinsing solution or air.

[0041] Furthermore, a valve 20 is arranged in the milk suction line 14, which opens the milk suction line 14 in the direction of the suction side of the pump 16 and is designed as a check valve.

[0042] Upstream of the valve 20, a fluid line 22 opens into the milk suction line 14, via which a fluid can be supplied. In particular, the fluid is water, which preferably applies a definable temperature to the line system 12. "Applying" can be understood as both filling and holding as well as rinsing. The fluid, which can be introduced into the milk suction line 14 by means of the fluid line 22, which can be shut off by a second valve R2, can be introduced into the device 1 between two dispensings of milk and / or milk foam, preferably in a controlled manner by a control unit (not shown), and in particular can remain therein until a new dispensing of milk foam and / or milk is requested.

[0043] On the suction side of the pump 16, the line system 12 further comprises an air supply line 24 for metered and controlled air introduction into the milk intake line 14 at an inlet point 25. An air flow regulator 26, e.g., a proportional valve, is provided for this purpose. This allows a precisely determined amount of air to be introduced into the line system 12 or mixed with the pumped milk, so that a milk / air mixture is present in the milk intake line 14 downstream of the inlet point 25, which is pumped by the pump 16.

[0044] In Figure 1It is shown that a first check valve 27 and a second check valve 28 are provided in the air supply line 24. The first check valve 27 and / or the second check valve 28 can be designed as directly closing check valves and arranged in a vertical orientation, so that the force of gravity acting on a surrounding closing element assists in opening the first check valve 27 and / or the second check valve 28. Accordingly, the air supply line 24 opens even if the negative pressure generated may not be entirely sufficient for air intake.

[0045] A section of the fluid line 22 opens between the first check valve 27 and the second check valve 28, so that when the first valve R1 is open in this section, fluid is introduced into the air supply line 24 and can thus also flush this section of the line system 12. To cool the fluid, which can be introduced into the line system via the fluid line 22, a cooling unit 60 can be provided. The cooling unit 60 is designed as a latent heat storage device with a phase change material (PCM). Using the PCM technology used here, tap water provided by a supply network can be cooled to a temperature ≤ 7°C. Accordingly, the temperature of the fluid, in particular of the tap water, can be adjusted independently of the ambient temperature and the temperature of the tap water in the supply network.The cooling system 2 for the milk and parts of the device 1 is designed as a latent heat storage device with PCM in order to cool the fluid accordingly.

[0046] The pump 16 is connected on its pressure side via a single outlet line 30 to an outlet 32, at which processed milk and / or processed milk foam can be dispensed. A multi-way valve 33 is arranged upstream of the outlet 32 ​​to selectively provide flow toward the outlet 32 ​​or toward a spout 35. In a further position of the multi-way valve 33, circuit flushing can also be enabled.

[0047] Downstream of the pump 16, a flow heater is provided in the outlet line 30, which is a heating element 39 designed as a thick-film heater 40. The heating element 39 comprises an electrical heating resistor applied to a carrier and a fluid channel through which a fluid to be heated can flow. According to the invention, the heating element 39 designed as a thick-film heater 40 is permanently in an active state and is thus always heated to a temperature of, for example, approximately 60°C to 70°C. Furthermore, it is provided that between two dispensings of milk foam and / or milk at the outlet 32, the line system 12 is supplied with the fluid. The supply of the fluid has the effect that between two dispensings of milk foam and / or milk, the line system 12 is at least partially filled with fluid.Filling the piping system 12 and the thick-film heater 40 reduces the risk of overheating and allows the section of the outlet line 30 extending from the thick-film heater 40 and the components arranged thereon, e.g. the outlet 32, to heat up.

[0048] Furthermore, a throttle device 50 is arranged in the outlet line 30, particularly downstream of the thick-film heater 40, which is preferably adjustable by means of a control unit (not shown). The stability and quality of the milk foam produced can be positively influenced by means of the throttle device 50.

[0049] Before tempered milk foam and / or milk is dispensed at the outlet 32, the fluid is discharged from the line system 12 via the multi-way valve 33. To produce warm milk foam and / or warm milk, the milk / air mixture or the milk is passed through the heated heating element 39 and the heated section of the outlet line 30. To produce hot milk foam and / or milk, for example, the temperature of the thick-film heater 40 can be increased by a small temperature difference so that the flowing milk / air mixture and / or the milk can be heated to a temperature in the range of approximately 64°C to 68°C at the outlet 32. Cooling of the milk foam and / or milk in the line system 12 is significantly reduced by the tempered flow path. Even small quantities of milk / air mixture or milk can be brought to the correct temperature in a very short period of time.

[0050] To produce cold milk foam and / or cold milk, with the device and method according to the invention, it is no longer necessary to switch off the heating element 39 designed as a thick-film heater 40 and to take its thermal behavior into account. Rather, it is provided that when the multi-way valve 33 is open, the fluid in the line system is discharged and cold fluid, or fluid cooled by a cooling unit 60, is sucked into the line system 12 by means of the pump 16 via the fluid line 22 and conveyed therein, so that the cool fluid flowing in the fluid channel of the thick-film heater 40 cools the latter to such an extent that subsequent milk / air mixture or milk is not heated or is heated only slightly despite the thick-film heater 40 being switched on.

Claims

1. Method for selectively producing cold, warm or hot milk foam and / or milk, the method comprising the following steps: ▪ providing at least one container (10) for storing milk to be foamed; ▪ providing a fluid and a fluid line (22); ▪ conveying, by means of a pump (16), a predefinable amount of the milk to be foamed through a line system (12), which comprises a milk intake line (14), between the at least one container (10) and the pump (16), and an outlet line (30), between the pump (16) and at least one outlet (32); ▪ potentially supplying air into the milk intake line (14) via an air-flow regulator (26), which can be arranged in an air-supply line (24), in order to produce a milk / air mixture upstream of the pump (16); ▪ conveying the milk / air mixture or the milk through a heating element (39), which is designed as a flow heater and is arranged in the outlet line (30) and is in the form of a thick-film heating element (40); ▪ producing a milk foam from the milk / air mixture by means of a throttle device (50); and ▪ dispensing the milk foam or milk at the at least one outlet (32), characterized in that the thick-film heating element (40) is permanently heated to a predefinable temperature, and after each action of dispensing of the milk foam or the milk, fluid is applied to the line system (12) at least in part.

2. Method for selectively producing cold, warm or hot milk foam and / or milk according to claim 1, characterized in that before a dispensing of milk foam or milk at the outlet (32) the fluid is conveyed out of the line system (12) via a manifold valve (33).

3. Method for selectively producing cold, warm or hot milk foam and / or milk according to claim 1 or 2, characterized in that the fluid is water.

4. Method for selectively producing cold, warm or hot milk foam and / or milk according to one of the preceding claims, characterized in that the thick-film heating element (40) is permanently heated to a temperature between 60°C and 70°C.

5. Method for selectively producing cold, warm or hot milk foam and / or milk according to claim 4, characterized in that for producing hot milk foam and / or milk the temperature of the thick-film heating element (40) is increased by about 4°C to 7°C.

6. Method for selectively producing cold, warm or hot milk foam and / or milk according to one of the preceding claims, characterized in that for producing cold milk foam and / or cold milk the line system (12) and the thick-film heating element (40) is rinsed with fluid, so that the thick-film heating element (40) is cooled by the fluid flowing through in a time period of > 10 s to a temperature of ≤ 7°C.

7. Method for selectively producing cold, warm or hot milk foam and / or milk according to claim 6, characterized in that the feedable fluid has a temperature of ≤ 7°C.

8. Method for selectively producing cold, warm or hot milk foam and / or milk according to claim 7, characterized in that the feedable fluid is cooled to the temperature ≤ 7°C by means of a cooling unit (60) designed as a latent heat accumulator with a phase-change material.

9. Method for selectively producing cold, warm or hot milk foam and / or milk according to one of the preceding claims, characterized in that a control unit controls the method according to an instruction generated by a user.

10. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to the method according to one of the preceding claims, comprising ▪ at least one container (10), in which milk to be foamed is stored, ▪ a pump (16), ▪ a line system (12), comprising o a milk intake line (14), via which the at least one container (10) is connectible to the pump (16), and o an outlet line (30), via which the pump (16) is connectible to at least one outlet (32), and ▪ a fluid line (22), via which fluid is able to be applied to the line system (12), ▪ an air-flow regulator (26), by means of which air is able to be conveyed in a metered way via an air-supply line (24) at an inlet point (25) into the milk intake line (14), ▪ a heating element (39) designed as a flow heater, which is arranged in the outlet line (30) and designed as a thick-film heating element (40), ▪ a throttle device (50) which is able to be arranged downstream of the pump (16) in the outlet line (30), ▪ characterized in that a latent heat accumulator with a phase-change material is provided for temperature controlling of milk and / or fluid.

11. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to claim 10, characterized in that the thick-film heating element (40) comprises an electrical resistor installed on a support and a fluid channel in contact with the heating element (39).

12. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to claim 10 or 11, characterized in that the apparatus (1) is able to be arranged at least partially in a cooling system (2).

13. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to claim 10 to 12, characterized in that the latent heat accumulator is arranged to cool the milk and / or the fluid to a temperature ≤ 7°C.

14. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to claim 10 bis 13, characterized in that a conductance sensor (18) is provided for determining a conductance of a medium in the line system.

15. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to one of the claims 10 to 14, characterized in that a manifold valve (33) is provided in the outlet line (30), which manifold valve connects the outlet line (30) selectively to a drain (35) for discharging the fluid, to a circuit line for conducting the fluid in the circuit or to at least one outlet (32) at which milk foam or milk can be dispensed.

16. Apparatus (1) for selectively producing cold, warm or hot milk foam and / or milk according to one of the claims 10 to 15, characterized in that a first non-return valve (27) and a second non-return valve (28) are arranged in the air-supply line (24) in a vertical orientation and so that flow can pass through them from top to bottom, these being designed as directly closing non-return valves, and fluid can be introduced into the air-supply line (24) between the first non-return valve (27) and the second non-return valve (28) via a valve R2.