A mixing method and apparatus for a beverage preparation device

Abstract

A method of operating an outlet valve associated with a mixer of a beverage preparation device comprising the steps of: providing the outlet valve in an open position then moving the outlet valve from the open position to a closed position. Starting a flow of base liquid and a flow of ingredient into the mixer after the outlet valve is in the closed position, to enable the mixer to fill then starting the mixer after the flow of at least one of the base liquid and ingredient into the mixer has started. Then moving the outlet valve from the closed position to at least a partially open position over a period of time tfroth while the mixer is operating to dispense a mixed beverage.

Description

Technical Field of the Invention The present invention relates to a mixing method and apparatus for a beverage preparation device and a beverage preparation device comprising such apparatus. In particular, the invention relates to an outlet valve associated with a mixer of a beverage preparation device and a method of operating said outlet valve. Background to the Invention Beverages comprising microfoam are increasingly popular, especially milky coffee drinks. Crema on coffee is also a form of microfoam. Beverage preparation devices comprising a mixer to generate foam in coffee and / or milk-based beverages are known. It is also known to utilise a three-state valve to control dispensing of such beverages. One issue with beverage preparation devices used to prepare beverages comprising microfoams is that the formation and dispensing of the beverage may be relatively time consuming if the microfoam is to be retained. This is particularly an issue in higher throughput devices, where less time is available to dispense the beverages comprising microfoam, whilst maintaining the throughput. The throughput is reduced to retain the microfoam or alternatively, the beverage is dispensed more quickly to maintain the throughput, sacrificing the retention of the microfoam. A second issue with using a three-state valve to control dispensing is that the sudden movement between the valve states often causes shocks to be transmitted to the beverage. Such shocks result in the formation of large bubbles within the beverage which are visually unappealing and unappetising to the consumer. As a result, the first and last portion of the beverage, which usually comprises the majority of the larger bubbles, is often disposed of rather than being dispensed, resulting in a large amount of unnecessary waste. This is a particular issue in beverages comprising fresh milk. A further issue with such beverage preparation devices is that the mixer module is prone to a build-up of waste matter such as ingredient residue on the walls of the mixer. It is important that such waste matter is removed by cleaning and / or flushing of the module although this is often difficult to achieve given that access to the inside of the mixer can often be restricted. There is a need therefore, for an improved beverage preparation device which overcomes, or at least mitigates, some or all of the disadvantages of the known beverage preparation devices. There is a need, in particular, for a beverage preparation device capable of producing an improved beverage which is more aesthetically appealing and appetising, whilst maintaining or reducing the time taken to form and dispense the beverage and minimising waste. Summary of the Invention According to a first aspect of the present invention there is provided a method of operating an outlet valve associated with a mixer of a beverage preparation device comprising the steps of: a. providing the outlet valve in an open position; b. moving the outlet valve from the open position to a closed position; c. starting a flow of base liquid and a flow of ingredient into the mixer after the outlet valve is in the closed position, to enable the mixer to fill; d. starting the mixer after the flow of at least one of the base liquid and ingredient into the mixer has started; and e. moving the outlet valve from the closed position to at least a partially open position over a period of time, tfroth while the mixer is operating to dispense a mixed beverage. The purpose of step d is to cause mixing and foaming of the contents of the mixer to create a mixed beverage. When dispensed, the mixed beverage may comprise a foamed upper layer and an unfoamed lower layer. The method of operating an outlet valve associated with a mixer of a beverage preparation device is particularly advantageous as providing the outlet valve initially in the open position (step (a)) may assist in preventing the outlet valve sticking. In addition, it may also allow drainage of any potential leaks within the device, thereby acting as an early warning signal of a fault. Furthermore, starting the mixer after the flow of at least one of base liquid or ingredient has started allows more efficient mixing of the flows. Additionally, the buffer zone within the mixer i.e., the area of the mixer contacted by the flows of base liquid and / or ingredient is preferably minimised compared to the flows of base liquid and / or ingredient enter the mixer after the mixer had been started. As a result, the build-up of base liquid and / or ingredient within the mixer is minimised and the amount of base liquid and / or ingredient wasted is also reduced. Step (e) allows the mixed beverage to be dispensed gradually in a controlled manner. This is particularly advantageous in encouraging the formation and maintenance of small, regularly sized bubbles in the dispensed mixed beverage as opposed to large bubbles in the foamed layer of the dispensed mixed beverage. The partially open position may be an intermediate position. The intermediate position may be between the closed position and the open position. The method of operating the outlet valve associated with a mixer of a beverage preparation device may further comprise, before step (a), i.e. in a step (a’), providing a water supply valve in a closed position and running a precycle flow. Step (a’) may comprise providing the water control valve in a closed position and running a precycle flow of water. Step (a’) may comprise running the pre-cycle flow of water at a flow rate in the range of 1- 20 ml / s, more preferably of 5-15 ml / s or more preferably still of 7.512.5 ml / s. Step (a’) may comprise running the pre-cycle flow of water at a flow rate of at least 1 ml / s, more preferably of at least 5 ml / s or more preferably still of at least 7.5 ml / s. Step (a’) may comprise running the pre-cycle flow of water at a maximum flow rate of 12.5 ml / s, 15 ml / s, or more preferably still of 20 ml / s. Preferably, step (a’) may comprise running the pre-cycle flow of water at a flow rate of 10 ml / s. Running a precycle flow of water may enable the pre-cycle flow to flush a water supply system without entering the mixer. This may act to ensure that the water supply system is preheated prior to step (a), as well as assisting in removal of air pockets within the water supply system thereby assisting in maintaining a heated mixed beverage. Step (b) may comprise moving the outlet valve from the open position to the closed position over a period of time in the range of 0.01-0.5 seconds, more preferably 0.05- 0.25 seconds or more preferably still of 0.075-0.15 seconds. Preferably, step (b) may comprise moving the outlet valve from the open position to the closed position over a period of time of 0.1 seconds. By gradually moving the outlet valve from the open position to the closed position, any fluid remaining in the mixer e.g., as a result of previous beverage preparation, may be dispensed prior to the outlet valve reaching the closed position ready for use. Step (c) may comprise starting the flow of base liquid into the mixer as soon as the outlet valve is in the closed position. This may minimise the volume of wasted base liquid passing through the mixer as after the outlet valve is in the closed position, the mixer may begin to fill with base liquid (and ingredient) to be mixed and dispensed as a mixed beverage for a consumer. Step (c) may comprise starting the flow of base liquid into the mixer before starting the flow of ingredient into the mixer. Starting the flow of base liquid into the mixer before starting the flow of ingredient may assist with achieving efficient mixing and dissolving of any ingredient into the mixture, thereby creating a high-quality mixed beverage to be dispensed. Step (c) may comprise starting the flow of ingredient into the mixer after the flow of base liquid has been running for a period of time between 0.01-0.5 seconds, more preferably 0.05- 0.25 seconds or more preferably still of 0.075-0.15 seconds. Preferably, step (c) may comprise starting the flow of ingredient into the mixer after the flow of base liquid has been running for a period of time of 0.1 seconds. Step (c) may comprise starting the flow of base liquid into the mixer at a continuous flow rate. Step (c) may comprise starting the flow of base liquid into the mixer at a flow rate in the range of 5- 35 ml / s, more preferably of 10-30 ml / s, yet more preferably 15- 25 ml / s or most preferably of 17.5- 22.5 ml / s. Step (c) may comprise starting the flow of base liquid into the mixer at a flow rate of at least 5 ml / s, more preferably of 10 ml / s, yet more preferably of 15 ml / s or more preferably still of 17.5 ml / s. Step (c) may comprise starting the flow of base liquid into the mixer at a maximum flow rate of 22.5 ml / s, more preferably of 25 ml / s, yet more preferably of 30 ml / s or more preferably still of 35 ml / s. Preferably, step (c) may comprise starting the flow of base liquid into the mixer at a flow rate of 20 ml / s. Supplying a continuous, nonpulsated flow of base liquid helps to achieve consistent foaming of the mixed beverage once the mixer is started. This may encourage the formation of a high-quality foam and / or crema within the mixed beverage having regular sized small bubbles which are visually appealing to the consumer. Furthermore, supplying the base liquid at a continuous flow rate may reduce the buffer size within the mixer allowing for more efficient cleaning of the mixer as well as minimising waste by enabling a larger portion of the mixture to be foamed and dispensed for consumption. Step (c) may comprise starting the flow of ingredient into the mixer at a constant flow rate. Step (c) may comprise starting the flow of ingredient into the mixer at a flow rate in the range of 0.1-15 ml / s, more preferably of 1-10 ml / s, or most preferably of 2.57.5 ml / s. Providing a constant flow frequency of ingredient into the mixer may reduce the buffer size within the mixer i.e., the food contact area within the mixer may be greatly reduced allowing for more efficient cleaning of the mixer as well as minimising waste by enabling a larger portion of the mixture to be foamed and dispensed for consumption. Step (d) may comprise starting the mixer after the flow of both base liquid and ingredient into the mixer has started. Step (d) may comprise starting the mixer after the flow of base liquid has been running for a period of time in the range of 0.01-0.5 seconds, more preferably of 0.025-0.4 seconds, yet more preferably of 0.05- 0.3 seconds, or most preferably of 0.075-0.25 seconds. Preferably, step (d) may comprise starting the mixer after the flow of base liquid has been running for a period of time of 0.2 seconds. Step (d) may comprise starting the mixer after the flow of both base liquid and ingredient into the mixer has been running for a period of time in the range of 0.01-0.5 seconds, more preferably of 0.05- 0.25 seconds or more preferably again of 0.075-0.15 seconds. Preferably, step (d) may comprise starting the mixer after the flow of both base liquid and ingredient into the mixer has been running for a period of time of 0.1 seconds. Step (d) may comprise increasing the speed of the mixer over a period of time in the range of 0.01-0.5 seconds, more preferably of 0.05- 0.25 seconds or most preferably of 0.075-0.15 seconds. Preferably, step (d) may comprise increasing the speed of the mixer over a period of time of 0.1 seconds. This allows the mixer to reach full speed gradually such that the transmission of shock waves to the contents of the mixer are minimised helping to prevent the formation of large bubbles within the mixed beverage. The period of time, tfroth, may be broken into time segments of different lengths. During each time segment, the outlet valve may be provided in a different position i.e., there may be more than one intermediate position. The period of time, tfroth may comprise a first period of time tfrothj. The period of time, tfroth may comprise a second period of time tfrothj. The first period of time tfrothj may be immediately followed by the second period of time tfrothj. Step (e) may comprise moving the outlet valve to the intermediate position and subsequently moving the outlet valve to the open position. Step (e) may comprise moving the outlet valve to the intermediate position over a time period, tfrothj- Step (e) may comprise moving the outlet valve to the intermediate position over a time period tfrothj in the range of 1-5 seconds, more preferably of 1.5-4 seconds, or most preferably of 2-3 seconds. Preferably, step (e) may comprise moving the outlet valve to the intermediate position over a time period tfrothj of 2.6 seconds. Moving the outlet valve to the intermediate position gradually may reduce transmission of shocks within the mixture which could occur if the outlet valve was suddenly moved from the closed to the intermediate position. This is preferable as it minimises the formation of large bubbles and promotes formation of smaller bubbles within the mixed beverage which are more aesthetically pleasing for the consumer. Step (e) may comprise moving the outlet valve to the intermediate position over a time period, tfrothj which may be broken into time segments of different lengths. For example, tfrothj may comprise a time segment during which the outlet valve may change position, and a subsequent time segment during which the outlet valve may remain in the same position. Step (e) may comprise moving the outlet valve from the closed position to the intermediate position over a time period tfroth_l_opening. Step (e) may comprise moving the outlet valve from the closed position to the intermediate position over a time period tfrothjopening in the range of 0.01-0.5 seconds, more preferably of 0.025-0.4 seconds, yet more preferably of 0.05- 0.3 seconds, or most preferably of 0.075-0.25 seconds. Preferably, step (e) may comprise moving the outlet valve from the closed position to the intermediate position over a time period tfroth_l _opening of 0.2 seconds. The inventors appreciate that moving any valve between two positions will take time. However, moving a standard valve between a first and a second position occurs so quickly that it may be considered to occur instantaneously. By moving the outlet valve to the intermediate position over a prolonged period of timetfrothl-Opening, the shocks transmitted to the mixed beverage may be significantly less than those transmitted when using a standard valve. As such, the formation of large bubbles within the mixed beverage may be reduced. Step (e) may comprise leaving the outlet valve in the intermediate position for a time period tfroth_l _constant. Step (e) may comprise leaving the outlet valve in the intermediate position for a time period tfroth_i-constant in the range of 1-5 seconds, more preferably of 1.5-4 seconds, or most preferably of 2-3 seconds. Preferably, step (e) may comprise leaving the outlet valve in the intermediate position for a time period tfroth_i-constant of 2.4 seconds. Leaving the outlet valve in the same intermediate position may encourage the maintenance of small bubbles in the dispensed foamed portion of the mixed beverage. Step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth_2. Step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth_2 in the range of 1-5 seconds, more preferably 1.5-4 seconds, or most preferably 2-3 seconds. Preferably, step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth_2 of 2.6 seconds. Step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth—2_opening- Step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth—2_openingin the range of 0.01-0.5 seconds, more preferably of 0.025-0.4 seconds, yet more preferably of 0.05- 0.3 seconds, or most preferably of 0.075-0.25 seconds. Preferably, step (e) may comprise moving the outlet valve from the intermediate position to the open position over a time period tfroth—2_openi ng of 0.2 seconds. Step (e) may comprise leaving the outlet valve in the open position for a time period tfroth—2_constant. Step (e) may comprise leaving the outlet valve in the open position for a time period tfroth2constant in the range of 1-5 seconds, more preferably of 1.5-4 seconds, or most preferably of 2-3 seconds. Preferably, step (e) may comprise leaving the outlet valve in the open position for a time period tfroth_2_constant of 2.4 seconds. By leaving the outlet valve in the open position once the foaming of the mixture has occurred, the remaining fluid may drain more quickly. Step (e) may comprise stopping the mixer. Step (e) may comprise stopping the mixer whilst the outlet valve is in the intermediate position. Step (e) may comprise stopping the mixer after a period of time, tmixer. Step (e) may comprise stopping the mixer after a period of time tmixer in the range of 1-5 seconds, more preferably 1.5-4 seconds, or most preferably of 2-3 seconds. Preferably, step (e) may comprise stopping the mixer after a period of time, tmixer of 2.6 seconds. Step (e) may comprise stopping the mixer after a period of time, tmixer which is shorter than or equal to the time period tfrothj- By stopping the mixer whilst the outlet valve is in the intermediate position, i.e., before the outlet valve moves to the open position, the fluid in the mixer may no longer be being agitated when the outlet valve is in the intermediate position. As such, the mixed beverage dispensed when the valve is in the open position may form the lower unfoamed half of the beverage as opposed to the upper portion which is foam and / or crema. Step (e) may comprise stopping the flow of ingredient. Step (e) may comprise stopping the flow of ingredient after a time period, tingredient- Step (e) may comprise stopping the flow of ingredient after a time period, tingredientin the range of 2-8 seconds, more preferably of 3-7 seconds, or most preferably of 4-6 seconds. Preferably, step (e) may comprise stopping the flow of ingredient after a time period tmgrediento^ 5.2 seconds. Step (e) may comprise stopping the flow of ingredient when the outlet valve is in the open position. Step (e) may comprise stopping the flow of ingredient when the outlet valve has been in the open position for a period in the range of 1-5 seconds, more preferably of 1.5-4 seconds, or most preferably of 2-3 seconds. Preferably, step (e) may comprise stopping the flow of ingredient when the outlet valve has been in the open position for a period of 2.4 seconds. Step (e) may comprise stopping the flow of ingredient after the mixer has been stopped. Step (e) may comprise stopping the flow of ingredient after the mixer has been stopped for a period of time in the range of 1-5 seconds, more preferably of 1.5-4 seconds, or most preferably of 2-3 seconds. Step (e) may comprise stopping the flow of ingredient after the mixer has been stopped for a period of time of 2.5 seconds. Stopping the mixer before stopping the flow of ingredient is advantageous as it may ensure that the unfoamed lower portion of the dispensed mixed beverage is a mixture of both base liquid and ingredient and not just base liquid. The method of operating the outlet valve associated with a mixer of a beverage preparation device may further comprise, after step (e), i.e. in a step (f), moving the outlet valve between the open and a second intermediate position over a period of time, tflush. Step (f) may comprise moving the outlet valve between the open and the second intermediate position over a period of time tfush in the range of 0.1-5 seconds, more preferably 0.5-4 seconds, or most preferably 1-3 seconds. Preferably, step (f) may comprise moving the outlet valve between the open and the second intermediate position over a period of time tfiush of 2.2 seconds. The period of time tfiush may be broken into time segments of different lengths. During each time segment, the outlet valve may be provided in a different position. The period of time tfiush may comprise a first period of time tfushj. The period of time tfiush may comprise a second period of time tflush_2. The first period of time tfushj may be immediately followed by the second period of time tfushj. Step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tfushj. Step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tfushj in the range of 0.01-5 seconds, more preferably of 0.1-3 seconds, or most preferably of 1-2 seconds. Preferably, step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tfushj of 1.5 seconds. This is particularly advantageous as by restricting the outlet flow from the mixer, the mixer may begin to fill enabling flushing of the mixer to clean the surfaces before the next beverage is prepared. Step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tfUshj which may be broken into time segments of different lengths. Step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tflush_l _opening' Step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tflush_l _opening in the range of 0.01-0.5 seconds, more preferably of 0.05- 0.25 seconds or most preferably of 0.075-0.15 seconds. Preferably, step (f) may comprise moving the outlet valve from the open position to the second intermediate position over a time period tflush—1 —Opening of 0.1 seconds. Step (f) may comprise leaving the outlet valve in the second intermediate position for a period of time tflush—1 —Constant- Step (f) may comprise leaving the outlet valve in the second intermediate position for a period of time tfiush_i_constanan the range of 0.55 seconds, more preferably of 0.75-4 seconds, or most preferably 1-2 seconds. Step (f) may comprise leaving the outlet valve in the second intermediate position for a period of time tfiush_ 1_constantof 1.4 seconds. Step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tflush_2. Step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tfiush 2 in the range 0.1-3 seconds, more preferably of 0.25-2 seconds, or most preferably of 0.5-1 seconds. Preferably, step (f) may comprise moving the outlet valve from the intermediate position to the open position over a time period of tfiush_2 of 0.7 seconds. Moving the outlet valve into the open position preferably allows the water in the mixer to be quickly dispensed after flushing of the mixer has been completed. Step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tflush_2 which may be broken into time segments of different lengths. Step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tflush_2_opening-Step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tfiush 2_opening in the range of 0.01-0.5 seconds, more preferably of 0.05- 0.25 seconds or most preferably of 0.075-0.15 seconds. Preferably, step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tflush 2_opening of 0.1 seconds. Step (f) may comprise leaving the outlet valve in the open position for a period of time tfiush_ 2_constant- Step (f) may comprise leaving the outlet valve in the open position for a period of time tflush_2constant in the range of 0.1-3 seconds, more preferably of 0.22 seconds, or most preferably of 0.4-1 seconds. Preferably, step (f) may comprise leaving the outlet valve in the open position for a period of time tfiush_2constant of 0.6 seconds. The second intermediate position may be the same as the intermediate position. Alternatively, the second intermediate position may be different to the intermediate position, i.e., the intermediate position of the outlet valve whilst the mixed beverage is being dispensed may be the same intermediate position of the outlet valve during the flushing cycle or it may be different. Providing the valve in the intermediate position during dispensing of the mixed beverage may assist in maintaining the small bubbles in the mixed beverage, but providing the outlet valve in the intermediate position during the flushing cycle may allow a slight build-up of water in the mixer. Therefore, it is possible that different intermediate positions i.e., a first and second intermediate position may be beneficial in achieving each of these different effects. Step (f) may comprise stopping the flow of water into the mixer. Step (f) may comprise stopping the flow of water into the mixer after a time period in the range of 4-10 seconds, more preferably 5-9 seconds, or most preferably of 6.5-7.5 seconds. Preferably, step (f) may comprise stopping the flow of water after a period of 6.8 seconds. Step (f) may comprise stopping the flow of water into the mixer whilst the outlet valve is in the second intermediate position. Stopping the flow of water into the mixer whilst the valve is in the second intermediate position may minimise the volume of wasted water used for flushing as once the outlet valve is moved into the open position, any flow of water entering the mixer is more likely to pass straight through the mixer and be dispensed without actually flushing and cleaning the mixer. In a second aspect of the present invention, there is provided a mixer system comprising a mixer and an outlet valve associated with the mixer of a beverage preparation device configured to carry out any of the method steps of the first aspect of the present invention. The mixer may comprise a bowl. The bowl may be adapted to receive a flow of base liquid and / or a flow of ingredient and / or a flow of air. The base liquid may be water, and / or milk, and / or coffee and / or tea and / or chocolate. The flow of ingredient may comprise a fluid. The fluid may be a liquid. For example, the liquid may be milk, and / or coffee and / or tea and / or chocolate. Additionally, or alternatively, the flow of ingredient may be a solid. The solid may be a powder or particulate solid. For example, the powder may be milk, and / or coffee and / or tea and / or chocolate. The beverage preparation device may comprise a water supply system. The water supply system may be configured to supply the flow of water. The water supply system may be configured to supply a pre-cycle flow of water. The pre-cycle flow may be a flow of water. The pre-cycle flow and / or flow of water and / or flow of ingredient may be controlled. The pre-cycle flow and / or flow of water and / or flow of ingredient may be controlled using at least one control valve. For example, there may be provided a water control valve and / or an ingredient control valve. The bowl may comprise at least one inlet. The at least one inlet may be configured to receive the flow of base liquid and / or the flow of ingredient. The at least one inlet may be provided substantially horizontally. This may result in the pre-cycle flow and / or the flow of water and / or the flow of ingredient being delivered tangentially into the bowl helping to promote efficient mixing of the flows as well as leaving the mixer cleaner as the surface of the mixer may be flushed with water when the flow of water is allowed to run for a longer period of time than the flow of ingredient. Alternatively, the bowl may comprise at least a first inlet and a second inlet. The first inlet may be configured to receive the pre-cycle flow and / or the flow of water and / or the flow of base liquid. The second inlet may be configured to receive the flow of ingredient. The first inlet may be provided substantially horizontally. The second inlet may be provided substantially vertically. The second inlet may be positioned eccentrically with respect to the centre of the bowl. An upper portion of the bowl may comprise a dosing recess. The dosing recess may be in alignment with both the first inlet and the second inlet i.e., the dosing recess may be provided in the flow path of water and / or base liquid entering via the first inlet and it may also be provided directly beneath the second inlet. Provision of such a dosing recess may encourage efficient mixing as the flow of ingredient may combine with a running flow of water and / or base liquid. The bowl may comprise an air inlet. The air inlet may be configured to receive a flow of air. The bowl may comprise an impeller or agitator to mix. The impeller or agitator may be configured to cause mixing of the flow of base liquid and the flow of ingredient with the flow of air. The impeller or agitator may be configured to cause mixing of the flow of base liquid and the flow of ingredient with the flow of air into a mixed beverage. Provision of such an agitator is advantageous in assisting the formation of foam in the dispensed mixed beverage. The bowl may comprise an outlet. The outlet may be configured to dispense the mixed beverage. The outlet may comprise an outlet valve. The outlet valve may be configured to control dispensing of the mixed beverage. The outlet valve may be moveable between an open position, an intermediate position, and a closed position. The outlet valve may be operable to transition between the open position and / or the intermediate position and / or the closed position over a period of time in the range of 0.01-0.5 seconds, more preferably 0.025-0.4 seconds or most preferably 0.075-0.3 seconds. By transitioning the valve between positions over a period of time rather than suddenly, the transmission of shock waves into the mixed beverage may be minimised. The outlet valve may be selected from the group comprising a needle valve, a ceramic valve, or a pinch valve. In the intermediate position, the outlet valve may be configured to partially obstruct the outlet. The outlet valve may be configured to partially obstruct the outlet by covering 10-75%, more preferably 15-50% or most preferably 20-30% of the cross section of the outlet. The outlet valve may be configured to partially obstruct the outlet by covering 25% of the cross section of the outlet. The needle valve may comprise a tapered plunger. The needle valve may comprise a hollow housing. The tapered plunger may be housed within the hollow housing. The hollow housing may be provided substantially horizontally. The hollow housing may have a diameter in the range of 5-15 mm, preferably of 6-12 mm, or more preferably of 7-9 mm. Preferably, the hollow housing may have a diameter of 8 mm. The hollow housing may be provided at an angle in the range of 0-30°, more preferably in the range of 3-20°, or most preferably in the range of 5-10° to the horizontal axis of the mixer. Preferably, the hollow housing may be provided at an angle of 7° to the horizontal axis of the mixer. Providing the hollow housing at an angle may assist with draining the mixed beverage and / or the precycle flow and / or the flushing fluid. Alternatively, the hollow housing may be provided substantially vertically. The hollow housing may be provided at an angle in the range of 0-30°, more preferably in the range of 3-20°, or most preferably in the range of 5-10° to the vertical axis of the mixer. The ceramic valve may comprise at least a first cylindrical disc and a second cylindrical disc. The first cylindrical disc may be rotatable with respect to the second cylindrical disc. The first cylindrical disc may comprise a slit channel. A first end of the slit channel may be circular. The slit channel may taper from the first end to a second end i.e., the cross-sectional area of the slit channel may decrease from the first end to the second end. The second cylindrical disc may comprise a circular opening. The circular opening may correspond in size and shape to the first end of the slit channel of the first cylindrical disc. The pinch valve may comprise at least one external pinch element. Preferably the pinch valve may comprise at least two external pinch elements. The at least one external pinch element may be configured to compress the outlet, restricting the flow therethrough. The pinch valve may comprise an inner pad. The inner pad may be provided in the centre of the outlet. The inner pad may comprise at least one ridged surface. The or each external pinch element may be configured to abut the inner pad. The mixer may comprise an outlet valve control mechanism. The outlet valve control mechanism may be configured to detect the position of the outlet valve. The outlet valve control mechanism may be configured to adjust the position of the outlet valve in response to the detected position. The outlet valve control mechanism may be configured to adjust the position of the outlet valve via an actuator. In a third aspect of the present invention there is provided a beverage preparation system comprising a beverage preparation device and a mixer and an outlet valve associated with the mixer of the beverage preparation device configured to carry out any of the method steps of the first aspect of the present invention. The beverage preparation system may comprise the mixer system of the first aspect of the present invention. The mixer may comprise a bowl. The bowl may be adapted to receive a flow of base liquid and / or a flow of ingredient and / or a flow of air. The base liquid may be water, and / or milk, and / or coffee and / or tea and / or chocolate. The flow of ingredient may comprise a fluid. The fluid may be a liquid. For example, the liquid may be milk, and / or coffee and / or tea and / or chocolate. Additionally, or alternatively, the flow of ingredient may be a solid. The solid may be a powder or particulate solid. For example, the powder may be milk, and / or coffee and / or tea and / or chocolate. The beverage preparation device may comprise a water supply system. The water supply system may be configured to supply the flow of water. The water supply system may be configured to supply a pre-cycle flow of water. The pre-cycle flow may be a flow of water. The pre-cycle flow and / or flow of water and / or flow of ingredient may be controlled. The pre-cycle flow and / or flow of water and / or flow of ingredient may be controlled using at least one control valve. For example, there may be provided a water control valve and / or an ingredient control valve. The bowl may comprise at least one inlet. The at least one inlet may be configured to receive the flow of water and / or the flow of ingredient and / or the flow of base liquid. The at least one inlet may be provided substantially horizontally. This may result in the pre-cycle flow and / or the flow of water and / or the flow of ingredient being delivered tangentially into the bowl helping to promote efficient mixing of the flows as well as leaving the mixer cleaner as the surface of the mixer may be flushed with water when the flow of water is allowed to run for a longer period of time than the flow of ingredient. Alternatively, the bowl may comprise at least a first inlet and a second inlet. The first inlet may be configured to receive the pre-cycle flow and / or the flow of water and / or the flow of base liquid. The second inlet may be configured to receive the flow of ingredient. The first inlet may be provided substantially horizontally. The second inlet may be provided substantially vertically. The second inlet may be positioned eccentrically with respect to the centre of the bowl. An upper portion of the bowl may comprise a dosing recess. The dosing recess may be in alignment with both the first inlet and the second inlet i.e., the dosing recess may be provided in the flow path of water and / or base liquid entering via the first inlet and it may also be provided directly beneath the second inlet. Provision of such a dosing recess may encourage efficient mixing as the flow of ingredient may combine with a running flow of water and / or base liquid. The bowl may comprise an air inlet. The air inlet may be configured to receive a flow of air. The bowl may comprise an impeller or agitator to mix. The impeller or agitator may be configured to cause mixing of the base flow and the flow of ingredient with the flow of air. The impeller or agitator may be configured to cause mixing of the base flow and the flow of ingredient with the flow of air into a mixed beverage. Provision of such an agitator is advantageous in assisting the formation of foam in the dispensed mixed beverage. The bowl may comprise an outlet. The outlet may be configured to dispense the mixed beverage. The outlet may comprise an outlet valve. The outlet valve may be configured to control dispensing of the mixed beverage. The outlet valve may be moveable between an open position, an intermediate position, and a closed position. The outlet valve may be operable to transition between the open position and / or the intermediate position and / or the closed position over a period of time in the range of 0.01-0.5 seconds, more preferably 0.025-0.4 seconds or most preferably 0.075-0.3 seconds. By transitioning the valve between positions over a period of time rather than suddenly, the transmission of shock waves into the mixed beverage may be minimised. The outlet valve may be selected from the group comprising a needle valve, a ceramic valve, or a pinch valve. In the intermediate position, the outlet valve may be configured to partially obstruct the outlet. The outlet valve may be configured to partially obstruct the outlet by covering 10-75%, more preferably 15-50% or most preferably 20-30% of the cross section of the outlet. The outlet valve may be configured to partially obstruct the outlet by covering 25% of the cross section of the outlet. The needle valve may comprise a tapered plunger. The needle valve may comprise a hollow housing. The tapered plunger may be housed within the hollow housing. The hollow housing may be provided substantially horizontally. The hollow housing may have a diameter in the range of 5-15 mm, preferably of 6-12 mm, or more preferably of 7-9 mm. Preferably, the hollow housing may have a diameter of 8 mm. The hollow housing may be provided at an angle in the range of 0-30°, more preferably in the range of 3-20°, or most preferably in the range of 5-10° to the horizontal axis of the mixer. Preferably, the hollow housing may be provided at an angle of 7° to the horizontal axis of the mixer. Providing the hollow housing at an angle may assist with draining the mixed beverage and / or the precycle flow and / or the flushing fluid. Alternatively, the hollow housing may be provided substantially vertically. The hollow housing may be provided at an angle in the range of 0-30°, more preferably in the range of 3-20°, or most preferably in the range of 5-10° to the vertical axis of the mixer. The ceramic valve may comprise at least a first cylindrical disc and a second cylindrical disc. The first cylindrical disc may be rotatable with respect to the second cylindrical disc. The first cylindrical disc may comprise a slit channel. A first end of the slit channel may be circular. The slit channel may taper from the first end to a second end i.e., the cross-sectional area of the slit channel may decrease from the first end to the second end. The second cylindrical disc may comprise a circular opening. The circular opening may correspond in size and shape to the first end of the slit channel of the first cylindrical disc. The pinch valve may comprise at least one external pinch element. Preferably the pinch valve may comprise at least two external pinch elements. The at least one external pinch element may be configured to compress the outlet, restricting the flow therethrough. The pinch valve may comprise an inner pad. The inner pad may be provided in the centre of the outlet. The inner pad may comprise at least one ridged surface. The or each external pinch element may be configured to abut the inner pad. The mixer may comprise an outlet valve control mechanism. The outlet valve control mechanism may be configured to detect the position of the outlet valve. The outlet valve control mechanism may be configured to adjust the position of the outlet valve in response to the detected position. The outlet valve control mechanism may be configured to adjust the position of the outlet valve via an actuator. The overriding general principle embodied in the system and method of the present invention is to encourage the formation of a high-quality foam and / or crema within the mixed beverage having regular sized small bubbles. The present invention is therefore directed to operating the mixer hardware, and particularly the position of the outlet valve to minimise the transmission of forces (fluid forces and any mechanical forces) to the contents of the mixer once the mixer has foamed the contents of the mixer. Preferably, this will maximise the number of regular / uniform, small bubbles formed in the mixed beverage whilst minimising the formation of larger bubbles, and then maintaining the regular / uniform, small bubbles in the mixed beverage as the mixed beverage is dispensed from the mixer. The volume flow rates disclosed in this document have been calculated in relation to a mixer having a volume of approximately 25 ml. However, the skilled person will be able to select the correct volume flow rates accordingly. Detailed Description of the Invention In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a view of the mixer of the beverage preparation device of the present invention; Figure 2 is a cross sectional view of the mixer of the beverage preparation device of Figure 1; Figure 3 is a schematic cross-sectional view of an embodiment of the mixer of the beverage preparation device of the claimed invention; Figure 4 is a view of an alternative embodiment of a mixer of the beverage preparation device of the present invention; Figure 5 is a view of the mixer of the beverage preparation device of Figure 4; Figure 6a is a cross sectional view of the outlet valve of the beverage preparation device of Figures 4 and 5 in the open position; Figure 6b is a cross sectional view of the outlet valve of the beverage preparation device of Figures 4 and 5 in the closed position; Figure 7 is a view of an alternative outlet valve, a pinch valve; Figure 8 is a view of an alternative outlet valve, a ceramic valve; Figure 9 is a schematic view of the pre-flush apparatus of the beverage preparation device of the present invention; Figure 10 is a graphical representation of the operation of the mixer of the beverage preparation device of figures 1 to 6b; Figure 11 is an alternative embodiment of the operation of the mixer of the beverage preparation device of figures 1 to 6b; and Figure 12 is the operation of the mixer of the beverage preparation device of figures 1 to 6b. With reference to figures 1, 2 and 3 initially, a mixer 1 and outlet valve 2 of a beverage preparation device 3 in accordance with a first embodiment of the invention comprises a bowl 4. The bowl 4 comprises an upper portion 4a, a middle portion 4b, and a lower portion 4c. The upper portion of the bowl 4a is substantially funnel shaped, having a cylindrical form which tapers in a curved manner towards the centre of the middle portion of the bowl 4b. The middle portion of the bowl 4b is substantially cylindrical whereby the opposing flat faces of the cylinder are provided vertically, and the diameter of the cylinder is significantly larger than the depth of the cylinder. The lower portion of the bowl 4c comprises an outlet 5 formed from a substantially vertical duct. In this particular embodiment, the mixer 1 has a vertical height of approximately 106 mm, and the bowl 4 has an inner volume of approximately 25 ml although it will be understood that in alternative embodiments the mixer 1 may have a greater or lesser vertical height, for example, a vertical height in the range of 90-130 mm, and the bowl 4 may have a smaller or larger inner volume, for example, an inner volume in the range of 15-35 ml. The bowl 4 is adapted to receive a flow of base liquid 7. In this particular embodiment, the flow of base liquid 7 (also referred to as a base flow) is a flow of water. However, in alternative embodiments, the flow of base liquid may be a flow of milk, and / or coffee and / or tea and / or chocolate. The bowl 4 is connected to a water supply (not shown) via a water inlet 8. In this embodiment, the water supply is integrally provided within the beverage preparation device 3 although it is equally feasible that in alternative embodiments, the water supply may be provided external to the beverage preparation device 3 e.g., via a tap. The water inlet 8 is a conduit provided substantially horizontally, which connects the water supply to an aperture 9 (seen best in figure 3) in the upper portion of the bowl 4a. As a result, the flow of base liquid (water) 7 enters the upper portion of the bowl 4a tangentially. A water supply valve 10 is positioned along the water inlet 8 to control the flow rate of water into the bowl 4. Having such a water supply valve 10 may enable the water supply to meet a range of operational requirements i.e., the water supply may be operable to supply a flow rate of water in the range of 1-35 ml / s. However, the water supply may be operable to supply the flow of base liquid (water) 7 at a constant rate of 20 ml / s. Furthermore, provision of a water supply which is capable of providing a constant flow rate may assist in reducing the buffer sizes within the mixer 1 i.e., less area is contacted with the mixed beverage enabling more efficient cleaning of the mixer 1. The water supply may be configured to supply a pre-cycle flow of water 6 when the water supply valve 10 is provided in a closed position. The precycle flow of water may circulate through the water supply to pre-heat any pipes and components and assist in removing any air pockets. The bowl 4 is also configured to receive a flow of ingredient 11. The upper portion of the bowl 4a is connected to an ingredient supply (not shown) which provides the flow of ingredient 11. In this particular embodiment, the ingredient supply is integrated into the beverage preparation device 3 and may be pre-filled with ingredient. The ingredient may be a liquid such as milk, and / or coffee and / or tea and / or chocolate. Additionally or alternatively, the ingredient may be a solid such as a powder or particulate solid of milk, and / or coffee and / or tea and / or chocolate. The bowl 4 is also adapted to receive a flow of air (not shown) via an air inlet. With reference now to Figures 1 and 2, the upper portion of the bowl 4a comprises a cover 12 having an opening 13 positioned eccentrically with respect to the centre of the upper portion of the bowl 4a. The upper portion of the bowl is connected to the ingredient supply via an ingredient inlet 14 (shown in Figure 3) in the form of a substantially vertical conduit which connects the ingredient supply to the opening 13. The ingredient inlet 14 is positioned such that the flow of ingredient 11 enters the bowl 4 in alignment with the flow of base liquid (water) 7. The flow of ingredient 11 enters the bowl 4 and is combined with the running flow of base liquid (water) 7 in a dosing recess 35. As the flow of ingredient 11 is combined initially with a running flow of base liquid 7, dissolving of the flow of ingredient 11 may be improved. With reference now to Figure 3, in an alternative embodiment, the ingredient inlet 14 may be connected to the water inlet 8. In this instance, the substantially vertical ingredient inlet 14 is connected to the water inlet 8 via an opening in the water inlet 8 such that the flow of ingredient 11 and the flow of base liquid (water) 7 enter the bowl 4 via the same aperture 9 in the upper portion of the bowl 4a. With reference to Figures 1, 2, and 3, the flow of ingredient 11 is provided at a constant rate of 5 ml / s, although it will be understood that the flow of ingredient 11 into the mixer may be provided at a rate in the range of 0.1-15 ml / s. The bowl 4 further comprises an agitator in the form of an impeller 15, vertically mounted in the middle portion of the bowl 4b. The impeller has a diameter slightly smaller than the diameter of the middle portion of the bowl 4b such that it may freely rotate and agitate the flow of water 7 and / or the flow of ingredient 8 and / or the flow of air. For example, the impeller 15 is configured to cause mixing of the base flow (water) 7 and the flow of ingredient 11 with the flow of air to create a mixed beverage to be dispensed via the outlet 5. The mixed beverage may comprise foam and / or crema caused by the agitation and mixing achieved by the impeller 15 and the flow of air may assist in aerating the mixed beverage whilst the impeller 15 is in use which may help to promote the formation of small bubbles within the mixed beverage. In order to assist in the mixing and foaming of the contents of the bowl 4, the upper portion of the bowl 4a is shaped to direct the contents onto the eye of the impeller 15 such that more even mixing may be achieved, and the buffer sizes within the mixer 1 may be reduced. The impeller 15 is powered by a motor 16 and the two are connected via a shaft 17. The motor 16 in this embodiment is capable of causing the impeller to rotate at a speed of 16000 rpm and is provided outside of the bowl 4 i.e., external to the bowl 4 but internal to the beverage preparation device 3. It will be understood that in alternative embodiments, the motor may be capable of causing the impeller 15 to rotate at greater or lesser speeds, for example, in the range of 4000-20000 rpm. The outlet 5 in the lower portion of the bowl 4c is provided as a duct positioned to the rear of the impeller 15 i.e., the outlet 5 is positioned on the side of the impeller 15 connected to the shaft 17 such that the impeller 15 may be prevented from acting as a pump to dispense the mixed beverage via the outlet 5. The outlet 5 duct is configured to dispense the mixed beverage from the mixer 1 into a suitable receptacle (not shown) via an open face 18. In the embodiment of Figures 1 and 2, the outlet 5 duct is provided substantially vertically however, in the embodiment shown in Figure 3, the outlet 5 duct is provided at an angle of approximately 30° to the vertical axis of the mixer 1. The skilled person will appreciate that the outlet 5 duct may be provided at any an angle in the range of 0-90° to the vertical axis of the mixer 1. The dispensing of the mixed beverage from the mixer 1 via the outlet 5 duct is controlled by the outlet valve 2. The outlet valve 2 is moveable between an open position whereby the open face 18 of the outlet 5 duct is completely unobstructed, an intermediate position whereby the open face 18 of the outlet 5 duct is partially obstructed, and the closed position whereby the open face 18 of the outlet 5 duct is completely obstructed. In this way, the flow of fluid through the outlet 5 may be increased or decreased to achieve a variety of results such as foaming in the intermediate position, fast dispensing in the open position, or filling of the bowl 4 in the closed position. In these particular embodiments, when the outlet valve 2 is in the intermediate position, 25% of the open face 18 of the outlet 5 duct is unobstructed although it will be understood that a greater or lesser percentage of the open face 18 of the outlet 5 duct may be unobstructed. For example, 10-75% of the open face 18 of the outlet 5 duct may be unobstructed to allow greater or lesser flow rates to pass through. An outlet valve 2 control mechanism (not shown) is also provided. The outlet valve control mechanism is configured to detect and adjust the position of the valve 2 and cause the position of the valve 2 to be adjusted via an actuator. The outlet valve 2 seen in Figures 1, 2 and 3 is a needle valve 2 comprising a tapered plunger 19 housed in a hollow housing 20 formed from rigid plastic, connected to the outlet 5 duct at an angle of approximately 7° to the horizontal axis of the mixer 1 to assist draining. In this particular embodiment, the hollow housing 20 has a diameter of 8 mm although it will be understood that hollow housings 20 having smaller or larger diameters may also be used, for example, a diameter between 6-10 mm, and the open face of the outlet 5 duct is connected to an aperture in the hollow housing 20 positioned approximately halfway along the hollow housing 20. The tapered plunger 19 comprises a first end 19a having a conical shape, a main body 19b having a substantially constant diameter which is slightly smaller than that of the hollow housing 20, and a second end 19c which is positioned outside of the hollow housing 20 and has a substantially larger diameter than the first end 19a such that the second end 19c limits the insertion distance of the outlet tapered plunger 19 into the hollow housing 20. Provision of a tapered plunger having a conical end portion allows greater control when obstructing the open face of the outlet duct and ensures a smooth transition between the open and closed positions which helps to minimise formation of large shocks and subsequent large bubble formation in the mixed beverage. The tapered plunger 19 is moveable within the hollow housing 20 i.e., the tapered plunger 19 may move forwards and backwards to obstruct the open face 18 of the outlet 5 duct. In the closed position, the tapered plunger 19 is inserted into the hollow housing 20 such that the main body 19b covers the open face 18 of the outlet 5 duct and the flow of fluid is stopped. The tapered plunger 19 may then be withdrawn into the intermediate position wherein the first end 19a of the of the tapered plunger 19 covers the open face 18 of the outlet 5 duct and the flow of fluid is restricted. Finally, the tapered plunger 19 may be withdrawn further into the open position wherein the tapered plunger 19 does not cover the open face 18 of the outlet 5 and the flow of fluid is completely unobstructed. With reference now to Figures 4-6b, an alternative outlet valve 2 is shown. In this particular embodiment, the outlet valve 2 is a needle valve comprising a tapered plunger 19 moveable within the hollow housing 20. However, in this embodiment, the hollow housing 20 is connected vertically to the open face 18 of the outlet 5 duct. In the closed position, the first end of the tapered plunger 19a is lowered vertically into the hollow housing 20 such that the widest portion of the conical end completely obstructs the open face 18, thereby preventing outflow of mixed beverage from the mixer 1. In the open position, the tapered plunger 19 is vertically raised such that the tip of the first end of the tapered plunger 19a is aligned with the open face 18 of the outlet duct 5, and the outflow of mixed beverage is completely unobstructed. With reference now to Figure 7, an alternative outlet valve 2 is shown. In this embodiment, the outlet valve is a pinch valve 2 comprising two external pinch elements 21 configured to compress the outlet 5. In this embodiment, the outlet 5 has a square cross section and is formed from a deformable material. The two external pinch elements 21 are provided on opposite faces of the square outlet 5 such that as they apply a compressive force thereto, causing the cross-sectional area of the outlet 5 to reduce and restrict flow. The outlet valve 2 also comprises an inner pad 22 positioned within the outlet 5, having a ridged outer surface. In the open position, the external pinch elements 21 are provided in a neutral position whereby no compressive force is applied to the outlet 5 and as such, the flow remains unrestricted. In the intermediate and closed positions, each external pinch element 21 applies a compressive force causing the opposite faces of the outlet 5 to move towards each other, thereby restricting the flow until the faces abut the inner pad 22 in the closed position, completely restricting the flow of mixed beverage therethrough. The compressive force applied in the intermediate position is less than that applied in the closed position. With reference now to Figure 8, another alternative outlet valve 2 is shown. In this embodiment, the outlet valve 2 is a ceramic valve comprising a first cylindrical disc 23 and a second cylindrical disc 24. The first cylindrical disc 23 is rotatable with respect to the second cylindrical disc 24, and the second cylindrical disc 24 is fixed within the outlet 5. The first cylindrical disc comprises a slit channel 25 to allow flow of mixed beverage therethrough, which has a first end 25a and a second end 25b. The first end 25a has a circular cross section, which tapers in to the second end 25b which has a significantly smaller cross-sectional area i.e., the slit has an elongate curved tear-drop shape. The second cylindrical disc 24 comprises a circular opening 26 corresponding in size and shape to the first end 25a of the slit channel 25 of the first cylindrical disc 23. In the open position, the first cylindrical disc 23 is rotated such that the first end of the slit channel 25 is in direct alignment with the circular opening 26 of the second cylindrical disc 24 i.e., the flow is completely unobstructed. In the intermediate position, the first cylindrical disc 23 may be rotated such that the second end 25b of the slit channel 25 is in alignment with the circular opening 26 of the second cylindrical disc 24 i.e., the flow is partially obstructed. In the closed position, the first cylindrical disc 23 may be rotated such that the slit channel 25 is not aligned with the circular opening 26 of the second cylindrical disc 24 i.e., the flow through the outlet valve 2 is completely obstructed. With reference now to Figure 9, the apparatus of the pre-flush system of the beverage preparation device 3 may be seen. The pre-flush system comprises a first circuit 41 comprising a water supply tank 36, a water pump 37, and a heater 38, each connected via a plurality of insulated conduits 39. Water from the supply tank 36 may be pumped by the water pump 37, through the heater 38, around the insulated conduits 39, and return to the supply tank 36 such that the first circuit 41 may be preheated and / or any air pockets present may be removed. At least one water outlet 40 may be provided although in this embodiment, two water outlets 40 are provided. Water from the supply tank 36 may also pass out of the first circuit 41 via the two water outlets 40. Each water outlet may also form the water inlet 8 to the mixer 1 and comprises a water supply valve 10 to control the outflow of water from the first circuit. With reference now to Figure 10, a graphical representation of an operational cycle of the mixer 1 of the beverage preparation device 3 is shown. During a pre-cycle period 27, the water supply valve 10 is provided in the closed position and the outlet valve 2 is provided in the open position. The pre-cycle flow 6 is running at a constant rate of 10 ml / s, to preheat the water supply and remove air bubbles prior to use. The pre-cycle flow 6 doesn’t enter the mixer 1. Although in this embodiment the pre-cycle period lasts for approximately 2 seconds, it will be appreciated that the pre-cycle period may last for a longer or shorter period without any significant consequence. A beverage preparation period 28 immediately follows the pre-cycle period 27. Initially during the beverage preparation period 28, the outlet valve 2 is moved from the open position to the closed position over a period of approximately 0.1 seconds. Once the outlet valve is in the closed position, the pre-cycle flow 6 is stopped. In this embodiment, the base flow 7 is started (and the water supply valve 10 is moved to the open position) immediately after the outlet valve 2 is in the closed position although it will be understood that the base flow 7 does not need to be started immediately but instead may be started after a period e.g., 0.5 seconds. The base flow 7 enters the bowl 4 via the water inlet 8 at a continuous rate of 20 ml / s. Approximately 0.1 seconds after the base flow 7 is started, the flow of ingredient 11 begins. The flow of ingredient 11 enters the bowl 4 via the ingredient inlet at a constant rate of approximately 5 ml / s. As a result, the bowl 4 begins to fill with a combination of water and ingredient, and the flow of ingredient 11 begins to dissolve into the base flow 7. Approximately 0.1 seconds after the flow of ingredient 11 has started, the mixer 1 i.e., the impeller 15, is started. The impeller 15 takes approximately 0.1 seconds to reach its operating speed of 16000 rpm. The impeller 15 agitates the mixture of ingredient and water to form a mixed beverage by both encouraging the ingredient to dissolve and foaming the mixture. As soon as the impeller 15 has reached its operating speed, and whilst both the flow of base liquid (water) 7 and the flow of ingredient 11 are still running, the outlet valve 2 moves from the closed position whereby outflow of the mixed beverage via the outlet 5 is prevented, to at least the intermediate position over a period of time tfroth 29. The period of time tfroth 29 is broken into two time segments, tfrothj 29a and ^-0^2 29b, during which the outlet valve 2 is provided in two different positions. In this particular embodiment, tfrothj 29a is a period of 2.6 seconds although the period may be either shorter or longer. The period of time tfrothj 29a is also broken into time segments of different lengths, tfroth_l _opening 29c, and tfroth_ l_constant 29d. The time period tfroth _1 _openi ng 29c occurs over the first 0.2 seconds of tfrothj 29a. During tfroth_l _opening 29c, the outlet valve 2 gradually moves from the closed position to the intermediate position whereby 25% of the open face 18 is unobstructed and the flow through the outlet 5 is restricted. Moving the outlet valve 2 from the closed position to the intermediate position gradually may help to minimise the effects of shocks transmitted to the fluid within the mixer 1 thereby minimising the formation of large bubbles. Once the outlet valve 2 is in the intermediate position, the time period tfrothjconstant 29d begins, lasting for approximately 2.4 seconds. The outlet valve 2 remains in the same intermediate position, and the foamed portion of the mixed beverage is dispensed. By dispensing the foamed mixed beverage whilst the outlet valve 2 is in the intermediate position, the small regularly sized bubbles in the dispensed mixed beverage may be maintained. While the outlet valve 2 is in the intermediate position, the mixer 1 i.e., the impeller 15 is turned off after a period of time tmiXer30. In this embodiment, the period tmixer3Q is 2.6 seconds. As the mixer 1 is turned off, the mixing and foaming of the mixed beverage inside the mixer 1 ends. Approximately 0.1 seconds after the impeller 15 has been turned off, the outlet valve 2 is moved from the intermediate position to the open position over a time period tfrothj 29b of approximately 2.6 seconds. The period of time tfrothj 29b is broken into two time segments tfrothj_opemnS 29e, and tfrothj_constant 29f. The period of time tfrothJ-Opening 29e occurs over the first 0.2 seconds of tfroth 2 29b. During tfroth_2_openi ng 29e, the outlet valve 2 gradually moves from the intermediate position to the open position such that the open face 18 of the outlet 5 becomes completely unobstructed and the flow therethrough is no longer restricted. Once in the open position, the remaining unfoamed portion of the mixed beverage contained in the mixer 1 is dispensed rapidly via the outlet 5 over the time period tfrothj_constant     which lasts approximately 2.4 seconds. The flow of ingredient 11 is stopped after a time period ingredient 32. In this particular embodiment, the time period tmgredient32 is 5.2 seconds although a different time period is equally feasible e.g., a larger beverage size may require a longer period. The flow of ingredient 11 is stopped when the outlet valve 2 is in the open position, i.e., when the mixed beverage being dispensed is unfoamed, approximately 0.2 seconds before the termination of the beverage preparation period 28. By the termination of the beverage preparation period 28, the mixed beverage is fully dispensed. Immediately following the beverage preparation period 28 is a flushing period 33. The outlet valve 2 is moved between the open and intermediate positions over a period of time tfiush. 33. In this particular embodiment, the period of time tfiush. 33 is 2.2 seconds although it is understood that the period may be shorter or longer in alternative embodiments. The period of time tfiush. 33 is broken into two time segments, tfiush_i 33a and tfiush_2 33b. Initially the outlet valve 2 is gradually moved from the open position to the intermediate position over a period of time tfiush_i 33a. The time period tfiush_i 33a is also broken into two time segments tflush_l _opeing 33c and tfiush_l_constant 33d. During the period tflush_l _opening 33c, the outlet valve 2 is initially moved from the open to the intermediate position in a period of approximately 0.1 seconds, and then remains in the intermediate position over tfiush_iconstant 33d which lasts for approximately 1.4 seconds. By moving the outlet valve from the open position to the intermediate position, the base flow (water) 7 entering the bowl 4 is restricted from leaving via the outlet 5. As a result, the bowl 4 begins to fill slightly, and the waste matter on the bowl 4 is flushed away. Whilst the outlet valve 2 is in the intermediate position, the base flow (water) 7 into the mixer 1 is stopped after a period of approximately 6.8 seconds. At this point, a sufficient volume of water has entered the mixer 1 following the beverage preparation period to enable flushing of the mixer 1. Once a sufficient level of flushing has occurred, the outlet valve 2 is moved from the intermediate position to the open position over tfiush_2 33b to allow the remaining water in the mixer 1 to drain rapidly. The time period tfiush_2 33b is also split in to two time segments, tflush 2_opening 33e and tflush_2_constant 33f. During tflush_2_opening 33e, the outlet valve 2 is moved from the intermediate position to the open position over a period of 0.1 seconds. The outlet valve 2 then remains in the open position over tfiush_2_constant 33f, which lasts for approximately 0.6 seconds and / or until another precycle period 27 begins. With reference now to Figure Ila graphical representation of an alternative operational cycle of the mixer 1 of the beverage preparation device 3 is shown. During a pre-cycle period 127, the water supply valve 10 is provided in the closed position and the outlet valve 2 is provided in the open position. The pre-cycle flow 6 is running at a constant rate of 10 ml / s, to preheat the water supply and remove air bubbles prior to use. The pre-cycle flow 6 doesn’t enter the mixer 1. Although in this embodiment the pre-cycle period lasts for approximately 2 seconds, it will be appreciated that the precycle period may last for a longer or shorter period without any significant consequence. A beverage preparation period 128 immediately follows the pre-cycle period 127. Initially during the beverage preparation period 128, the outlet valve 2 is moved from the open position to the closed position over a period of approximately 0.1 seconds. Once the outlet valve is in the closed position, the pre-cycle flow 6 is stopped. In this embodiment, the base flow 7 is gradually started (and the water supply valve 10 is moved to the open position to enable the mixer 1 to begin to fill) immediately after the outlet valve 2 is in the closed position. The base flow 7 reaches a constant flow rate of 10 ml / s after a period of approximately 0.1 seconds, and it remains at this flow rate for a period of 3.1 seconds. As soon as the base flow 7 reaches a constant flow rate, the flow of ingredient 11 begins. The flow of ingredient 11 enters the bowl 4 via the ingredient inlet at a constant rate of approximately 4 ml / s. As a result, the bowl 4 begins to fill with a combination of water and ingredient, and the flow of ingredient 11 begins to dissolve into the base flow 7. Approximately 0.1 seconds after the flow of ingredient 11 has started, the mixer 1 i.e., the impeller 15, is started. The impeller 15 takes approximately 0.1 seconds to reach its operating speed of 16000 rpm. The impeller 15 agitates the mixture of ingredient and water to form a mixed beverage by both encouraging the ingredient to dissolve and foaming the mixture. Approximately 0.1 seconds after the impeller 15 has reached its operating speed, and whilst both the flow of base liquid 7 and the flow of ingredient 11 are still running, the outlet valve 2 moves from the closed position whereby outflow of the mixed beverage via the outlet 5 is prevented, to at least the intermediate position over a period of time tfroth 129. The period of time tfroth 129 is broken into two time segments, tfrothj 129a and tfroth_2 129b, during which the outlet valve 2 is provided in two different positions. In this particular embodiment, tfrothj 129a is a period of 3.1 seconds although the period may be either shorter or longer. The period of time tfrothj 129a is also broken into time segments of different lengths, tfroth J _opening 129c, and tfroth_l_constant 129d. The time period tfroth_l _opening 129c occurs over the first 0.2 seconds of tfroth_i 129a. During tfroth_l _opening 129c, the outlet valve 2 gradually moves from the closed position to the intermediate position whereby 25% of the open face 18 is unobstructed and the flow through the outlet 5 is restricted. Moving the outlet valve 2 from the closed position to the intermediate position gradually may help to minimise the effects of shocks transmitted to the fluid within the mixer 1 thereby minimising the formation of large bubbles. Once the outlet valve 2 is in the intermediate position, the time period tfrothj-constant 129d begins, lasting for approximately 2.9 seconds. The outlet valve 2 remains in the same intermediate position, and the foamed portion of the mixed beverage is dispensed. By dispensing the foamed mixed beverage whilst the outlet valve 2 is in the intermediate position, the small regularly sized bubbles in the dispensed mixed beverage may be maintained. While the outlet valve 2 is in the intermediate position, the mixer 1 i.e., the impeller 15 is turned off after a period of time tmiXer 130. In this embodiment, the period tmixer 130 is 3.2 seconds although the in the final 0.1 seconds, the mixer 1 is gradually turned off. As the mixer 1 is turned off, the mixing and foaming of the mixed beverage inside the mixer 1 ends. Approximately 0.2 seconds before the mixer 1 is turned off, the rate of the base flow 7 is increased over a period of approximately 0.1 seconds until the base flow reaches a constant flow rate of 20 ml / s. The base flow 7 remains at this constant rate for a period of 2.2 seconds. Approximately 0.1 seconds after the impeller 15 has been turned off, the outlet valve 2 is moved from the intermediate position to the open position over a time period tfrothj 129b of approximately 4.2 seconds. The period of time tfroth_2 129b is broken into two time segments tfroth 2_opening 129e, and tfroth_ 2_constant 129f. The period of time tfroth—2_openi ng 129e occurs over the first 0.2 seconds of tfroth_2 129b. During tfroth—2_opening 129e, the outlet valve 2 gradually moves from the intermediate position to the open position such that the open face 18 of the outlet 5 becomes completely unobstructed and the flow therethrough is no longer restricted. Once in the open position, the remaining unfoamed portion of the mixed beverage contained in the mixer 1 is dispensed rapidly via the outlet 5. The flow of ingredient 11 is stopped after a time period tingredient 132. In this particular embodiment, the time period tingredient 132 is 5.2 seconds. The flow of ingredient 11 is stopped when the outlet valve 2 has been in the open position for a period of 1.6 seconds, i.e., when the mixed beverage being dispensed is unfoamed, approximately 0.2 seconds before the termination of the beverage preparation period 128. By the termination of the beverage preparation period 128, the mixed beverage is fully dispensed. Immediately following the beverage preparation period 128 is a flushing period 133. During the entire flushing period 128, the outlet valve 2 remains in the open position. The flushing period begins approximately 0.2 seconds after the flow of ingredient has been stopped. As soon as the flushing period 128 begins, the base flow is stopped over a period of 0.1 seconds. The base flow remains off for a period of approximately 0.9 seconds, before it is gradually started again. The base flow reaches a constant flow rate of 20 ml / s over a period of 0.1 seconds and remains at the constant flow rate for a period of approximately 1 second before being gradually stopped again over a period of 0.1 seconds which coincides with the termination of the flushing period 133. The flushing period 133 of this particular embodiment is timed to effectively flush the mixer 1 by enabling the bowl 4 to drain slightly whilst the base flow is not running to remove any waste matter remaining from the beverage preparation period 128, before starting the base flow again before the bowl 4 is completely empty to flush the bowl 4. With reference now to Figure 12, a graphical representation of an alternative operational cycle of the mixer 1 of the beverage preparation device 3 is shown. During a pre-cycle period 227, the water supply valve 10 is provided in the closed position and the outlet valve 2 is provided in the open position. The pre-cycle flow 6 is running at a constant rate of 10 ml / s, to preheat the water supply and remove air bubbles prior to use. The pre-cycle flow 6 doesn’t enter the mixer 1. In this embodiment the pre-cycle period lasts for approximately 2 seconds. A beverage preparation period 228 immediately follows the pre-cycle period 227. Initially during the beverage preparation period 228, the outlet valve 2 is moved from the open position to the closed position over a period of approximately 0.1 seconds. Once the outlet valve is in the closed position, the pre-cycle flow 6 is stopped. In this embodiment, the base flow 7 is started (and the water supply valve 10 is moved to the open position) immediately after the outlet valve 2 is in the closed position. The base flow 7 enters the bowl 4 via the water inlet 8 and reaches a continuous rate of 12 ml / s after a period of approximately 0.1 seconds. Approximately 0.1 seconds after the base flow 7 is started, the flow of ingredient 11 begins for a time period tmgredient232 . The flow of ingredient 11 enters the bowl 4 via the ingredient inlet at a constant rate of approximately 6 ml / s. As a result, the bowl 4 begins to fill with a combination of water and ingredient, and the flow of ingredient 11 begins to dissolve into the base flow 7. As soon as the flow of ingredient 11 has started, the mixer 1 i.e., the impeller 15, is started. The impeller 15 takes approximately 0.1 seconds to reach its operating speed of 16000 rpm. The impeller 15 agitates the mixture of ingredient and water to form a mixed beverage by both encouraging the ingredient to dissolve and foaming the mixture. The mixer 1 i.e., the impeller 15 is turned off after a period of time tmixer 230. In this embodiment, the period tmixer 230 is 1.5 seconds. As the mixer 1 is turned off over a period of 0.1 seconds, the mixing and foaming of the mixed beverage inside the mixer 1 ends. As soon as the mixer 1 is turned off, the flow of ingredient 11 is also stopped. After the flow of ingredient 11 has been stopped for a period of approximately 0.1 seconds, the base flow 7 is also gradually stopped over a period of approximately 0.1 seconds. At this time, the bowl 4 comprises the whole volume of foamed mixed beverage as the outlet valve 2 is still in the closed position. Approximately 0.3 seconds after the base flow 7 has stopped, the outlet valve 2 is moved to the open position over a period of approximately 0.3 seconds to allow the mixed beverage to be dispensed rapidly over a period of time tdispense 234 lasting approximately 0.9 seconds. Immediately following the beverage preparation period 228 is a flushing period 233. During this period, the base flow 7 of water is started. The base flow 7 reaches a constant flow rate of 20 ml / s over a period of 0.1 seconds and remains at this flow rate for a period of 2 seconds, after which the base flow 7 is gradually stopped over a period of 0.1 seconds. The flushing period 233 is timed such that the base flow 7 of water is started before the mixer bowl 4 is completely empty of the remnants of the mixed 5 beverage to achieve efficient flushing of the mixer 1. The fluid within the mixer is flushed directly through the outlet valve 2 which remains in the open position throughout the flushing period 233. The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded 10 by the appended claims.

Claims

1. A method of operating an outlet valve associated with a mixer of a beverage preparation device comprising the steps of:(a) providing the outlet valve in an open position;(b) moving the outlet valve from the open position to a closed position;(c) starting a flow of base liquid and a flow of ingredient into the mixer after the outlet valve is in the closed position, to enable the mixer to fill;(d) starting the mixer after the flow of at least one of the base liquid and ingredient into the mixer has started; and(e) moving the outlet valve from the closed position to at least a partially open position over a period of time tfroth while the mixer is operating to dispense a mixed beverage.

2. The method of claim 1 wherein the partially open position is an intermediate position between the closed position and the open position.

3. The method of any preceding claim wherein step (c) comprises starting the flow of base liquid into the mixer as soon as the outlet valve is in the closed position.

4. The method of any preceding claim step (c) comprises starting the flow of base liquid into the mixer before starting the flow of ingredient into the mixer.

5. The method of any preceding claim wherein step (c) comprises starting the flow of base liquid into the mixer at a continuous flow rate.

6. The method of any preceding claim wherein step (c) comprises starting the flow of ingredient into the mixer at a constant frequency.

7. The method of any preceding claim wherein step (d) comprises starting the mixer after the flow of both base liquid and ingredient into the mixer has started.

8. The method of claim 2 wherein step (e) comprises moving the outlet valve to the intermediate position and subsequently moving the outlet valve to the open position.

9. The method of claims 2 or 8 wherein step (e) comprises moving the outlet valve to the intermediate position over a time period tfrothj-10. The method of claims 2 or 8-9 wherein step (e) comprises moving the outlet valve from the intermediate position to the open position over a time period tfroth_2-11. The method of claim 2 or 8-10 wherein step (e) comprises stopping the mixer whilst the outlet valve is in the intermediate position after a period of time tmixer.

12. The method of any preceding claim wherein step (e) comprises stopping the flow of ingredient when the outlet valve is in the open position and after the mixer has been stopped.

13. The method of any preceding claim further comprising a step (f) comprising moving the outlet valve between the open and a second intermediate position over a period of time tflush.

14. The method of claim 13 wherein step (f) comprises moving the outlet valve from the open position to the second intermediate position over a time period tflush_l•15. The method of claim 14 wherein step (f) may comprise moving the outlet valve from the second intermediate position to the open position over a time period of tflush_2-16. The method of claims 13-15 wherein step (f) comprises stopping the flow of water into the mixer whilst the outlet valve is in the second intermediate position.

17. A mixing system configured to carry out any of the method steps of claims 116.

18. A beverage preparation system configured to carry out any of the method steps of claims 1-16.

19. The mixing system of claim 17 or the beverage preparation system of claim 18, the system comprising a bowl adapted to receive the pre-cycle flow and / or the flow of base liquid and / or the flow of ingredient.

20. The system of claim 19 wherein the bowl comprises at least one inlet configured to receive the pre-cycle flow and / or the flow of base liquid and / or the flow of ingredient.

21. The system of claim 19 or 20 wherein the bowl comprises an impeller or agitator 5          configured to cause mixing of the flow of base liquid and the flow of ingredient.

22. The system of claims 19-20 wherein the bowl comprises an outlet.

23. The system of claim 22 wherein the outlet comprises the outlet valve.

24. The system of claim 22 wherein the outlet valve is moveable between an openposition, an intermediate position, and a closed position.10   25. The system of claim 23 or 24 wherein the outlet valve is selected from the groupcomprising a needle valve, a ceramic valve, or a pinch valve.

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