WO2004034857A1

WO2004034857A1 - Hot water supply for making a brewed beverage

Info

Publication number: WO2004034857A1
Application number: PCT/GB2003/004386
Authority: WO
Inventors: John Nicholas Reid
Original assignee: Vallid Limited
Priority date: 2002-10-14
Filing date: 2003-10-10
Publication date: 2004-04-29
Also published as: AU2003271930A1; GB0223909D0; GB2394215A; GB2394215B

Abstract

An apparatus for heating water to be used in making a beverage comprises a heating chamber (24) for containing a volume of water to be heated, a pump (14) for pumping water into the chamber (24) and an electrical heating element (30) arranged within the chamber (24) to heat the water within the chamber. A discharge valve (18) has a closed position to allow the chamber (24) to be pressurised while the water within it is being heated and an open position to allow the heated water to be discharged from the chamber. Pressuring the water allows it to reach a sufficiently high temperature to brew tea or coffee without the heating element (30) being damaged.

Description

HOT WATER SUPPLY FOR MAKING A BREWED BEVERAGE

Field of the invention

The present invention relates to a hot water supply for use in making a hot brewed beverage.

Background of the invention

Most current machines that dispense beverages such as tea, coffee and soups do so by dissolving a powder in hot water. The taste of beverages made from such instant or freeze dried powders is not entirely satisfactory and machines have more recently been developed that produce conventionally brewed tea and percolated coffee. Whereas it suffices to dissolve instant powders in water at the highest temperature that can be drunk without causing injury (about 65°C), to prepare brewed tea and percolated coffee one must commence with much hotter water, preferably at or even above 100°C.

It has already been proposed in GB 2 035 764 to provide a continuous flow heater to raise the temperature of water on its way to a water outlet in a dispensing machine. It has also been proposed in GB 2 340 590 to use a coil of bare resistance wire in a continuous electric flow boiler. However, a problem encountered when water is heated to its boiling point in this manner, especially when using bare resistance wire as a heating element, is that the heating element tends to overheat and burn out.

Object of the invention

The present invention therefore seeks to provide a water heater having a prolonged expected life that can supply water at a sufficiently high temperature to prepare a brewed beverage, such as tea or percolated coffee.

Summary of the invention

According to a first aspect of the invention, there is provided a method of heating water for making a brewed beverage, which comprises providing a chamber containing an electrical heating element, filling the chamber with water to cover the heating element, pressurising the chamber to above the ambient atmospheric pressure and supplying electrical power to the heating element while the chamber is pressurised to heat the water in the chamber.

The invention is predicated on the realisation that the heating element is damaged by cavitation in the water. When the water boils and large vapour bubbles form on the heating element, the parts of the heating element no longer in contact with liquid water tend to overheat because water vapour cannot extract heat from the element as effectively as liquid water. In the present invention, pressurising the water as it is being heated raises its boiling point and enables the water to reach a temperature sufficiently high to brew a beverage such as tea or coffee efficiently without the heating element being damaged by cavitation in the water .

It is possible to commence the heating of the water in the chamber before it is fully pressurised because there is little risk of damage to the element while the water is still relatively cold. However, at the end of a heating cycle, when the pressure in the chamber is reduced prior to, or as a result of, the heated water within it being dispensed, it is advisable to discontinue the supply of power to the heating element entirely as soon as the pressure within the chamber drops. According to a second aspect of the invention, there is provided an apparatus for heating water to be used in making a beverage, comprising a heating chamber for containing a volume of water to be heated, a pump for pumping water into the chamber and an electrical heating element arranged within the chamber to heat the water within the chamber, characterised in that a discharge valve is connected downstream of the chamber, the valve having a closed position to allow the chamber to be pressurised while the water within it is being heated and an open position to allow the heated water to be discharged from the chamber.

Preferably, a controller is provided for controlling the supply of electrical power to the heating element in such a manner that, at least when the water temperature is near its boiling point, the heating element is only energised when the pressure in the chamber is above the ambient atmospheric pressure.

Hitherto, heaters in dispensing machines have attempted to heat a continuous stream of water. By contrast, in the present invention, a predetermined quantity of water is heated under pressure in a chamber of which the volume is equal to or greater than the quantity of liquid required to make a beverage in one dispensing cycle. Consequently, in addition to prolonging the life of the heating element, the invention offers the advantage that all the electrical energy supplied to the heating element is used only to heat the volume of water being dispensed. This avoids energy being wasted on heating water that is not to be dispensed and allows the desired temperature of the water to be dispensed to be reached more rapidly.

Though the water heater of the invention is particularly suitable for incorporation in an automated beverage dispensing machine, it can be used as a stand alone heater to supply boiling water one cupful at a time. In a preferred embodiment of the invention, the heating element comprises a coil of bare, i.e. not electrically insulated, resistance wire. Because the water does not flow constantly through the heater and electrical power to the heating element is discontinued while water is being discharged from the heating chamber, the use of a bare wire does not present a safety hazard. This makes it possible to dispense with the use of an expensive, heavy and bulky isolation transformer, which is essential when the heating element water is used to heat a continuous stream of water.

Of course, it is alternatively possible to use an electrically insulated heating element, as found in conventional electric kettles, but this is more costly and less thermally and electrically efficient (because of the thermal inertia of the element itself) .

It is preferred that the heating chamber should be elongate with a substantially vertical axis, the pump being connected to the lower end of the heating chamber and the discharge valve to its upper end. With such a configuration, when cold water is pumped into the heating chamber to displace the heated water out of the discharge valve, there is only a small interface between the hot and the cold water and the difference in density ensures that the boiling water is not cooled by mixing to any significant extent with the cold water.

It has been found in practice that passing a high a.c. current through an unsupported coil of bare wire acting as a heating element causes it to vibrate significantly. This is particularly advantageous because it solves another problem associated with water heaters, especially in areas with hard water, namely the formation of limescale (a brittle mineral deposit) on the heating element. The vibration of the heating element dislodges any deposit that would otherwise adhere to the element and it falls under gravity to the bottom of the heating chamber. A tap may conveniently therefore be provided at the lower end of the heating chamber to allow any mineral deposit to be drained off.

Because only a cupful of water is being heated at any one time, it would be feasible to heat it in the heating chamber from ambient temperature to 100 °C. It is however advantageous to hold water preheated to a temperature of around 50°C to 65°C, preferably 55°C to 60°C, in a reservoir so as to reduce the cycle time still further. In this temperature range, the water is hot enough to kill off bacteria but not so hot as to create a problem with limescale.

To avoid the need for a second heating element, it is possible to recycle water through the heating chamber by returning water from the discharge valve to the reservoir. Water is also recycled to the reservoir to purge the heating chamber of air prior to its first cycle of operation. During preheating of the water in the reservoir, the water will not tend to cavitate because of its relatively low temperature. Furthermore, it will not be necessary to operate the heating element at full power as there will be a relatively long time available between dispensing cycles for heating the water in the reservoir.

Recirculation of water from the reservoir through the heating chamber and activation of the heating element may conveniently be effected by a thermostat that senses the temperature of the water in the reservoir.

The heating chamber is preferably constructed as a tube of an insulating material, such as a glass, plastics or ceramic material, to avoid short circuiting the individual turns of the coil but if the tube is itself conductive then an insulating sleeve or lining may be provided between the coil and the tube. Brief description of the drawing

The invention will now be described further, by way of example, with reference to the accompanying drawing, which is a schematic representation of a hot water supply of the invention.

Detailed description of the preferred embodiment

The single figure shows a hot water supply which comprises a reservoir 10 filled with water. The reservoir 10 may be connected to a mains cold water supply 45 and kept topped up by means of a ball cock valve 48.

A supply line 12 connected to the reservoir 10 passes in sequence through a pump 14 and a heater 16 to a three position discharge valve 18. In one position, the valve 18 serves to connect the supply line 12 to a delivery outlet 20. In a second position, the valve 18 connects the supply line 12 to a return line 22 that leads back to the reservoir to form a closed recirculation circuit. In the third position of the valve 18, the supply line is blocked and connected neither to the delivery outlet 20 nor to the return line 22.

The heater 16 comprises a heating chamber defined by a vertical tube 24 of a glass reinforced plastics material, the volume of which is greater than the quantity of water to be dispensed in any single dispensing cycle, i.e. a little larger than a cupful. The plastics tube 24, which for safety can preferably withstand a pressure of 5-7 atmospheres, contains a coil 30 of bare resistance wire which is totally immersed at all times in the water in the tube 24. The terminals 32 and 34 of the coil 30 pass through the plastics tube 24 and are connected by a controller 40 to an a.c. mains supply either through a fully isolating switch (no connection to live or neutral when the switch is open) or through an isolating transformer. The turns of the coil 30 need not be evenly distributed and it is preferred for the turns to be more closely spaced at the bottom of the heater 16 so that water in the tube 24 is heated more rapidly at the bottom than at the top of the heater 16 to promote convection.

The supply line 12 from the pump 14 is connected at a T-junction to the plastics tube 24 so that the bottom of the heater tube acts as a receptacle for mineral deposits that would normally settle on the coil 30. A tap 26 is provided to allow the heater tube 24 to be drained to empty it of any mineral sediment.

In use, the controller 40 can operate the heating supply in either a standby mode or an operating mode. In the standby mode, the valve 18 is set to connect the supply line 12 to the return line 22 to form a closed circuit. A temperature sensor 42 in the reservoir 10 senses the water temperature and if it drops below a first threshold then the pump 14 and the heater 16 are switched on by the controller 40. Water is thus recirculated through the heater 16 which in this mode need only be operated at a low power setting. Recycling of the water serves also to purge the heater tube of air.

When the water temperature reaches an upper threshold temperature, the heater 16 and the pump 14 are switched off. In this way, the temperature of the water in the reservoir 10 is always maintained at between 50°C to 65°C, preferably 55°C to 60 °C. Within this temperature range, the water is not hot enough to make a brewed beverage. However, the water does not present a hazard to personnel and it is hot enough to avoid microbial growth in the water. Further advantages of storing water at around 55°C to 60°C are that oxygen is not driven out of the water (which would tend to mar the taste of the resulting beverage) and the production of li escale in the reservoir is suppressed.

When water is to be dispensed, it is at first important to ensure that the heater tube has been purged of air by, if necessary, recycling water to the reservoir. A brief period of recycling will not only ensure air purging but that the water in the heater tube is at the temperature of the preheated water in the reservoir. The hot water supply is then operated by the controller 40 in its second mode which commences with the rotation of the valve 18 into its third position in which the supply line 12 is blocked. The pump 14 is then operated to pressurise the water in the heater tube 24 (to around 1.5 atmospheres) and an a.c. current is passed through the coil 30 to energise it at a high power setting. This can quickly heat the water to above its ambient atmospheric pressure boiling point and because the coil 30 is totally immersed in the water it is not damaged by the high current.

The temperature of the water in the heater tube 24 is sensed by a second temperature sensor 44, or a pressure sensor, to avoid an excessive build up of pressure in the heater tube 24. When the desired water temperature or pressure is reached, the current to the coil 34 is switched off and the valve 18 is turned to its second position to connect the supply line 12 to the delivery outlet 20. As water from the reservoir 10 is now pumped into the bottom of the tube 24, the boiling water will flow out of the top into the delivery outlet 20. Little mixing occurs at the interface between the hot and the cold water in the tube 24, on account of the difference in density and the fact that water is a bad conductor of heat. As a result, the hot water is not cooled to any significant extent as it is discharged.

Because the tube 24 holds more than enough water to make a single beverage, the heater need not be operated while water is being dispensed. On the contrary, it is important that the heater should not be operated at its higher setting while water is flowing through the delivery outlet 20 because if air should come into contact with the coil 30 the latter will be damaged almost immediately.

While heating the water in the tube 24, the electric current flowing through the heater coil 30 causes it to shake and in hard water areas this prevents a mineral deposit from building up on the coil. Instead, any mineral deposit falls off the coil 30 and drops as a sediment to the bottom of the heater tube 24. The tap 26 is provided to drain off the heater tube 24 from time to time to remove any sediment that collects in it. Because the mineral sediment collects in the receptacle at the bottom of the heater tube 24, it is not recirculated and this helps to keep the reservoir 10, the valve 18 and the various lines free of any deposit. It also removes the minerals from the water dispensed at the delivery outlet 18, which can mar the appearance and taste of the dispensed beverage.

Though boiling water is required to brew tea, water at a temperature of about 85°C would suffice for other beverages, such as coffee. Even if boiling water is used to brew the beverage, it is not necessary for the beverage to be that hot when it is dispensed. It is possible to add milk or cold water to the brewed beverage to bring down its temperature .

It is possible for the valve 18 to have four positions instead of three so that it can deliver boiling water to either one of two delivery outlets, instead of one. If the water from one outlet passes over, say, a tea bag while the other does not, then by varying the proportion of the water flowing through the two delivery outlets it is possible to control the strength of the resulting beverage. It will be clear to the person skilled in the art that various modifications may be made to the described hot water supply without departing from the scope of the invention as set forth in the appended claims. For example, it is not essential for the same heater to be used to heat the water in the reservoir and the water flowing towards the delivery outlet. Thus, it is possible to dispense with the return line and to provide an auxiliary kettle-like heater element in the reservoir to maintain water in the reservoir at the desired temperature.

Claims

1. A method of heating water for making a brewed beverage, which comprises providing a chamber containing an electrical heating element, filling the chamber with water to cover the heating element, pressurising the chamber to above the ambient atmospheric pressure and supplying electrical power to the heating element while the chamber is pressurised to heat the water in the chamber.

2. An apparatus for heating water to be used in making a beverage, comprising a heating chamber (24) for containing a volume of water to be heated, a pump (14) for pumping water into the chamber (24) and an electrical heating element (30) arranged within the chamber (24) to heat the water within the chamber, characterised in that a discharge valve (18) is connected downstream of the chamber, the valve (18) having a closed position to allow the chamber (24) to be pressurised while the water within it is being heated and an open position to allow the heated water to be discharged from the chamber.

3. An apparatus as claimed in claim 2, wherein a controller (40) is provided for controlling the supply of electrical power to the heating element (30) in such a manner that, at least when the water temperature is near its boiling point, the heating element (30) is only energised when the pressure in the chamber is above the ambient atmospheric pressure.

4. An apparatus as claimed in claim 2 or 3, wherein the heating element (30) comprises a coil of bare resistance wire.

5. An apparatus as claimed in claim 4, wherein the coil is unsupported whereby the turns of the coil vibrate when the heating element is energised.

6. An apparatus as claimed in any of claims 2 to 5, wherein the heating chamber (24) is elongate with a substantially vertical axis, the pump (14) being connected to the lower end of the heating chamber and the discharge valve to its upper end.

7. An apparatus as claimed in claim 6, wherein a tap (26) is provided at the lower end of the heating chamber to allow any mineral deposit collecting in the heating chamber to be drained off.

8. An apparatus as claimed in any one of claims 2 to 7, wherein the pump (14) is connected to draw water from a reservoir (10) containing preheated water.

9. An apparatus as claimed in claim 8, wherein the water in the reservoir (10) is maintained at a temperature in the range of 50°C to 65°C, preferably 55°C to 60°C.

10. An apparatus as claimed in claim 9, wherein in order to preheat the water in the reservoir, the pump (14) is operative to recirculate the water in a closed circuit (12, 14, 16, 22) that passes through the heating chamber (24) .