preferred embodiments of a system for preparing beverage and food products will now be described , by way of example only , with reference to the accompanying drawings in which : fig1 is a schematic diagram illustrating the system for preparing beverage and food products ; fig2 and 4 are cross sectional side elevations of two cartridges used in the system of fig1 ; fig3 and 5 are pictorial views of the collars of the cartridges of fig2 and 4 respectively ; fig6 is a cross sectional side elevation of the cartridge of fig2 in a schematic representation of a part of a machine of the system of fig1 ; and fig7 and 8 are cross sectional side elevations of the cartridge of fig4 in a schematic representation of a part of a machine of the system of fig1 . the system for preparing beverage and food products described herein comprises a machine for preparing beverage and food products and one or more cartridges containing one or more beverage or food ingredients for use in the machine . in order to cater for a selection of beverage and food types , requiring different pressures during the preparation process , the interface between the machine and the cartridge is such as to enable beverage and food products to be prepared at at least two , and more preferably a range of , different pressures without user intervention . this is preferably achieved by providing the machine with a valve downstream of where the cartridge is located and operation of the valve is determined by the interface between the cartridge and the valve , as described below . the system 1 for preparing beverages or food products is illustrated schematically in fig1 . the machine part of the system 1 generally comprises a reservoir 10 for a liquid . although water is likely to be the most common liquid used in preparing beverages such as coffee , the machine is also capable of handling other liquids , such as milk or milk preparations , for mixing with the beverage or food ingredients . any references herein to water should also be taken to include any form of liquid used in preparing beverages or food products . the reservoir 10 is fluidly connected to a pump 11 , via a flow meter 12 , which in turn is connected to a water heater 13 . the water heater 13 is fluidly connected to the brew head 14 . it should be noted that the system of the present disclosure is not limited to preparing products which must be “ brewed ”; the use of the term “ brew head ” is for convenience only as it originated from machines which were limited to brewing beverages . the brew head 14 includes a cartridge recognition device 15 , which will be described in more detail below . a valve 16 is located in the conduit which provides the fluid path between the water heater 13 and the brew head 14 . the valve 16 may be an expansion / contraction valve . if the pressure of the liquid flow is acceptable , the liquid is passed to the cartridge 30 . if the pressure is below or above predetermined limits then the liquid flow can be prevented by the valve . the brew head 14 generally comprises a cartridge holder ( not shown ) for holding , in use , a cartridge 30 . the brew head 14 further comprises means , such as inlet and outlet piercers , for forming in the cartridge 30 , in use , an inlet for liquid to enter the cartridge 30 and an outlet for the prepared beverage to exit the cartridge 30 . the flow meter 12 , the pump 11 , the water heater 13 and the brew head 14 ( and other components ) are connected to an electronic controller 17 . in addition water temperature monitors 18 , 19 located at the inflow to and the outflow from the water heater 13 , are also connected to the controller 17 . the operational behaviour of the machine is determined by software embedded in the controller 17 , for example as described in ep - a - 1440644 . the memory of the control processor includes one or more variables for one or more operational parameters for the machine . these typically include the temperature of the liquid to be passed through the cartridge 30 during the operating stage , the optimum speed of charging the cartridge 30 , the presence or otherwise of a soak step , the total dispensed volume of the beverage or food product , the flow rate of the liquid during the discharge stage , and the period of the purge stage . fig2 illustrates a first version of a cartridge 30 which is designed for use in preparing products which require low pressure during the preparation process , such as chocolate , coffee , tea , sweeteners , cordials , flavourings , alcoholic beverages , flavoured milk , fruit juices , squashes , sauces and desserts . a typical range of “ low ” pressures used for the preparation of such products is 0 . 5 to 2 bar . fig4 illustrates a second version of the cartridge 30 which is designed for use in preparing products which require high pressure during the preparation process , such as espresso - style products , where it is desirable to produce a crema . a typical range of “ high ” pressures used for the preparation of such products is 2 to 16 bar . the overall shape of the cartridges 30 is generally circular or disc - shaped . typically the overall diameter of the cartridges 30 is 45 mm ± 5 mm and the overall height is 40 mm ± 5 mm . typically the volume of the cartridges 300 , 320 when assembled is 50 ml ± 20 % although this will vary according to the nature of the food or beverage ingredients contained therein . the cartridges 30 typically comprise a first member 31 , which generally comprises a bowl - shaped shell , having an annular wall 32 , an open mouth and a base 34 . the annular wall 32 and base 34 together define a receptacle having a chamber 35 . beverage or food ingredients 33 are placed in the chamber 35 ( see fig6 ) and the mouth is sealed with a second member 36 which provides a lid , using a suitable process , such as heat or ultrasonic welding . in the middle of the base 34 is an outlet aperture 37 , which is surrounded by an annular collar 38 which projects away from the base 34 . the collar 38 of the low pressure cartridge 30 ( fig2 ) includes castellations 39 having gaps 39 a therebetween . the collar 38 of the high pressure cartridge 30 ( fig4 ) is solid and has no such castellations 39 . a lower surface 40 of the collar 38 is preferably at an inclined angle to the horizontal . prior to use the outlet aperture 37 is sealed by a septum 41 , which is preferably integrally formed with the base 34 . each member 31 , 36 is formed as a single integral piece from high density polyethylene , polypropylene , polystyrene , polyester , or a laminate of two or more of these materials . a layer 42 of a gas impermeable material , such as evoh , may be incorporated in the members 31 , 36 . a suitable process for manufacturing the members 31 , 36 would be injection moulding . the machine is preferably adapted to include a valve 50 located in the beverage / food product delivery outlet 20 to provide pressure control of the preparation process within the cartridge 30 . the valve 50 preferably comprises a retainer 51 which is mounted in the delivery outlet 20 . a lancet 52 , or other type of piercing device , is attached to the retainer 51 at one end 53 . the other end 54 of the lancet 52 is sharpened to provide means for piercing the septum 41 . the lancet 52 may be provided with one or more grooves 55 extending from the sharpened end 54 along a portion of the outer surface of the lancet 52 . located around the lancet 52 , and moveable relative thereto , is a piston 56 having a central bore 57 . the bore 57 is stepped , having a narrower section 58 , through which the sharpened end 54 of the lancet 52 passes , extending towards the distal end 60 of the piston 56 , and a wider section 59 extending towards the proximal end 61 of the piston 56 . the resulting inward step provides a locating seat 62 for an end of a compression spring 63 , which is also located around the lancet 52 within the wider section 59 of the piston bore 57 . the other end of the spring 63 is mounted within the retainer 51 , so as to bias the piston 56 away from the retainer 51 towards the top of the beverage delivery outlet 20 . the bias of the spring 63 sets the breaking pressure of the valve 50 . as an alternative to the spring mechanism an elastomer may be used to bias the lancet 52 . the distal end 60 of the piston 56 comprises a radially extending flange 64 . an upper surface 65 of the flange 64 , or a portion thereof , may be angled downwardly ( i . e . towards the perimeter of the flange 64 ), at substantially the same angle as that of the lower surface 40 of the collar 38 . an angled surface is preferable to a horizontal surface as it has the ability to self centre the piston 56 and creates a better geometry for shearing the liquid to create foam . operation of the machine comprises insertion of a cartridge 30 into the cartridge holder of the brew head 17 , carrying out the preparation cycle in which the beverage / food product is prepared and carrying out a dispense cycle in which the beverage / food product is dispensed , and removal of the ( substantially ) empty cartridge 30 from the machine . when the cartridge 30 is placed in the cartridge holder in the brew head 14 , as shown schematically in fig6 , and the cartridge head closed , the lancet 52 is forced through the septum 41 , thereby piercing it , and opening up the cartridge outlet aperture 37 . the lower surface 40 of the collar 38 is forced into contact with the flange upper surface 65 . the spring 63 biases the piston 56 into a “ closed position ” in contact with the collar 38 and maintains a good contact between the surfaces 40 , 65 . the preparation cycle typically has four main stages , although not all of these are used for all beverage or food types : in the pre - wet stage the cartridge 30 is charged with liquid under pressure from the reservoir 10 by means of the pump 11 . an inlet piercer pierces the lid 36 to provide a flow path for the liquid to enter the cartridge and pass into the brew chamber 35 , where it mixes with the ingredients 33 contained therein . the charging with liquid causes the ingredients in the chamber 35 to be wetted . the charging may take place at a “ fast ” flow rate , e . g . of 600 ml / min , or a “ slow ” flow rate , e . g . of 325 ml / min . a slow charging rate is particularly useful for cartridges 30 containing viscous liquid ingredients where the ingredients require some dilution before they are able to be pumped at a higher volume flow rate . the volume of liquid injected into the cartridge 30 is selected to ensure that liquid or beverage / food product does not exit the outlet aperture 37 during this stage . the pause stage allows the ingredients to soak in the liquid injected during the pre - wet stage for a predetermined period of time . both the pre - wetting and soaking stages are known to increase the yield of the extractibles from the ingredients and to improve the end flavour of the final product and soaking are particularly used where the ingredients are roast and ground coffee . in the brew stage liquid is passed through the cartridge 30 in order to produce the beverage or food product from the ingredients 33 . the temperature of the liquid is determined by the controller 17 , which sends instructions to the heater 13 to heat the liquid passing from the reservoir 10 to the brew head 14 . liquid enters the cartridge 30 and then passes into the chamber 35 of the cartridge 30 . brewing and / or mixing of the product in the cartridge 30 occurs before the prepared beverage or food product exits the cartridge outlet , passes through the delivery outlet 20 and may be directed into a suitably placed receptacle 21 . the beverage or food product formed by passage of the liquid through the ingredients 33 passes out of the cartridge 30 through the outlet aperture 37 and down the lancet 52 to the other side of the pierced septum 41 . the grooves 55 help to provide a fluid flow path through the pierced septum 41 , especially where the septum 41 is made of a fairly stiff material so that the gap formed by the piercing is not much larger than the diameter of the lancet 52 . in the low pressure cartridge 30 ( fig7 ), the gaps 39 a between the castellations 39 of the collar 38 provide passages for the beverage or food product to flow on through into the delivery outlet 37 . in the high pressure cartridge 30 ( fig8 ), there are no such gaps in the collar 38 . therefore as the beverage / food product flows through pierced septum 41 along the lancet 52 , it collects initially in a chamber 66 which is formed by the side walls of the collar 38 , the unpierced part of the septum 41 and the distal end 60 of the piston 56 . this allows the pressure to build up inside the cartridge chamber 35 . when the pressure is sufficient to overcome the spring force , the piston 56 is forced away from the collar 38 into an “ open position ” thereby opening a gap 67 between the surfaces 40 , 65 ( fig8 ) to allow the beverage or food product to flow out into the delivery outlet 20 . during the purge cycle the temperature of the water heater 13 is raised sufficiently high to convert the liquid remaining in the system to steam and blowing the pressurised steam through the machine and the cartridge 30 . this ensures that all beverage or food product is dispensed and that the flow path is cleared ready for dispensing another beverage or food product . the purge cycle may not commence immediately on cessation of the brew / mixing stage to allow for the majority of the fluid to clear the flow path . once the operating cycle has been completed , the machine automatically stops and the consumer removes the cartridge 30 by opening the cartridge holder and manually removing and disposing of the cartridge 30 . alternatively , the machine may be provided with an automatic ejection mechanism for removing the cartridge automatically on opening the cartridge holder . the combination of the valve 50 and the external cartridge geometry , as provided by the collar 38 , thus enables the machine 1 to produce a variety of beverages or food products , as it allows the cartridges 30 to be selectively prepared at either high or low pressure during the preparation cycle , depending on the type of cycle required for the ingredients 33 in the cartridge 300 . however , unlike any of the prior art systems , the pressure required is identified by the external geometry of the cartridge 30 thus providing an automated variable pressure system . such a machine is capable of producing beverages at a range of pressures , for example from 0 to 9 bar , and more preferably from 0 to 6 bar . alternative configurations for the collars 38 may be used . for the low pressure cartridge 30 , the collar 38 need not be castellated , but may comprise one or more apertures , orifices or other form of gap in the side walls of the collar 38 which enables liquid to pass from the outlet aperture 37 to the delivery outlet 20 . in another embodiment , the spring loaded valve is incorporated in the cartridge collar 38 , rather than in the machine . suitable spring means may be used to bias the collar 38 into contact with the upper surface 65 of a fixed element which replaces the piston 56 . when the requisite pressure in the chamber 66 is reached during the preparation process of a high pressure beverage or food product , the collar 38 is forced away from the fixed element , rather than the converse , to open the gap 67 between surfaces 40 , 65 .
this disclosure relates to improvements in beverage / food product preparation systems and in particular to beverage / food product preparation systems comprising machines of the type which use pre - packaged cartridges containing beverage or food ingredients . the cartridge contains one or more beverage or food ingredients for use in a machine for preparing a beverage or food product from said ingredients . the cartridge comprises a base , an outlet aperture in the base , and a collar extending from the cartridge base around the outlet aperture . the cartridge is inserted into a holding receptacle of a machine the collar interacts with an element of the machine and the collar is configured to determine the pressure in the cartridge during the preparation process .