fig1 illustrates an example of a system according to the present disclosure . the system 1 comprises a beverage preparation machine 2 and a beverage cartridge 3 which contains roasted ground coffee . the beverage preparation machine 2 comprises a reservoir 10 , a pump 11 and a brew head 12 . the reservoir 10 contains , in use , an aqueous medium such as water . the reservoir 10 may be manually fillable or plumbed in to a mains supply of water for automatic refilling . the reservoir 10 is connected to the pump 11 by a suitable conduit such as a pipe 13 . the pump 11 , in use , pumps water from the reservoir 10 to the brew head 12 via a suitable conduit such as a pipe 14 . the beverage cartridge 3 contains the roasted ground coffee within a closed chamber which forms an extraction chamber of the system . the beverage cartridge 3 is closed prior to use to maintain the freshness of the roasted ground coffee and is preferably pierced by the beverage preparation machine during use . an example of a suitable beverage cartridge is described in ep1440903 . however other types of beverage cartridge may be used . the brew head 12 comprises a chamber 15 for receiving the beverage cartridge 3 , an inlet mechanism for piercing an inlet in the beverage cartridge 3 and directing the water from pipe 14 into the beverage cartridge 3 , and an outlet mechanism for piercing an outlet in the beverage cartridge 3 and directing beverage formed from the water and the roasted ground coffee into an outlet conduit which may be in the form of flexible tubing 16 . a variable valve 17 is positioned below the location of the beverage cartridge 3 and operable on the flexible tubing 16 to alter the back pressure experienced during use in the brew head 12 . the variable valve 17 may be a pinch valve where the distance between the pinching elements can be varied to effectively vary the cross - sectional flow area of the flexible tubing 16 . the outlet of the variable valve 17 leads to the outlet 19 of the machine where the beverage is dischargeable into a receptacle 4 , such as a cup , mug or carafe . the brew head 12 further comprises a barcode reader 18 which , in use reads a barcode provided on the beverage cartridge 3 to determine certain brew parameters , for example the volume of beverage to be dispensed and the flow rate of the water to be pumped . a controller ( not shown ) controls operation of the pump 11 , variable valve 17 and barcode reader 18 . the beverage preparation machine 2 may comprise other components which have been omitted from fig1 for clarity . for example , a flow meter may be provided to determine the quantity of water pumped to the brew head 12 . it is to be noted that the beverage preparation machine 2 does not require a water heater for operation as the water in the reservoir 10 is preferably at ambient temperature or previously chilled below ambient temperature . b ) passing an aqueous medium through the extraction chamber to form the beverage ; and the roasted ground coffee in the beverage cartridge has a dry helos particle size distribution d50 of less than or equal to 200 microns . the roasted ground coffee may be produced by grinding roasted coffee beans using a coffee grinder . the particle size distribution for one sample at grinder setting 0 is shown in fig2 . the x - axis of fig2 shows the particle size in microns . the left - hand y - axis shows the cumulative distribution q 3 as a percentage . the right - hand y - axis shows the density distribution q31g . the dry helos particle size distribution d50 for fig2 is 60 . 88 microns . the particle size distribution for one sample at grinder setting 8 is shown in fig3 . the x - and y - axes are as above . the dry helos particle size distribution d50 for fig3 is 335 . 99 microns . three samples at each of grinder settings 0 , 2 , 4 , 6 and 8 were measured by the helos equipment with the results shown in table 1 : the use of very finely ground roasted ground coffee allows a greater weight of roasted ground coffee to be filled into a specific volume with or without compression of the roasted ground coffee . for example , a beverage cartridge 10 of the type shown in fig1 of ep1440903 and commercially available under the trade name tassimo ® kenco ® medium roast t - disc ®, from kraft foods uk ltd ., typically has an extraction chamber volume of 28 cm 3 and a fill weight of approximately 7 g of roasted ground coffee with a dry helos particle size distribution d50 of around 320 to 480 microns . the fine grinds of the present disclosure allow the t - disc ® extraction chamber to contain a fill weight of 9 to 13 g . for example , for roasted coffee ground at grinder setting 0 the free - flow density of the roasted ground coffee was at least 0 . 37 gcm − 3 ( at this grinder setting measurement of the free - flow density may not avoid inclusion of some air pockets within the measuring container resulting in the density result being a lower limit on the actual density ) as shown in table 2 below , when filled into a t - disc ® 25 extraction chamber of volume 28 cm 3 the following fill ratios were obtained : it is to be noted that the extraction chamber may be substantially fully filled with 0 . 4 g of roasted ground coffee ground at grinder setting 0 under free - flow conditions without any compaction . higher fill ratios are achievable by use of compaction , vibration , etc . in another example , for roasted coffee ground at grinder setting 8 the free - flow density of the roasted ground coffee was 0 . 32 gcm − 3 . as shown in table 3 below , when filled into a t - disc ® extraction chamber of volume 28 cm 3 the following fill ratios were obtained : the water in the reservoir 10 may have a temperature of 1 ° c . to 40 ° c . at temperatures below 1 ° c . the water will freeze and not be usable . as shown below , it has been found that temperatures of no more than 40 ° c . provide beneficial results . the water may be at ambient temperature — that is at the temperature of the beverage preparation machines local environment . for a typical setting of the machine in a domestic house or a retail shop ambient temperature may typically be 20 to 25 ° c . the water is pumped through the extraction chamber of the beverage cartridge 3 at a flow rate of 0 . 5 to 5 mls − 1 . table 4 illustrates the effect of changing the fill weight of the extraction chamber . for all samples in table 4 the roasted coffee beans were ground at grinder setting 0 and filled into a tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 ; the flow rate was 1 mls − 1 and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . samples which were rated “ good ” had good visual extraction that was attractive to samplers and a good or great taste and flavour according to samplers . samples which were rated “ acceptable ” had an acceptable taste and flavor according to samplers but the visual appearance of the extraction was less good than those samples rated “ good ”. samples rated “ not acceptable ” had a weak and / or bitter taste according to samplers . fig4 plots the averaged percentage soluble solids at each sampled fill weight . as can be seen , “ good ” and “ acceptable ” beverages were obtained according to the present method wherein the percentage soluble solids were greater than 4 %, this being achieved where the fill weight was 9 g or greater . table 5 illustrates the effect of varying the grind size of the roasted ground coffee . for all samples in table 5 the fill weight of the extraction chamber in the tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 was 12 g ; the flow rate was 1 mls − 1 , the water temperature was 21 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . samples which were rated “ good ” had a good or great taste according to samplers . samples which were rated “ acceptable ” had an acceptable taste according to samplers . samples rated “ not acceptable ” had a weak taste according to samplers . fig5 plots the averaged percentage solids at each grinder setting . as can be seen , “ good ” and “ acceptable ” beverages were obtained according to the present method wherein the percentage soluble solids were greater than 4 %, this being achieved where the grinder setting was 4 or lower ( which equates from table 1 to a dry helos particle size distribution d50 of around 180 to 200 microns or lower ) table 6 illustrates the effect of varying the water temperature . for all samples in table 6 the grinder setting was 0 , the fill weight in the extraction chamber of the tassimo ® kenco ® espresso t - disc ® with an extraction chamber volume of 28 cm3 was 13 g , the flow rate 1 mls − 1 and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . samples which were rated “ good ” had a strong visual extraction and an intense taste according to samplers . samples rated “ not acceptable ” had a taste that was too strong and bitter according to samplers . the sample at 90 ° c . failed due to overpressure developed in the extraction chamber . as can be seen , good beverages were obtained with a water temperature up to 40 ° c . however , operation of the method without heating of the water prior to use is preferred as it leads to lower energy requirements for each beverage . in addition , a simpler beverage reparation machine may be utilised that does not contain a heater . it has also been surprisingly found that the beverages obtained according to the methods of the present disclosure have an enhanced aroma profile ( as measured by the quantities of aromatic compounds that are desirable in coffee beverages ) compared to coffee beverages prepared by extraction with hot water . fig6 compares the relative quantity of various aromatic compounds produced by two samples as might be consumed . the first , comparative , sample was brewed in a tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 , with a fill weight of the extraction chamber of 7 g of roasted ground coffee having a d50 of 450 microns ; the flow rate was 2 mls − 1 , the water temperature was 90 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . the second sample was brewed in a tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 , with a fill weight of the extraction chamber of 13 g of roasted ground coffee having a d50 of 30 microns ; the flow rate was 1 mls − 1 , the water temperature was 22 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . as can be seen from fig6 enhanced quantities of nearly all of the listed compounds were achieved with the second sample . fig7 plots the same data as fig6 but with the quantity of the compounds normalised per gram weight of the fill weight to take into account the higher fill weight of the second sample . as can be seen , even on a per gram basis the second sample produced higher quantities of nearly all the listed compounds . fig8 compares the impact on the relative quantity of the aromatic compounds produced by varying the fill weight . the first sample was brewed in a tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 , with a fill weight of the extraction chamber of 7 g of roasted ground coffee having a d50 of 30 microns ; the flow 30 rate was 2 mls − 1 , the water temperature was 22 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . the second sample was identical except that the fill weight was 13 g . as can be seen from fig8 enhanced quantities of nearly all of the listed compounds were achieved with the second sample on an absolute and per gram basis . it has also been surprisingly found that the beverages obtained according to the methods of the present disclosure contain an unexpectedly high level of carbohydrates . fig9 compares the quantity per brew of arabinose , galactose , glucose , manose for three brew conditions . the first , comparative , sample was brewed in a tassimo ® kenco ® espresso tdisc ® with an extraction chamber volume of 28 cm 3 , with a fill weight of the extraction chamber of 7 g of roasted ground coffee having a d50 of 350 microns ; the flow rate was 2 mls − 1 , the water temperature was 90 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . the second sample was brewed in a tassimo ® kenco ® espresso t - disc ® with an extraction chamber volume of 28 cm 3 , with a fill weight of the extraction chamber of 7 g of roasted ground coffee having a d50 of 60 microns ; the flow rate was 2 mls − 1 , the water temperature was 22 ° c . and the variable valve 17 was set to achieve a back pressure within the extraction chamber of 6 bar . the third sample was brewed under the same conditions as the second sample except that the fill weight of the extraction chamber was increased to 13 g of roasted ground coffee having a d50 of 60 microns . in the past it has been commonly understood that extracting roasted ground coffee at a lower temperature will not fully extract carbohydrate compounds . however , using the 30 present methods the levels of carbohydrates produced even on a per gram basis ( as shown by the second sample ) are similar to or , for some carbohydrates , even exceed the levels produced by hot extraction . while in the above detailed description the system and method has been described using beverage cartridges for containing the roasted ground coffee , the disclosure is not so limited . the roasted ground coffee may , for example , be filled directly into an ingredient receptacle of a beverage preparation machine , such as an espresso group handle . also , while it is not necessary for the beverage preparation machine to include a water heating means the method can be used with a beverage preparation machine that has a heating means . in this case the heater is simply not utilised ( where the water is to be used at ambient temperature or chilled ) or is used only to heat the water up 15 to 40 ° c . the beverage preparation machine may be provided with a cooling mechanism for cooling the water in the reservoir 10 to a temperature below ambient . the beverage dispensed from the system may undergo a crema - production step to form a crema on the surface of the coffee beverage . the crema - generation step may be undertaken within the beverage cartridge by passing the beverage through an eductor as described in ep1440903 or similar constriction or may be undertaken downstream of the beverage cartridge by passing the beverage through a suitable constriction to form a mass of fine air bubbles within the fluid flow . the variable valve 17 may be used to provide the crema generation .
a beverage preparation machine of the type which uses pre - packaged containers of beverage ingredients includes a cartridge recognition device for determining the type of beverage to be prepared from a cartridge inserted into the machine and a variable geometry valve located downstream of a cartridge when inserted in the machine . the valve enables preparation of beverages at a range of pressures by having at least an open position and at least one restricted flow position , and a controller for selecting an initial valve position and controlling the subsequent operation of the valve according to the determination of the type of beverage to be prepared by the cartridge recognition device .