It exist systems for preparing beverages such as coffee by forcing a liquid through ingredients contained in the capsule using centrifugal forces.
WO 2008/148604 for example relates to a capsule for preparing a beverage or liquid food from a substance, in a centrifugal brewing unit, by passing water through the substance contained in the capsule by using brewing centrifugal forces comprising: an enclosure containing a predetermined dose of substance; opening means which opens under the centrifugal effect to allow the brewed liquid to leave the capsule. The capsule may also comprise means for engaging the capsule to external rotational driving means of a centrifugal brewing device wherein the engaging means are configured to offer a resistance to torque during rotation of the capsule for maintaining the capsule in a reference rotational position.
Thereby, the effect of centrifugal forces to brew coffee or prepare other food substances presents many advantages compared to the normal brewing methods using pressure pumps. For example, in traditional espresso or lungo coffee type brewing methods using a pressure pump, it is very difficult to master all the parameters which influence the quality of extraction of delivered coffee extract. These parameters are typically the pressure, the flow rate which decreases with the pressure, the compaction of the coffee powder which also influences the flow characteristics and which depends on the coffee ground particle size, the temperature, the water flow distribution and so on. In particular, it is not easy to vary the extraction pressure and flow rates because there are essentially determined by the static pressure deliverable by the pump, the resistance of the bed of coffee and the downstream filtering system.
For a centrifugal extraction, the rotating capsule is used as a centrifugal pump. The rotational speed thus determines the flow rate of the centrifuged liquid coming out of the capsule. The quality of the beverage to be prepared depends on the control, in particular, of the flow rate. In particular, the flow rate is influenced by two parameters: the rotational speed of the capsule in the device and the back-pressure exerted on the centrifuged liquid before it is projected out of the capsule. For a given back-pressure, the higher the rotational speed, the larger the flow rate. Conversely, for a given rotational speed, the larger the back-pressure, the smaller the flow.
Whereas the rotational speed of the capsule is usually controlled by control means selectively activating a rotational motor of a centrifugal beverage production device, a predefined back-pressure is preferably obtained by a flow restriction of the centrifuged liquid at the outlet of the capsule or at the outside of a centrifugal cell carrying the capsule.
For example EP 651 963 teaches that a pressure gradient is obtained by a rubber-elastic element interposed at the interface between the lid and the cup of the centrifugal cell. Such an element deforms elastically to leave a filtering passage for the liquid when a certain pressure is attained at the interface. The coffee grains are retained in the cell while centrifuged liquid is allowed to pass the filtering passage. Furthermore, document FR 2 487 661 and WO 2006/112691 relate to centrifugal systems wherein a fixed restriction is placed downstream of the filter to create a pressure gradient.
Moreover, WO 2008/148646 proposes a solution in which a flow restriction is placed in or outside the centrifugal cell. The flow restriction can comprise a regulating spring biased valve offering an effective back-pressure. The spring biased valve opens under the effect of a sufficient pressure of liquid exerting on the valve. The higher the speed, the larger the passage through the valve, and the higher the flow rate. The valve can be preloaded by a resilient element such as rubber or spring elements.
Therefore is a need for being able to provide beverages, (e.g. coffee) having different characteristics of intensity, taste, aroma, foam/crema in a system that is simple and versatile.
For prior art system without back-pressure regulation, the problem is that the flow can be increased only by increasing the centrifugation speed. Therefore, this creates limits to vary the flow rate of the beverage, thereby also limiting the possibility to deliver beverages of different characteristics. Furthermore, too high rotational speeds may create problems such as noise, vibration and premature wearing of the mechanical pieces of the device.
Therefore, there is a need for proposing a new system for which the brewing parameters and in particular the back-pressure and/or the flow rate during the beverage preparation be better and more independently controlled for improving quality of the delivered food liquid.
The present invention provides a solution to the before-mentioned problems as well as offers additional benefits to the existing art.