The present invention relates to a device for infusing a substance to be infused having an infusion chamber for receiving the substance to be infused and for passing a pressurised water flow through the substance to be infused, the infusion chamber having an inlet portion (4) for feeding water into the infusion chamber and an outlet portion (2) for the infused beverage, the injection channel in fluid communication via an injection end with the inlet portion (4) and adapted for connection via an intake end (39) to a pressurised water circuit, characterised in that it comprises adjustable means for varying the water pressure in the injection channel, adapted for generating a water pressure difference between the intake end (39) and the injection end (40) and controlled by control means outside the infusion chamber. The invention can be used in machines for preparing beverages such as espresso coffee
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