A machine for preparing an infusion includes: an infusion chamber (14) delimited by a lower vessel (3) and an upper packing head (6) that can move relative to one another; a supply of hot pressurized water to the infusion chamber, the packing head (6) having an inner conduit (26) having an inlet (27) that communicates with the infusion chamber and enabling the infusion to pass through the packing head (6) in an upward direction toward the distribution outlet, and; elements (30) located inside the conduit (26) in the vicinity of its inlet and configured for forming the foam in the infusion when passing through the packing head (6) and for preventing the infusion from returning into the infusion chamber. These elements are formed by a deformable flexible piece (30) passed through by at least one hole (35) calibrated for forming the foam and for preventing the infusion from returning.