Infuser unit for a coffee machine

An infuser unit (1) for a coffee machine, comprising a closing piston (3) and an infusion cylinder (2) which are axially movable selectively or in combination for reciprocal engagement and disengagement so as to close and open an infusion chamber inside the infusion cylinder (2), in which a dose of coffee can be positioned, an ejection piston (5) engaged in the infusion cylinder (2) and axially movable in the infusion cylinder (2) so as to expel the spent coffee grounds, a first radial hydraulic sealing means between said closing piston (3) and said infusion cylinder (2), and a second radial hydraulic sealing means between said infusion cylinder (2) and said ejection piston (5), at least one between the first hydraulic sealing means and the second hydraulic sealing means comprising at least one seal (100, 101) having an anti-friction surface coating made of a material free of grease and lubricating oils and compatible with use in contact with foodstuffs and drinking water.