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 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) to expel 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),
• wherein at least one of said first hydraulic sealing means and said second hydraulic sealing means comprises at least one seal (100, 101) having a single, anti-friction surface coating, of uniform thickness, chemically bonded to a core of the at least one seal (100, 101), over an entirety of an outer perimeter of the core of the at least one seal (100, 101), where the core is NBR or silicone rubber, where the single coating is selected from the group consisting of PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy) and FEP (fluorinated ethylene propylene), where the coating is made of a material free of grease and lubricating oils and compatible with use in contact with foodstuffs and drinking water, and where the outer perimeter of the at least one seal (100, 101) is uncovered, and configured for direct, sliding, anti-friction contact with the closing piston (3), the infusion cylinder (2), or the ejection piston (5).