The coffee machine infusion group comprises a closure piston and an infusion cylinder subjectable to a reversible movement between a position of engagement with the closure piston for the creation of an infusion chamber and a position of disengagement from the closure piston for the loading of a coffee powder load, the infusion group having an expulsion system of the spent coffee powder load from the infusion cylinder, the expulsion system comprising an expulsion piston displaceably housed in the infusion cylinder, the expulsion system further comprising a speed multiplier mechanism operatively connecting the infusion cylinder and the expulsion piston for their relative displacement between a receiving position of the coffee powder load into the infusion cylinder and an expelling position of the coffee powder load from the infusion cylinder.