A closure mechanism for a beverage preparation machine comprising a fixed lower part, an upper part rotatable relative to the lower part and a cartridge holder interposed between the lower part and the upper part and being rotatable relative to the lower part and the upper part, wherein the lower part comprises inlet piercing means and outlet piercing means for forming, respectively, an inlet and an outlet, in use, in a cartridge received in the cartridge holder, wherein rotation of the upper part towards the lower part causes the upper part to engage the cartridge holder and to move the cartridge holder into contact with the lower part and at the same time to cause, in use, the inlet piercing means and the outlet piercing means to pierce a cartridge received in the cartridge holder.