Machine for the preparation of beverages

A closure mechanism for a beverage preparation machine comprising a lower part, an upper part, and a resilient member, the upper part and lower part being movable relative to one another from an open position in which a beverage cartridge can be received in the closure mechanism and a closed position in which the beverage cartridge is fixedly retained between the upper part and lower part, wherein in the closed position the closure mechanism contacts a top surface and a bottom surface of the beverage cartridge at or near a center of the beverage cartridge to exert a compressive force of greater than 50N, wherein the resilient member contacts at least a part of the top surface of the beverage cartridge, and wherein the resilient member is a viewing window.