The invention provides a beverage preparation machine comprising a brew head for receiving beverage cartridges of various heights and means for passing an aqueous medium through said beverage cartridges to form a beverage from one or more beverage ingredients contained in said cartridges. The brew head comprises a first part and a second part, the first and second parts being movable relative to one another from an open position in which said beverage cartridges can be received in the brew head and a closed position in which said beverage cartridge can be fixedly retained in a brew head space defined between the first and second parts. The first part of the brew head comprises a clamping member which extends within the brew head space part-way towards the second part such that a distal end of the clamping member and the second part are a fixed distance from one another when the first and second parts are in the closed position. While in use, beverage cartridges of various heights may be clamped in the brew head space between the distal end of the clamping member and the second part. A beverage cartridge, a beverage preparation system and a method of preparing a single serving of a filtered beverage are also claimed.