Apparatus for dispensing a post-mix beverage is characterized by a beverage concentrate metering system comprising a reservoir of beverage concentrate, a disposable pump unit containing a pair of piston pumps and inlet and outlet valves from each piston pump. The inlet valves are coupled to the reservoir of beverage concentrate and the outlet valves are coupled to a mixer. A control valve introduces diluent to the concentrate intermediate the outlet valves and mixer and a reusable pump drive operates the piston pumps. The control valve and pump drive are operated by a control system in a manner such that a predetermined ratio of diluent to concentrate is delivered to the mixer. Downstream from the mixture the admixture of diluent and concentrate is dispensed as a beverage into a cup.