A system for dispensing mixed beverages has a processor (6) to control the liquid dispensed at an outlet (2) in dependence upon the demand of a user as input to a keypad (8). Carbonated water is fed to the outlet (2) by way of tubing (12) and a syrup concentrate is also fed thereto by way of a tubing (20). The water and syrup is mixed in the correct quantities by way of respective proportional valves (14) which adjust the quantity or flow rate of the two constituents fed through a mixing chamber (16) in accordance with flow rate readings provided to the processor (6) by respective flow transducers (22). The flow transducers (22) measure the speed of flow ultrasonically and are able to provide flow rate readings at a rate of 50 per second. The proportional valves (14) are able to adjust the quantities fed to the mixing chamber (16) at a similar rate such that the mix can be reliably determined even if there are transitory pressure drops or viscosity changes in the system.