Domestic carbonation based on high-pressure gas injection and depressurisation has been studied. Process parameters examined comprised temperature, gas injection method, nozzle design and control and release of head space pressure, with process efficacy measured in terms of residual dissolved levels and usage efficiency of the CO2. Key variables impacting on CO2 retention were found to be the spatial time periods over which the gas was injected, nozzle design and placement (which all impact on agitation) and pressure release time. A single straight nozzle orifice placed 25 mm above the waterline was found to be the most effective, in terms of mass of CO2 retained to mass injected, of all the nozzle and system configurations studied. Incremental gas introduction via five intermittent injections of 1 s on / 1 s off was found to be the most efficient mode of gas injection. Decreasing the exit orifice diameter, and so increasing depressurisation time, further improved gas retention. It was concluded that gas usage efficieney could be substantially increased by adjusting the nozzle placement, adopting an appropriate injection and depressurisation protocol and decreasing the depressurisation rate. (C) 2002 Elsevier Science Ltd. All rights reserved.