A continuous system with a mechanical whipper was designed to make protein stabilized foams. Three different impellers (four-blade, six-blade-straight and six-blade-curve disc) were employed to make foams stabilized by sodium caseinate and whey protein. The inlet liquid flow rate of protein solution was varied in the range of 5-15 mL/s, the whipper speed in the range of 5000-15,000 rpm and temperature ranged from 21 to 80 degrees C. The effects of whipper speed, flow rate, type of protein, temperature and whipper geometry on foamability, foam stability, power input, apparent viscosity index and bubble size distribution of foams were investigated. Higher foaming capacity was observed at higher whipper speeds, lower liquid flow rates, and in the case of sodium caseinate stabilized foams. The power input was found to be highest for the lowest liquid flow rate. A six-blade curved impeller rotating along and opposite to the direction of the curvature of vanes produced the most foam and smallest bubble size, respectively. Higher temperatures resulted in better foam stability for foams formed with whey protein whereas it had detrimental effect on foam stability with sodium caseinate. (C) 2008 Elsevier Ltd. All rights reserved.