Response surface methodology was used to optimize conditions for protein recovery using bovine serum albumin (BSA) as a model protein in a foam separation system. Factors examined were pore size, initial protein concentration, and airflow rate. The size of bubbles produced using frits of different pore size were measured by a photographic method and quantitatively correlated with key process variables. Bubble size was affected significantly by porosity of frits, and the average bubble diameter was 1.36, 2.14, 1.93, 2.44, and 2.76 mm for 1, 25, 50, 75, and 100 pm frit porosity, respectively. The process time increased as the pore size and concentration increased and decreased with increasing airflow rate. Maximum protein recovery (similar to 98%) was obtained with 1 micron pore size frit, and 200 mg/L initial protein concentration. Protein enrichment increased significantly with decreasing initial protein concentration. Crown Copyright (c) 2006 Published by Elsevier Ltd. All rights reserved.