recirculation loop [3], enabling a robust foaming control whilstoffering an independent in situ foam based separation process fromthe fermentation parameters.There is a lack of understanding how cells which have passedthrough the foam fractionation process are affected. In particular,there are few if any reports of whether cell concentration may beenriched or depleted by the foaming, whether foaming may sepa-rate cells based on some cell properties, whether cells are damagedor how cells behave upon being recycled into the production stage.The present study aimed therefore to study the impact of foamrecovery systems on the separation and surfactin producing abilityof Bacillus subtilis cells. Firstly, small-scale batch foaming experi-ments were employed which enabled foaming of cells cultured overa wide range of conditions. The cells were then recycled to assessthe influence of foaming on the subsequent fermentation perfor-mance. The foamed cultures were varied by age, initial cell densityand initial glucose concentration in order to assess the sensitiv-ity of cells to foaming over the most common range of conditions.Secondly, continuous stripping mode foam fractionation experi-ments were employed to investigate the applied process and whichenabled the segregation, and subsequent recycling, of the resultingcells located in the liquid pool, overflow and foamate compart-ments (Fig. 1).