BACKGROUND: Rhamnolipids biosurfactants mainly produced by Pseudomonas aeruginosa have a wide range of potential applications. However, production of rhamnolipids on a large scale is constrained by severe foaming in fermentation. This study addressed the applicability of organic solvents as both defoamer and carbon substrate in rhamnolipids fermentation. RESULTS: In this work, although isopropanol and n-butanol performed better defoaming activities against rhamnolipid-induced foams, ethanol was focused on as a potential defoamer due to its high bioavailability and low toxicity in a shaking culture of P. aeruginosa ZJU. The most appropriate dose of ethanol addition was determined to be 1% (v/v) and the best time for addition was after 48 h of culture in shaking flasks. The capability of ethanol to control foaming was further illustrated during rhamnolipids fermentation in 2 L and 50 L bioreactors. In both fermentations, the addition of ethanol not only suppressed severe foaming but also supported cell growth. CONCLUSIONS: The use of ethanol as a defoamer is a potential strategy to avoid undesirable foam in fermentation of biosurfactant. (C) 2012 Society of Chemical Industry