text: Perstraction has been combined with the ABE (acetone butanol ethanol) fermentation for butanol production. Butanol is toxic to the fermentation, therefore perstraction can be applied to remove the butanol from the vicinity of the bacteria as soon as it is produced. Liquid-liquid extraction (LLE) was combined with the ABE fermentation for in situ product recovery, but the extractants with the highest affinity for butanol tend to be toxic to the bacteria. The application of LLE would also require the extractant to be sterilised prior to contact with the fermentation broth. Perstraction can overcome these problems due to a membrane separating the fermentation broth from the extractant. As an in situ product recovery technique for the ABE fermentation perstraction is still in its development stages.