TECHNOLOGY FOCUS - BIOLOGY - Preferred Method: The step of fermenting the fermentable carbon source in the presence of an organic acid is conducted at a pH of 4-7 using a fibrous bed bioreactor. The step of stripping the organic acid from the organic solvent comprises the use of a base solution, a strong acid solution, hot water or steam. The organic ester is stripped from the extractant with steam in a distillation column. Preferred Components: The organic acid producing microorganism comprises at least one of Clostridium tyrobutyricum, Clostridium butyricum, Clostridium beijerinckii, Clostridium populeti, Clostridium thermobutyricum, Rhizopus oryzae or Propionibacterium acidipropionici, preferably engineered mutants of Clostridium tyrobutyricum ATCC 25755 obtained from inactivating the chromosomal ack gene encoding acetate kinase. The fermentable carbon source is derived from biomass feedstock comprising a carbohydrate source or at least one of agricultural residue or processing waste. The agricultural residues comprise corn stovers, corn cobs or rice straw. The processing wastes comprise at least one of cheese whey or corn fibers.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The extractant is an amine solvent, preferably a long-chain aliphatic amine solvent. The catalyst is sulfuric acid, a cation exchange resin or an enzyme (preferred) e.g. lipase produced from mutants of Candida lipolytica sp. 99-125. The alcohol is at least one of butanol or ethanol. The lipase is immobilized on a support surface comprising a fibrous matrix in a fibrous bed bioreactor. EXAMPLE - An extractive-fermentation from glucose by immobilized cells of Clostridium tyrobutyricum in a fibrous bed bioreactor was conducted. Extractant comprised of Alamine 336 (RTM: Water insoluble, tri-octyl/decyl amine) in oleyl alcohol (10 vol.%) was simultaneously regenerated by stripping with sodium hydroxide in a second membrane extractor. The fermentation pH was self-regulated by a balance between butyric acid production and removal of butyric acid by extraction, and was kept at pH 5.5 to obtain butyric acid (0.45 g/g). Then the butyric acid was first extracted into an amine solvent and reacted directly with butanol to form butyl butyrate ester under the catalytic action of a lipase.