Soybeans soaked in tap water for 24 to 36 h at 20, 30 or 37° C underwent a natural fermentation that was characterized by the growth of microorganisms to 10 8–10 10 cfu/ml (depending on temperature) and a reduction of pH from 6.5 to 4.5. Lactobacillus casei, Streptococcus faecium, Staphylococus epidermidis and Streptococcus dysgalactiae dominated the fermentation but, significant contributions were also made by Klebsiella pneumoniae, Klebsiella ozaenae, Enterobacter cloacae, Enterobacter agglomerans, Citrobacter diversus and Bacillus brevis, and the yeasts Pichia burtonii, Candida diddensiae and Rhodotorula rubra. Fermentation of surface-decontaminated beans in sterile water with pure cultures isolates showed L. casei, Strep. faecium and Staph, epidermidis to the main species responsible for the pH reduction. Soybeans were the main source of microorganisms for the fermentation for the fermentation. Boiled beans did not undergo an acid fermentation.