The composition of samples taken from the baceman stage of traditional Indonesian kecap (soy sauce) production can vary greatly from batch to batch and from manufacturer to manufacturer. This variability could be caused by physical factors such as salt concentration, temperature, dissolved oxygen tension and pH. The effect of these factors on the changes in microflora and biochemical composition during the baceman stage are described in this report. Salt concentration was found to have a large influence on the spoilage of the baceman. At low salt concentrations pellicle-forming yeasts were able to grow. The pellicle on the liquid surface formed by these yeasts provided an aerobic environment in which coryneform bacteria could grow. These bacteria consumed amino acids and fermentation products like acetate and lactate, which resulted in a rise in pH and subsequent spoilage of the baceman. An aerobic baceman showed the same development as those with a low salt concentration. Salt concentration as well as temperature had a large influence on the rate of growth of bacteria. Growth of bacteria and associated lactate and acetate production were also stimulated by a high pH, while growth of yeasts and ethanol and glycerol formation was better at low pH. Also, the production of formol nitrogen by enzymes resulting from the previous bungkil stage was greatly influenced by temperature and pH, with higher temperature and pH giving rise to higher formol nitrogen contents. The consequences of these physical factors on the production of traditional Indonesian kecap are discussed.