In Haday plant, about 1000-2000 bottles of soy sauce in some batches were found swelling and leaking. The total plate count of the swelling or leaking soy sauce was as low as 200-500 CFU/mL by traditional nutrient agar method, the flavor and pH of the soy sauce was normal, and there was no yeast or lactic acid bacteria detected in those swollen or leaking soy sauce bottles.
Furthermore, when non-contaminated bottled soy sauce was inoculated with bacteria isolated from the leaking bottles and grown on nutrient agar plates,no swelling and leaking of bottles resulted after 1-month incubation at 37 C. This investigation overlooked the major contributing chemical, physical and biological factors to soy sauce swelling and
leaking, leaving the problem of bottled soy sauce leakage unsolved.