A New Type of Flat Sour Spoilage of Commercial Canned Shiruko

In order to confirm that the flat sour spoilage of canned shiruko (a sweet bean drink) is the same as the new type of flat sour spoilage (O. A. flat sour spoilage) of canned coffee, investigations were carried out on commercial canned shiruko.Samples of canned shiruko were taken from a lot which had suffered from flat sour spoilage. The samples were incubated at 55°C and examined microbiologically. Six and thirty spoiled cans were found after 10 days and 30 days, the spoilage rates being 20% and 100%, respectively.The contents of the spoiled cans were reddish or yellowish, and had a slight smell of hydrogen sulfide and a slight bitterness. The spoiled cans of shiruko showed decreased pH values but not decreased vacuum levels. Though this is a difference from the spoilage of canned coffee, the 16 isolated strains have the same principal characteristics as the causative bacteria of O. A. flat sour spoilage of canned coffee.Therefore, sugar, which is the only common ingredient used in both canned shiruko and coffee, is likely to be the source of the causative bacteria.