[Bursting risk of capped PET bottles with leftover contents caused by yeast growth]

Accidents caused by the bursting of capped PET bottles with leftover contents have increased in Japan. Therefore, the bursting risk of capped PET bottles with leftover contents was investigated. The ratios of distension, after 10 days at 25 degrees C, of capped PET bottles with leftover orange juice were approx. 70% in the case of drinking while eating Kimuchi, and approx. 6% in the case of drinking but not eating. Among 58 distended bottles, none burst spontaneously, but 4 bottles (6.9%) burst upon physical shock (dropping onto a concrete floor from 1.5 m height). The greatest distensions of capped PET bottles were observed with leftover orange juice, apple juice and soured milk after 10 days at 25 degrees C. No distensions were observed in bottles containing leftover sports drink and green tea under the same conditions. Identified organisms from distended bottles were almost all Candida spp. When those Candida spp. strains were inoculated individually into PET bottles half full of orange, apple or sour milk, all bottles were distended after 7 days at 25 degrees C. From the above results, it appears that there is a risk that capped PET bottles with leftover contents, especially sour fruit juice or soured milk, may burst owing to high gas pressure caused by yeast growth during storage at room temperature for over 1 week.