CHILLING RATE OF COOKED RICE AND RISK OF Bacillus cereus GROWTH IN RESTAURANT OPERATION

Abstract

The emetic syndrome of B. cereus food poisoning is often connected with consumption of rice. When cooked rice is cooled slowly and stored between 10°C to 50°C B. cereus spores germinate and reach numbers high enough to cause illness. Cooked rice is often slowly chilled in most of the restaurants. In the absence of rapid cooling instruments such as blast chiller and cold room, cooked rice, as a common practice is kept at room temperature for cooling for a long time before putting into a refrigerator. In this study, cooked rice in 10 cm deep in a pan was chilled in a blast chiller, cold room, refrigerator and at ambient and the cooling rates between the temperature zone of 50ºC to 10ºC were determined. Except the chilling in a blast chiller, in no other chilling methods the instructed/recommended four hours chilling time was achieved. Chilling of rice from 50ºC to 10ºC in a refrigerator took 12.5-13.5 hours. Chilling time came down to around 10 hours when thickness of rice in the pan was reduced to 5 cm. Chilling time was much longer (15.5-16.5 hours) when the rice was held at ambient until the centre temperature was 30 ºC before putting into the refrigerator. It is obvious that the commonly applied rice chilling in the restaurants is not safe. Some other practical ways other than reducing the thickness of rice should also be applied.