Very few people realise that cooked rice can be responsible for their foodborne illness. Rice forms the basis of many ethnic foods and foods containing rice are frequently implicated in food poisoning episodes. It is common for food producers to prepare large quantities of rice a day ahead of use and leave it to cool slowly at room temperature, before heating and serving the next day. Such practices lend themselves to time/temperature abuse due to a slow rate of cooling. Temperature abuse allows pathogenic bacteria to grow, some of which produce toxins.
Uncooked rice frequently contains bacteria called Bacillus cereus. These bacteria can form protective spores that survive the cooking process. If cooled slowly, these spores can germinate, grow and produce an emetic (vomit inducing) toxin. Reheating rice before serving will not inactivate the emetic toxin or kill all the bacterial cells, so the rice may not be safe.
If you consume cooked rice that is contaminated with Bacillus cereus toxin you are likely to experience symptoms of nausea and vomiting within 1 to 6 hours, occasionally followed by diarrhoea within 10-12 hours. The illness is short lived with recovery within 12-24 hours.
There is no way of telling that cooked rice is contaminated. Cooked rice that contains toxin produced by Bacillus cereus will not look, taste or smell off or any different to normal rice.
To ensure that cooked rice is safe for eating, appropriate controls are needed to reduce the risk of illness.
- If rice is to be cooked in advance, do not cook too much at one time as large amounts take too long to cool.
- Either, keep cooked rice hot (>60ºC) or cool rice as quickly as possible. Rice will cool more quickly if removed from the hot container and divided into clean shallow containers (<10cm deep) that are kept separate, not stacked. Alternatively, cool in a colander under cold running water.
- Cover cooked rice and store in a refrigerator (<4ºC)
- Use a stock rotation system to ensure that the oldest rice is used first (“first in, first out” rule).