Bacillus Cereus

Safe cooling of cooked rice

Cooked rice is a common cause of foodborne illness. If you are preparing rice for family and friends you should be aware that leaving rice to cool slowly at room temperature creates the ideal environment for toxin producing bacteria such as Bacillus Cereus to develop. Bacillius cereus produces a toxin which can cause nausea, vomiting and diarrhoea.

What is the issue?

Very few people realise that cooked rice can be responsible for their 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 abusea allows pathogenic bacteria to grow, some of which produce toxins. This also applies to consumers preparing rice in the home.

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.

What can go wrong?

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.

How can I tell if product is contaminated?

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..

What can I do to protect the consumer?

To ensure that cooked rice is safe for eating, a number of steps can be taken 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 hot container and divided in clean shallow containers (<10cm deep). 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).

http://www.nzfsa.govt.nz/consumers/food-safety-topics/foodborne-illnesses/saf...

Microbial Pathogen Data Sheets : BACILLUS CEREUS

http://www.nzfsa.govt.nz/science/data-sheets/bacillus-cereus.pdf

Reducing the Risk
Bacillus cereus exists in normal bacterial and spore forms in foods. The normal form is inactivated by cooking, but most illness is a result of the multiplication of spores during inadequate refrigeration of moist cooked protein foods and rice. Because cooking often kills competing bacteria and heat activates the Bacillus cereus spores, storing large masses of cooked food between 4 deg C and 60 deg C can allow the bacteria to multiply.

Preventive measures that can be taken to help avoid the illness include:

• Ensuring adequate temperatures are reached during cooking of food mixes such as sauces, custards, and soups to inactivate the bacteria.
• Keeping cooked hot foods above 60 deg C (preferably 70 deg C) if not served immediately.
• Ensuring the rapid cooling of cooked food by dividing into smaller lots and refrigerating in shallow containers (less than 10cm deep).
• Storing cold foods at or below 4 deg C to prevent toxin being produced.
• Avoiding storing protein-containing foods with cooked rice because this stimulates the growth of Bacillus cereus.
• Reheating foods to 75 deg C or until steaming hot, as flash frying or brief rewarming is not adequate to destroy the toxin.
• Preventing cross-contamination from raw to cooked foods (by using separate preparation areas or sanitising between processes).
• Thoroughly washing fruit and vegetables with clean water of drinking standard before use.
• Ensuring food handlers have good personal hygiene and adequate food safety training.

http://www.ccc.govt.nz/Health/cereus.asp