Sunday, November 11, 2012

How to avoid food poisoning from rice

One of my clients asked me recently about the risk of food poisoning from eating reheated rice.

Yes – food poisoning from consuming reheated rice does occur.

It is not, however, the reheating that causes the problem but the way the rice was stored before it was reheated.  Many outbreaks of food poisoning which emerge from the catering industry are found to be caused by the inadequate cooling of food.

To put things in perspective, there have only been 85 reported cases of rice food poisoning in the UK since 1992.   These are often associated with restaurants and take-aways where large quantities of rice are cooked and held at warm temperatures for long periods.

One of the organisms associated with food poisoning in rice is Bacillus cereusSalmonella spp and various other organisms are also implicated.

Cooked rice and Bacillus cereus

Bacillus cereus is a spore-forming bacterium that occurs naturally in many kinds of foods and can cause illness in humans.   It forms spores which are resistant to heating and dehydration and can therefore survive cooking and dry storage.  These spores will survive the cooking process but present little risk provided that cooked rice is:

a) Served and eaten immediately, or
b) Kept hot above 63°C prior to eating, or
c) Cooled rapidly (less than 1 hour) and then kept refrigerated (4˚C or less) or frozen until required

When foods containing B. cereus spores are in the ‘temperature danger zone’ (4˚C to 60˚C) the spores may germinate, and the bacteria may grow, produce toxins, and make people sick. Such illness is frequently linked with starchy foods of plant origin such as rice, pasta, potatoes, pastry and noodles.

B. cereus can cause vomiting or diarrhoea and, in some cases, both. This depends on the kinds of toxin it produces.

When B. cereus grows and produces ‘emetic toxin’ in food, it can cause vomiting, even if the food is cooked again and no live bacteria are eaten. This is because the toxin is not easily destroyed by heating.

When food containing live B. cereus is eaten, the bacteria may grow and produce another toxin, ‘diarrhoeal toxin’, in the gut. This can result in diarrhoeal symptoms.

Illness from B. cereus can be prevented by making certain that hot foods are kept hot and cold foods are stored cold.  It is important to remember that re-heating food that has been ‘temperature abused’ will not make it safe.  Recovery from illness is usually between 12-24 hours.  Very rarely there can be complications and even fatalities.

10 rules of safe handling of rice

  1. Always keep dry rice in cool, dry conditions off the floor.
  2. Do not expose dry rice to moisture as this can encourage mould growth.
  3. Never leave cooked rice to cool on its own. Always chill it quickly (definitely within an hour and preferably faster) either under running cold water or spread thinly on trays in a fridge.  The temperature in the fridge should be no higher than 4˚C.
  4. If cooked rice is to be kept hot e.g. on a serving counter, ensure it is always above 63°C
  5. Avoid keeping rice hot for more than 2 hours and throw away any leftovers.
  6. If cooked rice has been chilled or frozen ensure that it is thoroughly reheated (temperature must be greater than 63˚C) and is piping hot throughout.
  7. Cold rice salads should be kept chilled (4˚C or below).  If part of a buffet, they should not be kept at room temperature for longer than 1 hour.
  8. Never re-chill once it has been kept at room temperature – throw it away.
  9. Never keep rice chilled for longer than 3 days or frozen for longer than 1 month.
  10. Once cooked rice has been re-heated, throw away any leftovers. Never re-heat rice more than once.

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The EFSA Journal (2005) 175, 1-48, “Bacillus cereus and other Bacillus spp in foodstuffs”

NHS Choices.  How to store food safely

Health Protection Agency.  Reported outbreaks of B. cereus 1992-2010

Tilda – Cooking basmati rice

J. Hyg., Camb (1974), 73, 433.  The survival and growth of Bacillus cereus in boiled and fried rice in relation to outbreaks of food poisoning

1 comment:

  1. Nice summary Jane, food safety of rice is one of those you don't get drummed into you as a child (at least in Western Europe) like raw and cooked meat handeling. I must confess I tend to think of keeping anything warm for a while as 'incubating' I guess that helps.