Bacillus cereus bacteria in rice and other starchy food

Bacillus cereus is a bacterium often present in starchy food. Starchy foods include rice, dried potato flakes, and powdered dairy products. Find out how Bacillus cereus can make you sick, and ways to avoid illness.

Symptoms of Bacillus cereus illness

Illness from Bacillus cereus usually occurs 1 to 6 hours after eating contaminated food.

Symptoms include nausea, vomiting, and diarrhoea.

Most people recover within 6 to 24 hours.

How you can be exposed to Bacillus cereus

Bacillus cereus occurs naturally in many foods. Most illnesses from Bacillus cereus are caused by eating contaminated:

  • rice
  • other starchy foods like potato flakes and pasta
  • powdered dairy products like custard powder.

The bacteria grow to dangerous numbers and produce a toxin when these foods are:

  • cooled too slowly
  • not stored in a fridge.

Further cooking or reheating doesn't destroy the toxin.

In starchy foods, such as potato flakes, Bacillus cereus survives the drying process by producing resistant spores. When these foods are rehydrated and left sitting at room temperature for a few hours, the spores germinate, multiply, and produce the toxin that can make us ill.

How to avoid exposure

Don't leave cooked or prepared rice and other starchy food to cool slowly at room temperature. Make sure the cooked product is either:

  • eaten immediately
  • kept hot at above 60 degrees Celsius
  • cooled and stored in the fridge until used.

Advice for rice

  • Don't cook and cool rice in large quantities – separate into smaller amounts so that it will cool quickly.
  • If rice has been cooked for sushi or fried rice, cool it in the fridge until it is ready to use.
  • Sushi rice usually contains sushi vinegar and a mixture of sugar and salt, which helps prevent the growth of Bacillus cereus bacteria.

Note that Bacillus cereus spores survive in both dried raw rice and cooked rice.

Find out more

Meet the bugs – pamphlet [PDF, 1.3 MB]

Who to contact

If you have questions about Bacillus cereus in foods, email info@mpi.govt.nz

Last reviewed: