Asked by: Jenny Porter, Swansea
Dormant bacteria (spores) called Bacillus cereus can be found lurking in uncooked rice. The bacteria transfer to the rice from paddy field soil and their spores last for years, even surviving cooking. But when cooked rice is left at room temperature, the warm, damp conditions awaken the bacteria and they produce toxins that can cause vomiting and diarrhoea.
The trick is to serve and eat rice as soon as it has been cooked. If you do need to keep it for a later sitting, cool it as quickly as possible and transfer straight to the fridge.
Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.